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乌兰县二郎洞南侧一带的矽线石榴黑云斜长片麻岩矿物组合为石榴子石+黑云母+长石+石英+矽线石,是典型的低压高温高角闪岩相岩石.岩石学和矿物化学研究表明其峰期变质P-T条件为:T=677~696℃,P=0.349~0.419 GPa.LA-ICP-MS锆石U-Pb测年获得二郎洞南侧低压高温矽线石榴黑云斜长片麻岩的峰期变质年龄为450~483 Ma.研究区内同时期岛弧岩浆作用、混合岩化作用的存在,以及低压高温峰期变质的P-T条件,共同指示二郎洞一带低压高温高角闪岩相岩石形成于柴达木地块与祁连地块之间的原特提斯洋向北俯冲过程中,俯冲形成的岛弧岩浆侵入并加热大陆地壳,在该热异常强烈区内形成了低压高温高角闪岩相岩石.通过分析该套低压高温变质岩与柴北缘高压-超高压变质带内岩石的变质属性、峰期变质时代和大地构造位置关系,二郎洞地区低压高温高角闪岩相岩石可能与其南部柴北缘大洋俯冲阶段形成的高压变质岩构成了双变质带.
The silanite-biotite plagioclase gneiss in the south of Erlang-dong, Wulan County is a combination of garnet + biotite + feldspar + quartz + sillimanite, which is a typical low pressure and high temperature amphibolite rock. The study of mineralogy and mineral chemistry showed that the PT conditions of peak metamorphism were: T = 677-696 ℃, P = 0.349-0.419 GPa.A zircon U-Pb zircon zircon dating from the south of Erlang-dong was obtained. The peak metamorphic ages of the biotite plagiogneiss are 450 ~ 483 Ma. The contemporaneous island arc magmatism, mixed lithification and PT conditions of low-pressure and high-temperature peak metamorphism jointly indicate the area of Erlang Cave Low-pressure and high-temperature amphibolite facies rock was formed in the former Tethys ocean subduction process between the Qaidam block and the Qilian block. The subducted island arc magma invaded and heated the continental crust. Low-pressure, high-temperature amphibolite facies formed in the area.By analyzing the metamorphic properties of the rocks in the HP-UHPM metamorphic belt and the relationship between the metamorphic epoch and tectonic setting, the low pressure and high temperature High-amphibolite rock may be associated with its southern Chai North High pressure metamorphic oceanic subduction formed constitutes a double metamorphic belt.