中祁連地塊北緣榴閃巖的發(fā)現(xiàn)、鋯石U-Pb定年及其地質(zhì)意義
發(fā)布時間：2018-12-12 06:37
【摘要】：本次研究在中祁連地塊北緣首次發(fā)現(xiàn)榴閃巖。榴閃巖是一種變質(zhì)程度介于角閃巖相和榴輝巖相之間的高壓變質(zhì)巖,關(guān)于中祁連北緣榴閃巖的研究對深入探討北祁連造山帶的發(fā)展演化模式有重要意義。中祁連北緣榴閃巖在研究區(qū)大羊隴地區(qū)和大黑茨溝地區(qū)出露,都呈透鏡體產(chǎn)于中祁連地塊基底—古元古系托賴巖群片巖巖組中,與圍巖斷層接觸。大羊隴榴閃巖圍巖巖性為二云石英片巖、含石榴子石二云石英片巖以及斜長角閃巖,在榴閃巖局部見淺色長英質(zhì)脈體;大黑茨溝榴閃巖圍巖巖性為含石榴子石白云母石英片巖。巖石地球化學(xué)研究表明,中祁連北緣榴閃巖富集Rb、Ba、K等大離子親石元素,Nb、P、Ti等高場強(qiáng)元素略虧損,Th元素富集程度較高,輕重稀土元素分異程度較低,(La/Yb)N比值介于1.45-2.62之間,具弱的Eu負(fù)異常,其原巖為大洋玄武巖。LA-ICP-MS鋯石原位微量元素分析及微區(qū)定年分析得出中祁連北緣榴閃巖的變質(zhì)年齡為485±22Ma,原巖年齡為650-800Ma;榴閃巖的圍巖斜長角閃巖原巖年齡為1480-1700Ma;榴閃巖中的淺色長英質(zhì)脈體為花崗閃長質(zhì),其鋯石U-Pb年齡為481.6±8.7Ma。電子探針分析表明榴閃巖的圍巖云母片巖中的白云母為高壓條件下形成的多硅白云母。通過巖石學(xué)、巖相學(xué)的初步研究和區(qū)域?qū)Ρ?推測中祁連北緣榴閃巖的峰期變質(zhì)P-T條件為450-600℃,0.3-0.7GPa。地球化學(xué)分析表明榴閃巖中的淺色長英質(zhì)脈體為花崗閃長質(zhì),是榴閃巖折返時發(fā)生局部熔融的產(chǎn)物。結(jié)合區(qū)域地質(zhì)背景資料本文認(rèn)為:中祁連北緣榴閃巖原巖為新元古代羅迪尼亞大陸裂解后中祁連地塊北部的古祁連洋洋殼物質(zhì),在早古生代加里東期中祁連地塊與阿拉善地塊匯聚的過程中與部分陸殼物質(zhì)一起被帶入較深部發(fā)生高壓變質(zhì),但變質(zhì)程度未達(dá)到榴輝巖相,僅形成榴閃巖;俯沖停止后榴閃巖快速折返,形成石榴石的白眼圈構(gòu)造和淺色花崗閃長質(zhì)脈體。中祁連北緣榴閃巖的發(fā)現(xiàn),與本文所依托之區(qū)調(diào)項目在中祁連北緣識別出的一系列呈NW-SE向帶狀分布的早奧陶世同碰撞花崗巖一起,證明了古祁連洋板塊在加里東期存在向南俯沖。
[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 鹵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 鹵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，
本文編號：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 鹵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 鹵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，
本文編號：2374104
本文鏈接：http://sikaile.net/kejilunwen/diqiudizhi/2374104.html
最近更新
教材專著
