Dai, Zuowen, Guangming, L. I., Liu, Hong, Huang, Hanxiao, Jiangang, F. U., and Huizenga, Jan Marten (2025) Petrogenesis of the Xuexiumaer Biotite Quartz Monzonite Porphyry in Southern Gangdese and its Implications for Paleo-Crustal Thickness of the Qinghai–Tibet Plateau. Acta Geologica Sinica, 99 (4). pp. 978-994.

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Abstract

The Qinghai–Tibet Plateau possesses the thickest continental crust on Earth, yet the timing of its formation remains debated. In this study, we conducted zircon U-Pb isotopic dating, geochemical and Sr-Nd-Pb-Hf isotopic analyses on the Xuexiumaer biotite quartz monzonite porphyry (BQMP) sampled from the Lake Dajia area in southern Gangdese. This study aims to estimate the paleo-crustal thickness beneath this region during the early India-Asia collision stage using whole-rock Sr/Y and (La/Yb)<inf>N</inf> ratios as proxies. Results reveal that the Xuexiumaer BQMP was formed at ~51 Ma in a collisional tectonic setting following Neo-Tethyan slab breakoff, and is an I-type granitoid derived primarily from partial melting of juvenile mafic lower crust with subordinate ancient crustal input. The estimated paleo-crustal thickness in the Lake Dajia area at ~51 Ma is less than 40 km. This indicates that although the Qinghai–Tibet Plateau had already undergone significant crustal thickening and attained an exceptionally thick crust (>50 km) prior to the India–Asia collision as demonstrated by previous studies, some regions still maintained a crust only slightly thicker than the average continental crust (~35 km) at the initial collision stage. This limited crustal thickening likely resulted from underplating of subduction-related mafic magma at the mantle-crust boundary.

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