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Granitic rocks forming in the syn- to post-orogenic stages can trace the compositional and structural complexity of the crust beneath an orogenic belt. The Qinling orogenic belt undertook multiple stages of tectonics and magmatism, resulting in the multifaceted evolution and compositional diversity of the crust. In the present study, the Guangtoushan and Miba plutons in South Qinling were chosen to reveal the crustal heterogeneity in study area via isotopic geochemistry and zircon geochronology. The Guangtoushan pluton was emplaced between ~215 Ma and ~202 Ma and the Miba pluton formed at ~213 Ma, as constrained by zircon U-Pb isotopic dating. Granitic rocks of the Miba pluton are characterized by amphibole bearing and homogeneous composition, with relatively depleted Sr-Nd isotopic compositions (initial 87Sr/86Sr values of 0.7060 to 0.7084 and initial εNd values of −5.4 to −9.5) and high Pb isotopic values. The Guangtoushan pluton contains muscovite and complex inherited zircon grains and has variable Sr-Nd isotopic composition (initial 87Sr/86Sr values of 0.7050 to 0.7091 and initial εNd values of −4.5 to −12.9) and low Pb isotopic values. Felsic magmas of the Guangtoushan pluton should be derived mainly from meta-sedimentary rocks beneath South Qinling, while the Miba pluton originated primarily from partial melting of meta-igneous rocks. The compositional diversity recorded in the Early Mesozoic plutons was caused by the heterogeneous crust, and partial melting was induced by heating of the up-welling asthenosphere in a post-collision setting. [ABSTRACT FROM AUTHOR]

The Qinling Orogen resulted from the collision between the North and South China blocks in the Triassic. Mesozoic granitoids, ranging from the Triassic to the Cretaceous, are widely distributed in this orogen, and they provide excellent clues for understanding the crustal evolution and geodynamic evolution of the orogenic belt. The Triassic belt is mostly located in the South Qinling, whereas the Cretaceous belt is located mostly in the North Qinling. The Taibai complex pluton is located at the conjunction of the two belts. Here we present a data set comprising zircon U-Pb dating and elemental and Sr-Nd isotopic geochemistry for Late Mesozoic granite and microgranular enclaves (MME) exposed in the Taibai complex pluton. The granite and MME yield concordant U-Pb zircon ages of 124 to 118 Ma, indicating that they were products of roughly simultaneous magmatism in the Late Mesozoic. The granite rocks are high-K, calc-alkaline, and weakly peraluminous in compositions, and they are characterized by enrichment in large ion lithophile elements (e. g., Rb, Ba), depletion in high field strength elements (e.g., Nb, Ta, Zr, Ti), and variable Sr/Y ratios of 7.64 to 63.6. Low MgO, Cr, and Ni contents imply that the magma(s) were essentially crust-derived. Both the granite and the MME show relative depletion in Sr-Nd isotopic composition (initial 87Sr/86Sr of 0.704 4 to 0.706 7, initial εNd values of −3.4 to −2.6), suggesting that the magma(s) originated from juvenile crustal rocks. These Sr-Nd isotopic characteristics are significantly different from those of other Late Mesozoic granitoids exposed elsewhere in the Qinling orogenic belt, which formed from much older and enriched sources and with negligible contributions from mantle or juvenile crust. We propose a reworking event of the juvenile crust during the Late Mesozoic that was triggered by the tectonic extension and subsequent asthenospheric upwelling that occurred in eastern China. [ABSTRACT FROM AUTHOR]

The eastern Qinling belt is characterized by widespread Mesozoic post-orogenic magmatism and abundant Mo–(Au–Ag) polymetallic mineralization. Most Mo deposits in this belt are genetically related to Mesozoic granitoids. The tectonic context of this close spatial and temporal relationship is still debated. This study reports U–Pb ages and Hf isotopic composition of zircons, major and trace element and Sr–Nd–Pb isotopic composition of the Donggou granite porphyry, host rock to one of the important Mesozoic Mo deposits in this orogen. Based on geochemical results, the Donggou granite porphyry is a silica-supersaturated, high-K metaluminous A-type granite showing enrichment in light REEs, depletion in middle REEs and significant negative Eu, Ba, Nb, Sr, P, and Ti anomalies. Negative initial ϵNdvalues of −17.0 to −13.2 for whole-rock and negative initial ϵHfvalues of −19.9 to −7.8 for zircon suggest that the magma was derived from a mixture of Archaean/Proterozoic crustal rocks and mantle-derived or newly added crust. Its Pb isotopic composition is similar to the lower crust of the North China block, but different from superjacent country rocks (Xiong'er and Taihua Groups). Zircon U–Pb dating yields a late Mesozoic emplacement age of 118–117 Ma, identical with the third episode of Mo mineralization in the eastern Qinling–Dabie belt. We postulate that the Donggou Mo-related porphyry granite formed by reworking of North China lower crust with significant input of juvenile material. The magmas formed in an extensional tectonic setting, induced by lithospheric thinning and asthenospheric upwelling beneath eastern China during Cretaceous time. [ABSTRACT FROM AUTHOR]

Abstract: The North Qinling terrain reveals a different geological history from the North China block to the north and the South Qinling micro-continental block to the south. The timing of events and geochemical features of the North Qinling terrain are essential for understanding the evolution of the Qinling orogenic belt that joins the North and South China blocks. This study presents detrital zircon ages and Hf isotopic compositions from the Guandaokou Group, a cover sequence of the North China block, and from the Kuanping Group, an upper basement sequence of the North Qinling terrain. The youngest detrital zircon U–Pb ages constrain the initiation of sedimentation in the Guandaokou Group to 1.85Ga and the maximum depositional age of the Kuanping Group to ~640Ma. Zircon U–Pb ages and Hf data testify to a major phase of magmatism in the North Qinling terrain at ~1000–900Ma. The magmatic rocks were largely produced from reworking of early Paleoproterozoic (~2.5–2.0Ga) crust with minor contribution of late Paleoproterozoic (~1.7Ga) juvenile material. This age record differs in time from the two important thermal events of ~1.85Ga and ~2.5Ga, widely manifested in the North China block. The North Qinling terrain can thus be regarded as a separate micro-continent with a pre-Neoproterozoic evolution different from that of the North China block. The final assembly of the North Qinling terrain to the North China block took place after about 640Ma. [Copyright &y& Elsevier]

The lithospheric root underneath the Dabie orogen, which is the key part of the Central Orogen of China, experienced a cycle of thickening during Triassic continent-continent collision with subsequent post-collisional collapse during the Early Cretaceous. However, the process and mechanism of how thickened lithospheric roots are removed generally remain controversial. U–Pb ages and oxygen isotopes of zircons along with whole-rock geochemistry of post-collisional mafic–intermediate dykes in the region were used to track magmatic contributions from the lower crust, and constrain magma provenance from compositionally variable reservoirs in the upper mantle. Relict zircons show evidence of recycling of subducted continental crust of South China Block that not only has the Neoproterozoic ages and experienced the Triassic metamorphism, but also contains both 18O-depleted and enriched components. A first generation of hypersthene-normative tholeiitic dykes and nepheline-normative alkaline dykes were emplaced at ca. 130–120 Ma. They are overall characterized by arc-like geochemical patterns with εNd values from −21.6 to −4.6 and initial 87Sr/86Sr from 0.7056 to 0.7094. Coeval alkaline dykes are shifted towards more depleted-mantle like compositions, indicating simultaneous melt extraction from different mantle domains and depths. In contrast, second-generation hypersthene-normative mafic dykes (ca. 115–110 Ma) show OIB-like characteristics with εNd values from −1.5 to +4.8 and initial 87Sr/86Sr ratios from 0.7039 to 0.7049, indicating an increasing contribution from upwelling asthenospheric mantle during lithospheric thinning. The temporal evolution of the geochemical characteristics of mafic melts derived from the upper mantle in the Dabie orogen is consistent with foundering of thickened lithosphere and subsequent influx of asthenospheric mantle. The removal of thickened lithosphere root is suggested to be triggered by subduction of the Paleo-Pacific plate and lasted from ca. 130–115 Ma as constrained by the intrusive ages of two distinct types of tholeiitic dykes. • The Dabie orogen underwent post-collisional collapse during the Early Cretaceous. • First-generation of Hy- and Ne- normative dykes originated from hybrid mantle domains. • Second-generation tholeiitic dykes indicate removal of thickened lithospheric root. • Xenocrystic zircons show close affinities to crustal rocks of the South China Block. • The post-collisional collapse was triggered by subduction of Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]