Linking Cenozoic Magmatism in the North-Central Tibetan Plateau With Plateau Growth

Abstract

Accurate reconstruction of paleo-crustal and lithospheric thicknesses is crucial for understanding the deep geodynamic processes driving the uplift and growth of the Tibetan Plateau (TP) and their association with Cenozoic magmatism. We reconstruct the Cenozoic crustal thickness evolution of the north-central TP using a machine learning model for intermediate to felsic rocks, and estimate the lithospheric thickness based on geobarometers for mafic magmas. We find that the northern Qiangtang terrane (QT) underwent crustal thickening during the late Cretaceous-early Eocene, with the crust thickening to 60.2 ± 4.8 km by 45 Ma, while the lithospheric thickness was only 60.9 ± 4.5 km. This suggests wholesale delamination of the lithospheric mantle shortly before ∼45 Ma, explaining the formation of high MgO adakitic rocks and the uplift of the Tanggula Mountain to ≥5 km. To the south, the southern QT crust thickened by ∼16 km during the late Eocene-early Oligocene, contributing to ≥2 km uplift of the valley south of the Tanggula Mountain. To the north the Songpan-Ganzi terrane (SGT) had a crustal thickness of 60.6 ± 3.6 km at ∼18 Ma and underwent ∼25 km of lithospheric thinning during ∼16–13 Ma. This process contributed to the formation of Miocene shoshonitic mafic rocks and adakitic rocks in the SGT, and the uplift of the Hoh-Xil Basin to its present elevation. The recovered crustal and lithospheric thickness evolution demonstrates that progressive removal of the lower lithosphere following crustal shortening is the main driver for the uplift and magmatism of different regions in the TP.