Geochemical Characteristics And Tectonic Setting Of Early Cretaceous Granites In Central Xingmeng Orogen,Inner Mongolia

The Xingmeng Orogen is part of the Central Asian Orogen and located in the eastern segment of the Central Asian Orogen.In addition,its evolutionary history is more complicated.The study area is located in the middle of the Xingmeng Orogen and has a large number of granites.At present,the studies of the study area's granites focuse on the Hercynian granites formed in the Late Paleozoiic.However,the studies of granites formed in the Mesozoic Indosinian-Yanshan is relatively insufficient,especially for the Early Cretaceous.Therefore,the studies of granites formed in the Early Cretaceous is particularly important.The samples collected from Xiwuqi and Suniteyou.The studies of the granites is based on the petrological,geochemical and geochronological characteristics.Analysis result: The obtained ages with the LA-ICP-MS zircon U-Pb isotope dating are138.5±1.4Ma and 132.19±0.77 Ma,respectly for the Xiwuqi and the Suniteyou granites,of which the intrusion developed in the Early Cretaceous.The average saturation temperatures of zircons from the two granites are 848.79? and 865.52?,separately,showing high temperature petrogenic enviroment.The granites of Xiwuqi and Suniteyou are characterized by higi silica,enrichment of alkaline,TFe O/Mg O,low alumina,calcium oxide and magnesium oxide.The granitic rocks of Xiwuqi and Suniteyou,have obvious Eu negative anoma.REE distribution patterns show the type of "gull".They also show LILE enrichment(Rb,Th,U,K),HFSE depletion(Ba,Sr,P,Ti)and enrichment of(Nb,Ta,Zr,Hf).LREE is more enrichment than HREE.The rock samples show an affinity to A-type granite.The geochemical features of the Xiwuqi and Suniteyou show that they belong to high-K calc-alkaline rock series.Through the above results and the tectonic evolution characteristics of Xingmeng Orogin formed in the Mesozoic,I think the formation mechanism of the granites of Xiwuqi and Suniteyou is that while the post-orogenic extension caused by the subduction of the Paleo-Pacific Ocean.The temperature for granites formation is provided by the mantle material moving upwards.In addition,the Crustal material is mixed with the mantle material.So the study of granites formed in Early Cretaceous.