柴北缘造山带沙柳河地区榴辉岩相高压变质岩石的发现及初步研究

DISCOVERY OF HIGH-PRESSURE METAMORPHIC ROCKS OF ECLOGITE FACIES IN SHALIUHE AREA OF THE NORTH MARGIN OROGENIC BELT OF QAIDAM BASIN AND ITS PRELIMINARY STUDY

沙柳河榴辉岩主要由石榴石、绿辉石、金红石等矿物组成,呈构造布丁楔入体产出,具正变质岩特征,原岩为基性岩类,形成温压条件为:P=1.275～1.504GPa,T=927.83～990.20℃;高压岩石的成岩(变质)年龄为1050±51Ma(Sm—Nd 等时线),后期退变质年龄为521.3±29.5Ma(Sm—Nd 等时线),其围岩片麻岩的原岩年龄为2489±63Ma(单颗粒锆石 U—Pb),该榴辉岩形成于四堡期末中国西部陆壳趋于稳定的基础上由裂解到闭合的构造背景。

The eclogite of Shaliuhe,which occurred in shape of structural pudding- wedging body,is mainly composed of garnet,omphatic and rutile etc.,is characterized by orthometamorphite,the protolith of which is basic rock;the temperature and pressure condi- tion is as follow:p=1.275～1.504Gpa,T=927.83～990.20℃;the diagentic (metamorphic) age of high-pressure roeks is 1050±51Ma(Sm—Nd isochrom);the later stage retrograde metamorphic age is 521.3±29.5 Ma(Sm—Nd isochrom);the protolite age of its surround- ing rock,gneiss,is 2489±63Ma(single-grain zireon U—Pb).The eelogite was formed in a special tectonic setting at the end of Sibao stage when West China continental crust which tend to stability evolved from splitting to closing process.