内蒙古北山地区阿民乌素公婆泉组变质火山岩年代学、地球化学特征及地质意义

内蒙古北山地区阿民乌素一带公婆泉组变质火山岩主要由钠长阳起岩、斜长阳起岩和斜长阳起片岩组成.三者主量元素显示相对高钠w(Na2O)=0.32％～2.46％,低钾w(K2O)=0.08％～0.38％、钛w(TiO2)=0.93％～1.03％,略富镁 w(MgO)=9.61％～12.04％、钙 w(CaO)=9.96％～1...

THE GEOCHEMICAL,CHRONOLOGICAL CHARACTERISTICS AND GEO-LOGICAL SIGNIFICANCE OF THE ARMINWUSU GONGPOQUAN FORMA-TION META VOLCANIC ROCKS IN BEISHAN AREA,INNER MONGOLIA

The Gongpoquan Formation metavolcanic rocks at Aminwusu,Beishan area,Inner Mongolia are mainly composed of sodium actinolite,anorthosity and plagioclase actinolite schist.The main elements of the three types of rock are relatively high in sodium w(Na2O)=0.32%-2.46%,low in potassium w(K2O)=0.08%-0.38%,titanium w(TiO2)=0.93%-1.03%,and slightly rich in magnesium w(MgO)=9.61%-12.04%and calcium w(CaO)=9.96%-12.53%.SiO2 is in the range of 45.48%-48.76%.The discrimination diagram of A-C-Fm and(Al+Fm)-(C+Alk)-Si shows that the protolith of the Gongpoquan Formation metavolcanic rocks are basic volcanic rocks,and the Zr/Ti-Nb/Y and FeOt/MgO-w(SiO2)diagrams show the characteristics of subalkaline basalts and tholeiite series.ΣREE(31.83-40.13×10-6)is significantly higher than chondrite values without Eu anomalies,and displays flat type rare earth distribution patterns.The chondrite standardized cobweb map shows that large ion lithophile elements(Rb,Ba,K)are relatively enriched,while high field strength elements(Nb,Ta,P,Zr,Ti)are significantly depleted,and the characteristic of volcanics is related to subduction zones.LA-ICP-MS zircon U-Pb dating for sodium actinolite yields an age of 475±2 Ma(early Ordovician).Research data show that the Paleo-Asian Ocean has been subducting northward since the Early Ordovician,forming a magmatic arc(O-S)with a long time span along the line of Gongpoquan and Dongqiyi Mountain.The Aminwusu metavolcanic rock is an important part of the magmatic arc,which is the geological record of the ocean-continent transition of the Beishan orogenic belt in the Early Paleozoic,and is of great significance to the study of tectonic evolution in the Beishan area.