Eocene–Oligocene Crustal Thickening-Collapse of the Eastern Tibetan Plateau: Evidence from the Potassic Granitoids in SW China

Abstract The eastern Tibetan Plateau is a key part of the India–Asia collisional zone, region that records multiple overprinting tectonic and magmatic events. This study presents new geochronological, geochemical, Sr–Nd–Hf–O isotopic data for Cenozoic potassic granitoids in Tibet, southwestern China, which recorded evolution Plateau. These are formed between 37.6 32.9 Ma geochemically subdivided into following: Group 1, adakite-like granites; 2, syenites; 3, low-εNdt granitoids. 1 samples similar to high-silica adakites they have variable SiO2 contents (63.31–73.62 wt.%) high Sr/Y La/Yb ratios. εNdt εHft values range from −5.8 −0.6 −4.3 +5.2, respectively, with δ18O 6.78‰–7.36‰. 2 syenites, contain 56.36–63.86 wt.% concentrations Y Yb, −8.4 −2.4, −6.1 +1.1, 6.37‰–6.89‰. 3 narrow (62.27–64.59 wt.%), ratios, 6.31‰–6.82‰, low (−12.6 −10.9 −11.4 −6.6, respectively) obtained contemporaneous Yao’an lamprophyres. indicate magmas sourced heterogeneous thickened lower crust containing an enriched mantle component. were most likely derived mafic melts ancient lithospheric previously modified by incorporation recycled components. distinct Sr–Nd–Hf compositions indicative derivation generated fractional crystallization crustal Yangtze Block. Combining these results previous research suggests igneous rocks Tibet as result thinning associated collapse event, potentially representing regional late Eocene early Oligocene transition compression transtension or younger than Qiangtang Block, suggesting response event was initiated central before propagating towards margin this region.