Geochemical Characteristics, Ghronology Research And Its Tectonic Signigicance Of The Intrusive Rocks In Xi Wuqi Area,Inner Mongolia

Late Paleozoic intrusive rocks widely developed near the DaQing pasture and QianJinChang, south of Xi wuqi. The area is tectonically situated at the suture zone between the Erlian-Hegenshan ophiolite and Solon-Xar Moron deep fault. Geochronology and geochemistry studies on these rocks are helpful to understand the evolution of Paleo-Asian Ocean in late Paleozoic.The quartzdiorite exposed in DaQing pasture area and granodiorite, biotite-granite exposed in QianJinChang area were selected for testing of Rock Geochemistry and LA-ICP-MS zircon U-Pb Ghronology, in addition, quartzdiorite was used to do Lu-Hf isotope test in zircon situ. Geochemical characteristics showed that quartzdiorite belongs to metaluminous-low potassium-calc-alkaline series, With low REE, weakly negative Eu anomaly; granodiorite, biotite-granite belong to peraluminous-high potassium-calc-alkaline series, their negative Eu anomalys are clear, the depletion of element Sr、Ba reflects the magma has occurred Crystallization-Separation Effect. Rocks relatively enrich elements of LILE such as Rb、U、K、Pb et,al. depletion of HFSE such as Mb、Ta、P、Ti et,al. this characteristic reflected the rock formed in island arc or continental margin arc environment, presence of which may be related to subduction event. Zircon U-Pb dating results:quartzdiorite (P01) was330.1+1.9/-1.3Ma; Granodiorite (XW01) was273.8±1.1Ma; Biotite granite (XW03, XW09) were281.8±1.2Ma and271.3±1.3Ma, All zircons have shown the magmatic origion, measuring age on behalf of the rock formation age. The Hf isotopic study showed that the value of εHf(t) was7.5～11.5, positive and large, reflected depleted mantle participation, TDMC is between603Ma to862Ma, Similar to the formation age of Xilingele complex plot, there may be a mixture of material of lower crust.In combination with the research achievements of predecessors in this area, the arc magmatite belt of Late Early-Carboniferous—Early-Permian developed in the Suzuoqi-Xilinhot-Xiwuqi areas was result of the subduction of Hegenshan ocean-basin underneath the Xilingele complex plot, the subduction environment turned into post-orogeny environment until middle Permian, and a large amount of alkaline granite output on both sides of the ocean basin.