Chronology And Geochemical Reserch Of Intrusive Rocks In Xishanwan Area Of Inner Mongolia

The first-order tectonic units of Xishanwan area is located in the north China margin,secondary tectonic units belong to the Lang mountain – Zhaertai mountain,in the east margin of Mesoproterozoic-neoproterozoic rift groove,and is located in the south of Suolun suture zone.In this region developed a large areas of granitic intrusive body,based on the research of the Xishanwan granitic rock mass can fill the blank of research on intrusion in the area of,and the tectonic evolution of North China Plate mechanism interpretation.This article selects the late Carboniferous intrusive rocks and early Permian intrusive rocks as the research objects,and around the petrology characteristics,geochemical characteristics and the characteristics of high accuracy of isotope chronology etc aspects comprehensive research work,the formation of granitic rock mass of The Times,rock properties,material source area,tectonic environment and evolution pattern were discussed,for the following:The late Carboniferous intrusive rocks usually output as the batholith,the main types can devided as quartz diorite and biotite quartz diorite;Their zircon U-Pb dating ages were 307.4±5.6 Ma and 308.7±5.1 Ma,both belongs to late Carboniferous.The early Permian intrusive rocks types can be divided into the fine and coarse grain adamellite biotite monzonitic granite;Their zircon U-Pb dating ages were 281.1±4.0 Ma and 282.6±3.7 Ma,belong to the early Permian.Late carboniferous intrusive rocks belong to the Adike rocks,geochemical studies of rock show that ??SiO₂?=59.48%⁵9.48%,average 60.33%,less than 56%;??Al₂O₃?=18.45% 19.54%,the average was 19.14%,more than 15.00%;??MgO?= 0.70% ¹.17%,and average is 0.91%,less than 3.00%,and have high Sr content and lower Y,Yb content,with postive Eu anomalies.But the average unmber of Na₂O/K₂O product is less than 2;?La/Yb?N > 12;Mg# averages of 31.33;zircon saturated temperature average is 833.1°C;MgO+ Fe₂O₃ + Ti O₂ + MnO > 0.5;those characteristics are different from the Ocean Adike rocks or TTG rock.They refluct the Crust Adike which comes from the melted lower crust.So we can draw concludtion that formed in the lower crust thickening environment.Use geochemical studies to the early Permian intrusive rocks we found that ??SiO₂?= 73.49%⁷9.12%;??Na₂O?=3.13%⁴.26%;??K₂O?= 3.98%⁵.34%;REE image just like "swan" partition,through the 10⁴× Ga/Al,FeOT-Zr+Nb+Ce+Y,SiO₂-Zr series diagrammatizes we can know that the early Permian instusive rocks belong to the the A-type granite.Its characteristics such as Rb/Sr > 0.34,Nb/U < 8,Mg^# < 40 can reflect the collision environment and the crustal material.Combining previous research results and two phase of the instusive rocks in the studied area we draw the conclusion that the intrusion of the rocks in the research area are caused by the collision resistance and the thickening of the crust.