Petrogenesis And Tectonic Setting Of Granitic Porphyry In The Taerqi Region,Inner Mongolia

This paper summarizes the characteristics of zircon U-Pb ages, the Hf isotope,geochemistry of the granitic porphyry in Taerqi, Inner Mongolia and determine the formation age of the granitic porphyry,discuss its petrogenesis and tectonic setting.The LA-ICP-MS zircon U-Pb dating results of the three samples indicate that granitic porphyry formed in early cretaceous,respectively early Early Cretaceous(136.5±1.3Ma) and late Early Cretaceous(127.2±1.5Ma,126.4±1.3Ma).The analysis of geo-chemical data show that granitic porphyry is characterized by high silicon, alkali-rich, show metaluminous to weakly peraluminous attribute(A/CNK=1.0~1.29) and high differential degree, Which belongs to high-k calc-alkaline series. Granitic porphyry has rich LREE with steep right_dipping REE distribution curves, LREE and HREE fractionation is obvious, HREE fractionation is not that obvious which is mild concave. The samples show strong depletion of Eu which indicate that Magma source area has residual plagioclase or experienced separation of plagioclase crystallization during magma evolution.In a Spider diagram of trace element can be seen in the study area with rich granitic porphyry magma K, Rb, Th, U, depleted of Ba, Si, Nb, Ta, Ti, similar to the low strontium I type granite in greate Xi`an Range.The samples fall into high differentiation I-type granite area in the granite genesis discriminant diagram,show that they are belong to low strontium I type granitic porphyry of high differentiation. We found that at least some of granitic porphyry have the same period and source with Baiyingaolao Formation in this area.Zircon characteristics of Hf isotopic compositions suggest that most of the granitic porphyry have high εHf(t) =(+7.2~+7.3) and TDM2= 851Ma~569Ma, Only two of the zircon εHf(t) < 0(-15.3 and-15.6) and older two-phase model age(2184 Ma,2162 Ma),which implies these granitic porphyry might be the partial meltdown of the crustal substance from depleted mantle during Neoproterozoic-Early Palaeozoic, at the same time may have old crustal materia’s participation.Combining with tectonic discrimination diagrams and regional tectonic settings, granitic porphyry in this area could be formed in the Extensional Setting of subduction of the Paleo-Pacific plate to the Eurasian plate, At the same time may affected by Mongolia-Okhotsk ocean tectonic system.