内蒙古乌拉乌苏－德言其庙地区角闪岩相变质带Sm－Nd同位素等时线年龄及其意义

AGE OF Sm -Nd ISOTOPIC ISOCHRON OF AMPHIBOLITE FACIES METAMORPHIC ZONE AND ITS SIGNIFICANCE IN WULAWUSU-DEYANQIMIAO AREA OF INNER MONGOLIA

乌拉乌苏地区的斜长角闪岩和德言其庙地区的斜长角闪岩变质较深，已达角闪岩相，两者在变质程度、空间展布型式以及岩石学、岩石化学和稀土配分型式上都十分相似，二者形成时代相近，应为同一套变质岩系，具有相同的形成环境和构造成因。样品的εＮｄ（ｔ）值反映了它们来源于中等亏损的地幔，稀土元素配分曲线呈平坦型，与之有关的幔源花岗岩在ＡＣＦ图解中投影在拉张区，具有拉张过渡壳特征。乌拉乌苏斜长角闪岩和德言其庙斜长角闪岩Ｓｍ—Ｎｄ同位素全岩等时线年龄分别为（６０７±４６）Ｍａ和（６３８±１４）Ｍａ，这表明华北地台北缘中段晚元古代－早古生代经历了拉张解体的演化阶段，Ｓｍ—Ｎｄ同位素等时线年龄代表了这一拉张解体演化的开始时间。

he amphibolite metamorphic zone located in Wulawusu-Deyanqimiao area ismetamorphosed amphibolite factes. The metamorphic grade, distribution,lithology, lithochemistry and REE patterns in theregion indicate that amphibolitemetamorphic zones of Wulawusu and Deyanqimiao are the same in forming environment and tectonic genesis. There are three whole-rock samples in Wulawusuzone and five in Deyanqimiao from amphibolite have been analysed and age ofSin - Nd isochron, (607 ± 46. 5 ) Ma and (638 ± 13. 5 ) Ma, has been determined.The data shows that the zones were not only same in forming period but alsopassed the stage of extended falled into pieces evolved in late Proterozoic-earlyPaleozoic. Sin- Nd isotopic isochron age represents the beginning of continentalmargin extended falled into pieces evolved.