Geochemical Characteristics And Tectonic Significance Of The Granites In Zongnaishan Area In Alashan Block

Central Asian orogenic belt?CAOB?is one of the largest hyperplastic orogenic belts in the Phanerozoic.It is located between the North China-tarim plate and the Siberian plate,with different types of granites.Zongnaishan is located in the southeast part of the Alashan block,it is of great geological significance to study the tectonic evolution history of the area.The moyite which was collected in the Zongnaishan is research object in the article.Through the comprehensive research of field geological survey,petrology,zircon U-Pb chronology,and trace elements and Sr-Nd isotopes,combining previous research achievements in the area,analyzing the late Permian moyite petrogenesis and the tectonic evolution process of Zongnaishan-shalazhashan tectonic belt,we obtained the following understanding:1.In Zongnaishan the late Permian moyite LA-ICP-MS zircon U-Pb ages is 266.9±2.2Ma.Rock was formed in the late Permian.2.Late Permian moyite has high content of SiO₂?SiO₂ content of 67.32⁶9.87wt%,with a mean of 68.22 wt%?,Al₂O₃=15.72¹6.18 wt%,rich in alkali?Na₂O+K₂O content 8.29⁸.69wt%,K₂O/Na₂O=1.12¹.20?,CaO content is 1.52².07wt%,Low magnesium?MgO content0.54⁰.61wt%,Mg^#=27.20³2.11?.TFe₂O₃ is 2.56³.15wt%;P₂O₅ content was 0.09⁰.17wt%,10000Ga/Al=2.58².86,Y-Nb=1.02¹.26,which is A₂-type granites with weak aluminum,high potassium,calcium and alkali?A/CNK=1.05¹.14,mean 1.10,the average of the Rittmann index was 2.81?.Primitive mantle standardization of trace element spider diagram shows rock loss in Nb,Ta,Ti elements,enrichment of Rb,Th,U,K elements,REE chondrite standardized distribution diagram to present rich in LREE,the ratio of light and heavy rare earth elements?_LREE/?_HREE is 4.75⁸.66.?La/Yb?_N=15.99⁴5.32,indicating that heavy and light rare earth elements fractionation is relatively obvious.The average?Eu=0.30⁰.49,indicating strong negative Eu anomaly,(⁸⁷Sr/⁸⁶Sr)_i=0.7075⁰.7084,?_Nd?t?=-0.60^-0.53,T_DM=1.43¹.55Ga,Combined with the above geochemical characteristics,it is shown that the granite rock mass of Zongnaishan granite is product of partial melting from the material from proterozoic,mixed with a small amount of mantle source material,shows the characteristics of mixing with mantle and crust.3.Through the Zongnaishan granite field geological investigation and the study of petrological and geochemical characteristics,combining previous research results,holding that potassium granite formed in the stretch tension tectonic environment after the collision,reveals the region in the late hercynian granites had entered the stage of the evolution of post-collision.