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在东昆仑东段郎木日上游最新识别出榴辉岩,其野外产状为透镜状、块状,与围岩呈断层接触。含榴辉岩的变质带宽1~3km,榴辉岩呈透镜体状分布于古元古界白沙河岩组变质岩及新元古代花岗片麻岩中,榴辉岩相岩石组合为榴辉岩和榴闪岩。榴辉岩相矿物组合为石榴子石+绿辉石+金红石+石英。石榴子石-单斜辉石矿物温压计估算出榴辉岩形成的温压条件为T=650~750℃,p=1.8~2.0GPa,在石榴子石Alm+Spess-Pyr-Gross三角图解中落入C型榴辉岩区。榴辉岩中锆石阴极发光图像显示,大部分具有扇形分带或杉树叶结构,少数具有弱环带结构,31颗锆石Th/U值较低(0.06~0.135),其LA-ICP-MS锆石U-Pb年龄明显分为2类,一类谐和年龄值为431.9±2.3Ma,代表了榴辉岩相峰期变质年龄;另一类谐和年龄值为487±5.9Ma,可能为原岩在俯冲过程中受构造热事件影响发生变质的结果。参考区域蛇绿岩及构造岩浆事件,确定研究区本次高压变质的峰期时代为早志留世晚期,可能发生于东昆仑俯冲消减-碰撞环境,结合邻区发现的同类型榴辉岩,恢复了一条东昆仑地区早古生代的高压变质带。
The eclogite was newly identified in the upper reaches of Langmuri River in the eastern part of East Kunlun. The wild eclogites are lenticular and massive in shape and are in fault contact with the surrounding rock. The metamorphic belt containing eclogite is 1 ~ 3 km wide. The eclogite is lenticular in the Paleoproterozoic Baishahe Formation metamorphic rocks and Neoproterozoic granitic gneiss, and the eclogite facies rock assemblage is eclogite Rocks and Limestone. The eclogite facies mineral assemblage is garnet + omphacite + rutile + quartz. Pomegranate - clinopyroxene pyrometer estimates that the temperature and pressure conditions for the eclogite formation are T = 650 ~ 750 ℃, p = 1.8 ~ 2.0GPa, and in the triangular solution of Alm + Spess-Pyr-Gross C into eclogite area. The zircon cathodoluminescence images of eclogites show that most of them have fan-shaped zoning or fir leaf structure, a few of them have weak-band structure, and 31 zircons have low Th / U value (0.06-0.13 5) The U-Pb ages of MS zircons are obviously divided into two types, the first type of harmonic age value is 431.9 ± 2.3Ma, which represents the peak metamorphic ages of eclogite facies; the other is 487 ± 5.9Ma, which may be For the original rock in the subduction process by thermal events affect the results of deterioration. According to the ophiolite and tectonomagmatic events in the study area, the peak period of the high-pressure metamorphism in this study area is the Early Early Silurian, which may occur in the subduction-collision environment in the Eastern Kunlun. In combination with the similar eclogites discovered in the adjacent area, An Early Paleozoic high-pressure metamorphic belt in the East Kunlun area.