Abstract

We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt–lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2·4–2·5 Ga, 1·6–2·2 Ga and 0·6–1·2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt–peridotite interaction and subsequent high-pressure metamorphism. The ∼2·5 Ga zircons have positive εHf(t) values (2·9–10·6), whereas the younger Precambrian zircons are dominated by negative εHf(t) values, indicating an ancient continental crustal origin. These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 ± 3 Ma (2σ), 80–170 Ma and 48–64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt–peridotite interactions in the central zone of the NCC. The combination of the positive εHf(t) values (2·91–24·6) of the 315 Ma zircons with the rare occurrence of 302–324 Ma subduction-related diorite–granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt–peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80–170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies. The εHf(t) values of these zircons vary greatly from –47·6 to 24·6. The 170–110 Ma zircons are generally characterized by negative εHf(t) values, whereas the 110–100 Ma zircons have positive εHf(t) values. These observations suggest that melt–peridotite interactions at 80–170 Ma were induced by partial melting of recycled continental crust. The 48–64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive εHf(t) values. These features imply that the melt–peridotite interactions at 48–64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.

INTRODUCTION

Crust–mantle interactions can take place in two ways: (1) underplating of mantle-derived magma at the base of the lower crust (Furlong & Fountain, 1986; Voshage et al., 1990), and (2) recycling and subsequent melting of crustal rocks (via delamination or subduction) in the upper mantle, inducing silicate melt–peridotite interaction and eclogite + peridotite mixing (Kelemen, 1986; Kepezhinskas et al., 1996; Kelemen et al., 1998; Gao et al., 2004, 2008; Liu et al., 2005, 2008a; Sobolev et al., 2005). The former could have played an important role in the growth of the continental crust (Furlong & Fountain, 1986), whereas the latter is thought to be partially responsible for generating mantle heterogeneity (Anderson, 2006) and driving evolution of the continental crust to a bulk andesitic composition (Rudnick, 1995; Rudnick & Gao, 2003; Gao et al., 2004).

Abundant lower crustal and upper mantle xenoliths exhumed by the Neogene Hannuoba basalts along the northern margin of the North China Craton (NCC) provide a rare opportunity to study the two types of crust–mantle interaction referred to above (Liu et al., 2001, 2004, 2005; Xu, 2002; Zhou et al., 2002; Wilde et al., 2003; Tang et al., 2007; Zheng et al., 2009). Wilde et al. (2003) indicated that lithospheric thinning resulting from the break-up and dispersal of Gondwanaland also took place below the Hannuoba area. The isotopic characteristics of Mesozoic age lower crustal xenoliths (Zhou et al., 2002; Liu et al., 2004) have been interpreted to indicate recycling of ancient continental crust within the Trans-North China Orogen, similar to the Eastern Block of the NCC (Xu et al., 2002; Gao et al., 2004; Xu et al., 2006b; Liu et al., 2008a). However, the relatively high 87Sr/86Sr of some of the garnet pyroxenite xenoliths (Xu, 2002), and variable Li isotope ratios of peridotite xenoliths (Tang et al., 2007) from the Hannuoba basalts suggest contributions from the Late Jurassic–Early Cretaceous subduction of altered oceanic crust of the Mongol–Okhotsk plate.

Because of the lower melting temperatures (at a given pressure) of recycled pyroxenite or eclogite compared with anhydrous peridotite (Kogiso et al., 2003; Anderson, 2005), pyroxenite could melt preferentially relative to peridotite to produce a high-Si liquid that is highly reactive with peridotite (Rapp et al., 1999). As the silicate melt infiltrates the surrounding peridotite, it converts olivine to pyroxene, eventually forming an olivine-free or olivine-poor pyroxenite (Sobolev et al., 2005, 2007). A network of pyroxenite veins of different ages might be expected within the lithospheric mantle. Such pyroxenites could be what we sample as garnet/spinel pyroxenite veins hosted in the spinel lherzolite xenoliths carried by the Hannuoba basalts (Liu et al., 2005). Each vein must represent a single melt infiltration event into the shallow lithospheric mantle, and thus could be used to constrain the origin of the silicic melt and the time of melt–peridotite interaction in the lithospheric mantle.

Because of its ubiquitous occurrence and chemically resistant and refractory properties, zircon has been widely used as an indicator of sedimentary provenance (Fedo et al., 2003, and references therein) and igneous source-rock type (Belousova et al., 2002; Grimes et al., 2007), and to provide evidence for recycling of continental crust into the mantle (Bea et al., 2001; Gao et al., 2004). Although zircon has traditionally been thought of as a rare accessory mineral in mafic and ultramafic rocks, it has been recognized in peridotites, pyroxenites and kimberlites (e.g. Kinny & Dawson, 1992; Konzett et al., 1998; Rudnick et al., 1998; Bea et al., 2001; Katayama et al., 2003; Peltonen et al., 2003; Zheng et al., 2006); most occurrences have been interpreted as a record of mantle metasomatism.

Here, we report the results of a study of zircons extracted from garnet/spinel pyroxenite veins within the mantle xenoliths, formed by melt–peridotite interaction (Liu et al., 2005). The results provide new evidence for recycling of lower continental crust and oceanic crust into the mantle in the central zone of the NCC.

GEOLOGICAL SETTING AND SAMPLES

Geological setting

According to age, lithological assemblage, tectonic evolution and P–T–t paths, the NCC can be divided into an Eastern Block, a Western Block and the Trans-North China Orogen (Fig. 1, inset) (Zhao et al., 2000). The presence of ≥3·6 Ga crustal remnants exposed at the surface and in lower crustal xenoliths in both the northern and southern parts of the NCC suggests that it has remained partially intact since the early Archean (Liu et al., 1992a; Zheng et al., 2004). The NCC experienced widespread tectonothermal reactivation during the late Mesozoic and Cenozoic, as indicated by the emplacement of voluminous late Mesozoic granites and extensive Tertiary alkali basalt volcanism. Wilde et al. (2003) indicated that the lithospheric thinning resulting from Gondwana break-up influenced the Hannuoba area. Based on petrological, geochemical and isotopic studies of some of the xenoliths entrained in the Tertiary basalts and Ordovician diamond-bearing kimberlites, it has been suggested that the old, cold, thick and depleted lithospheric mantle has been replaced by young, hot, thin and fertile lithospheric mantle (Menzies et al., 1993; Griffin et al., 1998; Gao et al., 2002; Wu et al., 2003; Rudnick et al., 2004), which was accompanied by recycling of lower crustal eclogite into the mantle (Gao et al., 2004, 2008; Xu et al., 2006a; Liu et al., 2008a; Xu et al., 2008).

Fig. 1.

Simplified geological map of the Hannuoba area. The composite xenoliths were collected from the Damaping area. The divisions of the North China Craton (inset) are after Zhao et al. (2000).

Fig. 1.

Simplified geological map of the Hannuoba area. The composite xenoliths were collected from the Damaping area. The divisions of the North China Craton (inset) are after Zhao et al. (2000).

The Hannuoba basalts occur along the northern margin of the Trans-North China Orogen and have been dated at 14–27 Ma by the K–Ar method (Zhu, 1998). Abundant lower crustal and upper mantle xenoliths are found in the basalts and have been studied to varying extents (Song & Frey, 1989; Tatsumoto et al., 1992; Fan et al., 1998, 2001; Zhang et al., 1998; Chen et al., 2001; Liu et al., 2001, 2004, 2005; Xu, 2002; Zhou et al., 2002; Wilde et al., 2003; Rudnick et al., 2004; Zheng et al., 2009).

Sample descriptions

The mantle xenoliths from the Hannuoba basalts are dominated by spinel lherzolites and pyroxenites. Pyroxenites are classified into garnet pyroxenite, garnet-free spinel pyroxenite and plagioclase-bearing pyroxenite, based on the presence or absence of the dominant aluminous phase (i.e. garnet, spinel, or plagioclase). Two types of mantle-derived composite xenoliths have been identified based on their petrographic characteristics: clinopyroxene-rich spinel pyroxenite (cpx + ol + opx + sp) (Type I) and garnet pyroxenite (gt + cpx + opx + ol + sp) (Type II) veins hosted in spinel lherzolites (Liu et al., 2005). These xenoliths have previously been interpreted to be the products of mantle metasomatism (Song & Frey, 1989), high-pressure cumulates (Fan et al., 2001; Xu, 2002) and subsolidus differentiates produced by modal segregation of different minerals within the upper mantle (Chen et al., 2001).

Type II composite xenoliths are characterized by garnet/spinel pyroxenite layers or veins hosted in spinel lherzolite. The host spinel lherzolites contain 50–70% ol, 25–5% cpx and 25–5% opx. The mineral proportions within the pyroxenite veins vary significantly for the samples studied here: 30–70% clinopyroxene, 0–60% garnet and 0–10% orthopyroxene, olivine and spinel (Fig. 2). Grain size and orthopyroxene/clinopyroxene mode gradually increase from the lherzolite wall into the pyroxenite vein. The pyroxenite layers or veins are enriched in the highly incompatible elements (Rb, K, Na, Sr, Ba, Nb and Ta) and have high and uniform Ni contents and Mg-numbers (83–90). These petrological and geochemical features indicate that the Type II composite xenoliths are the products of interaction between a silicic melt and peridotite (Liu et al., 2005). Carbonate films and volatile-rich silicate glasses have been observed along the grain boundaries in the pyroxenite veins (Fig. 3); these occur together and extend into the peridotite wall-rocks in a few samples. These glasses or films have completely different major element compositions from the host basalt, indicating that they are not infiltrated host basalt (Table 1).

Fig. 2.

Thin-section photomicrographs of garnet pyroxenite veins hosted in lherzolite. The pink colour is kelyphite, black is spinel wrapped by kelyphite, buff is orthopyroxene, green is clinopyroxene and colourless is olivine. Representative inclusions in zircons from DMP552 and DMP555 are also shown (insets).

Fig. 2.

Thin-section photomicrographs of garnet pyroxenite veins hosted in lherzolite. The pink colour is kelyphite, black is spinel wrapped by kelyphite, buff is orthopyroxene, green is clinopyroxene and colourless is olivine. Representative inclusions in zircons from DMP552 and DMP555 are also shown (insets).

Fig. 3.

Photomicrographs of interstitial films or glasses in the xenoliths. IG, interstitial film or glass; Cpx, clinopyroxene; Opx, orthopyroxene; Sp, spinel; Kp, kelyphite assemblage recrystallized after garnet.

Fig. 3.

Photomicrographs of interstitial films or glasses in the xenoliths. IG, interstitial film or glass; Cpx, clinopyroxene; Opx, orthopyroxene; Sp, spinel; Kp, kelyphite assemblage recrystallized after garnet.

Table 1:

Major element compositions of the interstitial glass or film in the garnet pyroxenite veins

 SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2K2Mg-no. 
Interstitial glass           
DMP002.1 2·51 0·00 0·12 1·63 0·44 23·32 31·44 0·05 0·01 96·3 
DMP002.3 53·15 0·00 28·50 0·21 0·00 1·68 0·10 7·28 0·00 93·5 
DMP122.5 51·62 0·00 28·70 0·14 0·00 0·26 0·38 8·71 0·01 77·0 
DMP122.6 44·99 0·00 27·60 0·22 0·00 0·38 8·33 3·49 0·03 75·7 
DMP124.3 50·31 0·06 27·00 0·09 0·00 1·18 4·29 4·51 0·09 95·9 
DMP124.4 51·88 0·00 28·40 0·09 0·00 0·14 0·58 9·55 0·05 73·7 
DMP124.5 47·27 0·00 23·50 0·12 0·02 0·05 8·75 0·24 6·07 42·9 
DMP134.7 57·60 0·03 28·79 0·12 0·01 0·05 1·02 8·97 0·05 42·9 
Host basalt           
Basalt from           
Damaping 47·63 2·34 14·65 11·62 0·16 7·45 8·92 3·57 1·58 53·6 
 SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2K2Mg-no. 
Interstitial glass           
DMP002.1 2·51 0·00 0·12 1·63 0·44 23·32 31·44 0·05 0·01 96·3 
DMP002.3 53·15 0·00 28·50 0·21 0·00 1·68 0·10 7·28 0·00 93·5 
DMP122.5 51·62 0·00 28·70 0·14 0·00 0·26 0·38 8·71 0·01 77·0 
DMP122.6 44·99 0·00 27·60 0·22 0·00 0·38 8·33 3·49 0·03 75·7 
DMP124.3 50·31 0·06 27·00 0·09 0·00 1·18 4·29 4·51 0·09 95·9 
DMP124.4 51·88 0·00 28·40 0·09 0·00 0·14 0·58 9·55 0·05 73·7 
DMP124.5 47·27 0·00 23·50 0·12 0·02 0·05 8·75 0·24 6·07 42·9 
DMP134.7 57·60 0·03 28·79 0·12 0·01 0·05 1·02 8·97 0·05 42·9 
Host basalt           
Basalt from           
Damaping 47·63 2·34 14·65 11·62 0·16 7·45 8·92 3·57 1·58 53·6 

The major elements of the interstitial glasses were analyzed by electron microprobe using a spot size of 10 µm. Compositions of the host basalt are the average of data reported by Zhi et al. (1990).

Some of the xenoliths are garnet pyroxenites without peridotite hosts. They have a similar mineral assemblage and structure (e.g. coarse grained) to the garnet pyroxenite veins or layers and could be fragments of thick garnet pyroxenite layers or veins. Garnets in most samples have recrystallized into kelyphite assemblages consisting of extremely fine-grained spinel and plagioclase, but mostly preserve the bulk major-element composition of pyrope-rich garnet (Liu et al., 2003). The presence of minor Na2O (0·03–2·3 wt %) and K2O (0·01–0·87 wt %) in the kelyphite of some samples could indicate addition of alkalis and thus interaction with a silicate melt. Fresh garnet cores with kelyphite rims are preserved in a few garnet pyroxenites. Using the Ca-in-orthopyroxene thermometer (Brey & Kohler, 1990) and barometer of Nickel & Green (1985), gives calculated temperatures and pressures in the range of 866–997°C and 9·6–16 kbar for most of the garnet pyroxenites (Table 2; Liu et al., 2003).

Table 2:

Petrological information on the samples studied

Sample Pyroxenite vein Lherzolite wall No. of Size of T P 
   zircon xenolith (°C) (kbar) 
   grains (cm)   
Garnet pyroxenite       
DMP122 Coarse grain, thickness 4 cm Coarse grain 6 × 6 × 7 905 15 
 40%cpx + 35%grt + 15%opx + 5%ol + 5%Sp ol + cpx + opx + sp     
DMP134 Coarse grain, thickness 6 cm No 6 × 8 × 8 1132 12 
 55%cpx + 35%grt + 5%opx + 4%ol + 1%Sp      
DMP406 Coarse grain, thickness 8 cm Coarse grain 14 8 × 9 × 10 887  
 70%cpx + 15%opx + 14%Sp + 1%ol ol + cpx + opx + sp     
DMP444 Coarse grain, thickness 6 cm Coarse grain 6 × 8 × 10   
 50%cpx + 45%grt + 5%ol ol + cpx + opx + sp     
DMP552 Coarse grain, thickness 9 cm Coarse grain 42 10 × 10 × 20 1010  
 50%grt + 40%cpx + 5%ol + 3%Sp + 2%opx ol + cpx + opx + sp     
DMP554 Coarse grain, thickness 7 cm Coarse grain 7 × 8 × 10 981  
 60%cpx + 30%grt + 5%opx + 4%Sp + 1%ol ol + cpx + opx + sp     
DMP555 Coarse grain, thickness 8 cm Coarse grain 24 8 × 10 × 10 974  
 60%grt + 30%cpx + 5%ol + 5%opx ol + cpx + opx + sp     
Granulite       
DMP467 Coarse grain No 10 × 10 × 15   
 55%cpx + 43%grt + 2%pl      
Sample Pyroxenite vein Lherzolite wall No. of Size of T P 
   zircon xenolith (°C) (kbar) 
   grains (cm)   
Garnet pyroxenite       
DMP122 Coarse grain, thickness 4 cm Coarse grain 6 × 6 × 7 905 15 
 40%cpx + 35%grt + 15%opx + 5%ol + 5%Sp ol + cpx + opx + sp     
DMP134 Coarse grain, thickness 6 cm No 6 × 8 × 8 1132 12 
 55%cpx + 35%grt + 5%opx + 4%ol + 1%Sp      
DMP406 Coarse grain, thickness 8 cm Coarse grain 14 8 × 9 × 10 887  
 70%cpx + 15%opx + 14%Sp + 1%ol ol + cpx + opx + sp     
DMP444 Coarse grain, thickness 6 cm Coarse grain 6 × 8 × 10   
 50%cpx + 45%grt + 5%ol ol + cpx + opx + sp     
DMP552 Coarse grain, thickness 9 cm Coarse grain 42 10 × 10 × 20 1010  
 50%grt + 40%cpx + 5%ol + 3%Sp + 2%opx ol + cpx + opx + sp     
DMP554 Coarse grain, thickness 7 cm Coarse grain 7 × 8 × 10 981  
 60%cpx + 30%grt + 5%opx + 4%Sp + 1%ol ol + cpx + opx + sp     
DMP555 Coarse grain, thickness 8 cm Coarse grain 24 8 × 10 × 10 974  
 60%grt + 30%cpx + 5%ol + 5%opx ol + cpx + opx + sp     
Granulite       
DMP467 Coarse grain No 10 × 10 × 15   
 55%cpx + 43%grt + 2%pl      

Interstitial silicate glass is found in all of the garnet pyroxenite veins. Garnets in all samples have recrystallized into kelyphite assemblages consisting of extremely fine-grained spinel and plagioclase. Temperature and pressure were calculated using the Ca-in-Opx thermometer (Brey & Kohler, 1990) and barometer of Nickel & Green (1985).

Eighteen pyroxenite veins or layers (2–5 cm in thickness) from Type II xenoliths collected from Damaping (40°58′674′′N, 114°31′674′′E; Fig. 1), were selected for zircon separation. Because zircon is extremely rare in ultramafic rocks, laboratory cleanliness is vital. All instruments used for zircon separation were carefully cleaned to avoid the chance of introducing exotic zircon grains by contamination. The numbers of zircon grains separated from seven garnet/spinel pyroxenite veins or layers (Fig. 2), and one garnet-rich granulite (DMP467) are reported in Table 2. Quartz, feldspar, apatite and felsic melt inclusions were identified by laser-Raman spectrometry in some of the zircon grains (Fig. 2). The zircon grains were mounted in epoxy blocks, and polished to obtain an even surface, and then cleaned in a 5% HNO3 bath with ultrasonic washer prior to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis.

ANALYTICAL METHODS

Trace element analyses and U–Pb dating by LA-ICP-MS

Backscattered electron (BSE) and cathodoluminescence (CL) images were taken for all zircons at the State Key Laboratory of Continental Dynamics, Northwest University, China. CL images of the analyzed zircon grains are illustrated in Fig. 4. U–Pb dating and trace element analyses were conducted synchronously by LA-ICP-MS at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan. Laser sampling was performed using an excimer laser ablation system (GeoLas 2005). An Agilent 7500a ICP-MS instrument was used to acquire ion-signal intensities. Helium was used as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. To decrease the detection limit and improve precision at spot sizes of 16 and 24 µm, nitrogen was added to the central gas flow (Ar + He) of the Ar plasma, which increases the sensitivity for most elements by a factor of 2–3 (Hu et al., 2008). The carrier and make-up gas flows were optimized by ablating NIST SRM 610 to obtain maximum signal intensity for 208Pb, while keeping low ThO/Th ( < 0·3%) and Ca2+/Ca1+ ratios ( < 0·7%) to minimize the matrix-induced interferences. The ion-signal intensity ratio measured for 238U and 232Th (238U/232Th ∼1 for NIST SRM 610) was used as an indicator of complete vaporization (Günther & Hattendorf, 2005). Because high-purity argon and helium ( > 99·999%) were used, both the 204Pb and 202Hg intensities of the gas blank are always lower than 50 c.p.s. at a sensitivity of 1 × 106 c.p.s. 208Pb for NIST SRM 610 at a spot size of 32 µm. Detailed operating conditions for the laser and the ICP-MS instrument have been given by Liu et al. (2008b). Each analysis incorporated a background acquisition of ∼20–30 s (gas blank) followed by 50 s data acquisition from the sample. An Agilent Chemstation was utilized for the acquisition of each analysis. Off-line selection and integration of background and analyte signals, and time-drift correction and quantitative calibration for trace element analyses and U–Pb dating were performed using in-house software ICPMSDataCal, which can be obtained from the author on request. Common Pb correction and ages of the samples were calculated using ComPbCorr#3_17 (Andersen, 2002). Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 (Ludwig, 2003).

Fig. 4.

CL images of the analyzed zircon grains. The circles are analysis spots marked with ages.

Fig. 4.

CL images of the analyzed zircon grains. The circles are analysis spots marked with ages.

The USGS reference glasses BCR-2G and BIR-1G were analyzed as external standards for trace element content calibration (Liu et al., 2008b). The preferred values of element concentrations for the USGS reference glasses are from the GeoReM database (http://georem.mpch-mainz.gwdg.de/). Every 10 sample analyses were followed by one analysis of NIST SRM 610 to correct the time-dependent drift of sensitivity and mass discrimination for the trace element analysis (Liu et al., 2008b). Based on the classical equation of Longerich et al. (1996), multiple-reference material calibration combined with internal standardization was developed to calculate the trace element compositions of zircons according to the equation  

(1)
formula
where  
formula
 
formula
n is the number of reference materials used as external standards, forumla (forumla) and forumla (forumla) are concentrations of analyte element i (internal standard element ‘is’) in the sample and reference material j, forumla (forumla) and forumla (forumla) are net count rates (analyte signal minus background) of element i (internal standard element ‘is’) in the sample and the reference material j. Because high concentrations can be determined more accurately than low concentrations, lrm values were calculated based on the concentration-weighted average, which leads to the greatest reduction in uncertainty introduced by high uncertainties of those elements with low concentrations in the reference materials.

Using BCR-2G and BIR-1G as multiple-calibration standards without applying an internal standard (here named MCS) (Liu et al., 2008b) or using Si as internal standard, except for those elements with extremely low concentrations (e.g. La and Pr) and Sm and Pb, the trace element concentrations in zircon standard 91500 obtained at a spot size of 32 µm are generally consistent with the LA-ICP-MS working values within 10% relative deviation (Table 3). Sm concentration in 91500 is close to the secondary ionization mass spectrometry (SIMS) working value (0·38 ppm) (Wiedenbeck et al., 2004). The concentrations of Si, Zr and Hf obtained by MCS also agree with the values obtained by electron probe microanalysis (EPMA) and isotope dilution thermal ionization mass spectrometry (ID-TIMS) within 3% relative deviation as well. However, using Si as an internal standard, the results calibrated against NIST SRM 610 and 612 are systematically lower than the LA-ICP-MS working values by a factor of 10–30% for the trace elements and Zr, which are similar to the observations for MPI-DING glasses (Liu et al., 2008b). Because Zr shows relative deviation similar to most of the trace elements, the above systematic deviation (except for Si) can be remedied by using Zr as an internal standard. However, much higher Si contents were obtained when calibrated against NIST glasses, using Zr as an internal standard (Table 3).

Table 3:

Compositions of zircon 91500 calibrated by different methods (spot size 32 μm)

Method: USGS_MCS*
 
USGS_Si†
 
NIST_Si‡
 
NIST_Zr§
 
Working values¶
 
D.L. 
 Av. 2σ Av. 2σ Av. 2σ Av. 2σ LA-ICP-MS SIMS EPMA/ID  
SiO2 31·9 0·09 32·7  32·7  36·8 0·16   32·69 ± 0·30 0·022 
ZrO2 67·3 0·09 68·8 0·29 58·7 0·25 66·2    66·17 ± 0·54 0·001 
Ti 4·70 0·41 4·81 0·43 4·03 0·36 4·55 0·40    0·732 
143 2·98 147 3·13 120 2·57 136 2·81 140 153  0·032 
Nb 0·72 0·03 0·74 0·03 0·58 0·02 0·66 0·03 0·79   0·031 
La 0·005 0·004 0·005 0·004 0·005 0·003 0·005 0·004 0·006 0·013  0·019 
Ce 2·53 0·05 2·59 0·05 2·26 0·05 2·55 0·05 2·56 2·56  0·019 
Pr 0·016 0·005 0·017 0·005 0·014 0·004 0·015 0·005 0·024 0·02  0·016 
Nd 0·23 0·04 0·24 0·04 0·21 0·04 0·23 0·04 0·24 0·25  0·116 
Sm 0·40 0·04 0·39 0·04 0·36 0·04 0·41 0·04 0·50 0·38  0·101 
Eu 0·23 0·02 0·24 0·02 0·21 0·02 0·24 0·02 0·24 0·19  0·034 
Gd 2·26 0·11 2·31 0·11 1·94 0·09 2·19 0·11 2·21 1·76  0·179 
Tb 0·84 0·036 0·86 0·038 0·73 0·03 0·83 0·04 0·86 0·78  0·017 
Dy 11·2 0·32 11·5 0·33 9·77 0·28 11·0 0·31 11·8 10·3  0·069 
Ho 4·60 0·11 4·71 0·11 4·05 0·10 4·57 0·10 4·84 4·60  0·016 
Er 26·1 0·66 26·7 0·70 21·2 0·56 23·9 0·60 24·6 23·7  0·047 
Tm 6·28 0·14 6·42 0·15 5·33 0·13 6·01 0·14 6·89 5·95  0·015 
Yb 67·5 1·33 69·1 1·40 56·7 1·15 64·0 1·25 73·9 60·1  0·114 
Lu 13·3 0·25 13·6 0·26 11·4 0·22 12·8 0·23 13·1 14·1  0·018 
Hf 5939 23·8 6073 29·3 5545 26·8 6250 27·2  5923 5895 0·116 
Ta 0·50 0·02 0·51 0·02 0·42 0·01 0·48 0·02    0·020 
Pb 15·4 0·45 15·8 0·46 15·1 0·44 17·1 0·50 17·9   0·065 
Th 28·1 1·04 28·7 1·06 25·2 0·93 28·4 1·06 29·9   0·019 
77·5 2·11 77·4 2·10 71·8 1·95 80·9 2·22 80·0   0·014 
Method: USGS_MCS*
 
USGS_Si†
 
NIST_Si‡
 
NIST_Zr§
 
Working values¶
 
D.L. 
 Av. 2σ Av. 2σ Av. 2σ Av. 2σ LA-ICP-MS SIMS EPMA/ID  
SiO2 31·9 0·09 32·7  32·7  36·8 0·16   32·69 ± 0·30 0·022 
ZrO2 67·3 0·09 68·8 0·29 58·7 0·25 66·2    66·17 ± 0·54 0·001 
Ti 4·70 0·41 4·81 0·43 4·03 0·36 4·55 0·40    0·732 
143 2·98 147 3·13 120 2·57 136 2·81 140 153  0·032 
Nb 0·72 0·03 0·74 0·03 0·58 0·02 0·66 0·03 0·79   0·031 
La 0·005 0·004 0·005 0·004 0·005 0·003 0·005 0·004 0·006 0·013  0·019 
Ce 2·53 0·05 2·59 0·05 2·26 0·05 2·55 0·05 2·56 2·56  0·019 
Pr 0·016 0·005 0·017 0·005 0·014 0·004 0·015 0·005 0·024 0·02  0·016 
Nd 0·23 0·04 0·24 0·04 0·21 0·04 0·23 0·04 0·24 0·25  0·116 
Sm 0·40 0·04 0·39 0·04 0·36 0·04 0·41 0·04 0·50 0·38  0·101 
Eu 0·23 0·02 0·24 0·02 0·21 0·02 0·24 0·02 0·24 0·19  0·034 
Gd 2·26 0·11 2·31 0·11 1·94 0·09 2·19 0·11 2·21 1·76  0·179 
Tb 0·84 0·036 0·86 0·038 0·73 0·03 0·83 0·04 0·86 0·78  0·017 
Dy 11·2 0·32 11·5 0·33 9·77 0·28 11·0 0·31 11·8 10·3  0·069 
Ho 4·60 0·11 4·71 0·11 4·05 0·10 4·57 0·10 4·84 4·60  0·016 
Er 26·1 0·66 26·7 0·70 21·2 0·56 23·9 0·60 24·6 23·7  0·047 
Tm 6·28 0·14 6·42 0·15 5·33 0·13 6·01 0·14 6·89 5·95  0·015 
Yb 67·5 1·33 69·1 1·40 56·7 1·15 64·0 1·25 73·9 60·1  0·114 
Lu 13·3 0·25 13·6 0·26 11·4 0·22 12·8 0·23 13·1 14·1  0·018 
Hf 5939 23·8 6073 29·3 5545 26·8 6250 27·2  5923 5895 0·116 
Ta 0·50 0·02 0·51 0·02 0·42 0·01 0·48 0·02    0·020 
Pb 15·4 0·45 15·8 0·46 15·1 0·44 17·1 0·50 17·9   0·065 
Th 28·1 1·04 28·7 1·06 25·2 0·93 28·4 1·06 29·9   0·019 
77·5 2·11 77·4 2·10 71·8 1·95 80·9 2·22 80·0   0·014 

*Calibrated against BCR-2G and BIR-1G without applying an internal standard (Liu et al., 2008a).

†Calibrated against BCR-2G and BIR-1G using Si (SiO2 = 32·7 wt %) as internal standard.

‡Calibrated against NIST SRM 610 and 612 using Si (SiO2 = 32·7 wt %) as internal standard.

§Calibrated against NIST SRM 610 and 612 using Zr (ZrO2 = 66·2 wt %) as internal standard.

¶Working values are from Wiedenbeck et al. (2004); Pb was calculated based on the LA-ICP-MS working values of 206Pb, 207Pb and 208Pb. SiO2 and ZrO2 were determined by EPMA (Wiedenbeck et al., 2004) and Hf by isotope dilution (ID) (Wiedenbeck et al., 1995); Av., average of 16 analyses; 2σ is given as absolute uncertainty; D.L., average detection limit for LA-ICP-MS analysis.

Zircon 91500 was used as external standard for U–Pb dating, and was analyzed twice every five analyses. Time-dependent drifts of U–Th–Pb isotopic ratios were corrected using a linear interpolation (with time) for every five analyses (i.e. 91500 + five zircon samples + 91500) according to the variations of 91500, as demonstrated by the equation  

(2)
formula
where forumla is the measured isotopic ratio of sample at time tsam, forumla is the corrected isotopic ratio of the sample, forumla is the preferred isotopic ratio of the standard, forumla and forumla are the measured isotopic ratios of standard at time forumla and forumla (forumla < tsam < forumla). The standard deviation on the average of the isotopic ratios for each analysis (forumla) (standard error) was calculated according to the standard formula (forumla) (Altman & Bland, 2005). Preferred U–Th–Pb isotopic ratios used for 91500 are from Wiedenbeck et al. (1995). The uncertainty of the preferred values for the external standard 91500 was propagated to the ultimate results of the samples according to the equation  
3
formula

Zircon standards GJ-1 (Jackson et al., 2004) and SK10-2 (in-house standard) (Yuan et al., 2003) were analyzed as unknowns. Because the common Pb is low in these standards, no common Pb correction was made. The obtained mean 206Pb/238U ages for GJ-1 and SK10-2 are 602·9 ± 4·1 Ma (2σ, n = 31) and 32·1 ± 0·5 Ma (2σ, n = 29) with spot size of 16 µm, and 602·1 ± 4·9 Ma (2σ, n = 23) and 31·3 ± 0·5 Ma (2σ, n = 22) with spot size of 24 µm, respectively. These results are consistent with the reported or recommended values [SK10-2: 31·4 ± 0·3 Ma (2σ), Yuan et al., 2003; GJ-1: 599·8 ± 1·7 Ma (2σ), Jackson et al., 2004].

Lu–Hf isotopic analyses by LA-MC-ICP-MS

Lu and Hf isotopic analyses were conducted by LA-MC (multicollector)-ICP-MS at the State Key Laboratory of Continental Dynamics, Northwest University, China. Laser sampling was performed using an excimer laser ablation system (GeoLas 2005). Analyses were carried out using spot size of 32 µm and He as carrier gas. A Nu Plasma HR MC-ICP-MS instrument (Nu Instruments Ltd., UK) was used to acquire time-resolved signals. The detailed instrumental parameters of the laser-ablation system and MC-ICP-MS system are the same as those of Yuan et al. (2008). Every 10 sample analyses were followed by one analysis of 91500, GJ-1 and Monastery. Zircon standard 91500 (Blichert-Toft, 2008) was used as an external standard, and zircon standards GJ-1 (Morel et al., 2008) and Monastery (Woodhead & Hergt, 2005) were analyzed as unknowns. Interference correction for Yb and Lu is of paramount importance for precise in situ measurements of Hf isotopes in zircon (Woodhead et al., 2004). Applying an exponential fractionation law (Russell et al., 1978), the mass fractionations of Hf and Yb were calculated using values of 0·7325 for 179Hf/177Hf and 1·1248 for 173Yb/171Yb, respectively (Blichert-Toft et al., 1997). Because Lu and Yb have similar physicochemical properties, the mass fractionation of Yb was used to correct the mass fractionation of Lu. Using the calculated mass fractionation of Yb, the 176Lu and 176Yb interferences on 176Hf are subtracted using the signals of 175Lu and 173Yb and values of 0·02656 for 176Lu/175Lu (Blichert-Toft et al., 1997) and 0·7876 for 176Yb/173Yb (McCulloch et al., 1977). Time-dependent drifts of Lu–Hf isotopic ratios were corrected using a linear interpolation (with time) according to the variations of 91500 [equation (2)]. The interference and mass fractionation-corrected 176Hf/177Hf ratios of the samples were then calibrated against 91500 using the recommended 176Hf/177Hf ratio of 0·282308 ± 0·000006 (2σ) (Blichert-Toft, 2008). The correction factor is 0·46 ± 0·03%. Uncertainty in the preferred values for 91500 was propagated to the ultimate results for the samples according to equation (3). Off-line selection and integration of background and analyte signals, and interference and mass fractionation correction and external calibration of Lu–Hf isotopic ratios were also performed by ICPMSDataCal. The obtained Hf isotopic compositions are 0·282015 ± 0·000025 (2σ, n = 14) for GJ-1 and 0·282723 ± 0·000016 (2σ, n = 15) for Monastery, respectively.

RESULTS

Zircon U–Pb isotopic ages

A total of 107 spots on 75 zircon grains from the garnet pyroxenites and 15 spots on seven zircon grains from the garnet-rich granulite were analyzed by LA-ICP-MS (Tables 4 and 5 and Figs 5–10). Half of the analyses give concordant or near concordant U–Pb ages ranging from c. 2700 to 17 Ma. Discordance in zircon U–Pb dating by LA-ICP-MS arises principally from (1) loss of radiogenic Pb and (2) large uncertainty in 207Pb/235U because of the low amount of radiogenic 207Pb. The loss of radiogenic Pb would result in discordance in single zircon U–Pb geochronology, but has a lesser effect on 207Pb/206Pb. Time-integrated radiogenic 207Pb in the Precambrian zircons is generally high enough to be accurately determined by LA-ICP-MS. However, a high statistical uncertainty in 207Pb/235U is possible, especially for analyses with small ablation spots, because of the low radiogenic 207Pb content of some young zircons. Therefore, 207Pb/206Pb ages for the Precambrian zircons and 206Pb/238U ages for the Phanerozoic zircons were used in the following discussion.

Table 4:

Summary of U–Th–Pb isotopic ratios and ages

 207Pb/206Pb 207Pb/235206Pb/238208Pb/232Th 238U/232Th 207Pb/206Pb 207Pb/235206Pb/238208Pb/232Th 
 Ratio 1σ Ratio 1σ Ratio 1σ Ratio 1σ Ratio Age (Ma) 1σ Age (Ma) 1σ Age (Ma) 1σ Age (Ma) 1σ 
Garnet pyroxenite vein in the composite xenolith 
DMP122-1 0·0480 0·0021 0·0657 0·0038 0·0100 0·0002 0·0021 0·0002 4·76 102 109 65 64 43 
DMP122-2 0·0480 0·0020 0·0499 0·0032 0·0075 0·0001 0·0015 0·0001 1·72 98 96 49 48 30 
DMP122-3 0·0474 0·0033 0·0454 0·0034 0·0075 0·0003 0·0014 0·0001 3·78 78 150 45 48 28 
DMP122-4 0·0429 0·0023 0·0449 0·0032 0·0076 0·0001 0·0011 0·0000 1·32 error error 45 49 22 
DMP122-5 0·0483 0·0014 0·0600 0·0034 0·0089 0·0001 0·0020 0·0001 5·03 115 69 59 57 40 
DMP122-6 0·0506 0·0026 0·1251 0·0087 0·0179 0·0003 0·0076 0·0005 10·9 233 120 120 114 154 10 
DMP122-7 0·1508 0·0094 6·8892 0·6259 0·3341 0·0127 0·1112 0·0095 1·94 2355 101 2097 81 1858 62 2130 174 
DMP134-1 0·0506 0·0021 0·2806 0·0210 0·0401 0·0007 0·0121 0·0003 1·20 221 95 251 17 254 243 
DMP134-2 0·0590 0·0020 0·1729 0·0115 0·0213 0·0006 0·0066 0·0003 1·64 569 69 162 10 136 132 
DMP134-3 0·0521 0·0019 0·2273 0·0149 0·0314 0·0004 0·0095 0·0002 2·43 287 79 208 12 199 191 
DMP134-5 0·0512 0·0019 0·2542 0·0143 0·0360 0·0003 0·0115 0·0002 2·33 250 83 230 12 228 232 
DMP134-6 0·0586 0·0020 0·3124 0·0162 0·0387 0·0005 0·0150 0·0004 2·40 554 76 276 13 244 301 
DMP406-1 0·0515 0·0031 0·1244 0·0109 0·0174 0·0004 0·0060 0·0004 5·52 265 135 119 10 111 120 
DMP406-2 0·1614 0·0019 9·6082 0·5395 0·4309 0·0058 0·1230 0·0020 2·04 2472 25 2398 52 2310 26 2344 36 
DMP406-3 0·1613 0·0044 9·0344 0·5890 0·4061 0·0143 0·1206 0·0051 2·40 2469 41 2341 60 2197 66 2301 92 
DMP406-4 0·1107 0·0024 5·0479 0·2950 0·3332 0·0073 0·0962 0·0024 1·78 1811 39 1827 50 1854 35 1857 44 
DMP406-5 0·1120 0·0026 5·2380 0·3533 0·3403 0·0081 0·0974 0·0025 1·32 1832 42 1859 58 1888 39 1879 45 
DMP406-6 0·1328 0·0172 3·9099 0·5170 0·2262 0·0124 0·0641 0·0058 1·36 2135 223 1616 107 1314 65 1255 109 
DMP406-7 0·1334 0·0118 6·5955 0·6709 0·3651 0·0164 0·1172 0·0164 3·12 2144 155 2059 90 2006 78 2240 297 
DMP406-8 0·1091 0·0016 5·0284 0·2298 0·3322 0·0057 0·0697 0·0016 2·24 1784 27 1824 39 1849 28 1363 31 
DMP406-9 0·0929 0·0011 3·3199 0·1212 0·2572 0·0037 0·0838 0·0022 9·23 1487 22 1486 28 1476 19 1627 41 
DMP406-10* 0·0657 0·0030 0·7373 0·0341 0·0815 0·0012 0·0576 0·0027 10·9 794 94 561 20 505 1131 52 
DMP406-11* 0·0821 0·0037 0·7625 0·0364 0·0672 0·0011 1·7819 0·4223 509 1250 117 575 21 419 error error 
DMP406-12 0·1231 0·0012 6·1607 0·1250 0·3595 0·0037 0·0991 0·0010 1·49 2002 18 1999 18 1980 18 1911 18 
DMP406-13 0·1114 0·0020 3·9485 0·1180 0·2554 0·0031 0·0936 0·0028 6·00 1822 31 1624 24 1466 16 1808 52 
DMP406-14 0·0501 0·0037 0·1271 0·0102 0·0184 0·0003 0·0049 0·0003 2·04 198 172 121 117 98·3 
DMP406-15 0·0751 0·0029 1·2730 0·0750 0·1245 0·0027 0·0306 0·0009 0·64 1072 79 834 34 757 16 609 17 
DMP406-16 0·0753 0·0026 1·2943 0·0866 0·1242 0·0015 0·0330 0·0009 0·93 1077 70 843 38 755 656 17 
DMP406-18 0·0502 0·0053 0·2458 0·0291 0·0355 0·0009 0·0131 0·0008 1·33 211 220 223 24 225 262 16 
DMP406-19 0·0623 0·0020 0·8165 0·0507 0·0944 0·0016 0·1225 0·0119 62·9 683 69 606 28 582 10 2336 214 
DNP444-1 0·1481 0·0016 8·0246 0·5507 0·3923 0·0055 0·1049 0·0016 1·78 2324 18 2234 62 2133 26 2015 29 
DNP444-2 0·1559 0·0015 9·5468 0·5926 0·4426 0·0077 0·1240 0·0022 2·21 2413 16 2392 57 2362 34 2363 40 
DNP444-3 0·0638 0·0048 0·4801 0·0452 0·0550 0·0017 0·0175 0·0007 1·29 744 161 398 31 345 10 352 15 
Garnet pyroxenite vein in the composite xenolith 
DMP552-1 0·1010 0·0105 0·2923 0·0317 0·0221 0·0007 0·0072 0·0004 0·83 1644 194 260 25 141 145 
DMP552-2 0·1267 0·0055 5·7693 0·4582 0·3507 0·0224 0·0804 0·0024 1·94 2054 76 1942 69 1938 107 1563 45 
DMP552-3 0·0692 0·0042 0·1573 0·0118 0·0169 0·0003 0·0062 0·0003 2·11 906 126 148 10 108 125 
DMP552-4 0·0489 0·0024 0·1077 0·0076 0·0160 0·0004 0·0051 0·0002 2·56 139 117 104 103 104 
DMP552-5 0·1630 0·0014 9·9442 0·5481 0·4391 0·0044 0·1374 0·0028 4·83 2487 15 2430 51 2346 20 2603 50 
DMP552-6 0·1544 0·0020 5·1734 0·3225 0·2416 0·0034 0·0677 0·0020 10·4 2395 22 1848 53 1395 18 1324 39 
DMP552-8 0·1578 0·0015 10·108 0·5607 0·4608 0·0063 0·1214 0·0025 0·51 2432 17 2445 51 2443 28 2316 45 
DMP552-9 0·0504 0·0015 0·1101 0·0065 0·0158 0·0002 0·0054 0·0002 2·70 213 70 106 101 108 
DMP552-10 0·0550 0·0036 0·0968 0·0063 0·0133 0·0005 0·0053 0·0003 10·6 413 148 94 85 107 
DMP552-11 0·0717 0·0009 1·8394 0·1012 0·1845 0·0025 0·0534 0·0009 2·56 976 26 1060 36 1092 14 1052 18 
DMP552-12 0·0697 0·0014 1·7958 0·1132 0·1852 0·0028 0·0561 0·0015 3·08 920 41 1044 41 1095 15 1104 29 
DMP552-13 0·0493 0·0031 0·0208 0·0017 0·0031 0·0000 0·0010 0·0000 1·63 161 150 21 20 20 
DMP552-14 0·0482 0·0024 0·2376 0·0169 0·0353 0·0004 0·0101 0·0003 5·10 109 124 216 14 224 204 
DMP552-15 0·0483 0·0019 0·1167 0·0068 0·0176 0·0002 0·0056 0·0002 4·63 117 89 112 112 114 
DMP552-16 0·0533 0·0016 0·1155 0·0066 0·0156 0·0002 0·0052 0·0002 4·63 343 38 111 100 106 
DMP552-18 0·0500 0·0018 0·1300 0·0088 0·0187 0·0003 0·0056 0·0002 2·77 195 83 124 119 113 
DMP552-19 0·0548 0·0032 0·1407 0·0113 0·0186 0·0003 0·0055 0·0001 0·51 406 99 134 10 119 111 
DMP552-20 0·1662 0·0016 11·042 0·5603 0·4776 0·0069 0·1339 0·0030 1·61 2520 15 2527 47 2517 30 2540 53 
DMP552-21* 0·0668 0·0081 0·0975 0·0123 0·0100 0·0003 0·0030 0·0003 4·35 831 256 94 11 64 60 
DMP552-22 0·1607 0·0012 10·363 0·5576 0·4641 0·0052 0·1250 0·0020 3·26 2465 12 2468 50 2458 23 2381 36 
DMP552-23 0·1601 0·0013 9·6246 0·5939 0·4328 0·0038 0·1267 0·0018 5·29 2457 13 2400 57 2318 17 2412 32 
DMP552-24† 0·0521 0·0014 0·1033 0·0058 0·0142 0·0002 0·0048 0·0002 4·3 288 60 100 91 98 
DMP552-25 0·1061 0·0021 4·5683 0·2535 0·3071 0·0054 0·0971 0·0025 1·48 1733 37 1743 46 1727 26 1873 46 
DMP552-26 0·0725 0·0026 1·5309 0·0956 0·1510 0·0024 0·0822 0·0052 30·2 1011 72 943 38 906 14 1596 97 
DMP552-27 0·0490 0·0036 0·1320 0·0128 0·0191 0·0006 0·0057 0·0003 0·94 146 163 126 12 122 116 
DMP552-28 0·0535 0·0050 0·0193 0·0021 0·0026 0·0001 0·0008 0·0001 1·96 350 213 19 17 17 
DMP552-29 0·0773 0·0049 0·3611 0·0311 0·0337 0·0006 0·0141 0·0013 2·06 1129 126 313 23 213 284 25 
DMP552-30 0·0755 0·0015 1·9523 0·1172 0·1844 0·0022 0·0528 0·0007 0·58 1081 40 1099 40 1091 12 1039 14 
DMP552-31 0·0503 0·0021 0·2195 0·0160 0·0312 0·0004 0·0112 0·0009 9·56 209 98 202 13 198 224 17 
DMP552-32† 0·0660 0·0014 1·1967 0·0877 0·1295 0·0034 0·0390 0·0017 2·27 805 45 799 41 785 19 773 34 
DMP552-33 0·0522 0·0022 0·2018 0·0175 0·0280 0·0006 0·0456 0·0052 132 300 98 187 15 178 902 101 
DMP552-37 0·0569 0·0043 0·1221 0·0113 0·0157 0·0004 0·0054 0·0002 2·37 487 167 117 10 100 109 
DMP552-38 0·0599 0·0037 0·1278 0·0102 0·0158 0·0005 0·0051 0·0002 2·21 611 133 122 101 103 
Garnet pyroxenite vein in the composite xenolith 
DMP552-39 0·0491 0·0028 0·0698 0·0056 0·0103 0·0002 0·0034 0·0001 0·52 154 133 69 66 69 
DMP552-40 0·1028 0·0028 3·5219 0·2241 0·2482 0·0058 0·0640 0·0026 2·81 1676 45 1532 50 1429 30 1254 49 
DMP552-41 0·0624 0·0044 0·1672 0·0137 0·0195 0·0006 0·0062 0·0003 1·51 687 150 157 12 124 125 
DMP552-42 0·0480 0·0027 0·1028 0·0075 0·0154 0·0004 0·0061 0·0003 4·67 98 135 99 98 124 
DMP552-43 0·1004 0·0023 3·5441 0·0878 0·2529 0·0040 0·0762 0·0018 2·22 1631 43 1537 20 1453 21 1485 34 
DMP552-44 0·0516 0·0025 0·1420 0·0075 0·0196 0·0005 0·0071 0·0003 1·12 333 111 135 125 144 
DNP554-1 0·0570 0·0032 0·3868 0·0281 0·0499 0·0007 0·0146 0·0005 1·36 500 124 332 21 314 292 
DNP554-2 0·0552 0·0040 0·3884 0·0354 0·0514 0·0012 0·0173 0·0009 1·51 420 161 333 26 323 347 18 
DNP554-3 0·0535 0·0031 0·2028 0·0159 0·0272 0·0004 0·0088 0·0003 1·07 350 131 187 13 173 177 
DNP554-4 0·1032 0·0063 0·5697 0·0460 0·0407 0·0010 0·0211 0·0013 2·41 1683 113 458 30 257 423 26 
DNP554-5 0·1038 0·0093 0·5783 0·0584 0·0412 0·0008 0·0162 0·0009 0·93 1694 165 463 38 260 325 18 
DNP554-6 0·0625 0·0009 0·8592 0·0457 0·0992 0·0010 0·0308 0·0003 0·81 700 30 630 25 610 613 
DNP554-7 0·1119 0·0093 0·5748 0·0577 0·0369 0·0009 0·1160 0·0137 18·1 1831 152 461 37 234 2218 248 
DNP554-8 0·1161 0·0125 0·1144 0·0108 0·0082 0·0003 0·0024 0·0002 1·15 1898 190 110 10 52 49 
DNP554-9 1·7261 0·2395 3·1317 0·3708 0·0324 0·0032 0·0442 0·0071 0·93 error error 1441 91 205 20 874 138 
DNP554-10 0·0681 0·0026 0·6670 0·0511 0·0711 0·0015 0·0286 0·0007 1·33 872 80 519 31 443 570 13 
DMP554-11 0·0843 0·0066 0·5905 0·0424 0·0537 0·0021 0·0181 0·0012 1·69 1299 158 471 27 337 13 362 23 
DMP554-12 0·0542 0·0064 0·2670 0·0313 0·0365 0·0027 0·0091 0·0008 1·20 389 264 240 25 231 17 184 17 
DMP554-15 0·0843 0·0108 0·8278 0·1189 0·0732 0·0038 0·0378 0·0050 1·63 1298 253 612 66 455 23 751 98 
DMP555-1 0·0490 0·0008 0·3514 0·0227 0·0513 0·0005 0·0158 0·0002 1·38 150 39 306 17 323 317 
DMP555-3 0·0535 0·0015 0·3722 0·0217 0·0501 0·0007 0·0153 0·0004 1·78 350 63 321 16 315 307 
DMP555-4 0·0510 0·0012 0·3471 0·0198 0·0491 0·0005 0·0146 0·0002 0·93 239 56 303 15 309 294 
DMP555-5 0·0496 0·0015 0·3454 0·0224 0·0506 0·0006 0·0163 0·0003 1·71 176 69 301 17 318 326 
DMP555-6 0·0520 0·0024 0·3469 0·0258 0·0483 0·0006 0·0155 0·0005 2·08 283 104 302 19 304 311 11 
DMP555-7 0·0511 0·0018 0·3517 0·0225 0·0497 0·0007 0·0153 0·0003 1·78 256 81 306 17 312 308 
DMP555-8 0·0553 0·0021 0·3753 0·0228 0·0492 0·0006 0·0156 0·0005 2·19 433 83 324 17 310 312 
DMP555-9 0·0544 0·0012 0·3664 0·0204 0·0484 0·0006 0·0146 0·0002 1·16 387 48 317 15 305 292 
DMP555-10 0·0606 0·0017 0·4041 0·0253 0·0485 0·0007 0·0163 0·0003 1·90 633 63 345 18 305 327 
DMP555-11 0·0568 0·0012 0·3453 0·0209 0·0438 0·0004 0·0133 0·0002 1·23 483 46 301 16 276 266 
DMP555-13 0·0530 0·0017 0·3599 0·0208 0·0492 0·0007 0·0153 0·0003 2·08 328 70 312 16 309 306 
DMP555-15 0·0552 0·0035 0·3986 0·0337 0·0533 0·0009 0·0153 0·0006 1·45 420 141 341 24 335 306 12 
DMP555-16 0·0530 0·0030 0·2933 0·0249 0·0393 0·0006 0·0116 0·0004 1·78 328 130 261 20 248 234 
DMP555-17 0·0616 0·0039 0·4137 0·0336 0·0498 0·0013 0·0151 0·0007 2·10 661 135 352 24 313 302 13 
Garnet pyroxenite vein in the composite xenolith 
DMP555-19 0·0512 0·0010 0·3680 0·0218 0·0516 0·0006 0·0155 0·0002 0·74 256 44 318 16 324 312 
DMP555-20 0·0551 0·0035 0·3831 0·0337 0·0510 0·0009 0·0172 0·0008 2·02 417 110 329 25 320 345 16 
DMP555-21 0·0505 0·0013 0·3232 0·0214 0·0461 0·0006 0·0144 0·0002 0·92 217 55 284 16 291 288 
DMP555-22 0·0546 0·0018 0·3779 0·0230 0·0496 0·0006 0·0159 0·0003 1·86 398 79 325 17 312 318 
DMP555-23 0·1361 0·0150 0·3568 0·0381 0·0220 0·0009 0·0104 0·0007 1·22 2189 193 310 28 140 208 13 
DMP555-24 0·0557 0·0012 0·3955 0·0213 0·0509 0·0008 0·0167 0·0003 0·86 439 46 338 15 320 334 
DMP555-29 0·0522 0·0031 0·3719 0·0346 0·0501 0·0009 0·0177 0·0005 1·57 295 140 321 26 315 354 11 
DMP555-30 0·0553 0·0027 0·3981 0·0343 0·0510 0·0009 0·0159 0·0005 0·72 433 105 340 25 321 319 
DMP555-37 0·0556 0·0046 0·3713 0·0360 0·0497 0·0015 0·0156 0·0009 1·60 436 184 321 27 312 313 17 
DMP555-47 0·5251 0·2391 0·4959 0·0617 0·0192 0·0012 0·0155 0·0019 1·43 4313 917 409 42 122 310 38 
Garnet-rich granulite xenolith 
DMP467-1 0·0461 0·0022 0·2192 0·0159 0·0344 0·0007 0·0112 0·0002 0·42 111 201 13 218 226 
DMP467-2* 0·0461 0·0027 0·2178 0·0197 0·0346 0·0012 0·0114 0·0004 0·45 400 error 200 16 219 228 
DMP467-4 0·0534 0·0027 0·2355 0·0145 0·0322 0·0005 0·0104 0·0004 1·17 346 113 215 12 205 208 
DMP467-5 0·0501 0·0053 0·2156 0·0255 0·0309 0·0005 0·0106 0·0005 1·88 211 220 198 21 196 214 10 
DMP467-6 0·0520 0·0018 0·2709 0·0156 0·0378 0·0004 0·0169 0·0004 1·42 283 75 243 12 239 339 
DMP467-7 0·0473 0·0042 0·2214 0·0231 0·0336 0·0004 0·0098 0·0008 2·05 65 200 203 19 213 197 16 
DMP467-8 0·0488 0·0030 0·2285 0·0188 0·0345 0·0004 0·0085 0·0003 0·92 139 141 209 16 218 170 
DMP467-9 0·0487 0·0036 0·2144 0·0194 0·0319 0·0005 0·0103 0·0003 0·70 132 167 197 16 202 207 
DMP467-11 0·0493 0·0019 0·2167 0·0137 0·0316 0·0004 0·0102 0·0002 0·59 167 95 199 11 201 206 
DMP467-12 0·0697 0·0024 1·3424 0·0922 0·1399 0·0023 0·0456 0·0008 2·04 918 66 864 40 844 13 901 16 
DMP467-14 0·1818 0·0024 12·834 0·5622 0·5110 0·0059 0·1433 0·0023 1·85 2669 22 2668 41 2661 25 2706 41 
DMP467-15 0·1804 0·0019 12·668 0·5681 0·5074 0·0075 0·1339 0·0023 1·15 2657 18 2655 42 2646 32 2541 40 
DMP467-16 0·1851 0·0030 13·308 0·6225 0·5193 0·0056 0·1438 0·0023 1·63 2699 26 2702 44 2696 24 2716 40 
DMP467-20 0·0754 0·0017 1·8473 0·0808 0·1760 0·0017 0·0501 0·0009 2·54 1080 46 1062 29 1045 987 17 
DMP467-21 0·0778 0·0020 1·9020 0·0890 0·1764 0·0026 0·0537 0·0014 2·61 1143 45 1082 31 1048 14 1057 26 
 207Pb/206Pb 207Pb/235206Pb/238208Pb/232Th 238U/232Th 207Pb/206Pb 207Pb/235206Pb/238208Pb/232Th 
 Ratio 1σ Ratio 1σ Ratio 1σ Ratio 1σ Ratio Age (Ma) 1σ Age (Ma) 1σ Age (Ma) 1σ Age (Ma) 1σ 
Garnet pyroxenite vein in the composite xenolith 
DMP122-1 0·0480 0·0021 0·0657 0·0038 0·0100 0·0002 0·0021 0·0002 4·76 102 109 65 64 43 
DMP122-2 0·0480 0·0020 0·0499 0·0032 0·0075 0·0001 0·0015 0·0001 1·72 98 96 49 48 30 
DMP122-3 0·0474 0·0033 0·0454 0·0034 0·0075 0·0003 0·0014 0·0001 3·78 78 150 45 48 28 
DMP122-4 0·0429 0·0023 0·0449 0·0032 0·0076 0·0001 0·0011 0·0000 1·32 error error 45 49 22 
DMP122-5 0·0483 0·0014 0·0600 0·0034 0·0089 0·0001 0·0020 0·0001 5·03 115 69 59 57 40 
DMP122-6 0·0506 0·0026 0·1251 0·0087 0·0179 0·0003 0·0076 0·0005 10·9 233 120 120 114 154 10 
DMP122-7 0·1508 0·0094 6·8892 0·6259 0·3341 0·0127 0·1112 0·0095 1·94 2355 101 2097 81 1858 62 2130 174 
DMP134-1 0·0506 0·0021 0·2806 0·0210 0·0401 0·0007 0·0121 0·0003 1·20 221 95 251 17 254 243 
DMP134-2 0·0590 0·0020 0·1729 0·0115 0·0213 0·0006 0·0066 0·0003 1·64 569 69 162 10 136 132 
DMP134-3 0·0521 0·0019 0·2273 0·0149 0·0314 0·0004 0·0095 0·0002 2·43 287 79 208 12 199 191 
DMP134-5 0·0512 0·0019 0·2542 0·0143 0·0360 0·0003 0·0115 0·0002 2·33 250 83 230 12 228 232 
DMP134-6 0·0586 0·0020 0·3124 0·0162 0·0387 0·0005 0·0150 0·0004 2·40 554 76 276 13 244 301 
DMP406-1 0·0515 0·0031 0·1244 0·0109 0·0174 0·0004 0·0060 0·0004 5·52 265 135 119 10 111 120 
DMP406-2 0·1614 0·0019 9·6082 0·5395 0·4309 0·0058 0·1230 0·0020 2·04 2472 25 2398 52 2310 26 2344 36 
DMP406-3 0·1613 0·0044 9·0344 0·5890 0·4061 0·0143 0·1206 0·0051 2·40 2469 41 2341 60 2197 66 2301 92 
DMP406-4 0·1107 0·0024 5·0479 0·2950 0·3332 0·0073 0·0962 0·0024 1·78 1811 39 1827 50 1854 35 1857 44 
DMP406-5 0·1120 0·0026 5·2380 0·3533 0·3403 0·0081 0·0974 0·0025 1·32 1832 42 1859 58 1888 39 1879 45 
DMP406-6 0·1328 0·0172 3·9099 0·5170 0·2262 0·0124 0·0641 0·0058 1·36 2135 223 1616 107 1314 65 1255 109 
DMP406-7 0·1334 0·0118 6·5955 0·6709 0·3651 0·0164 0·1172 0·0164 3·12 2144 155 2059 90 2006 78 2240 297 
DMP406-8 0·1091 0·0016 5·0284 0·2298 0·3322 0·0057 0·0697 0·0016 2·24 1784 27 1824 39 1849 28 1363 31 
DMP406-9 0·0929 0·0011 3·3199 0·1212 0·2572 0·0037 0·0838 0·0022 9·23 1487 22 1486 28 1476 19 1627 41 
DMP406-10* 0·0657 0·0030 0·7373 0·0341 0·0815 0·0012 0·0576 0·0027 10·9 794 94 561 20 505 1131 52 
DMP406-11* 0·0821 0·0037 0·7625 0·0364 0·0672 0·0011 1·7819 0·4223 509 1250 117 575 21 419 error error 
DMP406-12 0·1231 0·0012 6·1607 0·1250 0·3595 0·0037 0·0991 0·0010 1·49 2002 18 1999 18 1980 18 1911 18 
DMP406-13 0·1114 0·0020 3·9485 0·1180 0·2554 0·0031 0·0936 0·0028 6·00 1822 31 1624 24 1466 16 1808 52 
DMP406-14 0·0501 0·0037 0·1271 0·0102 0·0184 0·0003 0·0049 0·0003 2·04 198 172 121 117 98·3 
DMP406-15 0·0751 0·0029 1·2730 0·0750 0·1245 0·0027 0·0306 0·0009 0·64 1072 79 834 34 757 16 609 17 
DMP406-16 0·0753 0·0026 1·2943 0·0866 0·1242 0·0015 0·0330 0·0009 0·93 1077 70 843 38 755 656 17 
DMP406-18 0·0502 0·0053 0·2458 0·0291 0·0355 0·0009 0·0131 0·0008 1·33 211 220 223 24 225 262 16 
DMP406-19 0·0623 0·0020 0·8165 0·0507 0·0944 0·0016 0·1225 0·0119 62·9 683 69 606 28 582 10 2336 214 
DNP444-1 0·1481 0·0016 8·0246 0·5507 0·3923 0·0055 0·1049 0·0016 1·78 2324 18 2234 62 2133 26 2015 29 
DNP444-2 0·1559 0·0015 9·5468 0·5926 0·4426 0·0077 0·1240 0·0022 2·21 2413 16 2392 57 2362 34 2363 40 
DNP444-3 0·0638 0·0048 0·4801 0·0452 0·0550 0·0017 0·0175 0·0007 1·29 744 161 398 31 345 10 352 15 
Garnet pyroxenite vein in the composite xenolith 
DMP552-1 0·1010 0·0105 0·2923 0·0317 0·0221 0·0007 0·0072 0·0004 0·83 1644 194 260 25 141 145 
DMP552-2 0·1267 0·0055 5·7693 0·4582 0·3507 0·0224 0·0804 0·0024 1·94 2054 76 1942 69 1938 107 1563 45 
DMP552-3 0·0692 0·0042 0·1573 0·0118 0·0169 0·0003 0·0062 0·0003 2·11 906 126 148 10 108 125 
DMP552-4 0·0489 0·0024 0·1077 0·0076 0·0160 0·0004 0·0051 0·0002 2·56 139 117 104 103 104 
DMP552-5 0·1630 0·0014 9·9442 0·5481 0·4391 0·0044 0·1374 0·0028 4·83 2487 15 2430 51 2346 20 2603 50 
DMP552-6 0·1544 0·0020 5·1734 0·3225 0·2416 0·0034 0·0677 0·0020 10·4 2395 22 1848 53 1395 18 1324 39 
DMP552-8 0·1578 0·0015 10·108 0·5607 0·4608 0·0063 0·1214 0·0025 0·51 2432 17 2445 51 2443 28 2316 45 
DMP552-9 0·0504 0·0015 0·1101 0·0065 0·0158 0·0002 0·0054 0·0002 2·70 213 70 106 101 108 
DMP552-10 0·0550 0·0036 0·0968 0·0063 0·0133 0·0005 0·0053 0·0003 10·6 413 148 94 85 107 
DMP552-11 0·0717 0·0009 1·8394 0·1012 0·1845 0·0025 0·0534 0·0009 2·56 976 26 1060 36 1092 14 1052 18 
DMP552-12 0·0697 0·0014 1·7958 0·1132 0·1852 0·0028 0·0561 0·0015 3·08 920 41 1044 41 1095 15 1104 29 
DMP552-13 0·0493 0·0031 0·0208 0·0017 0·0031 0·0000 0·0010 0·0000 1·63 161 150 21 20 20 
DMP552-14 0·0482 0·0024 0·2376 0·0169 0·0353 0·0004 0·0101 0·0003 5·10 109 124 216 14 224 204 
DMP552-15 0·0483 0·0019 0·1167 0·0068 0·0176 0·0002 0·0056 0·0002 4·63 117 89 112 112 114 
DMP552-16 0·0533 0·0016 0·1155 0·0066 0·0156 0·0002 0·0052 0·0002 4·63 343 38 111 100 106 
DMP552-18 0·0500 0·0018 0·1300 0·0088 0·0187 0·0003 0·0056 0·0002 2·77 195 83 124 119 113 
DMP552-19 0·0548 0·0032 0·1407 0·0113 0·0186 0·0003 0·0055 0·0001 0·51 406 99 134 10 119 111 
DMP552-20 0·1662 0·0016 11·042 0·5603 0·4776 0·0069 0·1339 0·0030 1·61 2520 15 2527 47 2517 30 2540 53 
DMP552-21* 0·0668 0·0081 0·0975 0·0123 0·0100 0·0003 0·0030 0·0003 4·35 831 256 94 11 64 60 
DMP552-22 0·1607 0·0012 10·363 0·5576 0·4641 0·0052 0·1250 0·0020 3·26 2465 12 2468 50 2458 23 2381 36 
DMP552-23 0·1601 0·0013 9·6246 0·5939 0·4328 0·0038 0·1267 0·0018 5·29 2457 13 2400 57 2318 17 2412 32 
DMP552-24† 0·0521 0·0014 0·1033 0·0058 0·0142 0·0002 0·0048 0·0002 4·3 288 60 100 91 98 
DMP552-25 0·1061 0·0021 4·5683 0·2535 0·3071 0·0054 0·0971 0·0025 1·48 1733 37 1743 46 1727 26 1873 46 
DMP552-26 0·0725 0·0026 1·5309 0·0956 0·1510 0·0024 0·0822 0·0052 30·2 1011 72 943 38 906 14 1596 97 
DMP552-27 0·0490 0·0036 0·1320 0·0128 0·0191 0·0006 0·0057 0·0003 0·94 146 163 126 12 122 116 
DMP552-28 0·0535 0·0050 0·0193 0·0021 0·0026 0·0001 0·0008 0·0001 1·96 350 213 19 17 17 
DMP552-29 0·0773 0·0049 0·3611 0·0311 0·0337 0·0006 0·0141 0·0013 2·06 1129 126 313 23 213 284 25 
DMP552-30 0·0755 0·0015 1·9523 0·1172 0·1844 0·0022 0·0528 0·0007 0·58 1081 40 1099 40 1091 12 1039 14 
DMP552-31 0·0503 0·0021 0·2195 0·0160 0·0312 0·0004 0·0112 0·0009 9·56 209 98 202 13 198 224 17 
DMP552-32† 0·0660 0·0014 1·1967 0·0877 0·1295 0·0034 0·0390 0·0017 2·27 805 45 799 41 785 19 773 34 
DMP552-33 0·0522 0·0022 0·2018 0·0175 0·0280 0·0006 0·0456 0·0052 132 300 98 187 15 178 902 101 
DMP552-37 0·0569 0·0043 0·1221 0·0113 0·0157 0·0004 0·0054 0·0002 2·37 487 167 117 10 100 109 
DMP552-38 0·0599 0·0037 0·1278 0·0102 0·0158 0·0005 0·0051 0·0002 2·21 611 133 122 101 103 
Garnet pyroxenite vein in the composite xenolith 
DMP552-39 0·0491 0·0028 0·0698 0·0056 0·0103 0·0002 0·0034 0·0001 0·52 154 133 69 66 69 
DMP552-40 0·1028 0·0028 3·5219 0·2241 0·2482 0·0058 0·0640 0·0026 2·81 1676 45 1532 50 1429 30 1254 49 
DMP552-41 0·0624 0·0044 0·1672 0·0137 0·0195 0·0006 0·0062 0·0003 1·51 687 150 157 12 124 125 
DMP552-42 0·0480 0·0027 0·1028 0·0075 0·0154 0·0004 0·0061 0·0003 4·67 98 135 99 98 124 
DMP552-43 0·1004 0·0023 3·5441 0·0878 0·2529 0·0040 0·0762 0·0018 2·22 1631 43 1537 20 1453 21 1485 34 
DMP552-44 0·0516 0·0025 0·1420 0·0075 0·0196 0·0005 0·0071 0·0003 1·12 333 111 135 125 144 
DNP554-1 0·0570 0·0032 0·3868 0·0281 0·0499 0·0007 0·0146 0·0005 1·36 500 124 332 21 314 292 
DNP554-2 0·0552 0·0040 0·3884 0·0354 0·0514 0·0012 0·0173 0·0009 1·51 420 161 333 26 323 347 18 
DNP554-3 0·0535 0·0031 0·2028 0·0159 0·0272 0·0004 0·0088 0·0003 1·07 350 131 187 13 173 177 
DNP554-4 0·1032 0·0063 0·5697 0·0460 0·0407 0·0010 0·0211 0·0013 2·41 1683 113 458 30 257 423 26 
DNP554-5 0·1038 0·0093 0·5783 0·0584 0·0412 0·0008 0·0162 0·0009 0·93 1694 165 463 38 260 325 18 
DNP554-6 0·0625 0·0009 0·8592 0·0457 0·0992 0·0010 0·0308 0·0003 0·81 700 30 630 25 610 613 
DNP554-7 0·1119 0·0093 0·5748 0·0577 0·0369 0·0009 0·1160 0·0137 18·1 1831 152 461 37 234 2218 248 
DNP554-8 0·1161 0·0125 0·1144 0·0108 0·0082 0·0003 0·0024 0·0002 1·15 1898 190 110 10 52 49 
DNP554-9 1·7261 0·2395 3·1317 0·3708 0·0324 0·0032 0·0442 0·0071 0·93 error error 1441 91 205 20 874 138 
DNP554-10 0·0681 0·0026 0·6670 0·0511 0·0711 0·0015 0·0286 0·0007 1·33 872 80 519 31 443 570 13 
DMP554-11 0·0843 0·0066 0·5905 0·0424 0·0537 0·0021 0·0181 0·0012 1·69 1299 158 471 27 337 13 362 23 
DMP554-12 0·0542 0·0064 0·2670 0·0313 0·0365 0·0027 0·0091 0·0008 1·20 389 264 240 25 231 17 184 17 
DMP554-15 0·0843 0·0108 0·8278 0·1189 0·0732 0·0038 0·0378 0·0050 1·63 1298 253 612 66 455 23 751 98 
DMP555-1 0·0490 0·0008 0·3514 0·0227 0·0513 0·0005 0·0158 0·0002 1·38 150 39 306 17 323 317 
DMP555-3 0·0535 0·0015 0·3722 0·0217 0·0501 0·0007 0·0153 0·0004 1·78 350 63 321 16 315 307 
DMP555-4 0·0510 0·0012 0·3471 0·0198 0·0491 0·0005 0·0146 0·0002 0·93 239 56 303 15 309 294 
DMP555-5 0·0496 0·0015 0·3454 0·0224 0·0506 0·0006 0·0163 0·0003 1·71 176 69 301 17 318 326 
DMP555-6 0·0520 0·0024 0·3469 0·0258 0·0483 0·0006 0·0155 0·0005 2·08 283 104 302 19 304 311 11 
DMP555-7 0·0511 0·0018 0·3517 0·0225 0·0497 0·0007 0·0153 0·0003 1·78 256 81 306 17 312 308 
DMP555-8 0·0553 0·0021 0·3753 0·0228 0·0492 0·0006 0·0156 0·0005 2·19 433 83 324 17 310 312 
DMP555-9 0·0544 0·0012 0·3664 0·0204 0·0484 0·0006 0·0146 0·0002 1·16 387 48 317 15 305 292 
DMP555-10 0·0606 0·0017 0·4041 0·0253 0·0485 0·0007 0·0163 0·0003 1·90 633 63 345 18 305 327 
DMP555-11 0·0568 0·0012 0·3453 0·0209 0·0438 0·0004 0·0133 0·0002 1·23 483 46 301 16 276 266 
DMP555-13 0·0530 0·0017 0·3599 0·0208 0·0492 0·0007 0·0153 0·0003 2·08 328 70 312 16 309 306 
DMP555-15 0·0552 0·0035 0·3986 0·0337 0·0533 0·0009 0·0153 0·0006 1·45 420 141 341 24 335 306 12 
DMP555-16 0·0530 0·0030 0·2933 0·0249 0·0393 0·0006 0·0116 0·0004 1·78 328 130 261 20 248 234 
DMP555-17 0·0616 0·0039 0·4137 0·0336 0·0498 0·0013 0·0151 0·0007 2·10 661 135 352 24 313 302 13 
Garnet pyroxenite vein in the composite xenolith 
DMP555-19 0·0512 0·0010 0·3680 0·0218 0·0516 0·0006 0·0155 0·0002 0·74 256 44 318 16 324 312 
DMP555-20 0·0551 0·0035 0·3831 0·0337 0·0510 0·0009 0·0172 0·0008 2·02 417 110 329 25 320 345 16 
DMP555-21 0·0505 0·0013 0·3232 0·0214 0·0461 0·0006 0·0144 0·0002 0·92 217 55 284 16 291 288 
DMP555-22 0·0546 0·0018 0·3779 0·0230 0·0496 0·0006 0·0159 0·0003 1·86 398 79 325 17 312 318 
DMP555-23 0·1361 0·0150 0·3568 0·0381 0·0220 0·0009 0·0104 0·0007 1·22 2189 193 310 28 140 208 13 
DMP555-24 0·0557 0·0012 0·3955 0·0213 0·0509 0·0008 0·0167 0·0003 0·86 439 46 338 15 320 334 
DMP555-29 0·0522 0·0031 0·3719 0·0346 0·0501 0·0009 0·0177 0·0005 1·57 295 140 321 26 315 354 11 
DMP555-30 0·0553 0·0027 0·3981 0·0343 0·0510 0·0009 0·0159 0·0005 0·72 433 105 340 25 321 319 
DMP555-37 0·0556 0·0046 0·3713 0·0360 0·0497 0·0015 0·0156 0·0009 1·60 436 184 321 27 312 313 17 
DMP555-47 0·5251 0·2391 0·4959 0·0617 0·0192 0·0012 0·0155 0·0019 1·43 4313 917 409 42 122 310 38 
Garnet-rich granulite xenolith 
DMP467-1 0·0461 0·0022 0·2192 0·0159 0·0344 0·0007 0·0112 0·0002 0·42 111 201 13 218 226 
DMP467-2* 0·0461 0·0027 0·2178 0·0197 0·0346 0·0012 0·0114 0·0004 0·45 400 error 200 16 219 228 
DMP467-4 0·0534 0·0027 0·2355 0·0145 0·0322 0·0005 0·0104 0·0004 1·17 346 113 215 12 205 208 
DMP467-5 0·0501 0·0053 0·2156 0·0255 0·0309 0·0005 0·0106 0·0005 1·88 211 220 198 21 196 214 10 
DMP467-6 0·0520 0·0018 0·2709 0·0156 0·0378 0·0004 0·0169 0·0004 1·42 283 75 243 12 239 339 
DMP467-7 0·0473 0·0042 0·2214 0·0231 0·0336 0·0004 0·0098 0·0008 2·05 65 200 203 19 213 197 16 
DMP467-8 0·0488 0·0030 0·2285 0·0188 0·0345 0·0004 0·0085 0·0003 0·92 139 141 209 16 218 170 
DMP467-9 0·0487 0·0036 0·2144 0·0194 0·0319 0·0005 0·0103 0·0003 0·70 132 167 197 16 202 207 
DMP467-11 0·0493 0·0019 0·2167 0·0137 0·0316 0·0004 0·0102 0·0002 0·59 167 95 199 11 201 206 
DMP467-12 0·0697 0·0024 1·3424 0·0922 0·1399 0·0023 0·0456 0·0008 2·04 918 66 864 40 844 13 901 16 
DMP467-14 0·1818 0·0024 12·834 0·5622 0·5110 0·0059 0·1433 0·0023 1·85 2669 22 2668 41 2661 25 2706 41 
DMP467-15 0·1804 0·0019 12·668 0·5681 0·5074 0·0075 0·1339 0·0023 1·15 2657 18 2655 42 2646 32 2541 40 
DMP467-16 0·1851 0·0030 13·308 0·6225 0·5193 0·0056 0·1438 0·0023 1·63 2699 26 2702 44 2696 24 2716 40 
DMP467-20 0·0754 0·0017 1·8473 0·0808 0·1760 0·0017 0·0501 0·0009 2·54 1080 46 1062 29 1045 987 17 
DMP467-21 0·0778 0·0020 1·9020 0·0890 0·1764 0·0026 0·0537 0·0014 2·61 1143 45 1082 31 1048 14 1057 26 

*High 204Pb.

†REE-rich inclusion was found.

1σ, standard deviation of the mean. Uncertainty of preferred values for the external standard was propagated to the ultimate results of the samples.

Table 5:

Trace element compositions of zircons from the garnet pyroxenite veins in the composite xenoliths and garnet-rich granulite xenolith

Element: Ti Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th 
Isotope: 49 89 93 139 140 141 143 147 151 155 159 163 165 166 169 173 175 179 181  232 238 
Garnet pyroxenite vein in the composite xenolith 
DMP122-1 61·9 6814 234 6·48 38·9 6·00 38·5 59·4 2·65 180 76·5 843 264 1122 253 2277 346 16318 115 146 2183 10207 
DMP122-2 176 16407 612 68·2 188 28·4 164 189 12·3 671 236 2185 636 2505 523 4509 708 10862 154 361 16134 27798 
DMP122-3 198 12601 624 21·4 94·8 18·4 126 171 9·52 487 183 1780 503 1978 427 3764 554 19382 259 227 5439 19446 
DMP122-4 179 37889 527 486 935 120 596 398 80·7 1281 448 4256 1169 4432 859 6984 1039 12152 164 259 16576 21724 
DMP122-5 121 18673 376 19·3 123 20·1 119 146 44·1 486 196 2048 626 2666 591 5466 898 24572 313 292 4624 23490 
DMP122-6 1·80 229 1·91  5·86 0·016 0·18 0·25 0·18 2·42 1·20 14·4 7·01 39·3 10·4 107 20·6 7430 0·29 25·5 108 1194 
DMP122-7 6·65 163 1·39 0·008 1·62 0·018 0·16 0·12 0·13 1·71 0·80 11·8 5·09 22·1 4·68 41·5 7·87 11999 1·52 3·60 4·53 7·77 
DMP134-1 4·69 707 1·09 0·013 27·0 0·12 2·02 3·96 1·50 16·6 5·38 60·5 22·5 104 24·2 251 49·2 7756 0·48 20·6 307 369 
DMP134-2 78·5 3861 5·78 3·31 102 12·2 94·9 96·7 60·3 212 62·4 532 135 486 89·3 763 129 10556 0·46 40·1 850 1390 
DMP134-3 4·45 1071 5·40 1·38 6·75 0·37 3·23 4·10 1·12 24·2 7·71 92·1 34·3 160 36·3 362 70·2 6758 1·39 30·0 310 744 
DMP134-5 n.d. 1569 10·8 0·67 11·5 0·46 4·02 5·04 0·94 28·8 10·1 130 52·9 248 57·5 578 110 7710 2·54 47·3 456 973 
DMP134-6 n.d. 730 2·52 3·55 17·8 1·54 9·99 7·84 1·06 22·0 6·36 66·6 24·7 112 26·6 274 52·4 7250 0·91 25·8 227 485 
DMP406-1 7·19 1136 5·22 0·013 28·3 0·044 1·70 3·95 0·49 20·6 7·75 88·2 32·4 151 36·5 348 60·5 9908 6·00 10·9 107 528 
DMP406-2 7·26 674 3·18 0·84 31·3 0·74 7·35 6·47 1·88 20·1 5·89 61·3 21·8 94·7 20·7 192 35·4 8888 1·12 173 144 288 
DMP406-3 6·87 295 0·84 0·77 23·1 0·83 6·83 6·27 2·32 13·8 3·50 29·9 9·47 37·1 7·35 66·5 12·9 9277 0·21 31·2 24·4 55·5 
DMP406-4 7·61 349 1·59 0·023 12·5 0·081 1·21 1·67 0·17 7·38 2·56 30·0 11·5 51·1 11·4 106 20·3 8296 0·67 46·0 60·9 103 
DMP406-5 12·6 532 0·94 0·006 10·6 0·16 3·45 4·26 0·68 16·3 4·80 48·9 17·8 74·4 15·7 137 26·4 7691 0·33 27·9 49·0 58·1 
DMP406-6 7·72 355 1·34 0·003 21·2 0·059 0·69 1·79 0·35 7·91 2·68 31·8 11·3 53·1 11·8 117 22·3 9537 0·69 2·35 4·12 5·97 
DMP406-7 8·06 277 1·10 n.d. 15·8 0·011 0·69 1·08 0·16 6·05 1·87 22·7 8·87 40·1 9·15 86·6 17·8 9266 0·61 7·40 5·89 15·8 
DMP406-8 22·1 853 2·45 0·33 21·3 3·12 26·3 19·1 8·08 39·3 11·9 107 28·4 99·9 18·9 152 26·9 7863 1·34 277 297 645 
DMP406-9 6·84 2668 3·18 0·85 6·93 0·48 4·13 4·30 0·51 25·4 12·9 186 83·8 442 106 1061 208 9739 1·96 154 63·1 493 
DMP406-10 41·6 372 2·04 0·021 4·07 0·033 0·67 1·26 0·25 8·41 2·76 34·5 11·8 52·6 10·8 95·0 17·3 10909 0·47 34·6 35·2 342 
DMP406-11 n.d. 27·5 0·36 0·028 0·12 0·003 0·020 0·07 0·022 0·57 0·21 2·61 0·76 2·63 0·44 4·33 0·89 11724 0·20 13·9 0·47 170 
DMP406-12 8·87 1398 1·87 0·10 17·6 0·61 9·95 14·3 0·50 51·9 14·2 146 48·7 198 40·3 363 65·6 6039 0·83 250 334 493 
DMP406-13 7·01 485 1·96 0·064 4·68 0·058 0·48 0·96 0·22 7·62 2·74 38·2 15·7 81·1 21·1 240 48·3 9664 1·36 149 77·3 457 
DMP406-14 7·43 1696 16·9 2·90 23·9 1·89 12·3 12·1 0·12 37·4 13·8 161 58·4 256 54·3 466 83·6 8983 8·69 58·3 974 1989 
DMP406-15 45·7 2789 3·56 15·9 90·8 7·95 45·1 26·6 7·71 76·1 23·7 273 95·3 419 87·7 808 149 8147 0·77 30·7 265 166 
DMP406-16 18·5 1725 2·61 0·74 31·3 0·34 3·57 4·69 2·01 30·2 11·1 141 59·1 285 64·4 628 117 9024 0·85 22·4 131 120 
DMP406-18 1·34 243 1·54 0·027 16·9 0·015 0·45 0·73 0·31 4·19 1·61 20·5 7·31 37·5 10·1 105 21·0 10056 0·74 9·30 139 180 
DMP406-19 4·64 134 1·53 0·042 0·23 0·011 0·32 0·14 0·13 1·66 0·75 10·5 4·12 19·4 5·23 48·7 8·93 9990 0·61 37·9 6·70 345 
DMP444-1 19·7 1073 3·29 0·23 24·2 0·23 3·71 6·63 1·44 29·1 8·58 98·8 35·7 155 35·0 331 60·0 9728 2·18 234 245 442 
DMP444-2 13·1 743 2·46 0·063 24·8 0·10 1·68 3·06 0·77 14·4 4·87 59·8 23·6 112 26·9 272 51·4 8858 1·51 168 132 284 
DMP444-3 8·53 472 2·16 0·020 28·7 0·035 0·72 1·70 0·63 9·17 3·13 40·3 15·3 75·0 17·9 192 34·9 8901 0·75 11·9 119 155 
Garnet pyroxenite vein in the composite xenolith 
DMP552-1 11·9 673 1·82 n.d. 7·85 0·11 1·79 3·11 0·32 17·2 5·65 65·6 24·1 103 21·0 192 34·4 7811 0·84 2·80 91·3 82·2 
DMP552-2 17·3 434 1·39 0·19 13·3 0·22 1·56 2·52 0·87 9·78 3·65 40·3 14·4 66·4 15·0 157 30·6 10660 0·92 107 132 256 
DMP552-3 7·68 664 2·79 0·002 7·00 0·061 1·35 2·66 0·036 15·3 5·14 61·8 22·7 98·0 20·6 191 33·1 8480 1·70 10·4 218 470 
DMP552-4 3·00 907 5·20 0·072 9·19 0·053 1·12 2·65 0·028 17·3 6·45 84·7 31·9 145 31·5 288 47·4 9874 3·64 20·9 389 1047 
DMP552-5 7·81 592 1·36 0·032 6·21 0·018 0·40 1·18 0·14 6·93 2·98 41·7 18·5 98·6 25·9 296 62·7 10265 1·39 248 86·9 437 
DMP552-6 3·25 590 7·34 0·058 5·29 0·056 0·37 0·98 0·32 6·61 2·66 40·5 18·1 100 27·6 332 71·3 11410 8·77 348 108 1151 
DMP552-8 38·8 1090 4·89 4·34 88·9 2·06 22·7 22·9 5·81 63·7 15·7 135 38·4 138 24·7 201 33·9 7130 1·34 334 866 410 
DMP552-9 4·09 1463 16·2 0·029 8·89 0·043 1·01 3·21 0·011 25·8 9·94 132 50·6 223 47·9 436 71·1 9782 9·52 42·3 782 2229 
DMP552-10 7·02 2023 37·0 0·051 6·60 0·075 0·96 2·51 0·047 16·6 8·76 128 58·0 307 76·1 826 171 18419 64·9 54·5 369 3689 
DMP552-11 9·75 1032 3·62 0·020 17·8 0·040 0·78 2·66 0·29 15·7 6·04 82·3 34·5 168 39·6 388 76·0 9654 1·74 118 200 504 
DMP552-12 4·26 712 2·54 0·040 10·3 0·043 0·57 1·39 0·30 9·71 4·24 54·3 23·9 116 27·1 266 52·8 9471 1·16 72·5 102 313 
DMP552-13 7·26 1814 6·70 4·89 32·9 2·52 22·7 27·1 2·28 95·7 24·6 225 65·0 227 41·1 331 49·8 8305 2·66 9·10 1438 2211 
DMP552-14 22·4 2348 1·57 0·095 2·49 0·29 5·48 10·8 0·18 53·7 19·2 226 80·4 343 73·3 694 112 11399 1·47 28·9 165 699 
DMP552-15 2·70 734 8·69 0·016 4·34 0·025 0·53 1·64 n.d. 11·0 4·51 62·5 25·6 119 27·8 256 44·5 11320 7·72 27·4 281 1306 
DMP552-16 1·82 2008 26·9 0·26 8·15 0·12 1·69 3·30 0·017 27·1 12·6 168 67·4 318 70·4 678 116 12882 34·7 52·8 604 2901 
DMP552-18 2·40 1677 12·9 0·008 46·1 0·076 1·36 4·60 0·44 28·2 10·9 138 54·2 258 57·8 562 100 11196 9·27 63·9 968 2743 
DMP552-19 8·72 1806 8·50 n.d. 35·5 0·29 4·17 8·63 1·83 43·7 15·2 175 63·6 273 56·4 511 87·6 6927 3·09 15·0 855 447 
DMP552-20 5·03 893 2·02 0·032 53·8 0·20 3·27 6·22 2·82 27·7 8·38 85·5 28·7 120 26·0 247 46·3 7663 0·61 226 281 317 
DMP552-21 1·67 256 2·27 0·001 3·62 0·000 0·023 0·21 0·039 2·89 1·13 17·5 7·93 42·5 10·7 116 22·1 9927 2·57 5·57 86·1 381 
DMP552-22 5·50 1251 5·24 0·085 16·2 0·24 2·72 7·01 3·52 33·7 10·9 110 35·3 144 30·6 286 53·4 10350 2·90 497 237 791 
DMP552-23 5·36 302 2·25 0·013 10·3 0·025 0·62 1·35 0·54 6·40 2·26 25·5 9·66 47·1 11·6 124 26·0 10497 1·52 347 110 586 
DMP552-25 6·03 529 2·54 n.d. 16·7 0·11 1·11 2·25 0·95 10·5 3·58 41·3 17·1 82·9 19·8 206 40·6 7829 1·58 101 172 239 
DMP552-26 5·97 452 0·49 0·060 0·96 0·033 0·26 1·59 0·12 9·41 4·42 49·6 13·8 50·2 9·27 74·8 11·9 11379 0·68 111 23·7 639 
DMP552-27 5·96 1735 13·8 0·040 52·9 0·055 2·17 3·57 1·36 28·0 11·1 140 55·3 269 64·1 655 120 9832 5·30 28·4 1190 1084 
DMP552-28 4·65 1408 12·7 1·99 26·5 1·04 11·6 13·1 1·00 54·5 17·3 165 48·7 179 35·5 282 41·9 9690 5·00 9·51 1658 2836 
DMP552-29 21·5 1335 2·30 0·047 2·82 0·10 2·47 6·16 0·27 30·7 11·4 131 46·4 200 43·2 404 67·1 9904 1·20 14·4 168 325 
DMP552-30 27·7 3163 5·19 0·69 34·3 1·04 12·8 19·7 1·74 98·8 31·0 342 117 472 93·4 820 130 8236 1·91 163 977 532 
DMP552-31 7·36 3534 1·51 0·15 2·16 0·31 5·05 8·95 0·24 58·4 24·9 324 119 526 112 1039 188 12922 1·92 48·0 157 1372 
DMP552-33 0·34 744 1·22 n.d. 0·32 n.d. 0·25 0·82 0·097 4·66 3·17 58·3 24·8 138 43·0 536 105 12439 2·21 36·5 10·4 1182 
DMP552-37 5·96 1068 6·66 0·024 8·67 0·077 0·99 3·53 0·048 22·9 7·92 97·4 38·3 165 35·4 331 52·7 9966 3·99 21·8 494 1105 
DMP552-38 2·16 995 4·42 0·016 8·32 0·069 0·65 3·61 0·006 20·0 7·66 98·1 36·2 154 33·2 302 47·9 9242 3·19 17·1 406 847 
Garnet pyroxenite vein in the composite xenolith 
DMP552-39 6·80 8631 61·3 3·39 226 3·09 37·1 58·6 1·62 243 77·4 887 301 1240 253 2279 365 6346 15·0 94·4 10166 5050 
DMP552-40 7·85 71·1 0·45 n.d. 4·34 0·035 1·42 4·19 0·11 10·2 1·81 11·3 2·25 8·81 1·83 18·2 3·59 10776 0·26 64·9 79·2 204 
DMP552-41 6·46 1391 5·81 0·20 40·9 0·29 1·72 4·51 0·79 24·1 9·42 117 44·0 209 45·8 473 77·8 11701 3·81 26·2 671 973 
DMP552-42 n.d. 2260 20·9 0·55 9·59 0·34 1·35 3·67 0·12 27·7 13·2 180 75·9 371 77·2 706 130 10179 18·0 71·0 895 3853 
DMP552-43 7·24 1494 7·54 0·055 26·8 0·17 2·13 4·91 0·46 27·9 10·1 129 50·3 276 47·3 454 91·7 10215 2·03 165·5 233 511 
DMP552-44 1·10 2059 15·1 0·34 53·6 0·20 2·44 4·06 1·14 28·9 12·2 159 66·5 378 70·8 722 152 12103 5·26 25·8 895 1077 
DMP554-1 10·4 1210 1·24 0·007 23·0 0·053 1·05 2·85 1·29 20·4 7·10 94·9 39·0 189 44·5 456 89·9 8173 0·43 11·3 121 166 
DMP554-2 9·32 1034 0·76 0·001 15·2 0·036 1·20 2·24 0·91 16·1 5·89 79·9 33·7 161 37·5 391 79·0 8014 0·24 7·46 75·9 110 
DMP554-3 2·04 735 2·05 0·078 34·0 0·062 1·18 2·18 0·67 14·4 4·63 58·4 23·4 110 26·3 262 52·8 8940 0·70 8·47 202 214 
DMP554-4 11·7 214 0·83 0·034 7·46 0·030 0·42 0·46 0·23 3·23 1·08 14·7 6·36 32·8 8·88 102 23·9 9711 0·29 6·32 45·4 109 
DMP554-5 7·55 812 2·85 0·047 36·9 0·098 1·48 3·90 0·52 18·1 5·52 64·4 25·7 120 28·2 293 57·0 9038 1·01 15·3 267 254 
DMP554-6 10·8 2145 1·20 0·000 29·4 0·087 2·15 4·51 1·02 30·7 12·9 173 72·0 341 78·1 741 131 10963 0·93 155 1219 990 
DMP554-7 7·18 59·3 0·33 0·008 0·62 0·008 0·14 0·10 0·069 1·47 0·46 5·03 1·92 7·24 1·22 10·7 1·76 11455 0·16 5·29 5·99 103 
DMP554-8 16·4 562 1·11 0·001 15·2 0·032 0·84 1·89 0·20 10·6 4·07 47·0 18·5 84·6 19·0 187 36·2 9565 0·67 2·01 148 172 
DMP554-9 7·29 378 1·18 0·013 18·4 0·062 0·80 1·72 0·27 7·92 2·36 30·9 11·9 55·0 12·9 130 26·0 8704 0·38 0·07 2·82 2·46 
DMP554-10 13·9 2175 0·70 0·023 6·10 0·24 3·42 7·67 3·28 44·9 17·0 208 77·0 336 71·5 653 111 7685 0·42 28·4 205 269 
DMP554-11 33·7 243 2·19 0·11 15·6 0·19 2·93 1·61 0·36 3·76 1·44 16·7 6·99 40·5 11·7 155 32·1 8472 0·31 16·1 121 210 
DMP554-12 7·03 447 2·65 0·075 21·7 0·024 1·07 1·60 0·090 9·04 3·08 36·6 15·7 71·7 17·5 191 35·8 7309 0·92 11·0 203 221 
DMP554-15 11·6 2140 0·49 0·031 5·44 0·12 1·10 5·53 3·06 36·4 14·9 181 74·4 326 68·7 625 112 6980 0·13 29·6 174 267 
DMP555-1 5·91 1009 3·34 0·21 38·7 0·29 2·59 3·39 1·04 16·3 6·31 77·1 31·8 156 37·4 401 80·0 9001 1·94 95·1 987 1381 
DMP555-3 2·32 622 2·01 n.d. 24·8 0·031 0·66 1·21 0·60 9·44 3·51 45·6 19·2 98·0 25·0 263 54·5 9279 1·41 35·5 305 548 
DMP555-4 27·5 1579 4·31 0·029 51·5 0·15 2·63 5·25 1·85 30·7 10·9 135 52·4 242 55·9 554 104 7941 1·66 70·8 1032 973 
DMP555-5 2·63 405 0·95 n.d. 14·7 0·033 0·37 1·13 0·36 6·00 2·41 29·4 12·1 62·5 16·1 173 35·9 9336 0·93 40·1 344 592 
DMP555-6 5·05 427 0·66 n.d. 7·89 0·041 0·74 1·31 0·47 6·59 2·38 29·6 13·2 67·3 17·3 195 42·3 7901 0·46 16·3 122 257 
DMP555-7 2·25 494 1·73 n.d. 23·5 0·009 0·35 1·17 0·35 8·11 2·63 36·2 15·1 74·5 18·9 202 41·5 9837 1·15 35·0 308 539 
DMP555-8 2·20 357 0·71 0·018 7·78 0·028 0·48 0·66 0·36 5·14 1·78 24·4 10·8 56·4 14·8 171 37·7 8811 0·60 20·4 143 319 
DMP555-9 6·05 1070 4·64 0·40 50·8 0·47 4·02 3·66 1·35 17·1 6·16 77·3 32·8 162 40·6 427 85·6 9203 2·35 77·1 981 1115 
DMP555-10 8·10 715 2·35 n.d. 18·5 0·036 0·60 1·91 0·68 10·1 3·89 50·2 21·8 113 28·9 320 67·0 8876 1·25 33·8 275 524 
DMP555-11 4·80 964 2·87 0·072 40·2 0·090 1·39 2·39 1·02 16·3 5·83 76·8 30·7 143 33·6 336 69·4 11357 1·58 60·6 802 973 
DMP555-13 2·78 691 2·47 0·16 24·3 0·22 1·62 1·56 0·49 9·85 3·69 49·9 21·4 109 27·6 288 58·4 10446 1·57 36·1 271 569 
DMP555-15 2·40 2346 2·76 0·084 20·2 0·088 1·92 5·49 1·41 46·6 17·1 211 86·0 378 75·6 660 123 6795 0·91 11·1 104 153 
DMP555-16 7·96 162 0·65 0·016 13·1 n.d. 0·29 0·39 0·12 2·08 0·64 8·99 4·30 25·1 7·80 105 29·4 10183 0·15 12·3 132 232 
DMP555-17 6·06 254 0·89 0·003 13·1 0·004 0·19 0·80 0·14 4·38 1·36 17·8 7·78 41·2 10·5 118 26·3 9694 0·48 7·74 56·3 127 
Garnet pyroxenite vein in the composite xenolith 
DMP555-19 6·38 1463 4·80 n.d. 56·5 0·11 1·96 5·18 1·95 32·6 10·7 131 49·8 222 50·3 491 91·6 8110 2·02 128 2099 1562 
DMP555-20 6·13 238 0·43 0·007 6·65 0·004 0·38 0·51 0·17 3·51 1·38 19·1 7·65 38·3 9·47 102 21·3 8409 0·34 8·52 61·8 125 
DMP555-21 34·9 1201 2·62 0·015 30·8 0·10 1·90 3·64 1·68 24·8 8·14 98·4 38·8 178 41·5 441 85·7 7411 1·28 84·5 1315 1214 
DMP555-22 3·86 916 2·29 0·036 22·6 0·046 1·00 2·15 0·74 14·9 5·33 71·9 29·8 147 36·0 376 74·3 9156 1·08 37·4 310 567 
DMP555-23 7·01 833 1·86 0·003 16·9 0·19 3·09 4·96 0·74 23·8 7·44 81·0 29·5 125 26·5 238 42·1 6512 0·82 1·96 46·3 55·7 
DMP555-24 6·91 4736 11·4 0·30 149 0·67 10·3 17·2 7·16 101 34·0 424 160 717 163 1564 282 6800 2·97 118 1933 1520 
DMP555-29 3·04 995 3·01 1·58 33·9 0·57 4·42 3·52 1·04 18·2 6·10 81·6 32·0 154 37·9 382 72·3 9406 1·79 47·8 474 682 
DMP555-30 6·94 4505 11·7 1·40 190 2·02 20·6 27·6 7·16 121 33·9 417 146 666 141 1315 231 7142 2·81 129 2226 1474 
DMP555-37 0·00 520 0·47 0·01 9·80 0·05 0·86 1·87 0·56 11·0 3·08 43·6 17·2 86 21·7 226 48·5 8957 0·54 19·7 184 292 
DMP555-47 29·0 593 1·51 0·006 15·1 0·15 2·11 3·30 0·62 15·8 5·41 59·2 22·2 93·3 19·8 189 31·1 7075 0·49 1·42 31·2 44·5 
Garnet-rich granulite xenolith 
DMP467-1 14·4 2981 26·6 19·8 315 2·89 20·2 19·0 9·45 78·2 24·9 273 93·5 381 80·1 700 102 9683 7·74 213 8097 3084 
DMP467-2 25·1 2501 22·6 22·4 272 3·17 18·1 16·2 7·42 66·0 20·7 227 78·7 326 68·8 616 87·2 10414 6·63 179 6760 2670 
DMP467-4 5·73 796 4·16 5·87 56·8 1·54 7·12 3·98 1·19 16·5 5·51 65·3 24·6 113 26·3 260 49·2 8861 1·43 21·9 540 488 
DMP467-5 3·11 485 1·92 0·11 21·7 0·086 0·70 1·48 0·55 8·28 3·20 38·4 15·1 71·8 18·0 188 33·7 8950 0·80 9·95 145 255 
DMP467-6 2·12 453 3·50 0·79 32·9 0·29 2·06 2·32 0·94 8·98 3·02 37·8 13·8 61·8 14·7 143 26·6 9320 1·15 45·1 655 850 
DMP467-7 26·5 446 1·41 14·2 40·1 2·07 9·86 2·55 1·07 8·25 2·75 33·2 12·8 63·5 15·5 157 30·3 8366 0·59 32·9 347 638 
DMP467-8 6·23 967 4·18 7·32 61·4 1·91 11·1 5·13 2·17 20·1 6·84 83·2 30·4 134 31·1 295 48·7 9233 1·17 31·9 795 596 
DMP467-9 6·80 499 4·17 0·29 9·00 0·10 1·10 1·66 0·10 9·11 3·27 41·0 16·3 74·3 17·1 165 27·7 8240 2·35 28·7 87·2 164 
DMP467-11 29·4 2931 12·2 8·05 150 2·59 19·6 19·1 7·21 75·0 24·0 270 96·8 412 90·4 828 135 7244 2·76 90·8 2546 1673 
DMP467-12 5·42 5280 16·9 0·71 205 1·32 18·0 29·5 11·7 127 41·7 479 170 721 154 1393 221 7040 3·67 74·5 2558 1384 
DMP467-14 5·07 573 0·71 0·24 3·95 0·36 3·26 2·79 1·29 11·8 3·86 44·3 17·4 81·9 20·0 209 41·7 5320 0·32 67·2 55·7 96·1 
DMP467-15 56·8 1658 2·54 1·35 17·5 2·06 14·8 12·2 4·69 39·4 11·6 129 48·9 227 54·7 559 111 4921 1·03 270 343 368 
DMP467-16 4·35 680 0·46 0·11 2·97 0·26 2·91 3·38 1·38 14·4 4·66 53·7 20·8 97·2 23·7 246 47·7 5508 0·26 72·5 65·3 99·8 
DMP467-20 5·36 726 2·19 0·012 7·87 0·083 1·04 2·55 0·11 16·0 6·00 71·1 26·1 113 23·5 214 35·4 8333 1·26 74·0 128 318 
DMP467-21 4·23 674 1·95 0·12 6·70 0·12 1·45 3·21 0·28 16·2 5·96 69·6 24·8 102 21·9 201 31·8 8302 1·16 67·5 111 285 
D.L. 0·73 0·03 0·03 0·02 0·02 0·02 0·12 0·10 0·03 0·18 0·02 0·07 0·02 0·05 0·02 0·11 0·02 0·12 0·02 0·07 0·02 0·01 
Element: Ti Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th 
Isotope: 49 89 93 139 140 141 143 147 151 155 159 163 165 166 169 173 175 179 181  232 238 
Garnet pyroxenite vein in the composite xenolith 
DMP122-1 61·9 6814 234 6·48 38·9 6·00 38·5 59·4 2·65 180 76·5 843 264 1122 253 2277 346 16318 115 146 2183 10207 
DMP122-2 176 16407 612 68·2 188 28·4 164 189 12·3 671 236 2185 636 2505 523 4509 708 10862 154 361 16134 27798 
DMP122-3 198 12601 624 21·4 94·8 18·4 126 171 9·52 487 183 1780 503 1978 427 3764 554 19382 259 227 5439 19446 
DMP122-4 179 37889 527 486 935 120 596 398 80·7 1281 448 4256 1169 4432 859 6984 1039 12152 164 259 16576 21724 
DMP122-5 121 18673 376 19·3 123 20·1 119 146 44·1 486 196 2048 626 2666 591 5466 898 24572 313 292 4624 23490 
DMP122-6 1·80 229 1·91  5·86 0·016 0·18 0·25 0·18 2·42 1·20 14·4 7·01 39·3 10·4 107 20·6 7430 0·29 25·5 108 1194 
DMP122-7 6·65 163 1·39 0·008 1·62 0·018 0·16 0·12 0·13 1·71 0·80 11·8 5·09 22·1 4·68 41·5 7·87 11999 1·52 3·60 4·53 7·77 
DMP134-1 4·69 707 1·09 0·013 27·0 0·12 2·02 3·96 1·50 16·6 5·38 60·5 22·5 104 24·2 251 49·2 7756 0·48 20·6 307 369 
DMP134-2 78·5 3861 5·78 3·31 102 12·2 94·9 96·7 60·3 212 62·4 532 135 486 89·3 763 129 10556 0·46 40·1 850 1390 
DMP134-3 4·45 1071 5·40 1·38 6·75 0·37 3·23 4·10 1·12 24·2 7·71 92·1 34·3 160 36·3 362 70·2 6758 1·39 30·0 310 744 
DMP134-5 n.d. 1569 10·8 0·67 11·5 0·46 4·02 5·04 0·94 28·8 10·1 130 52·9 248 57·5 578 110 7710 2·54 47·3 456 973 
DMP134-6 n.d. 730 2·52 3·55 17·8 1·54 9·99 7·84 1·06 22·0 6·36 66·6 24·7 112 26·6 274 52·4 7250 0·91 25·8 227 485 
DMP406-1 7·19 1136 5·22 0·013 28·3 0·044 1·70 3·95 0·49 20·6 7·75 88·2 32·4 151 36·5 348 60·5 9908 6·00 10·9 107 528 
DMP406-2 7·26 674 3·18 0·84 31·3 0·74 7·35 6·47 1·88 20·1 5·89 61·3 21·8 94·7 20·7 192 35·4 8888 1·12 173 144 288 
DMP406-3 6·87 295 0·84 0·77 23·1 0·83 6·83 6·27 2·32 13·8 3·50 29·9 9·47 37·1 7·35 66·5 12·9 9277 0·21 31·2 24·4 55·5 
DMP406-4 7·61 349 1·59 0·023 12·5 0·081 1·21 1·67 0·17 7·38 2·56 30·0 11·5 51·1 11·4 106 20·3 8296 0·67 46·0 60·9 103 
DMP406-5 12·6 532 0·94 0·006 10·6 0·16 3·45 4·26 0·68 16·3 4·80 48·9 17·8 74·4 15·7 137 26·4 7691 0·33 27·9 49·0 58·1 
DMP406-6 7·72 355 1·34 0·003 21·2 0·059 0·69 1·79 0·35 7·91 2·68 31·8 11·3 53·1 11·8 117 22·3 9537 0·69 2·35 4·12 5·97 
DMP406-7 8·06 277 1·10 n.d. 15·8 0·011 0·69 1·08 0·16 6·05 1·87 22·7 8·87 40·1 9·15 86·6 17·8 9266 0·61 7·40 5·89 15·8 
DMP406-8 22·1 853 2·45 0·33 21·3 3·12 26·3 19·1 8·08 39·3 11·9 107 28·4 99·9 18·9 152 26·9 7863 1·34 277 297 645 
DMP406-9 6·84 2668 3·18 0·85 6·93 0·48 4·13 4·30 0·51 25·4 12·9 186 83·8 442 106 1061 208 9739 1·96 154 63·1 493 
DMP406-10 41·6 372 2·04 0·021 4·07 0·033 0·67 1·26 0·25 8·41 2·76 34·5 11·8 52·6 10·8 95·0 17·3 10909 0·47 34·6 35·2 342 
DMP406-11 n.d. 27·5 0·36 0·028 0·12 0·003 0·020 0·07 0·022 0·57 0·21 2·61 0·76 2·63 0·44 4·33 0·89 11724 0·20 13·9 0·47 170 
DMP406-12 8·87 1398 1·87 0·10 17·6 0·61 9·95 14·3 0·50 51·9 14·2 146 48·7 198 40·3 363 65·6 6039 0·83 250 334 493 
DMP406-13 7·01 485 1·96 0·064 4·68 0·058 0·48 0·96 0·22 7·62 2·74 38·2 15·7 81·1 21·1 240 48·3 9664 1·36 149 77·3 457 
DMP406-14 7·43 1696 16·9 2·90 23·9 1·89 12·3 12·1 0·12 37·4 13·8 161 58·4 256 54·3 466 83·6 8983 8·69 58·3 974 1989 
DMP406-15 45·7 2789 3·56 15·9 90·8 7·95 45·1 26·6 7·71 76·1 23·7 273 95·3 419 87·7 808 149 8147 0·77 30·7 265 166 
DMP406-16 18·5 1725 2·61 0·74 31·3 0·34 3·57 4·69 2·01 30·2 11·1 141 59·1 285 64·4 628 117 9024 0·85 22·4 131 120 
DMP406-18 1·34 243 1·54 0·027 16·9 0·015 0·45 0·73 0·31 4·19 1·61 20·5 7·31 37·5 10·1 105 21·0 10056 0·74 9·30 139 180 
DMP406-19 4·64 134 1·53 0·042 0·23 0·011 0·32 0·14 0·13 1·66 0·75 10·5 4·12 19·4 5·23 48·7 8·93 9990 0·61 37·9 6·70 345 
DMP444-1 19·7 1073 3·29 0·23 24·2 0·23 3·71 6·63 1·44 29·1 8·58 98·8 35·7 155 35·0 331 60·0 9728 2·18 234 245 442 
DMP444-2 13·1 743 2·46 0·063 24·8 0·10 1·68 3·06 0·77 14·4 4·87 59·8 23·6 112 26·9 272 51·4 8858 1·51 168 132 284 
DMP444-3 8·53 472 2·16 0·020 28·7 0·035 0·72 1·70 0·63 9·17 3·13 40·3 15·3 75·0 17·9 192 34·9 8901 0·75 11·9 119 155 
Garnet pyroxenite vein in the composite xenolith 
DMP552-1 11·9 673 1·82 n.d. 7·85 0·11 1·79 3·11 0·32 17·2 5·65 65·6 24·1 103 21·0 192 34·4 7811 0·84 2·80 91·3 82·2 
DMP552-2 17·3 434 1·39 0·19 13·3 0·22 1·56 2·52 0·87 9·78 3·65 40·3 14·4 66·4 15·0 157 30·6 10660 0·92 107 132 256 
DMP552-3 7·68 664 2·79 0·002 7·00 0·061 1·35 2·66 0·036 15·3 5·14 61·8 22·7 98·0 20·6 191 33·1 8480 1·70 10·4 218 470 
DMP552-4 3·00 907 5·20 0·072 9·19 0·053 1·12 2·65 0·028 17·3 6·45 84·7 31·9 145 31·5 288 47·4 9874 3·64 20·9 389 1047 
DMP552-5 7·81 592 1·36 0·032 6·21 0·018 0·40 1·18 0·14 6·93 2·98 41·7 18·5 98·6 25·9 296 62·7 10265 1·39 248 86·9 437 
DMP552-6 3·25 590 7·34 0·058 5·29 0·056 0·37 0·98 0·32 6·61 2·66 40·5 18·1 100 27·6 332 71·3 11410 8·77 348 108 1151 
DMP552-8 38·8 1090 4·89 4·34 88·9 2·06 22·7 22·9 5·81 63·7 15·7 135 38·4 138 24·7 201 33·9 7130 1·34 334 866 410 
DMP552-9 4·09 1463 16·2 0·029 8·89 0·043 1·01 3·21 0·011 25·8 9·94 132 50·6 223 47·9 436 71·1 9782 9·52 42·3 782 2229 
DMP552-10 7·02 2023 37·0 0·051 6·60 0·075 0·96 2·51 0·047 16·6 8·76 128 58·0 307 76·1 826 171 18419 64·9 54·5 369 3689 
DMP552-11 9·75 1032 3·62 0·020 17·8 0·040 0·78 2·66 0·29 15·7 6·04 82·3 34·5 168 39·6 388 76·0 9654 1·74 118 200 504 
DMP552-12 4·26 712 2·54 0·040 10·3 0·043 0·57 1·39 0·30 9·71 4·24 54·3 23·9 116 27·1 266 52·8 9471 1·16 72·5 102 313 
DMP552-13 7·26 1814 6·70 4·89 32·9 2·52 22·7 27·1 2·28 95·7 24·6 225 65·0 227 41·1 331 49·8 8305 2·66 9·10 1438 2211 
DMP552-14 22·4 2348 1·57 0·095 2·49 0·29 5·48 10·8 0·18 53·7 19·2 226 80·4 343 73·3 694 112 11399 1·47 28·9 165 699 
DMP552-15 2·70 734 8·69 0·016 4·34 0·025 0·53 1·64 n.d. 11·0 4·51 62·5 25·6 119 27·8 256 44·5 11320 7·72 27·4 281 1306 
DMP552-16 1·82 2008 26·9 0·26 8·15 0·12 1·69 3·30 0·017 27·1 12·6 168 67·4 318 70·4 678 116 12882 34·7 52·8 604 2901 
DMP552-18 2·40 1677 12·9 0·008 46·1 0·076 1·36 4·60 0·44 28·2 10·9 138 54·2 258 57·8 562 100 11196 9·27 63·9 968 2743 
DMP552-19 8·72 1806 8·50 n.d. 35·5 0·29 4·17 8·63 1·83 43·7 15·2 175 63·6 273 56·4 511 87·6 6927 3·09 15·0 855 447 
DMP552-20 5·03 893 2·02 0·032 53·8 0·20 3·27 6·22 2·82 27·7 8·38 85·5 28·7 120 26·0 247 46·3 7663 0·61 226 281 317 
DMP552-21 1·67 256 2·27 0·001 3·62 0·000 0·023 0·21 0·039 2·89 1·13 17·5 7·93 42·5 10·7 116 22·1 9927 2·57 5·57 86·1 381 
DMP552-22 5·50 1251 5·24 0·085 16·2 0·24 2·72 7·01 3·52 33·7 10·9 110 35·3 144 30·6 286 53·4 10350 2·90 497 237 791 
DMP552-23 5·36 302 2·25 0·013 10·3 0·025 0·62 1·35 0·54 6·40 2·26 25·5 9·66 47·1 11·6 124 26·0 10497 1·52 347 110 586 
DMP552-25 6·03 529 2·54 n.d. 16·7 0·11 1·11 2·25 0·95 10·5 3·58 41·3 17·1 82·9 19·8 206 40·6 7829 1·58 101 172 239 
DMP552-26 5·97 452 0·49 0·060 0·96 0·033 0·26 1·59 0·12 9·41 4·42 49·6 13·8 50·2 9·27 74·8 11·9 11379 0·68 111 23·7 639 
DMP552-27 5·96 1735 13·8 0·040 52·9 0·055 2·17 3·57 1·36 28·0 11·1 140 55·3 269 64·1 655 120 9832 5·30 28·4 1190 1084 
DMP552-28 4·65 1408 12·7 1·99 26·5 1·04 11·6 13·1 1·00 54·5 17·3 165 48·7 179 35·5 282 41·9 9690 5·00 9·51 1658 2836 
DMP552-29 21·5 1335 2·30 0·047 2·82 0·10 2·47 6·16 0·27 30·7 11·4 131 46·4 200 43·2 404 67·1 9904 1·20 14·4 168 325 
DMP552-30 27·7 3163 5·19 0·69 34·3 1·04 12·8 19·7 1·74 98·8 31·0 342 117 472 93·4 820 130 8236 1·91 163 977 532 
DMP552-31 7·36 3534 1·51 0·15 2·16 0·31 5·05 8·95 0·24 58·4 24·9 324 119 526 112 1039 188 12922 1·92 48·0 157 1372 
DMP552-33 0·34 744 1·22 n.d. 0·32 n.d. 0·25 0·82 0·097 4·66 3·17 58·3 24·8 138 43·0 536 105 12439 2·21 36·5 10·4 1182 
DMP552-37 5·96 1068 6·66 0·024 8·67 0·077 0·99 3·53 0·048 22·9 7·92 97·4 38·3 165 35·4 331 52·7 9966 3·99 21·8 494 1105 
DMP552-38 2·16 995 4·42 0·016 8·32 0·069 0·65 3·61 0·006 20·0 7·66 98·1 36·2 154 33·2 302 47·9 9242 3·19 17·1 406 847 
Garnet pyroxenite vein in the composite xenolith 
DMP552-39 6·80 8631 61·3 3·39 226 3·09 37·1 58·6 1·62 243 77·4 887 301 1240 253 2279 365 6346 15·0 94·4 10166 5050 
DMP552-40 7·85 71·1 0·45 n.d. 4·34 0·035 1·42 4·19 0·11 10·2 1·81 11·3 2·25 8·81 1·83 18·2 3·59 10776 0·26 64·9 79·2 204 
DMP552-41 6·46 1391 5·81 0·20 40·9 0·29 1·72 4·51 0·79 24·1 9·42 117 44·0 209 45·8 473 77·8 11701 3·81 26·2 671 973 
DMP552-42 n.d. 2260 20·9 0·55 9·59 0·34 1·35 3·67 0·12 27·7 13·2 180 75·9 371 77·2 706 130 10179 18·0 71·0 895 3853 
DMP552-43 7·24 1494 7·54 0·055 26·8 0·17 2·13 4·91 0·46 27·9 10·1 129 50·3 276 47·3 454 91·7 10215 2·03 165·5 233 511 
DMP552-44 1·10 2059 15·1 0·34 53·6 0·20 2·44 4·06 1·14 28·9 12·2 159 66·5 378 70·8 722 152 12103 5·26 25·8 895 1077 
DMP554-1 10·4 1210 1·24 0·007 23·0 0·053 1·05 2·85 1·29 20·4 7·10 94·9 39·0 189 44·5 456 89·9 8173 0·43 11·3 121 166 
DMP554-2 9·32 1034 0·76 0·001 15·2 0·036 1·20 2·24 0·91 16·1 5·89 79·9 33·7 161 37·5 391 79·0 8014 0·24 7·46 75·9 110 
DMP554-3 2·04 735 2·05 0·078 34·0 0·062 1·18 2·18 0·67 14·4 4·63 58·4 23·4 110 26·3 262 52·8 8940 0·70 8·47 202 214 
DMP554-4 11·7 214 0·83 0·034 7·46 0·030 0·42 0·46 0·23 3·23 1·08 14·7 6·36 32·8 8·88 102 23·9 9711 0·29 6·32 45·4 109 
DMP554-5 7·55 812 2·85 0·047 36·9 0·098 1·48 3·90 0·52 18·1 5·52 64·4 25·7 120 28·2 293 57·0 9038 1·01 15·3 267 254 
DMP554-6 10·8 2145 1·20 0·000 29·4 0·087 2·15 4·51 1·02 30·7 12·9 173 72·0 341 78·1 741 131 10963 0·93 155 1219 990 
DMP554-7 7·18 59·3 0·33 0·008 0·62 0·008 0·14 0·10 0·069 1·47 0·46 5·03 1·92 7·24 1·22 10·7 1·76 11455 0·16 5·29 5·99 103 
DMP554-8 16·4 562 1·11 0·001 15·2 0·032 0·84 1·89 0·20 10·6 4·07 47·0 18·5 84·6 19·0 187 36·2 9565 0·67 2·01 148 172 
DMP554-9 7·29 378 1·18 0·013 18·4 0·062 0·80 1·72 0·27 7·92 2·36 30·9 11·9 55·0 12·9 130 26·0 8704 0·38 0·07 2·82 2·46 
DMP554-10 13·9 2175 0·70 0·023 6·10 0·24 3·42 7·67 3·28 44·9 17·0 208 77·0 336 71·5 653 111 7685 0·42 28·4 205 269 
DMP554-11 33·7 243 2·19 0·11 15·6 0·19 2·93 1·61 0·36 3·76 1·44 16·7 6·99 40·5 11·7 155 32·1 8472 0·31 16·1 121 210 
DMP554-12 7·03 447 2·65 0·075 21·7 0·024 1·07 1·60 0·090 9·04 3·08 36·6 15·7 71·7 17·5 191 35·8 7309 0·92 11·0 203 221 
DMP554-15 11·6 2140 0·49 0·031 5·44 0·12 1·10 5·53 3·06 36·4 14·9 181 74·4 326 68·7 625 112 6980 0·13 29·6 174 267 
DMP555-1 5·91 1009 3·34 0·21 38·7 0·29 2·59 3·39 1·04 16·3 6·31 77·1 31·8 156 37·4 401 80·0 9001 1·94 95·1 987 1381 
DMP555-3 2·32 622 2·01 n.d. 24·8 0·031 0·66 1·21 0·60 9·44 3·51 45·6 19·2 98·0 25·0 263 54·5 9279 1·41 35·5 305 548 
DMP555-4 27·5 1579 4·31 0·029 51·5 0·15 2·63 5·25 1·85 30·7 10·9 135 52·4 242 55·9 554 104 7941 1·66 70·8 1032 973 
DMP555-5 2·63 405 0·95 n.d. 14·7 0·033 0·37 1·13 0·36 6·00 2·41 29·4 12·1 62·5 16·1 173 35·9 9336 0·93 40·1 344 592 
DMP555-6 5·05 427 0·66 n.d. 7·89 0·041 0·74 1·31 0·47 6·59 2·38 29·6 13·2 67·3 17·3 195 42·3 7901 0·46 16·3 122 257 
DMP555-7 2·25 494 1·73 n.d. 23·5 0·009 0·35 1·17 0·35 8·11 2·63 36·2 15·1 74·5 18·9 202 41·5 9837 1·15 35·0 308 539 
DMP555-8 2·20 357 0·71 0·018 7·78 0·028 0·48 0·66 0·36 5·14 1·78 24·4 10·8 56·4 14·8 171 37·7 8811 0·60 20·4 143 319 
DMP555-9 6·05 1070 4·64 0·40 50·8 0·47 4·02 3·66 1·35 17·1 6·16 77·3 32·8 162 40·6 427 85·6 9203 2·35 77·1 981 1115 
DMP555-10 8·10 715 2·35 n.d. 18·5 0·036 0·60 1·91 0·68 10·1 3·89 50·2 21·8 113 28·9 320 67·0 8876 1·25 33·8 275 524 
DMP555-11 4·80 964 2·87 0·072 40·2 0·090 1·39 2·39 1·02 16·3 5·83 76·8 30·7 143 33·6 336 69·4 11357 1·58 60·6 802 973 
DMP555-13 2·78 691 2·47 0·16 24·3 0·22 1·62 1·56 0·49 9·85 3·69 49·9 21·4 109 27·6 288 58·4 10446 1·57 36·1 271 569 
DMP555-15 2·40 2346 2·76 0·084 20·2 0·088 1·92 5·49 1·41 46·6 17·1 211 86·0 378 75·6 660 123 6795 0·91 11·1 104 153 
DMP555-16 7·96 162 0·65 0·016 13·1 n.d. 0·29 0·39 0·12 2·08 0·64 8·99 4·30 25·1 7·80 105 29·4 10183 0·15 12·3 132 232 
DMP555-17 6·06 254 0·89 0·003 13·1 0·004 0·19 0·80 0·14 4·38 1·36 17·8 7·78 41·2 10·5 118 26·3 9694 0·48 7·74 56·3 127 
Garnet pyroxenite vein in the composite xenolith 
DMP555-19 6·38 1463 4·80 n.d. 56·5 0·11 1·96 5·18 1·95 32·6 10·7 131 49·8 222 50·3 491 91·6 8110 2·02 128 2099 1562 
DMP555-20 6·13 238 0·43 0·007 6·65 0·004 0·38 0·51 0·17 3·51 1·38 19·1 7·65 38·3 9·47 102 21·3 8409 0·34 8·52 61·8 125 
DMP555-21 34·9 1201 2·62 0·015 30·8 0·10 1·90 3·64 1·68 24·8 8·14 98·4 38·8 178 41·5 441 85·7 7411 1·28 84·5 1315 1214 
DMP555-22 3·86 916 2·29 0·036 22·6 0·046 1·00 2·15 0·74 14·9 5·33 71·9 29·8 147 36·0 376 74·3 9156 1·08 37·4 310 567 
DMP555-23 7·01 833 1·86 0·003 16·9 0·19 3·09 4·96 0·74 23·8 7·44 81·0 29·5 125 26·5 238 42·1 6512 0·82 1·96 46·3 55·7 
DMP555-24 6·91 4736 11·4 0·30 149 0·67 10·3 17·2 7·16 101 34·0 424 160 717 163 1564 282 6800 2·97 118 1933 1520 
DMP555-29 3·04 995 3·01 1·58 33·9 0·57 4·42 3·52 1·04 18·2 6·10 81·6 32·0 154 37·9 382 72·3 9406 1·79 47·8 474 682 
DMP555-30 6·94 4505 11·7 1·40 190 2·02 20·6 27·6 7·16 121 33·9 417 146 666 141 1315 231 7142 2·81 129 2226 1474 
DMP555-37 0·00 520 0·47 0·01 9·80 0·05 0·86 1·87 0·56 11·0 3·08 43·6 17·2 86 21·7 226 48·5 8957 0·54 19·7 184 292 
DMP555-47 29·0 593 1·51 0·006 15·1 0·15 2·11 3·30 0·62 15·8 5·41 59·2 22·2 93·3 19·8 189 31·1 7075 0·49 1·42 31·2 44·5 
Garnet-rich granulite xenolith 
DMP467-1 14·4 2981 26·6 19·8 315 2·89 20·2 19·0 9·45 78·2 24·9 273 93·5 381 80·1 700 102 9683 7·74 213 8097 3084 
DMP467-2 25·1 2501 22·6 22·4 272 3·17 18·1 16·2 7·42 66·0 20·7 227 78·7 326 68·8 616 87·2 10414 6·63 179 6760 2670 
DMP467-4 5·73 796 4·16 5·87 56·8 1·54 7·12 3·98 1·19 16·5 5·51 65·3 24·6 113 26·3 260 49·2 8861 1·43 21·9 540 488 
DMP467-5 3·11 485 1·92 0·11 21·7 0·086 0·70 1·48 0·55 8·28 3·20 38·4 15·1 71·8 18·0 188 33·7 8950 0·80 9·95 145 255 
DMP467-6 2·12 453 3·50 0·79 32·9 0·29 2·06 2·32 0·94 8·98 3·02 37·8 13·8 61·8 14·7 143 26·6 9320 1·15 45·1 655 850 
DMP467-7 26·5 446 1·41 14·2 40·1 2·07 9·86 2·55 1·07 8·25 2·75 33·2 12·8 63·5 15·5 157 30·3 8366 0·59 32·9 347 638 
DMP467-8 6·23 967 4·18 7·32 61·4 1·91 11·1 5·13 2·17 20·1 6·84 83·2 30·4 134 31·1 295 48·7 9233 1·17 31·9 795 596 
DMP467-9 6·80 499 4·17 0·29 9·00 0·10 1·10 1·66 0·10 9·11 3·27 41·0 16·3 74·3 17·1 165 27·7 8240 2·35 28·7 87·2 164 
DMP467-11 29·4 2931 12·2 8·05 150 2·59 19·6 19·1 7·21 75·0 24·0 270 96·8 412 90·4 828 135 7244 2·76 90·8 2546 1673 
DMP467-12 5·42 5280 16·9 0·71 205 1·32 18·0 29·5 11·7 127 41·7 479 170 721 154 1393 221 7040 3·67 74·5 2558 1384 
DMP467-14 5·07 573 0·71 0·24 3·95 0·36 3·26 2·79 1·29 11·8 3·86 44·3 17·4 81·9 20·0 209 41·7 5320 0·32 67·2 55·7 96·1 
DMP467-15 56·8 1658 2·54 1·35 17·5 2·06 14·8 12·2 4·69 39·4 11·6 129 48·9 227 54·7 559 111 4921 1·03 270 343 368 
DMP467-16 4·35 680 0·46 0·11 2·97 0·26 2·91 3·38 1·38 14·4 4·66 53·7 20·8 97·2 23·7 246 47·7 5508 0·26 72·5 65·3 99·8 
DMP467-20 5·36 726 2·19 0·012 7·87 0·083 1·04 2·55 0·11 16·0 6·00 71·1 26·1 113 23·5 214 35·4 8333 1·26 74·0 128 318 
DMP467-21 4·23 674 1·95 0·12 6·70 0·12 1·45 3·21 0·28 16·2 5·96 69·6 24·8 102 21·9 201 31·8 8302 1·16 67·5 111 285 
D.L. 0·73 0·03 0·03 0·02 0·02 0·02 0·12 0·10 0·03 0·18 0·02 0·07 0·02 0·05 0·02 0·11 0·02 0·12 0·02 0·07 0·02 0·01 

Unit is ppm; n.d., not detected; D.L., average of the detection limits.

Fig. 5.

(a) Cumulative diagram of all the zircon ages. Detrital zircons from major river sediments in the North China Craton (Yang et al., 2009) are shown for comparison. (b) Temperatures calculated with the Ti-in-zircon thermometer (Watson et al., 2006).

Fig. 5.

(a) Cumulative diagram of all the zircon ages. Detrital zircons from major river sediments in the North China Craton (Yang et al., 2009) are shown for comparison. (b) Temperatures calculated with the Ti-in-zircon thermometer (Watson et al., 2006).

Fig. 6.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP122, DMP134 and DMP444. Data-point error ellipses are 2σ. Chondrite (CI) values from Taylor & McLennan (1985).

Fig. 6.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP122, DMP134 and DMP444. Data-point error ellipses are 2σ. Chondrite (CI) values from Taylor & McLennan (1985).

Fig. 7.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP406. Symbols as in Fig. 6.

Fig. 7.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP406. Symbols as in Fig. 6.

Fig. 8.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP552. Symbols as in Fig. 6.

Fig. 8.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP552. Symbols as in Fig. 6.

Fig. 9.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP554 and DMP555. Symbols as in Fig. 6.

Fig. 9.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from DMP554 and DMP555. Symbols as in Fig. 6.

Fig. 10.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from the garnet-rich granulite xenolith DMP467. Symbols as in Fig. 6.

Fig. 10.

Variation of 206Pb/238U vs 207Pb/235U and chondrite-normalized REE patterns of zircons from the garnet-rich granulite xenolith DMP467. Symbols as in Fig. 6.

The Precambrian zircons from the garnet pyroxenite veins were mostly extracted from DMP406 and DMP552, and commonly show no internal zonation. Some of them are composed of a core and an overgrowth rim (Fig. 4). Except for three analyses on the rim and small grains, the Precambrian zircons from DMP-552 (n = 12) record concordant or near concordant U–Pb ages, whereas half of the Precambrian zircons from DMP-406 (n = 8) record concordant or near concordant U–Pb ages.

Ages of the Precambrian zircons are dominated by 2·4–2·5 Ga, 1·6–2·2 Ga and 0·6–1·2 Ga populations (Fig. 5). Zircons of 2·4–2·5 Ga were found in four garnet pyroxenite veins (DMP122, DMP444, DMP406 and DMP552), zircons of 1·8 Ga and 2·1 Ga in DMP406, and zircons of 1·7 Ga and 2·1 Ga in DMP552. Zircons with Neoproterozoic and Mesoproterozoic ages (610–1488 Ma) were found in three garnet pyroxenite veins (DMP406, DMP552 and DMP554) (Figs 7–9). Precambrian zircons (0·9–1·1 Ga and 2·7 Ga) were also found in the garnet-rich granulite xenolith (DMP467) (Fig. 10).

Zircons with Phanerozoic ages were found in all samples (Figs 5–10). Of these, Carboniferous zircons generally show well-developed growth zoning (Fig. 4) and have concordant U–Pb ages (Fig. 9). These zircons were mostly separated from DMP555 with a few from DMP554 and DMP444. Zircons of 300–340 Ma age in DMP555 give a concordia age of 314·7 ± 2·7 Ma (2σ, MSWD = 1·10, n = 19) (Fig. 9). A few zircons with Permian 206Pb/238U ages were separated from DMP554 and DMP555. They have generally discordant U–Pb ages (Fig. 9) and show no oscillatory zonation (Fig. 4). Triassic zircons are generally composed of a core and an overgrowth rim (Fig. 4), and were mainly found in the garnet-rich granulite (Fig. 10) and a few from garnet pyroxenites (Fig. 5). No zircon with an age of <196 Ma was found in the garnet-rich granulite xenolith (Fig. 10). Although zircons with Cretaceous ages were not abundant, they were found in all garnet pyroxenite veins (Figs 5–9) and generally show oscillatory zonation (Fig. 4). Zircons with Cenozoic ages (17–66 Ma) were also identified in three garnet pyroxenite veins (DMP122, DMP552 and DMP554). CL images of ∼48 Ma zircons from DMP122 show well-developed growth zoning, whereas the 20 Ma and 64 Ma (DMP552) and 52 Ma (DMP554) zircons show characteristics of metamorphic zircon, with a core and an overgrowth rim (Fig. 4).

Trace element compositions of zircons

Analyses with light rare earth element (LREE)-rich inclusions were ruled out by monitoring the signal variations of trace elements with time. The Precambrian zircons are mostly characterized by enrichments in heavy rare earth elements (HREE) and a slight negative Eu anomaly (Figs 6–10). However, the 1·3 Ga zircon in DMP406, the 1·7 Ga zircon in DMP552 and the 2·4 Ga zircon in DMP122 have distinctly lower rare earth element (REE) contents. One 1·7 Ga zircon in DMP552 has a flat HREE pattern (Fig. 8), a feature of zircon equilibrated with garnet (Rubatto, 2002; Rubatto & Hermann, 2007). The Carboniferous zircons in DMP-554 and DMP-555 have HREE-rich REE patterns (Fig. 9) and high Th/U ratios (0·44–1·51; Fig. 11a). The REE patterns of the Mesozoic zircons vary from sample to sample. Zircons with 114 Ma and 2·4 Ga ages in DMP122 have similarly HREE-rich REE patterns, without a Ce anomaly. Zircons of 111–225 Ma in DMP406 are characterized by significant negative Eu anomalies (Fig. 11b). The Mesozoic zircons from DMP552 can be classified into three groups. Zircons of 180–224 Ma are characterized by low Ce contents (0·3–2·8 ppm) and large negative Eu anomalies (Eu/Eu* = 0·02–0·15), zircons of 119–141 Ma are characterized by high Ce contents (7·85–52·9 ppm) and slight negative Eu anomalies (Eu/Eu* = 0·13–0·41), and zircons of 102 ± 5 Ma are characterized by high Ce contents (4·34–9·59 ppm) and large negative Eu anomalies (Eu/Eu* ≤ 0·04) (Fig. 11b). The igneous zircons of 48–66 Ma in DMP122 and DMP-552 are characterized by enrichments in LREE and a negligible Ce anomaly and extremely high Th and U contents (Figs 6 and 8, Table 3). However, zircons of 52 Ma (in DMP554) and 64 Ma (in DMP552), showing CL characteristics of metamorphic zircon (Fig. 4), have similar REE patterns to the older zircons in these samples (Figs 8 and 9).

Fig. 11.

Variation of Th/U and Eu anomaly (Eu/Eu*) with age for zircons from different samples.

Fig. 11.

Variation of Th/U and Eu anomaly (Eu/Eu*) with age for zircons from different samples.

The REE patterns of zircons from the garnet-rich granulite vary with age (Fig. 10). Zircons of 2·7 Ga show HREE enrichment and negligible negative Eu anomalies (Ce/Ce* = 2·8–4·3l, Eu/Eu* = 0·60–0·69), whereas the other Precambrian zircons have large positive Ce and negative Eu anomalies (Ce/Ce* = 9·54–72·3, Eu/Eu* = 0·05–0·12) (Fig. 11b). REE patterns of the 196–240 Ma zircons from DMP467 are all characterized by high enrichments in Ce, slight negative Eu anomalies and high Th/U ratios (0·54–2·63) (Fig. 11a).

Hf isotopic compositions of zircons from the garnet pyroxenite veins

Seventy-nine spots were analyzed on 60 zircon grains for Hf isotopic composition. The Lu–Hf isotope data are given in Table 6 and shown in Fig. 12. The εHf(t) value, the deviation of initial 176Hf/177Hf from the model chondritic value at a specified age, varies with the assumed age, as a result of the age dependence of the chondritic reference value (Amelin et al., 2000). Thus, the following discussion about Hf isotopic compositions will mainly focus on zircons with discordance of <10% in terms of U–Pb isotopic ages. The ∼2·5 Ga zircons have positive εHf(t) values (2·9–10·6), whereas the other Precambrian zircons are dominated by negative εHf(t) values with a few with positive εHf(t) values (Fig. 12a). The Carboniferous zircons with concordant U–Pb ages have high εHf(t) values ranging from 2·91 to 24·6. The εHf(t) values of the Jurassic–Permian zircons mostly lie between the values expected for a chondritic reservoir and 2·7 Ga bulk continental crust (Fig. 12b). The εHf(t) values of the 120–100 Ma zircons vary greatly from –47·6 for the ∼120 Ma zircons to 14·2 for the ∼100 Ma zircons (Fig. 12b). The 48–64 Ma igneous zircons have positive εHf(t) values (9·51–16·1), and the ∼20 Ma zircon has a negative εHf(t) value (–13·0).

Table 6:

Hf isotopic compositions of zircons from the composite xenoliths

 Age ± 1σ 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf εHf(t) 
 (Ma) ( ± 1σ) ( ± 1σ) ( ± 1σ) ( ± 1σ) 
DMP122-1 64 ± 1 0·173316 ± 0·003446 0·005027 ± 0·000089 0·283193 ± 0·000026 16·1 ± 1·39 
DMP122-3 48 ± 2 0·173147 ± 0·003442 0·005027 ± 0·000089 0·283189 ± 0·000026 15·7 ± 1·39 
DMP122-4 49 ± 1 0·291012 ± 0·001211 0·008683 ± 0·000035 0·283019 ± 0·000161 9·51 ± 5·80 
DMP122-6 114 ± 2 0·015735 ± 0·000156 0·000581 ± 0·000008 0·282622 ± 0·000095 −2·85 ± 3·50 
DMP122-7* 2355 ± 107 0·003384 ± 0·000033 0·000116 ± 0·000001 0·281583 ± 0·000029 10·6 ± 2·88 
DMP134-2* 136 ± 4 0·064171 ± 0·001667 0·002057 ± 0·000034 0·282151 ± 0·000254 −19·2 ± 9·04 
DMP134-5* 228 ± 2 0·046951 ± 0·000879 0·001716 ± 0·000030 0·282683 ± 0·000049 1·61 ± 2·02 
DMP134-6 244 ± 3 0·048771 ± 0·000548 0·001789 ± 0·000019 0·282538 ± 0·000052 −3·19 ± 2·12 
DMP134-1 254 ± 4 0·042045 ± 0·001401 0·001448 ± 0·000043 0·282136 ± 0·000056 −17·2 ± 2·24 
DMP406-1 111 ± 2 0·019064 ± 0·000223 0·000698 ± 0·000007 0·281659 ± 0·000053 −37·0 ± 2·15 
DMP406-14 117 ± 2 0·085284 ± 0·002787 0·002920 ± 0·000088 0·281359 ± 0·000151 −47·6 ± 5·43 
DMP406-18 225 ± 6 0·014808 ± 0·000372 0·000572 ± 0·000013 0·282473 ± 0·000045 −5·71 ± 1·89 
DMP406-19 684 ± 69 0·001445 ± 0·000067 0·000053 ± 0·000002 0·282252 ± 0·000075 −3·33 ± 3·24 
DMP406-10* 797 ± 96 0·001190 ± 0·000036 0·000044 ± 0·000001 0·282460 ± 0·000055 6·57 ± 3·06 
DMP406-15 1072 ± 79 0·076853 ± 0·001099 0·002922 ± 0·000038 0·282510 ± 0·000065 12·4 ± 3·08 
DMP406-16* 1078 ± 71 0·053325 ± 0·000659 0·002052 ± 0·000026 0·282572 ± 0·000116 15·4 ± 4·54 
DMP406-11* 1249 ± 90 0·000908 ± 0·000063 0·000036 ± 0·000002 0·282489 ± 0·000069 17·7 ± 3·35 
DMP406-9 1488 ± 25 0·030948 ± 0·001387 0·001262 ± 0·000052 0·282052 ± 0·000038 6·36 ± 1·80 
DMP406-4 1814 ± 40 0·014393 ± 0·000273 0·000530 ± 0·000010 0·281488 ± 0·000058 −5·62 ± 2·47 
DMP406-5 1835 ± 44 0·012286 ± 0·000159 0·000443 ± 0·000005 0·281432 ± 0·000061 −7·03 ± 2·62 
DMP406-8 1784 ± 27 0·050007 ± 0·001799 0·001468 ± 0·000047 0·281585 ± 0·000041 −3·98 ± 1·91 
DMP406-12 2002 ± 20 0·039891 ± 0·000184 0·001663 ± 0·000009 0·281945 ± 0·000050 13·3 ± 2·13 
DMP406-6* 2138 ± 228 0·014604 ± 0·000422 0·000506 ± 0·000012 0·281368 ± 0·000065 −2·59 ± 5·82 
DMP406-2 2473 ± 21 0·020816 ± 0·000238 0·000776 ± 0·000008 0·281427 ± 0·000044 6·67 ± 1·95 
DMP444-2 2411 ± 18 0·025896 ± 0·000381 0·000992 ± 0·000015 0·281300 ± 0·000087 0·40 ± 3·31 
DMP444-1 2324 ± 20 0·021306 ± 0·000135 0·000812 ± 0·000006 0·281267 ± 0·000041 −2·44 ± 1·86 
DMP552-13 20 ± 0·3 0·020966 ± 0·000201 0·000686 ± 0·000006 0·282391 ± 0·000049 −13·0 ± 2·00 
DMP552-21* 64 ± 2 0·019687 ± 0·001145 0·000806 ± 0·000047 0·282783 ± 0·000046 1·75 ± 1·93 
DMP552-23 2547 ± 16 0·018008 ± 0·000188 0·000742 ± 0·000008 0·280604 ± 0·000075 −22·9 ± 2·90 
DMP552-16* 100 ± 2 0·045579 ± 0·001077 0·001594 ± 0·000036 0·283013 ± 0·000094 10·6 ± 3·47 
DMP552-9 101 ± 2 0·031827 ± 0·000151 0·001175 ± 0·000009 0·283112 ± 0·000051 14·2 ± 2·07 
DMP552-3* 108 ± 2 0·018343 ± 0·000289 0·000670 ± 0·000010 0·282769 ± 0·000057 2·23 ± 2·26 
DMP552-15 112 ± 2 0·044056 ± 0·000709 0·001621 ± 0·000028 0·282909 ± 0·000051 7·20 ± 2·09 
DMP552-18 119 ± 2 0·065532 ± 0·000513 0·002393 ± 0·000016 0·282200 ± 0·000084 −17·8 ± 3·15 
DMP552-19* 119 ± 2 0·048954 ± 0·000211 0·001840 ± 0·000007 0·282653 ± 0·000072 −1·74 ± 2·73 
DMP552-1* 141 ± 5 0·035288 ± 0·000747 0·001261 ± 0·000025 0·282538 ± 0·000053 −5·28 ± 2·13 
DMP552-14 224 ± 3 0·068836 ± 0·001976 0·002360 ± 0·000065 0·282152 ± 0·000055 −17·4 ± 2·21 
DMP552-11 977 ± 28 0·023702 ± 0·000554 0·000913 ± 0·000017 0·281949 ± 0·000061 −8·12 ± 2·47 
DMP552-2 2052 ± 77 0·017125 ± 0·000174 0·000643 ± 0·000006 0·281553 ± 0·000052 1·88 ± 2·76 
DMP552-8 2433 ± 19 0·010721 ± 0·000286 0·000371 ± 0·000009 0·281098 ± 0·000054 −5·29 ± 2·24 
DMP552-5 2487 ± 17 0·032458 ± 0·000497 0·001429 ± 0·000022 0·281344 ± 0·000048 2·90 ± 2·07 
DMP552-20 2520 ± 18 0·046911 ± 0·000604 0·001715 ± 0·000018 0·281554 ± 0·000067 10·6 ± 2·66 
DMP554-8* 52 ± 2 0·016166 ± 0·000196 0·000625 ± 0·000005 0·282844 ± 0·000039 3·68 ± 1·72 
DMP554-3 173 ± 3 0·024587 ± 0·000384 0·000951 ± 0·000012 0·281850 ± 0·000034 −28·9 ± 1·59 
DMP554-9* 205 ± 20 0·011298 ± 0·000055 0·000437 ± 0·000002 0·281662 ± 0·000051 −34·8 ± 2·12 
DMP554-12 231 ± 17 0·012113 ± 0·000109 0·000489 ± 0·000004 0·282065 ± 0·000029 −20·0 ± 1·49 
DMP554-1 314 ± 5 0·044383 ± 0·000439 0·001691 ± 0·000019 0·283047 ± 0·000034 16·3 ± 1·57 
DMP554-2 323 ± 7 0·040277 ± 0·000217 0·001535 ± 0·000008 0·282992 ± 0·000032 14·5 ± 1·53 
DMP554-11* 337 ± 13 0·011466 ± 0·000116 0·000529 ± 0·000005 0·281928 ± 0·000060 −22·6 ± 2·38 
DMP554-6 610 ± 6 0·012049 ± 0·000896 0·000412 ± 0·000031 0·282617 ± 0·000044 7·80 ± 1·88 
DMP555-47* 122 ± 7·55 0·026619 ± 0·000090 0·000924 ± 0·000002 0·282392 ± 0·000074 −10·8 ± 2·82 
DMP555-23 140 ± 5·72 0·032574 ± 0·000176 0·001125 ± 0·000007 0·282370 ± 0·000055 −11·2 ± 2·19 
DMP555-16 248 ± 4·08 0·013294 ± 0·000113 0·000587 ± 0·000003 0·282143 ± 0·000046 −16·9 ± 1·93 
DMP555-11 276 ± 2·76 0·032684 ± 0·000456 0·001279 ± 0·000017 0·282775 ± 0·000062 5·95 ± 2·41 
DMP555-9 305 ± 4·01 0·027693 ± 0·000339 0·001084 ± 0·000014 0·282762 ± 0·000036 6·15 ± 1·65 
DMP555-10* 305 ± 4·60 0·031486 ± 0·000128 0·001284 ± 0·000005 0·282726 ± 0·000043 4·81 ± 1·83 
DMP555-4 309 ± 3·60 0·082002 ± 0·000298 0·002975 ± 0·000009 0·282745 ± 0·000048 5·24 ± 1·99 
DMP555-13 309 ± 4·71 0·057792 ± 0·000607 0·002185 ± 0·000022 0·282719 ± 0·000041 4·46 ± 1·79 
DMP555-8 310 ± 3·84 0·023892 ± 0·000468 0·001007 ± 0·000018 0·282723 ± 0·000043 4·89 ± 1·84 
DMP555-7 312 ± 4·31 0·015224 ± 0·000071 0·000653 ± 0·000003 0·282920 ± 0·000046 12·0 ± 1·91 
DMP555-22 312 ± 3·80 0·029194 ± 0·000154 0·001090 ± 0·000005 0·282720 ± 0·000034 4·80 ± 1·58 
DMP555-37 312 ± 9·15 0·028296 ± 0·000667 0·001133 ± 0·000025 0·282667 ± 0·000034 2·91 ± 1·61 
DMP555-17* 313 ± 7·87 0·021492 ± 0·000464 0·000824 ± 0·000017 0·282240 ± 0·000048 −12·1 ± 1·98 
DMP555-3 315 ± 4·35 0·035021 ± 0·000351 0·001377 ± 0·000014 0·282792 ± 0·000032 7·35 ± 1·54 
DMP555-5 318 ± 4·02 0·020045 ± 0·000132 0·000834 ± 0·000005 0·282744 ± 0·000037 5·81 ± 1·66 
DMP555-20 320 ± 5·74 0·055719 ± 0·000085 0·002269 ± 0·000002 0·282720 ± 0·000054 4·72 ± 2·16 
DMP555-30 321 ± 5·61 0·169208 ± 0·003374 0·005950 ± 0·000114 0·283053 ± 0·000057 15·7 ± 2·27 
DMP555-1 323 ± 3·20 0·037931 ± 0·000381 0·001528 ± 0·000014 0·282815 ± 0·000042 8·29 ± 1·80 
DMP555-19 324 ± 3·83 0·063270 ± 0·000378 0·002405 ± 0·000012 0·282773 ± 0·000051 6·63 ± 2·09 
DMP555-15 335 ± 5·88 0·084375 ± 0·000346 0·002938 ± 0·000009 0·283278 ± 0·000041 24·6 ± 1·79 
 Age ± 1σ 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf εHf(t) 
 (Ma) ( ± 1σ) ( ± 1σ) ( ± 1σ) ( ± 1σ) 
DMP122-1 64 ± 1 0·173316 ± 0·003446 0·005027 ± 0·000089 0·283193 ± 0·000026 16·1 ± 1·39 
DMP122-3 48 ± 2 0·173147 ± 0·003442 0·005027 ± 0·000089 0·283189 ± 0·000026 15·7 ± 1·39 
DMP122-4 49 ± 1 0·291012 ± 0·001211 0·008683 ± 0·000035 0·283019 ± 0·000161 9·51 ± 5·80 
DMP122-6 114 ± 2 0·015735 ± 0·000156 0·000581 ± 0·000008 0·282622 ± 0·000095 −2·85 ± 3·50 
DMP122-7* 2355 ± 107 0·003384 ± 0·000033 0·000116 ± 0·000001 0·281583 ± 0·000029 10·6 ± 2·88 
DMP134-2* 136 ± 4 0·064171 ± 0·001667 0·002057 ± 0·000034 0·282151 ± 0·000254 −19·2 ± 9·04 
DMP134-5* 228 ± 2 0·046951 ± 0·000879 0·001716 ± 0·000030 0·282683 ± 0·000049 1·61 ± 2·02 
DMP134-6 244 ± 3 0·048771 ± 0·000548 0·001789 ± 0·000019 0·282538 ± 0·000052 −3·19 ± 2·12 
DMP134-1 254 ± 4 0·042045 ± 0·001401 0·001448 ± 0·000043 0·282136 ± 0·000056 −17·2 ± 2·24 
DMP406-1 111 ± 2 0·019064 ± 0·000223 0·000698 ± 0·000007 0·281659 ± 0·000053 −37·0 ± 2·15 
DMP406-14 117 ± 2 0·085284 ± 0·002787 0·002920 ± 0·000088 0·281359 ± 0·000151 −47·6 ± 5·43 
DMP406-18 225 ± 6 0·014808 ± 0·000372 0·000572 ± 0·000013 0·282473 ± 0·000045 −5·71 ± 1·89 
DMP406-19 684 ± 69 0·001445 ± 0·000067 0·000053 ± 0·000002 0·282252 ± 0·000075 −3·33 ± 3·24 
DMP406-10* 797 ± 96 0·001190 ± 0·000036 0·000044 ± 0·000001 0·282460 ± 0·000055 6·57 ± 3·06 
DMP406-15 1072 ± 79 0·076853 ± 0·001099 0·002922 ± 0·000038 0·282510 ± 0·000065 12·4 ± 3·08 
DMP406-16* 1078 ± 71 0·053325 ± 0·000659 0·002052 ± 0·000026 0·282572 ± 0·000116 15·4 ± 4·54 
DMP406-11* 1249 ± 90 0·000908 ± 0·000063 0·000036 ± 0·000002 0·282489 ± 0·000069 17·7 ± 3·35 
DMP406-9 1488 ± 25 0·030948 ± 0·001387 0·001262 ± 0·000052 0·282052 ± 0·000038 6·36 ± 1·80 
DMP406-4 1814 ± 40 0·014393 ± 0·000273 0·000530 ± 0·000010 0·281488 ± 0·000058 −5·62 ± 2·47 
DMP406-5 1835 ± 44 0·012286 ± 0·000159 0·000443 ± 0·000005 0·281432 ± 0·000061 −7·03 ± 2·62 
DMP406-8 1784 ± 27 0·050007 ± 0·001799 0·001468 ± 0·000047 0·281585 ± 0·000041 −3·98 ± 1·91 
DMP406-12 2002 ± 20 0·039891 ± 0·000184 0·001663 ± 0·000009 0·281945 ± 0·000050 13·3 ± 2·13 
DMP406-6* 2138 ± 228 0·014604 ± 0·000422 0·000506 ± 0·000012 0·281368 ± 0·000065 −2·59 ± 5·82 
DMP406-2 2473 ± 21 0·020816 ± 0·000238 0·000776 ± 0·000008 0·281427 ± 0·000044 6·67 ± 1·95 
DMP444-2 2411 ± 18 0·025896 ± 0·000381 0·000992 ± 0·000015 0·281300 ± 0·000087 0·40 ± 3·31 
DMP444-1 2324 ± 20 0·021306 ± 0·000135 0·000812 ± 0·000006 0·281267 ± 0·000041 −2·44 ± 1·86 
DMP552-13 20 ± 0·3 0·020966 ± 0·000201 0·000686 ± 0·000006 0·282391 ± 0·000049 −13·0 ± 2·00 
DMP552-21* 64 ± 2 0·019687 ± 0·001145 0·000806 ± 0·000047 0·282783 ± 0·000046 1·75 ± 1·93 
DMP552-23 2547 ± 16 0·018008 ± 0·000188 0·000742 ± 0·000008 0·280604 ± 0·000075 −22·9 ± 2·90 
DMP552-16* 100 ± 2 0·045579 ± 0·001077 0·001594 ± 0·000036 0·283013 ± 0·000094 10·6 ± 3·47 
DMP552-9 101 ± 2 0·031827 ± 0·000151 0·001175 ± 0·000009 0·283112 ± 0·000051 14·2 ± 2·07 
DMP552-3* 108 ± 2 0·018343 ± 0·000289 0·000670 ± 0·000010 0·282769 ± 0·000057 2·23 ± 2·26 
DMP552-15 112 ± 2 0·044056 ± 0·000709 0·001621 ± 0·000028 0·282909 ± 0·000051 7·20 ± 2·09 
DMP552-18 119 ± 2 0·065532 ± 0·000513 0·002393 ± 0·000016 0·282200 ± 0·000084 −17·8 ± 3·15 
DMP552-19* 119 ± 2 0·048954 ± 0·000211 0·001840 ± 0·000007 0·282653 ± 0·000072 −1·74 ± 2·73 
DMP552-1* 141 ± 5 0·035288 ± 0·000747 0·001261 ± 0·000025 0·282538 ± 0·000053 −5·28 ± 2·13 
DMP552-14 224 ± 3 0·068836 ± 0·001976 0·002360 ± 0·000065 0·282152 ± 0·000055 −17·4 ± 2·21 
DMP552-11 977 ± 28 0·023702 ± 0·000554 0·000913 ± 0·000017 0·281949 ± 0·000061 −8·12 ± 2·47 
DMP552-2 2052 ± 77 0·017125 ± 0·000174 0·000643 ± 0·000006 0·281553 ± 0·000052 1·88 ± 2·76 
DMP552-8 2433 ± 19 0·010721 ± 0·000286 0·000371 ± 0·000009 0·281098 ± 0·000054 −5·29 ± 2·24 
DMP552-5 2487 ± 17 0·032458 ± 0·000497 0·001429 ± 0·000022 0·281344 ± 0·000048 2·90 ± 2·07 
DMP552-20 2520 ± 18 0·046911 ± 0·000604 0·001715 ± 0·000018 0·281554 ± 0·000067 10·6 ± 2·66 
DMP554-8* 52 ± 2 0·016166 ± 0·000196 0·000625 ± 0·000005 0·282844 ± 0·000039 3·68 ± 1·72 
DMP554-3 173 ± 3 0·024587 ± 0·000384 0·000951 ± 0·000012 0·281850 ± 0·000034 −28·9 ± 1·59 
DMP554-9* 205 ± 20 0·011298 ± 0·000055 0·000437 ± 0·000002 0·281662 ± 0·000051 −34·8 ± 2·12 
DMP554-12 231 ± 17 0·012113 ± 0·000109 0·000489 ± 0·000004 0·282065 ± 0·000029 −20·0 ± 1·49 
DMP554-1 314 ± 5 0·044383 ± 0·000439 0·001691 ± 0·000019 0·283047 ± 0·000034 16·3 ± 1·57 
DMP554-2 323 ± 7 0·040277 ± 0·000217 0·001535 ± 0·000008 0·282992 ± 0·000032 14·5 ± 1·53 
DMP554-11* 337 ± 13 0·011466 ± 0·000116 0·000529 ± 0·000005 0·281928 ± 0·000060 −22·6 ± 2·38 
DMP554-6 610 ± 6 0·012049 ± 0·000896 0·000412 ± 0·000031 0·282617 ± 0·000044 7·80 ± 1·88 
DMP555-47* 122 ± 7·55 0·026619 ± 0·000090 0·000924 ± 0·000002 0·282392 ± 0·000074 −10·8 ± 2·82 
DMP555-23 140 ± 5·72 0·032574 ± 0·000176 0·001125 ± 0·000007 0·282370 ± 0·000055 −11·2 ± 2·19 
DMP555-16 248 ± 4·08 0·013294 ± 0·000113 0·000587 ± 0·000003 0·282143 ± 0·000046 −16·9 ± 1·93 
DMP555-11 276 ± 2·76 0·032684 ± 0·000456 0·001279 ± 0·000017 0·282775 ± 0·000062 5·95 ± 2·41 
DMP555-9 305 ± 4·01 0·027693 ± 0·000339 0·001084 ± 0·000014 0·282762 ± 0·000036 6·15 ± 1·65 
DMP555-10* 305 ± 4·60 0·031486 ± 0·000128 0·001284 ± 0·000005 0·282726 ± 0·000043 4·81 ± 1·83 
DMP555-4 309 ± 3·60 0·082002 ± 0·000298 0·002975 ± 0·000009 0·282745 ± 0·000048 5·24 ± 1·99 
DMP555-13 309 ± 4·71 0·057792 ± 0·000607 0·002185 ± 0·000022 0·282719 ± 0·000041 4·46 ± 1·79 
DMP555-8 310 ± 3·84 0·023892 ± 0·000468 0·001007 ± 0·000018 0·282723 ± 0·000043 4·89 ± 1·84 
DMP555-7 312 ± 4·31 0·015224 ± 0·000071 0·000653 ± 0·000003 0·282920 ± 0·000046 12·0 ± 1·91 
DMP555-22 312 ± 3·80 0·029194 ± 0·000154 0·001090 ± 0·000005 0·282720 ± 0·000034 4·80 ± 1·58 
DMP555-37 312 ± 9·15 0·028296 ± 0·000667 0·001133 ± 0·000025 0·282667 ± 0·000034 2·91 ± 1·61 
DMP555-17* 313 ± 7·87 0·021492 ± 0·000464 0·000824 ± 0·000017 0·282240 ± 0·000048 −12·1 ± 1·98 
DMP555-3 315 ± 4·35 0·035021 ± 0·000351 0·001377 ± 0·000014 0·282792 ± 0·000032 7·35 ± 1·54 
DMP555-5 318 ± 4·02 0·020045 ± 0·000132 0·000834 ± 0·000005 0·282744 ± 0·000037 5·81 ± 1·66 
DMP555-20 320 ± 5·74 0·055719 ± 0·000085 0·002269 ± 0·000002 0·282720 ± 0·000054 4·72 ± 2·16 
DMP555-30 321 ± 5·61 0·169208 ± 0·003374 0·005950 ± 0·000114 0·283053 ± 0·000057 15·7 ± 2·27 
DMP555-1 323 ± 3·20 0·037931 ± 0·000381 0·001528 ± 0·000014 0·282815 ± 0·000042 8·29 ± 1·80 
DMP555-19 324 ± 3·83 0·063270 ± 0·000378 0·002405 ± 0·000012 0·282773 ± 0·000051 6·63 ± 2·09 
DMP555-15 335 ± 5·88 0·084375 ± 0·000346 0·002938 ± 0·000009 0·283278 ± 0·000041 24·6 ± 1·79 

Initial 176Hf/177Hf ratios, denoted as εHf(t), are calculated relative to a chondritic reservoir with a 176Hf/177Hf ratio of 0·282772 and 176Lu/177Hf of 0·0332 (Blichert-Toft & Albarède, 1997). The decay constant value of 1·865 × 10–11 year–1 for 176Lu reported by Scherer et al. (2001) was used.

*The discordance of U–Pb ages is >10%.

Fig. 12.

Variation of Hf isotopic composition with age. The filled and open symbols are zircons with concordance >90% and <90%, respectively. The uncertainty bars are 2σ. CHUR is chondritic reservoir (Blichert-Toft & Albarède, 1997); Lu–Hf isotopic compositions of depleted mantle (DM) and bulk continental crust (BCC) are from Griffin et al. (2000).

Fig. 12.

Variation of Hf isotopic composition with age. The filled and open symbols are zircons with concordance >90% and <90%, respectively. The uncertainty bars are 2σ. CHUR is chondritic reservoir (Blichert-Toft & Albarède, 1997); Lu–Hf isotopic compositions of depleted mantle (DM) and bulk continental crust (BCC) are from Griffin et al. (2000).

DISCUSSION

The petrology and geochemical characteristics of the composite xenoliths indicate that the garnet/spinel-rich pyroxenite veins or layers are reaction products between a silicic melt and a lherzolite or harzburgite host-rock (Liu et al., 2005), as predicted from phase petrology (Kelemen, 1986) and confirmed by experiment (Rapp et al., 1999). However, this raises some questions: where did the silicic melt come from and when did the melt–peridotite reaction take place?

Origin of the silicic melts: partial melts of recycled crust in the mantle

Our previous work demonstrates that the garnet/spinel pyroxenite veins or layers are enriched in highly incompatible elements but have high and uniform Ni contents and Mg-numbers (83–90). Many of the coexisting Mesozoic intermediate granulite xenoliths (SiO2 > 50 wt %) have unusually high Mg-number (54–71) and high Ni contents (21–147 ppm) for their SiO2 contents (Liu et al., 2005). These paradoxical geochemical features can be explained by recycled crust-derived melt–peridotite interaction in the mantle. However, there was no active subduction zone in the Hannuoba region during Mesozoic times. Thus, Liu et al. (2005) speculated that partial melting of delaminated lower crust or basaltic layers that were previously subducted (e.g. a fossil oceanic slab) or underplated onto the base of the lithospheric mantle induced silicic melt–peridotite reaction and generated evolved magmas with high Mg-number and Ni contents.

Each pyroxenite vein in the composite xenoliths probably represents a single melt infiltration event into the shallow lithospheric mantle. Therefore, zircons from the pyroxenite veins or layers either could be xenocrysts injected with the silicic melt into the vein, or could have crystallized during melt infiltration and later high-pressure metamorphism. Zircons crystallized during melt infiltration should show igneous textures (e.g. oscillatory growth zoning). CL images of the Precambrian zircons generally show residual cores with overgrowths, most of which show no internal zoning (Fig. 4). These features are typical of metamorphic zircons (Corfu et al., 2003). Zircons crystallized under garnet-forming metamorphic conditions (especially at high temperature) would be characterized by a relative depletion in HREE (Rubatto & Hermann, 2007), as demonstrated by some zircons formed during ultrahigh-pressure (UHP) metamorphism (Wu et al., 2007). However, although abundant garnets are found in the pyroxenite veins (Fig. 2), few zircon grains show REE patterns consistent with equilibration of zircon with garnet (Figs 7 and 8). In contrast, most of the Precambrian zircons exhibit the geochemical characteristics of igneous zircons; that is, high HREE contents and HREE-enriched REE patterns (Belousova et al., 2002) (Figs 6–10). These observations indicate that the Precambrian zircons did not crystallize during melt–peridotite interaction and subsequent high-pressure metamorphism. Instead, we suggest that they are xenocrysts, injected along with silicate melt into the garnet/spinel pyroxenite vein.

The Precambrian zircon age groups within the pyroxenite veins are consistent with geological events in the North China Craton, as documented by the ages of detrital zircons from major river sediments (Fig. 5) (Yang et al., 2009). The trace element compositions of the zircons from both the garnet/spinel pyroxenite veins and garnet-rich granulite xenolith generally fall in the range of zircons from continental granitoid rocks in plots of U/Yb vs Hf and Y (Fig. 13). Such diagrams are very helpful in distinguishing zircons from oceanic gabbros and evolved continental crust (Grimes et al., 2007). A granitoid source is consistent with the presence of quartz and feldspar inclusions in some of the Precambrian zircon grains (Fig. 2). Although a number of Precambrian zircons have positive εHf(t) values, implying a depleted mantle source or contribution from a recycled oceanic eclogite residue for Hf (Schmidberger et al., 2005, 2007; Wu et al., 2009), most of the Precambrian zircons have negative εHf(t) values, indicating an old source of Hf (Fig. 12a). Moreover, CL images of those Precambrian zircons with positive εHf(t) values show no growth zoning, and are generally composed of a core and an overgrowth rim (Fig. 4), which are features of metamorphic zircons (Corfu et al., 2003). Combination of these observations suggests that the silica-rich melts containing Precambrian zircon xenocrysts were probably derived from delaminated lower continental crust (Gao et al., 2004), and/or Mongol–Okhotsk oceanic sediments shed from the NCC and then brought to mantle depths by Paleozoic Mongol–Okhotsk oceanic crust subduction.

Fig. 13.

U/Yb vs Hf and Y for zircons from the composite xenoliths. Continuous line encompasses the range of oceanic crust zircons and the dashed line is the range of zircons from continental crust (Grimes et al., 2007). Wide gray line is the range of zircons from some granitoid rocks (Ballard et al., 2002; Belousova et al., 2006).

Fig. 13.

U/Yb vs Hf and Y for zircons from the composite xenoliths. Continuous line encompasses the range of oceanic crust zircons and the dashed line is the range of zircons from continental crust (Grimes et al., 2007). Wide gray line is the range of zircons from some granitoid rocks (Ballard et al., 2002; Belousova et al., 2006).

Contributions of altered oceanic crust and subducted terrigenous sediments would significantly increase the 87Sr/86Sr ratio of the mantle (Jackson et al., 2007). Garnet pyroxenite xenoliths from the Hannuoba basalts have highly variable Sr isotopic compositions. Although some garnet pyroxenite xenoliths have relatively high 87Sr/86Sr at a given εNd, suggesting a contribution from altered oceanic crust (Xu, 2002), most of the garnet pyroxenite veins in the composite xenoliths and some garnet pyroxenite xenoliths have relatively low 87Sr/86Sr ratios (Xu, 2002, and our unpublished data). This implies that, in addition to the subducted Mongol–Okhotsk altered oceanic crust and sediments shed from the NCC, foundered lower continental crust could also have contributed to the silicic melts. Delamination of thickened continental lithosphere at 117–160 Ma in the NCC has been proposed to account for an Early Cretaceous giant igneous event (Wu et al., 2005), and the petrogenesis of Mesozoic high Mg-number adakites (Gao et al., 2004; Xu et al., 2006a; Xu et al., 2008). Foundering of mafic lower continental crust into the underlying convecting mantle could have resulted from, or even accompanied, the Mesozoic lithospheric thinning of the NCC (Menzies et al., 1993, 2007; Griffin et al., 1998; Menzies & Xu, 1998; Gao et al., 2004, 2008; Xu et al., 2006a; Xu et al., 2008). This could be related to a number of possible tectonic events: the subduction of the Palaeo-Pacific Ocean (Niu, 2005; Wu et al., 2005), collision of an amalgamated North China–Mongolian plate with the Siberian plate during the closure of the Mongol–Okhotsk ocean, Triassic collision between the Yangtze craton and the NCC, or a combination of these events.

The subducted oceanic–continental crust or delaminated continental crust could be melted to a relatively high degree in the mantle ( > 9% at 2 GPa) as a result of the lower solidus of crustal rocks (e.g. Sen & Dunn, 1994; Rapp & Watson, 1995; Winther, 1996; Pertermann & Hirschmann, 2003; Kogiso & Hirschmann, 2006). Such a relatively high degree of melting of crustal rocks would facilitate focused melt percolation enough to transport crystals. Thus, upward migration of the subducted oceanic–continental crust or delaminated continental crust derived melts will not only cause melt–peridotite interaction to crystallize new zircons, but also introduce refractory inherited zircons. This kind of process can reasonably account for the wide zircon age spectrum obtained from these composite xenoliths. The calculated equilibration temperatures of the composite xenoliths are mostly in the range 866–997°C (Table 2) (Liu et al., 2003), which is close to the blocking temperature of zircon ( > 900°C) (Mezger & Krogstad, 1997; Cherniak & Watson, 2000). Furthermore, the degree of Pb diffusion out of zircon has been shown to be dependent on the U + Th content (Mezger & Krogstad, 1997; Cherniak & Watson, 2000). The relatively ‘cool’ and dry uppermost lithospheric mantle is favorable for preserving the Pb isotope compositions of inherited Precambrian zircons with low U and Th contents (Table 5).

Palaeo-Asian oceanic crust subduction-related melt–peridotite interactions

The long-lived Palaeo-Asian Ocean, located between the Siberian–Kazakhstan and Tarim–North China Blocks (Dobretsov et al., 1995; Windley et al., 2007), began to form near Lake Baikal in Siberia by at least 1·0 Ga (Khain et al., 2002) and terminated in Inner Mongolia in the Permian (Xiao & Windley, 2003). Southward subduction of the Palaeo-Asian Ocean plate beneath the NCC resulted in the formation of late Carboniferous subduction-related magmas on the northern margin of the NCC (Zhang et al., 2007, 2009). Thus, it is reasonable to speculate that recycling of Palaeo-Asian oceanic crust into the mantle could also have induced melt–peridotite interaction, as suggested by Xu (2002) and Tang et al. (2007). Xu (2002) showed that some garnet pyroxenite xenoliths from the Hannuoba basalts have enriched radiogenic Sr isotopic compositions at given εNd values, and suggested that these garnet pyroxenites were segregates from melts derived from partial melting of hydrothermally altered oceanic crust associated with subduction of the Mongol–Okhotsk plate beneath the NCC. A similar process was suggested by Tang et al. (2007) to interpret the variable Li isotope compositions of the peridotite xenoliths.

Zircons in DMP555 are mainly 315 ± 3 Ma (2σ) in age and no zircon with an age greater than 340 Ma has been found. The well-developed growth zoning and HREE-rich REE patterns of these zircons indicate an igneous origin (Figs 4 and 9). This suggests that the garnet pyroxenite vein in DMP555 was formed by melt–peridotite interaction at 315 ± 3 Ma (2σ). The relatively high εHf(t) values (2·91–24·6) of the 315 Ma zircons imply a mantle source for the Hf (Fig. 12b). Nevertheless, most of the zircons from DMP555 fall in the field of continental rocks in plots of U/Yb vs Hf and Y (Fig. 13), suggesting derivation from evolved magmas (e.g. partial melts of basaltic rocks) rather than directly from a reservoir like modern mid-ocean ridge basalt (MORB) (Grimes et al., 2007). The slight negative Eu anomalies of these zircons could be inherited from partial melts derived from recycled crustal rocks; no Ca-feldspar has been found in the garnet pyroxenite veins. Combination of these observations leads us to speculate that the 315 Ma melt–peridotite interactions could have resulted from infiltration of recycled Palaeo-Asian oceanic crust-derived partial melts into mantle peridotite, forming garnet pyroxenites and resulting in the crystallization of zircons with a hybrid signature. The absence of inherited zircons in the 315 Ma garnet pyroxenites implies that partial melting of the recycled Palaeo-Asian oceanic crust must have taken place under relatively high P–T and probably water-rich conditions, and thus completely altered only pre-existing zircons.

Diorite of c. 310 Ma (Chen et al., 2000), garnet-bearing granite of 316 Ma (Shi et al., 2003) and granitic plutons of 302–324 Ma (Zhang et al., 2007) have been found within the northern margin of the North China Craton (Inner Mongolia), and have been interpreted as the products of partial melting of mantle metasomatized in a supra-subduction zone setting. (Chen et al., 2000), or partial melting of a subducted oceanic slab (Wang et al., 2000). According to the coupled relationship between the Nd and Hf isotopic compositions of terrestrial materials (εHf(t) = 1·36εNd(t) + 2·95) (Vervoort et al., 1999), the εNd(t) value ( + 2·4) of the 310 Ma diorite (Chen et al., 2000) is consistent with the average εHf(t) value (6·6) of the 315 Ma zircons. Furthermore, the positive or near zero εHf(t) values (–0·9 to 1·2) of zircons from some granitic plutons of 302–324 Ma age suggest contributions from the lithosphere mantle and possibly a subducted slab of Palaeo-Asian oceanic origin (Zhang et al., 2009). Collectively, these observations suggest that the melts involved in the melt–peridotite interaction at 315 ± 3 Ma (2σ) could share a common petrogenesis with some of the 302–324 Ma diorite–granite plutons; that is, with Palaeo-Asian oceanic crust subduction.

Overprints of multi-episodic melt– or fluid–peridotite interactions

The garnet/spinel pyroxenite veins or layers in the composite xenoliths could have been formed by multi-episodic melt–peridotite interactions and affected by later metasomatic and/or thermal events. The small population of garnet pyroxenite veins with zircons of ∼315 Ma (Fig. 5) and rare occurrence of 302–324 Ma igneous rocks in the northern margin of the North China (Chen et al., 2000; Shi et al., 2003; Zhang et al., 2007) suggest that Palaeo-Asian oceanic crust subduction could have contributed to melt–peridotite interactions in the lithospheric mantle under the NCC (Xu, 2002; Xu et al., 2003; Liu et al., 2005, 2008a; Zhang, 2005; Gao et al., 2008; Xu et al., 2008). Zircons of 220–254 Ma age (eight analyses) are generally characterized by metamorphic zircon CL textures (Fig. 4) and negative εHf(t) values (–20·0 to –3·14) (Fig. 12). These characteristics suggest that (1) the 220–254 Ma zircons could be inherited from recycled continental crust, and (2) continental crust recycling and resultant melt–peridotite interaction occurred after 220 Ma.

Although zircons of the 80–170 Ma population (22 analyses) are not dominant, they occur widely in most of the garnet/spinel pyroxenite veins (Fig. 5) and the coexisting olivine pyroxenite and garnet-free granulite xenoliths (Fan et al., 1998; Liu et al., 2001, 2004; Wilde et al., 2003). Zircons of 80–150 Ma age found in the coexisting granulite xenoliths typically show metamorphic CL textures, and have been interpreted as the products of granulite-facies metamorphism resulting from a basaltic underplating event (Fan et al., 1998; Liu et al., 2001, 2004; Zhou et al., 2002; Wilde et al., 2003). However, the 80–170 Ma zircons in the garnet/spinel pyroxenite veins show HREE-enriched REE patterns and oscillatory zoning, suggesting an igneous origin and thus a melt–peridotite interaction event. Igneous zircons of 97–158 Ma age have also been found in a coexisting olivine pyroxenite xenolith by Liu et al. (2004). Combination of these observations suggests that melt–peridotite interaction at 80–170 Ma could be related to late Mesozoic magmatic underplating.

It is worth noting that many of the 85–124 Ma igneous zircons were separated from DMP552, in which the 2·5 Ga zircons were also mainly found. Compared with the zircons of ∼315 Ma in DMP555 (Fig. 9), the 85–124 Ma igneous zircons have lower Ce/Yb and Th/U ratios (Fig. 11a), higher U/Yb ratios and more pronounced negative Eu anomalies (Fig. 8). The significant negative εHf(t) values (–47·6 to –2·85) of the 110–120 Ma zircons suggest involvement of ancient continental crust, whereas the positive εHf(t) values (2·23–14·2) of the ∼100–110 Ma zircons indicate a depleted mantle component (Fig. 12b) (Blichert-Toft et al., 1999; Vervoort & Blichert-Toft, 1999) or recycled eclogite residue (Schmidberger et al., 2005, 2007; Wu et al., 2009). According to the coupled relationship between the Nd and Hf isotopic compositions of terrestrial materials (Vervoort et al., 1999), the εHf(t) values (10·6–14·2) of the ∼100 Ma zircons are consistent with the εNd(t) values (3·4–4·4) of the 100 Ma basalts in the NCC (Zhang et al., 2003). On the other hand, based on Nb/Ta and Fe/Mn ratios, trace element and Sr–Nd isotopic compositions, Liu et al. (2008a) suggested that the >110 Ma basalts from the NCC were derived from orthopyroxene/garnet-rich mantle sources formed by recycled crust-derived melt– or fluid–peridotite interaction, whereas the < 110 Ma basalts were derived from a clinopyroxene/garnet-rich mantle source formed by peridotite + rutile-bearing eclogite mixing. Delamination of thickened continental crust into the convecting mantle has been proposed to explain the Precambrian zircon-bearing 130–160 Ma high Mg-number adakites in the NCC (Gao et al., 2004; Xu et al., 2006a; Xu et al., 2008).

The above observations collectively suggest that the silicic melts that induced melt–peridotite interaction at 80–170 Ma could have been derived by partial melting of delaminated continental crust during the Mesozoic lithospheric thinning of the NCC (Menzies et al., 1993; Griffin et al., 1998). This agrees with the rare occurrence of quartz and feldspar inclusions in the Precambrian zircons and felsic melt inclusions in the 125 Ma zircons from DMP-552 (Fig. 2).

The eruption of Cenozoic basalts was widespread in the NCC (Liu et al., 1992b), which could also have induced extensive melt–peridotite interactions. Recently, 45–47 Ma zircons were identified in the lower crust-derived granulite and pyroxenite xenoliths in the Hannuoba basalts, and interpreted as the products of basaltic underplating (Zheng et al., 2009). These observations imply that the 48–64 Ma zircon population might be the product of cryptic metasomatism induced by the Cenozoic basalts or basaltic underplating in Paleogene times. However, the pronounced enrichments in REE, U and Th of the 48–64 Ma zircons in pyroxenite vein DMP122 could not be produced by a silicate melt of the same composition as the 45–47 Ma pyroxenite xenoliths (Zheng et al., 2009). Instead, they are more likely to be attributable to a carbonate melt (Hoernle et al., 2002; Moine et al., 2004). The unusually high REE, U and Th contents and the absence of a Ce anomaly in the 48–64 Ma igneous zircons in DMP122 (Table 5 and Fig. 6), therefore indicate that the garnet pyroxenite vein in DMP122 could have suffered from an overprint of carbonate melt or fluid metasomatism, as indicated by the carbonate film along grain boundaries and/or within micro-fractures in the xenoliths (Table 1 and Fig. 3). The positive εHf(t) values (9·51–16·1) of these zircons suggest that the carbonate melt could be derived from the depleted mantle (Fig. 12b).

The 206Pb/238U ages of 17–20 Ma for one zircon overlap with the eruption age of the host basalts (14–27 Ma) (Liu et al., 1992b; Zhu, 1998). This has a negative εHf(t) value (−13), which is decoupled from the εNd(t) values (0·14–7·10) of the host basalts (Song et al., 1990). The negative εHf(t) value and metamorphic CL texture of this zircon indicate that it is an inherited zircon grain in which U–Pb isotopic system was completely reset by the thermal event of the host basalt eruption.

CONCLUSIONS

Composite mantle xenoliths carried by the Neogene Hannuoba basalts were formed by multi-episodic silicic melt– or fluid–peridotite interactions at c. 315 Ma and 80–170 Ma. Some of them also underwent cryptic metasomatism by mantle-derived carbonate melts at 48–64 Ma. Igneous zircons with ages of 315 ± 3 Ma (σ) probably record Palaeo-Asian oceanic crust subduction-induced melt–peridotite interactions in the lithospheric mantle. These melts may share a common petrogenesis with 302–324 Ma diorite–granite plutons along the northern margin of the NCC. The 80–170 Ma igneous zircons record melt–peridotite interaction induced by partial melting of delaminated continental crust, possibly associated with the Mesozoic lithospheric thinning of the NCC.

Precambrian age zircons were also found in the pyroxenite veins in the composite xenoliths, whose age range coincides with that of the major geological events in the evolution of the NCC. Their trace element and Hf isotopic compositions suggest that they are xenocrysts that survived melting of recycled continental crustal rocks and were then injected with the silicate melt into the veins.

ACKNOWLEDGEMENTS

Drs Daniela Rubatto, Craig Grimes and one anonymous reviewer are thanked for the detailed and constructive comments and suggestions to improve the manuscript. Professor Marjorie Wilson is thanked for the editorial work and suggestions to improve the manuscript. Dr Neng Jiang and Professor Moti Stein are thanked for the helpful discussion. We are grateful to Dr Hujun Gong for the assistance with CL imaging, and to Chunlei Zong for her assistance with LA-MC-ICP-MS zircon Hf isotope analysis. Dr Mouchun He is thanked for the assistance with laser-Raman spectrometry analysis. This research is co-supported by NSFC (90914007, 40673026 and 90714010), the Ministry of Education of China (IRT0441 and B07039) and MOST Special funds of State Key Laboratory of Geological Processes and Mineral Resources and State Key Laboratory of Continental Dynamics.

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