青海省都兰县艾日克汗森地区榴辉岩地球化学特征及其地质意义

Geochemical Characteristics and Geological Significance of Eclogite in Airikehansen Area,Dulan County,Qinghai Province

青海省都兰县艾日克汗森地区的榴辉岩位于都兰北榴辉岩带西北方向约12 km,是最新发现的较大规模榴辉岩产地。此榴辉岩为柴北缘高压超高压变质带的一部分,大部分退变质程度较高。锆石U Pb年龄为(435±4)Ma,代表了此榴辉岩峰期变质年龄;该榴辉岩SiO 2含量为48.36%~49.22%,(Na 2O+K 2O)含量为3.28%~3.65%,Na 2O含量均大于K 2O;原岩为基性玄武岩,为亚碱性拉斑玄武岩系列,构造环境为大洋中脊玄武岩环境。榴辉岩稀土配分曲线表现为右倾型模式,弱富集轻稀土元素,亏损重稀土元素,(La/Sm)N=1.70~2.34,(La/Yb)N=1.18~2.54,属于幔源E MORB型。微量元素表现为强烈亏损Th、P、Zr等高场强元素,富集Rb、Ba等大离子亲石元素。指示了柴北缘晚奥陶世到早志留世时期柴达木陆块与欧龙布鲁克微陆块的深俯冲与碰撞造山背景。

The eclogite discovered in the Airikehansen area of Dulan County Qinghai Province,is about 12km northwest of northern Dulan eclogite belt.It is the newly discovered large-scale eclogite producing area and is a part of the HUP metamorphic belt in the Northern Qaidam.Most eclogites in the belt have a high degree of retrograde metamorphism.Its zircon U-Pb age is 435+4Ma,which represents the peak metamorphic age of the eclogite.The content of SiO 2 in eclogite ranges from 48.36%to 49.22%,(Na 2O+K 2O)from 3.28%to 3.65%w(Na 2O)>w(K 2O).The original rocks of eclogites are basic basalts,subalkaline tholeiite series.The tectonic setting is mid-ocean ridge environment.The REE distribution curve of eclogite shows a right-leaning pattern,with weak enrichment of light REE and deficiency of heavy REE,(La/Sm)N=1.70-2.34,(La/Yb)N=1.18-2.54,which belongs to mantle-derived E-MORB type.The trace elements of eclogites show strong depletion of high field strength elements such as Th,P and Zr,and enrichment of large ion lithophile elements such as Rb and Ba.This indicates the deep subduction and orogenic collision background of the Qaidam block and the Olongbluk micro-block in the northern Qaidam basin from Late Ordovician to Early Silurian.