Magma mixing in the Karamay rock body of west Junggar,Xinjiang: evidence from geochemistry

Abstract：The Karamay intrusive body in west Junggar of Xingjiang is associated with abundant dioritic microgranular enclaves and magma mixed rock of quartz diorite. Under microscope, the enclaves consist mainly of diorite and are of magmatic texture. The enclaves exhibit excellent evidence for magma mixing and mingling, such as long prisms of apatite, malcrystalline augite wrapped in hornblende, and etched girdle of feldspar. Host rocks, magma mixed rocks, dioritic microgranular enclaves and diorite porphyrite dykes of the Karamay rock body are products of different proportions of magma mixing. Geochemically, the major oxide content of the dioritic enclaves, magma mixed rocks and their host rocks all have the same linear trends in the plot. The patterns of REE and trace elements and isotopic signatures of the dioritic enclaves and magma mixed rocks are similar to those of the host granites. Exchanges of elements occurred between the enclaves and the host rocks and almost reached equilibrium. The ratios of characteristic elements and isotopic signatures show that the source rock of the dioritic enclaves is the mantle-derived basic magma, and that the host rock is the crust-derived acidic rock. The geochemical characteristics of the rock further prove the existence of magma mixing in the Karamay rock body, suggesting that the magma mixing was an important style of post-collisional magmatism in northern Xinjiang.