Special Topic : The Tibetan Plateau New paleomagnetic data confirm a dual-collision process in the Himalayas

The India–Asia collision and continual plate convergence have created the Himalayan–Tibetan Orogen, which is the youngest and most spectacular continent–continent collision belt on Earth, and thus an ideal place for the study of continent–continent collisions [1,2]. Although a large number of geological and geophysical investigations have been performed in the Himalayan– Tibetan Orogen and its surroundings in the last four decades, several hotly debated issues, such as the India–Asia collision process, the northern extension ofGreater India, and even the paleogeography of the Neo-Tethyan Ocean, still remain to be understood [3,4]. There have been two schools of contrasting models: (1) a simple collision of India and its postulated northern extension (Greater India) directly with Asia; (2) multiple terrane amalgamation with either by an earlier India–Arc collision followed by a final India/Arc–Asia collision or an independent Tethyan Himalaya terrane amalgamated with multiple terranes between Eurasia and India. Yang et al. [5] obtained high-quality Early Cretaceous paleomagnetic results from lavas of the Lakang Formation in the southern Tethyan Himalaya. These new paleomagnetic data, without compaction-induced inclination shallowing, characterize secular variation and satisfy all the seven widely accepted quality criteria for appraising the reliability of paleomagnetic data, which support that: (1) the Tethyan Himalaya was part of a contiguous Indian subcontinent at 134–130 Ma and its southern margin was located at 52.2◦± 5.7◦S; (2) the Neo-Tethyan Ocean lies between the Tethyan Himalaya and the Lhasa terrane and it opened up to 7000 ± 650 km during 134−130 Ma; (3) a Late Cretaceous extension, represented perhaps by a small post-Neo-Tethyan Ocean, occurred between the Indian craton and the Tethyan Himalaya after 130 Ma; (4) the India–Asia collision was a dual-collision process, which includes an early collision between the Tethyan Himalaya and the Lhasa terrane (Asia) at 54.9 ± 2.3 Ma and a final continent–continent collision of the Indian craton with the Tethyan Himalaya at 40.0 ± 3.3 Ma (Figure 1). The dual-collision process confirmed by paleomagnetic data of Yang et al. [5] seems to support multiple terrane amalgamation, instead of the simple earlier collisional model. The major framework of the dual-collision process is consistent with geological and geophysical data from Eurasia, India and Indian Ocean [6]. However, the controversy regarding the final collisional timing and detailed convergent processes of the Himalayan–Tibetan Orogen has been continuing, and more work needs to be done to reconcile early collision events with the complicated younger events [4,7]. Combined with other investigations on the Himalayan–Tibetan Orogen, it is reasonable to conclude that more than one collisional eventmight haveoccurred in the Himalayas. More and more work on the Tethyan and other orogens envisages that continent–continent collision orogens might have recorded convergence of multiple archipelagos with relatively long duration of orogenesis, which is similar to the features of accretionary orogens as indicated by theCentral Asian Orogenic Belt [8].


Wenjiao Xiao
The India-Asia collision and continual plate convergence have created the Himalayan-Tibetan Orogen, which is the youngest and most spectacular continent-continent collision belt on Earth, and thus an ideal place for the study of continent-continent collisions [1,2].Although a large number of geological and geophysical investigations have been performed in the Himalayan-Tibetan Orogen and its surroundings in the last four decades, several hotly debated issues, such as the India-Asia collision process, the northern extension of Greater India, and even the paleogeography of the Neo-Tethyan Ocean, still remain to be understood [3,4].There have been two schools of contrasting models: (1) a simple collision of India and its postulated northern extension (Greater India) directly with Asia; (2) multiple terrane amalgamation with either by an earlier India-Arc collision followed by a final India/Arc-Asia collision or an independent Tethyan Himalaya terrane amalgamated with multiple terranes between Eurasia and India.
Yang et al. [5] obtained high-quality Early Cretaceous paleomagnetic results from lavas of the Lakang Formation in the southern Tethyan Himalaya.These new paleomagnetic data, without compaction-induced inclination shallowing, characterize secular variation and satisfy all the seven widely accepted quality criteria for appraising the reliability of paleomagnetic data, which support that: (1) the Tethyan Himalaya was part of a contiguous Indian subcontinent at 134-130 Ma and its southern margin was located at 52.2 • ± 5.7 • S; (2) the Neo-Tethyan Ocean lies between the Tethyan Himalaya and the Lhasa terrane and it opened up to 7000 ± 650 km during 134−130 Ma; (3) a Late Cretaceous extension, represented perhaps by a small post-Neo-Tethyan Ocean, occurred between the Indian craton and the Tethyan Himalaya after 130 Ma; (4) the India-Asia collision was a dual-collision process, which includes an early collision between the Tethyan Himalaya and the Lhasa terrane (Asia) at 54.9 ± 2.3 Ma and a final continent-continent collision of the Indian craton with the Tethyan Himalaya at 40.0 ± 3.3 Ma (Figure 1).
The dual-collision process confirmed by paleomagnetic data of Yang et al. [5] seems to support multiple terrane amalgamation, instead of the simple earlier collisional model.The major framework of the dual-collision process is consistent with geological and geophysical data from Eurasia, India and Indian Ocean [6].However, the controversy regarding the final collisional timing and detailed convergent processes of the Himalayan-Tibetan Orogen has been continuing, and more work needs to be done to reconcile early collision events with the complicated younger events [4,7].
Combined with other investigations on the Himalayan-Tibetan Orogen, it is reasonable to conclude that more than one collisional event might have occurred in the Himalayas.More and more work on the Tethyan and other orogens envisages that continent-continent collision orogens might have recorded convergence of multiple archipelagos with relatively long duration of orogenesis, which is similar to the features of accretionary orogens as indicated by the Central Asian Orogenic Belt [8].

48.1°S
LK Observed paleolatitude and its abbreviation (See Table 1 of the Tethyan Himalaya and the Lhasa terrane (Asia) was at 16.6°±1.6°Nand 54.9±2.3Ma.I n d ia n c r a t o n ZP The southern margin of the Lhasa terrane (Asia) during the whole Cretaceous at 16.6°±1.6°N[c m / y r d u r i n g 1 3 2 -6 8 M a 5 . 2 c m / y r d u r in g 1 3 0 -6 8 M a T e t h y a n H i m a l a y a Lhasa terrane (Asia) 46.5°SThe latitudinal width of the Neo-Tethyan Ocean opened up to 7000±650 km (63.1°±5.9°)during 130-134 Ma.The final continent-continent collision of the Indian Craton and the Tethyan Himalaya was at 40.0±3.3Ma.

igure 1 .
[5])The precollisional northern margin of the Tethyan Himalaya after correcting 1.6° crustal shortening L a t e C r e t a c e o u s e x t e n s i o n Paleolatitude plots for the Indian craton, the Tethyan Himalayan and the Lhasa terranes.The shaded areas and vertical bars display the errors of the paleolatitudes.Expected and observed paleolatitudes were calculated for the reference point at 29.0 • N, 87.5 • E. Modified after[5].