Petrogenesis and tectonic setting of the Wuzhuxinwusu granite, western Xing-Meng Orogenic Belt : Evidences from geochemistry, zircon U-Pb geochronology and Sr-Nd-Hf isotopes

The tectonic evolution of Xing-Meng Orogenic Belt and closure timing of Paleo-Asian Ocean is still in debate. The emplacement timing and geochemical signatures of granites exposed along the suture zone can provide constraints on evolution of Paleo-Asian Ocean. The Wuzhuxinwusu granite pluton is located along the Solonker suture zone in the western part of Xing-Meng Orogenic Belt. These granites have SiO2 contents of 73. 13% similar to 75.43% , Na2O + K2O contents of 7. 14% similar to 9. 36% , Al2O3 contents of 13. 18% similar to 13. 49% , and K2O/Na2O ratios of 1. 10 similar to 1. 52 , and are high-K calc-alkaline series in origin. They are characterized by enriched REE contents (174. 8 x 10(-6) similar to 213. 7 x 10(-6)) and medium REE fractionation [(La/Yb-N) = 3. 68 - 5. 41] with enrichments of LREEs and slightly negative Eu anomaly. These rocks are enriched in Rb, Th, Hf and depleted in Nb, Sr, P and Ti. Moreover, they yield depleted Sr but high Yb contents, and negative Eu negative anomalies, resembling typical characteristics of highly fractionated A-type granites. Tectonic discrimination diagrams show that the Wuzhuxinwusu granites have geochemical characteristics of A(2)-type, indicating that they were formed in a post-collision setting. Zircons separated from Wuzhuxinwusu granites yielded weighted mean Pb-206/U-238 ages of 279 +/- 2. 7Ma (MSWD = 1. 6) and 276 +/- 1. 9Ma (MSWD = 0. 69). These granites have positive whole-rock epsilon(Nd) (t) values (2. 1 similar to 2. 7) and zircon epsilon(Hf)( t) values (7. 7 similar to 10. 2) , as well as corresponding young Nd model ages of 826 to 874Ma and twostage Hf mantle model ages of 655 similar to 931Ma, consistent with that of the Early Permian A-type granitoids in the West Ujimqin, Xilinhot, Baiyinwula, indicating that the Wuzhuxinwusu granites were probably derived from the partial melting of Neoproterozoic lower crust. We therefore proposed that the Wuzhuxinwusu area in the western Xing-Meng Orogenic Belt was emplaced in a post-collision extensional regime.