【摘要】：阿爾金造山帶位于青藏高原東北緣,地處塔里木盆地與柴達(dá)木盆地之間,是我國(guó)中央造山系的重要組成部分,其殼幔結(jié)構(gòu)特征、區(qū)域地質(zhì)以及構(gòu)造演化歷史具有獨(dú)特性,長(zhǎng)期受到國(guó)內(nèi)外研究者的持續(xù)關(guān)注。紅柳溝-拉配泉蛇綠混雜巖帶是阿爾金造山帶內(nèi)一條重要的構(gòu)造界線,其地質(zhì)演化過程對(duì)探討阿爾金造山帶構(gòu)造演化具有重要意義。本文通過對(duì)北阿爾金拉配泉地區(qū)火成巖組合的野外地質(zhì)、鋯石年代學(xué)、巖相學(xué)及巖石地球化學(xué)等方面的分析研究,并結(jié)合區(qū)內(nèi)紅柳溝一帶相關(guān)火成巖的組合、年代學(xué)以及高壓變質(zhì)作用等研究成果,初步建立了北阿爾金早古生代洋盆的形成演化過程。本文取得的主要成果和認(rèn)識(shí)有:1、發(fā)現(xiàn)和確定了代表拉配泉地區(qū)大洋擴(kuò)張或初始裂解的斜長(zhǎng)花崗巖和輝綠巖-輝長(zhǎng)巖組合,確定其形成時(shí)代為517Ma～500Ma。其中斜長(zhǎng)花崗巖具有極低的K20/Na20(0.03～0.05),較高的Mg#(36～55),輕微的LREE富集等特征,以及具有高的正εHf(t)值(0.18～7.69),結(jié)合實(shí)驗(yàn)巖石學(xué)資料等認(rèn)為其是由洋殼運(yùn)移時(shí)剪切帶中角閃巖相物質(zhì)部分熔融形成。高曉峰等[2012]和蓋永升等[2015]在紅柳溝地區(qū)發(fā)現(xiàn)的可以限定紅柳溝地區(qū)洋盆開啟時(shí)限的斜長(zhǎng)花崗巖,與本文所述斜長(zhǎng)花崗巖的地球化學(xué)特征和形成時(shí)代基本一致;輝綠巖和輝長(zhǎng)巖的地球化學(xué)投圖均落于板內(nèi)玄武巖和E-MORB玄武巖之間,反映其形成環(huán)境可能為初始裂解的洋盆環(huán)境。共同表明:紅柳溝-拉配泉有限洋盆可東延至拉配泉地區(qū),且在約517Ma～500Ma時(shí)北阿爾金洋盆打開。2、對(duì)拉配泉地區(qū)洋殼俯沖事件提供了更進(jìn)一步的約束,確定其俯沖時(shí)代為480-475Ma。通過巖相學(xué)、巖石地球化學(xué)以及全巖Sr-Nd-Pb同位素分析,確定了一套輝綠巖和枕狀玄武巖形成于拉配泉洋盆俯沖過程中拉開的弧后盆地環(huán)境,其中輝綠巖的形成時(shí)代為480Ma;確定白尖山花崗閃長(zhǎng)巖,是俯沖洋殼脫水產(chǎn)生的流體導(dǎo)致下地殼基性巖石部分熔融的產(chǎn)物,形成于和洋殼俯沖有關(guān)的島弧環(huán)境,其形成時(shí)代為475Ma。3、發(fā)現(xiàn)和確定代表拉配泉地區(qū)洋盆閉合事件的鉀長(zhǎng)花崗巖,確定其形成時(shí)代為468Ma。鉀長(zhǎng)花崗巖顯示低Sr高Yb及強(qiáng)負(fù)Eu異常,為典型A型花崗巖的特征,在構(gòu)造環(huán)境判別圖中,鉀長(zhǎng)花崗巖主要投入火山弧花崗巖和板內(nèi)花崗巖區(qū),綜合表明其形成于洋殼閉合、陸陸碰撞后的伸展環(huán)境。4、對(duì)比和梳理拉配泉地區(qū)與紅柳溝地區(qū)的火成巖的組合、年代學(xué)、成因機(jī)制,結(jié)合區(qū)內(nèi)高壓巖石、蛇綠巖等的研究成果,將北阿爾金洋盆的構(gòu)造演化階段劃分為三個(gè)階段:(1)初始裂解及大洋擴(kuò)張階段,≥518Ma～479Ma;(2)洋殼俯沖作用階段,介于513Ma～475Ma;(3)洋殼閉合后伸展階段,時(shí)代介于474Ma～431Ma。
[Abstract]:The Altun orogenic belt is located in the northeastern margin of the Qinghai-Tibet Plateau and between the Tarim basin and the Qaidam basin. It is an important part of the central orogenic system in China. Its crust-mantle structure, regional geology and tectonic evolution history are unique. Long-term attention has been paid by researchers at home and abroad. The Hongliugou-Lapizan ophiolite melange belt is an important tectonic boundary in the Altun orogenic belt, and its geological evolution process is of great significance to discuss the tectonic evolution of the Altun orogenic belt. In this paper, the field geology, zircon chronology, lithofacies and petrogeochemistry of the igneous rock assemblage in the northern Altun Lapiquan area are studied, and the assemblages of related igneous rocks in the Hongliugou area are combined. The early Paleozoic oceanic basin formation and evolution process in North Altun was preliminarily established by geochronology and high pressure metamorphism. The main achievements and understandings in this paper are as follows: 1. The plagioclase granite and diabase gabbro assemblages representing oceanic expansion or initial pyrolysis in Lapiquan area have been discovered and determined to be 517 Ma-500 Ma. Among them, plagioclase granites are characterized by very low K20/Na20 (0.03 ~ 0. 05), high Mg# (36 ~ 55), slight LREE enrichment, and high positive 蔚 Hf (t) value (0. 18 ~ 7. 69). Combined with experimental petrological data, it is considered that it was formed by partial melting of amphibolite facies in shear zone during oceanic crust migration. The plagioclase granite discovered in Hongliugou area by Gao Xiaofeng [2012] and Gaiyongsheng [2015], which can limit the opening time of oceanic basin in Hongliugou area, is basically consistent with the geochemical characteristics and forming age of the plagioclase granite described in this paper. The geochemical maps of diabase and gabbro fall between intraplate basalt and E-MORB basalt, which indicates that their forming environment may be an initial splitting oceanic basin environment. The results show that the limited ocean basin of Hongliugou-Lapiquan can be extended to the Lapizan area to the east, and the North Altun Ocean Basin opens at about 517Ma~500Ma. 2, which provides further constraints on the oceanic crust subduction events in the Lapizumi area. The subduction age was determined to be 480-475Ma. A set of diabase and occipital basalts formed in the back-arc basin during the subduction process of the Tapequan Ocean basin were determined by petrography, petrogeochemistry and Sr-Nd-Pb isotopic analysis of the whole rock. The age of diabase formation was 480 Ma. It is determined that the granodiorite in Baijianshan is the product of partial melting of basic rock rocks in the lower crust caused by dehydration of the subduction oceanic crust, and formed in the island arc environment related to the subduction of the oceanic crust. The age of its formation is 475Ma.3. Potassium feldspar granite, which represents the closure event of ocean basin in Lapiquan area, is discovered and determined, and its forming age is 468 Ma. Potassium feldspar granite shows low Sr, high Yb and strong negative Eu anomaly, which is the characteristic of typical A-type granite. In tectonic environment discriminant diagram, potassium feldspar granite is mainly put into volcanic arc granite and intraplate granite area, which indicates that it formed Yu Yang crust closure. The extensional environment after continental collision. 4. Comparing and combing the assemblage, chronology, genetic mechanism of igneous rocks in Lapiquan area and Hongliugou area, combining with the research results of high-pressure rocks and ophiolite in the area, The tectonic evolution stage of the northern Altun ocean basin is divided into three stages: (1) initial pyrolysis and oceanic expansion, 鈮，

本文編號(hào)：2404090