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The Mid-Late Mesozoic magmatic arc in southern Qiangtang block was associated with the long-lasting subduction of the Bangong-Nujiang Tethyan and the subsequent Lhasa-Qiangtang collision. The detailed processes associated with the transition from oceanic lithosphere subduction to lithosphere delamination remain unclear. This paper reports zircon U-Pb age, major and trace element and Sr-Nd isotopic data for the Cretaceous two-phase magmatic rocks in the Shuanghu region of the southern Qiangtang block located in central Tibet. Zircon dating on the Qushenla volcanic rocks yields a 206Pb/238U age of 114 ± 4 Ma. The Abushan volcanic rocks comprise rhyolites. Zircon dating on two rhyolites yields a 206Pb/238U age of 74 ± 1 to 76 ± 1 Ma. In contrast with the Qushenla volcanic rocks, the Abushan rhyolites exhibit features typical of high-fractionated I-type granitoids, high K calc-alkaline and shoshonite, and peraluminous, suggesting that the Abushan rhyolites formed in post-collision setting. The Qushenla volcanic rocks have slightly higher initial 87Sr/86Sr (0.70466–0.70537), and εNd(t) (1.71–2.89) in comparison with the Abushan rhyolites (87Sr/86Sr = 0.70453–0.70491, εNd(t) = 1.63–2.35). The Qushenla volcanic rocks were most likely derived from the mixing of mantle-derived components and crustal material. And the crust assimilation and fractional crystallization played a role during the ascent of magma. The Abushan volcanic rocks derived from magmatic mixing between the crustal materials and mantle-derived components, and undergoing extensive fractional crystallization. Taking into account the regional tectonic and magmatic data, we suggest that the transition from the oceanic lithosphere subduction to lithosphere delamination occurred during the Late Cretaceous in central Tibet. It evolved through three stages: 125–100 Ma, late subduction of Bangong-Nujiang Tethys; 100–87 Ma slab break-off of subduction Bangong-Nujiang Tethys; and 87–73 Ma lithosphere delamination. [ABSTRACT FROM AUTHOR]

The Qiangtang terrane preserves an important record of the growth of the Tibetan Plateau since the Mesozoic; however, its deformation and cooling history remain poorly understood. To unravel this issue, we conducted geological mapping in the Esima area and detrital apatite fission track and (U–Th)/He analyses of the Esima–Rongtang region in the east segment of Central Qiangtang terrane. Our results indicate that the east segment underwent two stages of structural deformation and rapid cooling during 120–110 Ma and 55–38 Ma. By combining our results with those of previous studies of the deformation and cooling history in the west segment, we reconstructed the early spatial and temporal geological evolution of the Central Qiangtang terrane since the Late Jurassic–Early Cretaceous. The structural deformation and cooling of the west segment at 150–130 Ma was related to northward flat subduction of the Bangong–Nujiang oceanic slab. The structural deformation and cooling of the east segment at 120–110 Ma and the west segment at 110–70 Ma was controlled by oblique convergence between Lhasa and Qiangtang terranes. The structural deformation and cooling of the west and east segments at 55–38 Ma was associated with northward intracontinental subduction beneath the Qiangtang terrane induced by the Indo–Asian collision. [ABSTRACT FROM AUTHOR]