How and How Much Did Western Central Tibet Raise by India–Asia Collision?

This study uses geochemical mohometers to investigate the paleo‐crustal thickness and elevation of western Tibet through the Cretaceous to Eocene. The northern Lhasa Block and southern Qiangtang Block (QB) had a similar paleo‐crustal thickness of ∼55 km during the Late Cretaceous, but the latter had reached its present‐day thickness (∼70 km) and elevation (∼5.5 km) by the mid‐Eocene, which was not caused by underthrusting of Indian crust according to isotopic evidence. Our study demonstrates the western and central QB shared a similar early Paleogene tectonomagmatic evolution with the formation of a continues proto‐plateau in central Tibet, resulting from crustal shortening and subsequent lithospheric foundering. This in turn implies underthrusting of the Indian lithosphere beneath the western QB after Eocene, given the present‐day lithospheric difference between the western and central QB. Our reconstruction of paleo‐crustal thickness and elevation, however, suggests the Indian underthrusting caused minimal further crustal thickening and uplift. Plain Language Summary: The Tibetan Plateau is a key locality to study large‐scale continental tectonics because of the well‐preserved Cenozoic geological records along with the validity of geophysical data. The western part of the Tibetan Plateau is not a simple extension of the central‐eastern part as demonstrated by numerous geophysical investigations on the lithospheric structure. The western Qiangtang Block (QB) in central Tibet is generally thought to be raised by the Miocene underthrusting of the Indian lithosphere, yet no palaeoaltimetry data are available to test this hypothesis. This provides the first quantitative constraint on the uplift history of the western QB. We use recently calibrated igneous geochemical proxies of continental thickness to investigate the paleo‐crustal thickness and elevation of western Tibet through the Early Cretaceous to Eocene. Our data demonstrate that the western Tibetan crust had reached its present‐day thickness (∼70 km) and elevation (∼5.5 km) by the Mid‐Eocene, as a result of crustal shortening and subsequent lithospheric foundering. Based on a synthesis of independent geological and seismic data, we contend that the post‐Eocene underthrusting of the Indian lithosphere beneath the western QB has caused minimal further crustal thickening and uplift. Key Points: First quantitative constraint on the uplift history of the western Qiangtang Block (QB) in central TibetThe western QB has reached its present‐day thickness and elevation by EoceneUnderthrusting of the Indian lithosphere caused minimal further thickening and uplift of the western Qiangtang crust [ABSTRACT FROM AUTHOR]