内蒙古多伦中酸性侵入岩岩石地球化学特征及构造环境分析

内蒙古多伦县北部分布四个中酸性岩体,其岩石类型为:二长花岗岩、石英正长岩、石英正长斑岩和石英二长斑岩,出露面积0.5~12.4km~2不等,产状为岩株。同位素测龄成果显示二长花岗岩形成年龄为143.8±1.2 Ma,属晚侏罗世晚期(J_3);石英二长斑岩形成年龄为138.4±0.6Ma,属早白垩世早期(K_1)。岩石系列为高钾、钙碱性系列。据岩石地球化学特征推断:研究区内的四个岩体具同源特征,是岩浆同源演变的产物,岩浆来源为中下地壳。结合岩石Q-Ab-Or-H_2O相图,岩浆结晶温度接近750~800℃。二长花岗岩形成于大陆碰撞地球动力学环境即陆内造山构造环境;石英正长岩、石英正长斑岩、石英二长斑岩形成于造山后期构造环境。研究区在晚侏罗世晚期陆内碰撞造山运动已经结束而转入造山后期构造环境,至早白垩世早期大规模双峰式火山岩的喷发标志着研究区全面进入陆内造山后的裂谷阶段或者陆内伸展运动阶段。

Geochemical characteristics of intermediate-acid intrusive rocks and tectonic environment in Duolun, Inner Mongolia

Four intermediate-acid rock masses are distributed in the north of Duolun county in Inner Mongolia,in type which are monzonitic granite,quartz-syenite,quartz-orthophyre and quartz monzonite porphyry,with exposed area about 0.5 km2-12.4km2 and stock occurrence.The results of isotope dating suggest that the rough formation time of these four rock masses are about 138.38 ～ 144.25Ma,attributed to late Jurassic epoch(J3).These rocks are part of high-potassium and calcium alkaline rock series.On the basis of geochemical characteristics of rocks we can deduce that they have the same source features,and are the results of magmatic homologous evolution.Their magma source is from the middle and lower crust.The Q-Ab-Or-H2O phase diagram indicates the magmatic crystallization temperature was between 700℃ and 800℃.Monzonitic granite formed in a continental collision dynamic environment,i.e.,a continental orogenic environment.The quartz-syenite,quartz-orthophyre and quartz monzonite formed in a post-orogenic tectonic environment.So we can deduce that the tectonic environment of the study area might have probably experienced continental collision orogenic movement-post orogenic extensional movement during late Jurassic epoch(J3) to early Cretaceous epoch(K1).