北阿尔金拉配泉地区火成岩的组合、地球化学、年代学及其构造意义
发布时间：2019-01-07 20:01
【摘要】：阿尔金造山带位于青藏高原东北缘,地处塔里木盆地与柴达木盆地之间,是我国中央造山系的重要组成部分,其壳幔结构特征、区域地质以及构造演化历史具有独特性,长期受到国内外研究者的持续关注。红柳沟-拉配泉蛇绿混杂岩带是阿尔金造山带内一条重要的构造界线,其地质演化过程对探讨阿尔金造山带构造演化具有重要意义。本文通过对北阿尔金拉配泉地区火成岩组合的野外地质、锆石年代学、岩相学及岩石地球化学等方面的分析研究,并结合区内红柳沟一带相关火成岩的组合、年代学以及高压变质作用等研究成果,初步建立了北阿尔金早古生代洋盆的形成演化过程。本文取得的主要成果和认识有:1、发现和确定了代表拉配泉地区大洋扩张或初始裂解的斜长花岗岩和辉绿岩-辉长岩组合,确定其形成时代为517Ma～500Ma。其中斜长花岗岩具有极低的K20/Na20(0.03～0.05),较高的Mg#(36～55),轻微的LREE富集等特征,以及具有高的正εHf(t)值(0.18～7.69),结合实验岩石学资料等认为其是由洋壳运移时剪切带中角闪岩相物质部分熔融形成。高晓峰等[2012]和盖永升等[2015]在红柳沟地区发现的可以限定红柳沟地区洋盆开启时限的斜长花岗岩,与本文所述斜长花岗岩的地球化学特征和形成时代基本一致;辉绿岩和辉长岩的地球化学投图均落于板内玄武岩和E-MORB玄武岩之间,反映其形成环境可能为初始裂解的洋盆环境。共同表明:红柳沟-拉配泉有限洋盆可东延至拉配泉地区,且在约517Ma～500Ma时北阿尔金洋盆打开。2、对拉配泉地区洋壳俯冲事件提供了更进一步的约束,确定其俯冲时代为480-475Ma。通过岩相学、岩石地球化学以及全岩Sr-Nd-Pb同位素分析,确定了一套辉绿岩和枕状玄武岩形成于拉配泉洋盆俯冲过程中拉开的弧后盆地环境,其中辉绿岩的形成时代为480Ma;确定白尖山花岗闪长岩,是俯冲洋壳脱水产生的流体导致下地壳基性岩石部分熔融的产物,形成于和洋壳俯冲有关的岛弧环境,其形成时代为475Ma。3、发现和确定代表拉配泉地区洋盆闭合事件的钾长花岗岩,确定其形成时代为468Ma。钾长花岗岩显示低Sr高Yb及强负Eu异常,为典型A型花岗岩的特征,在构造环境判别图中,钾长花岗岩主要投入火山弧花岗岩和板内花岗岩区,综合表明其形成于洋壳闭合、陆陆碰撞后的伸展环境。4、对比和梳理拉配泉地区与红柳沟地区的火成岩的组合、年代学、成因机制,结合区内高压岩石、蛇绿岩等的研究成果,将北阿尔金洋盆的构造演化阶段划分为三个阶段:(1)初始裂解及大洋扩张阶段,≥518Ma～479Ma;(2)洋壳俯冲作用阶段,介于513Ma～475Ma;(3)洋壳闭合后伸展阶段,时代介于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，
本文编号：2404090
[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，
本文编号：2404090
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