Petrogenesis, Magma Source and Tectonic Setting of the Yaozhuang Granitoids in Northern Qinling Belt, Central China: Constraints From Zircon U–Pb Geochronology, Whole‐Rock Geochemistry and Sr–Nd–Hf Isotopes

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ABSTRACT The Yaozhuang granitoids are located in the Northern Qinling Belt (NQB) and consist mainly of coarse‐grained monzogranite, medium‐grained biotite granite, granite porphyry, and diorite porphyry. Zircon U–Pb dating, geochemical, and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis, and magma source of the Yaozhuang granitoids. Zircon U–Pb dating yielded Late Jurassic to Early Cretaceous ages of 150.4 ± 1.7 Ma (monzogranite), 146.7 ± 1.3 Ma (biotite granite), 147.4 ± 1.6 Ma (granite porphyry), and 145.2 ± 1.6 Ma and 143.6 ± 1.2 Ma (diorite porphyry). The Yaozhuang granites are high‐K calc‐alkaline to shoshonitic and metaluminous I‐type. They are characterised by the enrichments in Rb, Th, and U, depletions in Nb, Ta, P, and Ti, and weakly negative Eu anomalies. They have variable initial 87 Sr/ 86 Sr (0.7016–0.7094), low ε Nd ( t ) (−15.8 to −9.8), and negative zircon ε Hf ( t ) (−25.8 to −4.2). Comparatively, the Yaozhuang diorite porphyry has lower SiO 2 (51.18–58.20 wt%) but higher MgO (1.95–5.33 wt%), Ni and Cr contents, and Mg # value (44–59). It is also characterised by Rb‐Ba‐Th‐U enrichments and Nb‐Ta‐Ti depletions, with positive Eu anomalies. They exhibit relatively uniform Sr‐Nd (initial 87 Sr/ 86 Sr = 0.7066–0.7099), ε Nd ( t ) = −11.0 to −9.5) but variable Hf (zircon ε Hf ( t ) = −16.6 to −4.0) isotopic compositions. Many inherited zircons have been identified in the Yaozhuang granitoids, with their ages clustering around 1883–1492 and 1043–801 Ma. These U–Pb ages resemble those of the Xiong'er Group in the southern margin of the North China Craton and the Kuanping Group in the NQB, and the Paleo‐Mesoproterozoic (1673–1543 Ma) inherited zircons share similar ε Hf ( t ) value (−8.8 to −2.3) to that of the Xiong'er Group. Compared with the Nantai and Taoguanping mineralised plutons in the NQB, the magma of the granite porphyry has high oxygen fugacity (ΔFMQ [relative fayalite‐magnetite‐quartz buffer]) value of +1.4 to +5.6) and has the potential to form porphyry Mo mineralisation. Combined with our datasets and previous studies, we suggest that the Late Jurassic–Early Cretaceous granitoids in the NQB were generated in an extensional setting associated with mantle upwelling, which was caused by the far‐field effect of the flat west‐dipping Paleo‐Pacific subduction. The magmas were likely derived from the underthrust of the Xiong'er Group and the Kuanping Group mafic rocks with minor mantle input.

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