Significance

Defining the size of Greater India is a critical parameter needed to reconstruct the kinematics and timing of the India–Asia collision. This article resolves discrepant interpretations surrounding the age and paleogeography of the Sangdanlin section, which was part of Greater India, now sandwiched between the Indian and Asian plates. Our geologic data clarify the ages of the rocks at Sangdanlin, while paleogeographic reconstructions stemming from our paleomagnetic data and revised age model demonstrate Greater India extended 2,000 to 3,000 km as a single plate before subducting under Asia. The existence of such a large crustal area argues against scenarios advocating that the Neotethys Ocean was subdivided into numerous, independent tectonic blocks that subsequently accreted to the southern margin of the Tibetan Plateau.

Abstract

The Sangdanlin section in southern Tibet represents a geologic Rosetta stone to constrain the initiation of the India–Asia collision from its sedimentary and paleomagnetic records. However, geoscientists have arrived at fundamentally divergent interpretations surrounding the age of the strata and its paleomagnetic record. Here, we report paleontologic, petrographic, and paleomagnetic data from the Sangdanlin section that recognize the sequence as a thrust complex containing interlaced Barremian–Albian (Early Cretaceous) and Paleocene strata, each separated by thrust faults. Recognizing two complexly interwoven formations of distinctly different ages contradicts a continuous stratigraphic superposition. Assigning an Early Cretaceous, instead of Paleocene, age to the units collected for paleomagnetic data revises paleogeographic models thereby supporting a large (2,000 to 3,000 km) extent of Greater India, with collision initiating at 55 ± 5 Ma in the western Himalayas. A contiguous plate in the Neotethys Ocean precludes that Asia’s southern margin was built through a succession of accreted terrains.

Article link: https://www.pnas.org/doi/abs/10.1073/pnas.2305928120