Evolution Of The Mesozoic Granites In The Xiong'Ershan-Waifangshan Region, Western Henan Province, China, And Its Tectonic Implications

Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-Sr I-type granite emplaced in the early stage (similar to 160 Ma), I-type granite in the middle stage (similar to 130 Ma) and anorogenic A-type granite in the late stage (415 Ma). Geochemical characteristics of the high-Ba-Sr I-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New Ar-40/Ar-39 plateau ages of the early-stage Wuzhangshan granite (156.0 +/- 1.1 Ma, amphibole) and middle-stage Heyu granite (131.8 +/- 0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at similar to 115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between similar to 160 Ma and similar to 115 Ma. The genesis of the early- and middle-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qinling -Dabic-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial Sr-87/Sr-86 ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.