中祁连地块北缘榴闪岩的发现、锆石U-Pb定年及其地质意义
发布时间：2018-12-12 06:37
【摘要】：本次研究在中祁连地块北缘首次发现榴闪岩。榴闪岩是一种变质程度介于角闪岩相和榴辉岩相之间的高压变质岩,关于中祁连北缘榴闪岩的研究对深入探讨北祁连造山带的发展演化模式有重要意义。中祁连北缘榴闪岩在研究区大羊陇地区和大黑茨沟地区出露,都呈透镜体产于中祁连地块基底—古元古系托赖岩群片岩岩组中,与围岩断层接触。大羊陇榴闪岩围岩岩性为二云石英片岩、含石榴子石二云石英片岩以及斜长角闪岩,在榴闪岩局部见浅色长英质脉体;大黑茨沟榴闪岩围岩岩性为含石榴子石白云母石英片岩。岩石地球化学研究表明,中祁连北缘榴闪岩富集Rb、Ba、K等大离子亲石元素,Nb、P、Ti等高场强元素略亏损,Th元素富集程度较高,轻重稀土元素分异程度较低,(La/Yb)N比值介于1.45-2.62之间,具弱的Eu负异常,其原岩为大洋玄武岩。LA-ICP-MS锆石原位微量元素分析及微区定年分析得出中祁连北缘榴闪岩的变质年龄为485±22Ma,原岩年龄为650-800Ma;榴闪岩的围岩斜长角闪岩原岩年龄为1480-1700Ma;榴闪岩中的浅色长英质脉体为花岗闪长质,其锆石U-Pb年龄为481.6±8.7Ma。电子探针分析表明榴闪岩的围岩云母片岩中的白云母为高压条件下形成的多硅白云母。通过岩石学、岩相学的初步研究和区域对比,推测中祁连北缘榴闪岩的峰期变质P-T条件为450-600℃,0.3-0.7GPa。地球化学分析表明榴闪岩中的浅色长英质脉体为花岗闪长质,是榴闪岩折返时发生局部熔融的产物。结合区域地质背景资料本文认为:中祁连北缘榴闪岩原岩为新元古代罗迪尼亚大陆裂解后中祁连地块北部的古祁连洋洋壳物质,在早古生代加里东期中祁连地块与阿拉善地块汇聚的过程中与部分陆壳物质一起被带入较深部发生高压变质,但变质程度未达到榴辉岩相,仅形成榴闪岩;俯冲停止后榴闪岩快速折返,形成石榴石的白眼圈构造和浅色花岗闪长质脉体。中祁连北缘榴闪岩的发现,与本文所依托之区调项目在中祁连北缘识别出的一系列呈NW-SE向带状分布的早奥陶世同碰撞花岗岩一起,证明了古祁连洋板块在加里东期存在向南俯冲。
[Abstract]:In this study, eclogite was first discovered in the northern margin of the Middle Qilian massif. Eclogite is a kind of high-pressure metamorphic rock with metamorphic degree between amphibolite facies and eclogite facies. The study on eclogite in the northern margin of Middle Qilian is of great significance to further study the evolution model of North Qilian orogenic belt. The eclogite in the northern margin of Middle Qilian is exposed in the Dayanglong area and the Dagheizgou area in the study area, both of which occur as lenses in the schist formation of the basement of the Middle Qilian block-Gu Yuan Paleozoic Tolaiyan group, and are in contact with the surrounding rock faults. The surrounding rock of Dayanglong eclogite is composed of two-cloud quartz schist, pomegranate quartz-schist and amphibolite, in which the light-colored feldspathic vein is found in the eclogite, and the garnet dolomite quartz schist is found in the surrounding rock of Dahezigou eclogite. The petrogeochemical study shows that the garnet diorite in the northern margin of Middle Qilian is rich in large ion lithophile elements such as Rb,Ba,K, and the high field strength elements such as Nb,P,Ti are slightly depleted, and the enrichment degree of Th element is higher, and the degree of differentiation of light and heavy rare earth elements is lower. The ratio of (La/Yb) N is between 1.45-2.62, with weak Eu negative anomaly. LA-ICP-MS zircon in situ trace element analysis and microzonal dating analysis show that the metamorphic age of eclogite in the northern margin of Middle Qilian is 485 卤22 Ma and the original age is 650-800 Ma. The age of the amphibolite in the eclogite is 1480-1700 Ma, and the feldspar vein in the eclogite is granodiorite, its zircon U-Pb age is 481.6 卤8.7 Ma. Electron probe analysis shows that Muscovite in the surrounding rock of eclogite is polysilicon Muscovite formed under high pressure. Based on the preliminary study of petrology, petrography and regional correlation, it is inferred that the peak metamorphic P-T conditions of eclogite in the northern margin of Middle Qilian are 450-600 鈩，
本文编号：2374104
[Abstract]:In this study, eclogite was first discovered in the northern margin of the Middle Qilian massif. Eclogite is a kind of high-pressure metamorphic rock with metamorphic degree between amphibolite facies and eclogite facies. The study on eclogite in the northern margin of Middle Qilian is of great significance to further study the evolution model of North Qilian orogenic belt. The eclogite in the northern margin of Middle Qilian is exposed in the Dayanglong area and the Dagheizgou area in the study area, both of which occur as lenses in the schist formation of the basement of the Middle Qilian block-Gu Yuan Paleozoic Tolaiyan group, and are in contact with the surrounding rock faults. The surrounding rock of Dayanglong eclogite is composed of two-cloud quartz schist, pomegranate quartz-schist and amphibolite, in which the light-colored feldspathic vein is found in the eclogite, and the garnet dolomite quartz schist is found in the surrounding rock of Dahezigou eclogite. The petrogeochemical study shows that the garnet diorite in the northern margin of Middle Qilian is rich in large ion lithophile elements such as Rb,Ba,K, and the high field strength elements such as Nb,P,Ti are slightly depleted, and the enrichment degree of Th element is higher, and the degree of differentiation of light and heavy rare earth elements is lower. The ratio of (La/Yb) N is between 1.45-2.62, with weak Eu negative anomaly. LA-ICP-MS zircon in situ trace element analysis and microzonal dating analysis show that the metamorphic age of eclogite in the northern margin of Middle Qilian is 485 卤22 Ma and the original age is 650-800 Ma. The age of the amphibolite in the eclogite is 1480-1700 Ma, and the feldspar vein in the eclogite is granodiorite, its zircon U-Pb age is 481.6 卤8.7 Ma. Electron probe analysis shows that Muscovite in the surrounding rock of eclogite is polysilicon Muscovite formed under high pressure. Based on the preliminary study of petrology, petrography and regional correlation, it is inferred that the peak metamorphic P-T conditions of eclogite in the northern margin of Middle Qilian are 450-600 鈩，
本文编号：2374104
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