Petrogeochemistry,Geochronology and Hf Isotopes of the Monzogranite from Xinxian,Southern Region in Henan Province

Liu Qingquan; Shao Yongjun; Chen Xinmeng; Liu Zhongfa; Zhang Zhe

doi:10.3799/dqkx.2016.507

Abstract：Xinxian monzogranites are located at the Qinling-Dabie orogenic belt,and a systematic geochemical study can facili-tate further studies on the Mesozoic tectono-magmatic evolution and the geodynamics background of Qinling-Dabie orogenic belt.This paper presents geochemistry,zircon U-Pb geochronology,and Hf-isotopic data of the rocks,with the aim of con-straining their petrogenesis,sources and tectonic implications.The geochemical analysis shows that Xinxian monzogranites are characterized by SiO2 =74.94%-78.16%,K2 O=3.87%-5.86%,Na2 O=3.82%-4.24%,Al2 O3 =12.38%-13.57%, A/CNK=1.05-1.11;the rocks are enriched in LREE,depleted HREE and negative Eu anomalies,enriched in Rb,U,Hf, Y and depleted Ba,Nb,Ta,Ti,which indicates that Xinxian monzogranites are peraluminous,high-K calc-alkaline Ⅰ-type granite.The three stages yield LA-ICP-MS zircon U-Pb ages 153.4±1.1 Ma,146.4±1.6 Ma and 131.6±1.8 Ma respective-ly.According to zircon Hf isotope analysis,theεHf (t)values of the granite range from -24.5 to -20.3,which locates below the depleted mantle line.The tDM2 values range from 2.68 to 2.93 Ga,which indicates the monzogranites resulted from the low-er crust of Yangtze Block.The component of the monzogranite is similar to that of Neoproterozoic TTG magmatic rocks.Xinx-ian monzogranites were emplaced after the major collisional period of the North China block and Yangtze block,in the post-collisional tectonic setting under the regional extension mechanism.The geodynamics setting is the transformation of tectonic regime of the Late Jurassic-Early Cretaceous and large-scale lithosphere delaminating thinning under post stretching mechanism.