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Jurassic continental arc magmatism occurred widely across the southern Qiangtang Terrane, and provides an opportunity to study how continental arc magmas evolve towards intermediate–felsic compositions. We present new LA–ICP–MS zircon U–Pb ages, whole-rock major and trace element compositions, and Sr–Nd and in-situ zircon Hf isotope data for late Jurassic intermediate–felsic intrusive rocks from the Rena Co area of southern Qiangtang, central Tibet. Jurassic intrusive rocks in this area consist mainly of granodiorite, diorite, and related gabbro–diorite mafic enclaves, which have been dated at 153.1–147.6 Ma. Combining our data with previous results shows that continental arc magmatism in the southern Qiangtang Terrane has relatively homogeneous Sr–Nd isotopic compositions, with (87Sr/86Sr) i ratios of 0.7069–0.7092 and ε Nd (t) values of −6.3 to −2.2. Assuming that the hot, hydrous, basaltic melt generated by the subduction of the oceanic slab has a composition similar to island arc basalts, mixing ~50% basaltic magma with ~50% lower crustal material can produce the Sr–Nd isotopic compositions of the Rena Co intrusive rocks. The southern Qiangtang arc magmatism also has similar Hf isotopic compositions, albeit with a large range of ε Hf (t) values (−10 to +3). The different Rena Co intrusive rocks have different geochemical characteristics, including major element and rare earth element (REE) contents, Mg#, and evolutionary trends on Harker diagrams. This suggests that these arc rocks were derived from a common parent magma, but experienced different magmatic processes. The diorites were derived from primitive arc magma through amphibole-dominated low-pressure fractional crystallization, whereas the granodiorites underwent garnet-dominated, high-pressure fractional crystallization in secondary magma chambers. Fractionation of igneous garnet and amphibole played a significant role in the evolution of the continental arc, and was likely an important mechanism in driving the continental arc towards silica-rich compositions. The fractionation of igneous garnet and amphibole possibly changes the Mg# and Nb/Ta ratios of the derivative magmas. • Amphibole-bearing schlieren (MEs) are the direct evidence of the fractional crystallization. • The diorites were derived from initial arc magma through an amphibole dominated LPFC. • The granodiorites were derived from initial magma through an a garnet dominated HPFC. • Igneous garnet and amphibole fractionation play a significant role in continental arc. [ABSTRACT FROM AUTHOR]

The processes and related rock types in post-collision setting are important to fully understand the geodynamic evolution of a collision zone. Bangong-Nujiang collision zone is the oldest collision zone in the Tibet Plateau. Slab break-off is one of the primary processes during post-collision, and is considered to have occured in the Bangong-Nujiang collision zone. Here, we report a newly identified rhyolite-biotite monzogranite (A2-type granite)-norite belt from this collision zone, which trend E-W for nearly 1000 km, and formed 115–104 Ma. The felsic rocks include rhyolite and biotite monzogranite, who share whole-rock geochemical similarities with A2-type granites. These felsic rocks were likely generated from a juvenile mafic crust melting at low pressure and high-temperature. The juvenile crust was derived from melting of metasomatized mantle wedge. The norites were generated from low degree (1–5%) melting of remnant enriched lithospheric mantle mixed with upwelling asthenospheric mantle at low pressure (~1.0 GPa) and high melting temperature (up to 1244 °C). A slab break-off beneath the Lhasa Terrane accounts for this post-collisional high-temperature extensional environment. The results provide important implications for the evolution of the Bangong-Nujiang collisional zone, including the subducting polarity, and timing of the Bangong-Nujiang ocean closure. • ~1000 km long rhyolite-A2-granite-norite belt in Bangong-Nujiang collision zone, Tibet • Felsic rocks formed from melting of a juvenile mafic crust. • Norites formed by asthenospheric and metasomatized lithospheric mantle interaction • The belt formed in a low-P/high-T post-collisional setting associated with slab break-off. [ABSTRACT FROM AUTHOR]