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The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative εHf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites. [ABSTRACT FROM AUTHOR]

The western Gonghe basin in the NE Tibetan Plateau, witnessed extensive magmatism during the Triassic, whereas only few magmatic flare-up events occurred during the Permian. Understanding the geodynamic setting of these magmatic pulses is important in the reconstruction of the Paleo-Tethys tectonic history. In this contribution, we present in-situ zircon U Pb geochronological and Lu Hf isotopic data, as well as whole-rock major and trace elements data from monzogranite and syenogranite dyke in the western Gonghe region to constrain their petrogenesis and tectonic implications. Zircon U Pb data show that the monzogranite (253–260 Ma) and syenogranite dyke (247-261 Ma) were formed during the Late Permian, rather than the Jurassic as presumed in previous studies. Mineralogical characteristics and geochemical affinities reveal that these rocks are high-K calc-alkaline, metaluminous to weakly peraluminous (ASI = 0.95–1.02), moderately-highly fractionated (DI = 81–95) I-type granites. The major and trace element characteristics (including Mg#, Ni, Cr, Zr/Hf, Nb/Ta, and Th/U contents), together with the zircon ε Hf (t) values (−5.90 to 1.22, T DMC = 845–1250 Ma) and 176Hf /177Hf ratios (0.282481 to 0.282674) suggest that the magmas were derived through partial melting of the Early Mesoproterozoic metagreywacke in the lower crust with minor juvenile crust addition. Extensive fractional crystallization of plagioclase and subordinate K-feldspar as well as apatite is inferred. Our findings in this study, in conjunction with those from previous studies, suggest that the magmatic flare-up event during the Late Permian in the western Gonghe area is related to local extension concomitant with the break-off of the subducting slab associated with the northward subduction of the Paleo-Tethys oceanic lithosphere. • Monzogranite and syenogranite dyke were emplaced at 253–260 Ma and 247–261 Ma. • Highly to moderately fractionated, arc-related I-type granites. • Magma derived from partial melting of Mesoproterozoic metagreywacke. • Magmatism correlated to slab break off of the Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]