【作者】 任军虎；

【导师】 柳益群；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2010， 博士

【摘要】 中国西北地区是我国大陆地质和大陆动力学研究的重点地区,作为本区重要组成部分的柴达木盆地南、北缘一直受到研究者的高度关注。本文重点选择柴南缘小庙、金水口、清水泉的基性岩墙及柴北缘牦牛山碎屑岩为研究对象,主要对其年代学及地球化学进行了详细研究,同时有针对性地对柴北缘全吉群、早古生代柴达木南北缘蛇绿岩、岩浆岩、高压—超高压变质岩及泥盆纪盆地性质进行了较为系统的综合分析研究,建立了研究区南华纪至泥盆纪比较精细的年代学格架,分析了区域地质演化过程,获得如下主要认识：1、对小庙辉绿岩脉及金水口变余辉长岩进行地质、地球化学及年代学详细的研究,确定小庙辉绿岩脉富集大离子亲石元素和LREE, Nb、Ta等高场强元素亏损,金水口变余辉长岩呈平坦型稀土配分模式,富集大离子亲石元素,Nb、Ta等高场强元素弱亏损,两者构造环境均为大陆裂谷,LA-ICP-MS锆石U-Pb同位素定年测得岩石结晶年龄分别为733.6±6.6Ma及796±41Ma,并结合对柴北缘全吉群沉积—火山岩系的伸展环境沉积特征研究,提出三者共同比较确切的证实了研究区存在南华纪Rodinia超大陆裂解。2、以清水泉辉绿岩脉为重点研究对象,确定其地球化学具轻稀土富集型,明显富集大离子亲石元素,Nb、Ta等高场强元素亏损,构造环境为活动大陆边缘岛弧,LA-ICP-MS锆石U-Pb同位素定年测得岩石结晶年龄为436.4±1.2Ma。在此基础上,结合对研究区早古生代蛇绿岩、岩浆岩及高压-超高压变质岩详细的剖析,并结合沉积学特征认为,柴北缘洋盆形成于447-521Ma,于486-445Ma发生俯冲并形成超高压榴辉岩,437-422Ma发生陆壳深俯冲；祁漫塔格弧后洋盆形成于早、中奥陶世,东昆中洋盆形成于522-460Ma,于455-436Ma发生俯冲,427-410Ma发生陆陆碰撞,并形成相应的弧后盆地及前陆盆地。3、通过对区内泥盆系进行野外地质和区域对比研究,并选择上泥盆统牦牛山组碎屑岩做年代学研究,认为上泥盆统牦牛山组下限不早于430-407Ma,牦牛山组为一套伸展磨拉石沉积,早、中泥盆世为前陆盆地,晚泥盆世为伸展型盆地。4、以关键地质事件的定时、定性为基础,结合前人的研究成果,确定了柴达木盆地南、北缘南华纪至泥盆纪构造演化如下框架：(1)柴达木盆地南、北缘在新元古代早期(950-982Ma)曾发育古洋盆,并于830-927Ma期间发生洋盆闭合、陆陆拼合的作用过程。(2)南华纪(796-733Ma)开始柴达木盆地南、北缘古陆块开始裂解、离散、向洋发展,分别在柴北缘形成具沉积特征的全吉群,柴南缘形成具裂谷构造环境的小庙辉绿岩脉及金水口变余辉长岩。晚寒武世—早奥陶世(467-522Ma)柴达木盆地南、北缘发展成为洋盆,分别形成蛇绿岩(蛇绿混杂岩),祁漫塔格可能为裂谷。早、中奥陶世(496-445Ma)柴北缘洋盆开始俯冲、消减,形成滩间山群的岛弧岩浆岩及弧后盆地沉积,随着俯冲的加剧,形成变质作用峰期在490Ma-450Ma之间的超高压榴辉岩,此阶段为大洋俯冲；中、晚奥陶世(455-436Ma)东昆中洋盆向北俯冲,在东昆北形成一条早古生代岛弧岩浆岩带,北部祁漫塔格弧后小洋盆向北俯冲,在北侧形成滩间山群岛弧火山岩建造的弧后盆地沉积。晚奥陶世—早志留世,柴北缘洋盆全部俯冲消减掉,陆壳在洋壳的拖拽下发生深俯冲,形成变质年龄在437-422Ma之间的超高压榴辉岩,赛什腾组的类复理石沉积可能为弧后前陆盆地沉积物；昆中洋盆与祁漫塔格洋盆在中、晚志留世(427-410Ma)闭合,祁漫塔格地区白干湖组沉积了一套复理石沉积,可能为前陆盆地的沉积物。中志留世至中泥盆世,碰撞造山作用加剧,在柴北缘、昆中及祁漫塔格形成缝合带,早、中泥盆世沉积因造山隆升未沉积而缺失,至中泥盆世,碰撞造山作用结束。(3)晚泥盆世柴达木南、北缘开始伸展构造演化,形成了一套伸展磨拉石沉积。更多还原

【Abstract】 Northwest China is the key area of China continental geology and dynamics, as an important part of the area the south and north Qaidam have been greatly concerned by researchers. This article focuses on the diabase selected from the south Qaidam area of Xiaomiao, Jinshuikou, Qingshuiquan and clastic rock from Maoniu Moutain in the north Qaidam, and their Chronology and geochemistry were studied in detail. Meanwhile the Quanji Group, Early Paleozoic ophiolite, igneous rocks, high pressure-ultra high pressure metamorphic rocks and the nature of the Devonian basin of South and north Qaidam were targeted to studied systematicly. At last, relatively fine chronology framework from Nanhua period to Devonian was established in the study, and the regional geological evolution was analyzed, then knowledge was obtained as follows:1. After geology, geochemistry and geochronology of basic dykes from Xiaomiao area and blasto-gabrro from Jinshuikou area being detailed researched, it was ascertained that the diabase was enriched in large ion lithophile elements and LREE, loss of high field strength elements such as Nb and Ta, the blasto-gabrro was flat REE pattern, enriched in large ion lithophile elements, loss of high field strength elements such as Nb and Ta. They all formed in continental rift tectonic setting, crystallization ages of rocks were 733.6±6.6Ma and 796±41 Ma respectively measured by zircon U-Pb isotopic LA-ICP-MS, after that sedimentary characteristics in extensional tectonic environment from the sedimentary-volcanic Quanji Group nouth Qaidam was detailed researched, then a conclusion can be made that all these precisely confirmed the existence of the Rodinia continent breakup during Nanhua period.2. Qingshuiquan diabase was choiced to major concern, it was confirmed that its geochemistry was LREE enrichment type, significantly enriched in large ion lithophile elements such as Nb and Ta, loss of high field strength elements, the diabase derived from the active continental margin arc tectonic setting, and its crystallization age is 436.4±1.2Ma measured by zircon U-Pb isotopic LA-ICP-MS. On this basis, combined with sedimentary characteristics and the detailed analysis of the features of Early Paleozoic ophiolite, igneous rocks and high pressure-ultra high pressure metamorphic rocks, a conclusion can be made that the north Qaidam Ocean formed in 447-521 Ma, then the subduction occurred and the UHP eclogite formed in 486-445Ma, deep subduction occurred in crust during the period of 437-422Ma; back-arc oceanic basin in Qimantage formed in the Early and Middle Ordovician, eastern Kunlun oceanic basin formed in 522-460Ma, then subduction occurred at 455-436Ma, at last continental collision occurred in 427-410Ma, at the same time the corresponding arc basin and the foreland basin were formed.3. after detailed study of the field geology and regional comparative on Devonian in the area researched, and selecting geochronology study of the Upper Devonian clastic rock, a conclusion can be made that the Upper Devonian Maoniushan group was not earlier than the 430-407Ma, Maoniushan group deposits was a stretch molasse, Early and Middle Devonian was foreland basin, Late Devonian was extensional basin.4. The key geological events to the timing and qualitative, combined with previous research results were been to determine the tectonic evolution framework from Nanhua period to Devonian in the area researched.(1) Early Neoproterozoic(950-982Ma)existed an ocean in the area studied, the ocean was closed during the period of 830-927Ma.Ancient continent started to crack and discrete to become an ocean during the period of 796-733Ma in the north and south Qaidam, there formed Quanji Group with extensional environment sediments in the nouth, and Xiaomiao basic dykes and Jinshuikou blasto-gabrro derived from cracking tectonic environment in the south.During the period of Late Cambrian to Early Ordovician(467-522Ma), the area researched evolved into an ocean basin, Qimantage orogenic belt may be a rift.North Qaidam ocean may start subducting during the Early to Middle Ordovician(496-445Ma), Tanjianshan Group deposited island arc magmatic rocks and sediments from back-arc basin, with the increase of the subduction, the UHP eclogite was formed in 490Ma-450Ma, this stage may be ocean subduction, eastern Kunlun ocean occurred subduction toward nouth during the period of Middle to Late Ordovician(455-436Ma), so Early Paleozoic island arc magmatic belt came into being in the nouth of eastern Kunlun ocean, at the same time, the Qimantage small ocean occurred subduction toward nouth, then it formed arc volcanic sediments from Back-arc basin existing in the north Tanjianshan Group.When all the subduction of oceanic crust reduced off during the Late Ordovician to Early Silurian, the continental crust occurred deep subduction under the drag of the oceanic crust, then eclogite was formed with the age of 437-422Ma, Class of flysch from Saishiteng group may be the sediments from retroarc foreland basin, eastern Kunlun ocean and Qimantage ocean was closed in the Late Silurian, the flysch deposit in Baiganhu Group may retroarc foreland basin sediments.During the period of Middle Silurian to Middle Devonian, with the increasing of collision orogeny, north Qaidam, eastern Kunlun, and Qimantage graduateed into suture zone, Early and Middle Devonian deposits became sedimentary gap due to the orogenic uplift, collision orogeny was finished until Middle Devonian.(3) Nouth and south Qaidam began to form extensional tectonic evolution in Late Devonian, and there deposited a series of extensional molasse.更多还原