Paleomagnetic Constraints On The Breakup Of Eastern Gondwana And The India-Asia Collision

The breakup of eastern Gondwana and subsequent northward drift of the Indian Plate were responsible for the formation of the eastern Indian Ocean,as well as the India-Asia collision and postcollisional convergence that produced the Himalayan-Tibetan Plateau.This tectonic event has had long-term impacts on the global paleoclimate,paleogeography,and the evolution of life.Although some geological and geophysical investigations have been conducted on the Tethyan Himalaya and the Lhasa Terrane,several key issues still remain to be fully resolved,such as the mechanism and process of the breakup of eastern Gondwana,and the India-Asia collision process.In view of the above scientific issues,a comprehensive paleomagnetic,rock magnetic,petrographic and geochronological study has been carried out in the Tethyan Himalaya and the Lhasa Terrane,and the obtained achievements are summarized as follows:?1?Our new zircon SHRIMP U-Pb dating indicates that the Zhela and Weimei Formations?Fms?lava flows in the Luozha area of the Tethyan Himalaya formed during 135.3±2.7 Ma and 137.6±3.8 Ma,rather than during the Middle and Late Jurassic as given by 1:250,000 scale Luozha regional geological survey report;?2?High-quality paleomagnetic pole have been obtained from the Luozha and Duina-Gangba area in the Tethyan Himalaya.The site-mean direction passes both fold and reversal tests,indicating a prefolding origin.The tilt-corrected site-mean direction for 31 sites and 30 sites yielded a paleopole at 0.9°N,293.4°E,A₉₅=7.0°and 58.7°N,330.3°E,A₉₅=2.5°,corresponding to a paleolatitude of–53.5°±7.0°N and 10.4°±2.5°N for the sampling area during the Early Cretaceous and Eocene,respectively;The tilt-corrected site-mean direction for 54 sites of the Geji area in the Lhasa terrane yielded a paleopole at 74.4°N,225.9°E,A₉₅=3.8°,which passes the fold test,demonstrating that the Geji sampling area was located at 19.6°±3.8°N during the Late Cretaceous;?3?Our geochronological and paleomagnetic results,combined with published geochronological,geochemical,and paleomagnetic results from the Australian Plate,Antarctic Plate,Indian craton,and Tethyan Himalaya,indicate that the Comei large igneous province in the eastern Tethyan Himalaya was erupted at⁵0°S during the Early Cretaceous?147–124 Ma?,fully consistent with the eruption center of the reconstructed Kerguelen mantle plume large igneous province.Theses results suggest that the Comei large igneous province may have been originated from the Kerguelen mantle plume;the eastern Gondwana initially rifted at¹47 Ma and that the Indian Plate fully separated from the Australian-Antarctic Plate before¹24 Ma;?4?Our paleomagnetic results,combined with published paleomagnetic results from the Lhasa terrane,Tethyan Himalaya,and Indian craton,indicate that the southern margin of the Asian continent?reference point:29.0?N,87.5?E?had been located at¹4.3?N during the whole Cretaceous,and had a relatively east-west alignment;neither a wide oceanic basin extended nor more than 1000 km north-south crustal shortening existed between the Indian craton and Tethyan Himalaya since the Late Jurassic;the Indian and Asian Plate had already collided by⁴8.1 Ma.