Chronology,geochemistry and petrogenesis of Deqin granodiorite body in the middle section of Jiangda-Weixi arc

This paper studied in detail the host rock of granodiorite body(granodiorite) and its mafic microgranular enclave(diorite).The dating results of granodiorite and diorite were separately 254.6±1.8Ma and 253.5±1.6Ma.The geochemical research of granodiorite and diorite indicated the granodiorite was enriched in K2O,Na2O,Al2O3 and K2ONa2O,and its A/CNK average was 0.96.The diorite was enriched in K2O,Na2O,Al2O3,MgO,but K2ONa2O,and its A/CNK average was 0.72.The REE gross of granodiorite was lower than diorite,and the LREE and HREE fractionationg of granodiorite and diorite was distinct.The partition curve was right-deviation and LREE-enriched,and they were enriched in LILEs and depleted in HFS elements such as Nb,Ta etc.Their Mg#(58.8~65.8) values were comparatively high.Zircon laser ablation LA-ICP-MS U-Pb analyses indicated the granodiorite was emplaced at 254.6±1.8Ma with average 176Hf/177Hf values of 0.282383 and negative eHf(t) values of-8.28,and the diorite was emplaced at 253.5±1.6Ma with average 176Hf/177Hf values of 0.282287 and negative eHf(t) values of-11.79.The granodiorite(host rock) and diorite(MME) were I-type granites and originate from the crust magama,and formed in the geological background of spread after the arc-continent collision.According to the evolvement history of regional tectonic and the forming age of magmatic rocks,we considered that Jinshajiang junction zone had been jointing after arc-continent collision about 255Ma.