The Composition And Evolution Of The Late Paleozoic Inner-Oceanic Arc In Xiwuqi,Inner Mongolia

Through detailed field geological survey of the Carboniferous magmatic arc in Xiwuqi,and large-scale geological mapping in the Diyanmiao ophiolitic melange area,select representative rock masses and volcanic rocks,and carry out detailed petrology and rock geochemistry,Sr-Nd isotope geochemistry of the whole rock,zircon U-Pb chronology and Lu-Hf isotope analysis,the following points are recognized:(1)The rock types of ophiolite in Diyanmiao area are relatively complete.Through detailed rock geochemical analysis,a set of forearc basalt series representing the geochemical properties of the intra-oceanic arc is identified,wich is the forearc basalt-HMA-Boninite-calcium-alkaline basalt-andesite-rhyolite can be compared with the IBM intra-oceanic arc,representing the intra-oceanic arc of the Paleo-Asian Ocean.The zircon U-Pb age of the plagiogranite is 359.7±3.3Ma,which is consistent with the gabbro age in the ophiolite.The zircon U-Pb age of the forearc basalt is 324.9±4.7Ma,and the intra-oceanic arc of the Diyanmiao is formed in the Early Carboniferous.(2)Through the detailed large-scale geological mapping,the ophiolitic melange in the Diyanmiao area is produced in the form of tectonic blocks in the Permian Shoushangou sandstones.The ophiolite is a tectonic block,the sandstones is the matrix,and the ophiolite is not a band extending.Instead,the rock blocks appearing in the subduction hyperplastic belt..(3)For the first time,we the divided Carboniferous magmatic arc of Xiwuqi into magma front and back arc,was structurally,and the Carboniferous magma front is made up of TTG,and a rear-arc comprise syenogranite.Among them,the formation of the TTG was in the early Carboniferous,and the formation of the rear arc are Late Carboniferous to the Early Permian.(4)According to the tectonic markers such as the identified subduction and accretionary complex-magma front-rear arc,it is considered that the subduction polarity of the inner arc of the Paleo-Asian Ocean is from southeast to northwest.(5)The tectonic evolution mode of intra-ocean arc and magma arc is proposed.