秦岭南缘勉略构造带康县—略阳地区组成特征及构造演化研究

发布时间：2018-03-03 15:04

本文选题：秦岭南缘　切入点：勉略构造带　出处：《长安大学》2016年博士论文　论文类型：学位论文

【摘要】：秦岭南缘勉略构造带是中国南北陆块完成拼合的主要结合带,其物质组成、构造属性及构造演化研究对于秦岭造山带的形成演化以及扬子板块和华北板块的碰撞造山过程研究具有重要意义。针对学术界存在的主要争议,本文对勉略构造带经典区段康向—略阳一带进行了系统的野外地质调查和室内岩石学、地球化学及同位素年代学研究,并取得了以下主要研究成果和认识:1、对勉略构造带内变火山岩岩石组成进行了岩石学、地球化学及年代学研究。通过系统的地球化学分析,将勉略带内火山岩分为洋壳型、O型埃达克质岩型、陆缘弧型及裂谷型四大类,其中洋壳型火山岩在康县地区和略阳地区略有差异,康县地区由N-MORB、E-MORB、OIB型等玄武岩组成,略阳地区主体为N-MORB;厘定略阳地区张儿沟O型埃达克质岩,并获得其成岩年龄为840Ma左右,为洋盆俯冲阶段洋壳部分熔融产物;获得研究区不同位置弧火山岩成岩年龄为837~797Ma,岩石组合为安山岩夹少量玄武岩、流纹岩及英安岩,地球化学特征及岩石组合具有陆缘弧特征;裂谷型火山岩年龄为783~728Ma。结合前人成果,认为勉略构造带及邻区火山岩主体形成于新元古代,少量为早古生代。2、将勉略构造带内(变质)沉积岩进行了系统梳理,并划分为南华纪—震旦纪裂解—稳定型沉积岩系、寒武纪—志留纪伸展裂陷型沉积岩系、泥盆纪—石炭纪稳定台盆—台地型沉积岩系等三个不同时代、不同沉积环境的沉积体系。获得上南华统关家沟组底部砂岩碎屑锆石年龄为877~718Ma和861~678Ma,物源主要为相邻新元古代岩浆岩。解体原临江组(Z2~?1)为相公山白云岩(Z2?1x)和临江组(?1l),并确定临江组硅质岩具有大陆边缘较深水环境地球化学特征,表征早古生代研究区可能无洋盆存在。3、综合本文及前人研究成果,对勉略构造带及其邻区区域构造演化进行了探讨。认为勉略洋盆存在时限主要为新元古代早中期,其在新元古代早中期(~800Ma)双向俯冲于秦岭微板块和扬子板块之下,并于800Ma左右两大板块完成拼合,形成了勉略构造带及扬子板块西北缘大面积分布的洋壳型火山岩及弧火山岩,新元古代中晚期(800Ma~)进入裂解进程,区域上发育呈点(面)状分布的裂谷型火山岩,这一过程很可能与全球性Rodinia超大陆的裂解事件相对应;新元古代中晚期裂解作用在震旦纪稍作停歇,于寒武纪进入新一轮陆缘裂解过程,并于志留纪形成勉略裂陷海槽,后经历晚古生代稳定台盆—台地型沉积,至早中三叠世海槽闭合并进入新一轮陆内演化阶段。
[Abstract]:The Mianliao tectonic belt on the southern margin of Qinling Mountains is the main conjunctive zone of the northern and southern continental blocks of China. The study of tectonic attributes and tectonic evolution is of great significance to the formation and evolution of the Qinling orogenic belt and the collision orogenic process between the Yangtze plate and the North China plate. In this paper, a systematic field geological survey and laboratory petrology, geochemistry and isotopic chronology have been carried out on the classical section of Mianliu structural belt, Kangxiang-Lueyang area. The petrology, geochemistry and geochronology of volcanic rocks in Mianliao tectonic belt are studied by systematic geochemical analysis. The volcanic rocks in the Mianliao belt are divided into four types: the oceanic crust type, the continental margin arc type and the rift type. The oceanic crustal volcanic rocks are slightly different in Kangxian area and Lueyang area, which are composed of N-MORBE-MORBOIB type basalt, etc. The main body of Lueyang area is N-MORB.The Zhangergou O-type adakitic rocks in Lueyang area were determined, and their diagenetic age was about 840Ma, which was the partial melting product of oceanic crust during the subduction stage of the ocean basin. The diagenetic age of arc volcanic rocks in different locations is 837797 Ma.The rock assemblage is composed of a small amount of basalt, rhyolite and dolomite. The geochemical characteristics and rock assemblages are characterized by continental margin arc. The age of rift volcanic rocks is 783 / 728 Ma.According to the previous results, it is considered that the main body of volcanic rocks in Mianliao structural belt and its adjacent areas were formed in Neoproterozoic, and a few in early Paleozoic. The sedimentary rocks in Mianliao tectonic belt were systematically sorted out. It is divided into three different periods: the South China Sinian pyrolysis stable sedimentary rock series, the Cambrian Silurian extensional rift sedimentary rock series, the Devonian Carboniferous stable platform basin platform platform sedimentary rock series. The zircon ages of sandstones at the bottom of Guanjiagou formation of Upper Nanhua formation are 877 718 Ma and 861 0 678 Ma, mainly derived from adjacent Neoproterozoic magmatic rocks, which are derived from adjacent Neoproterozoic magmatic rocks. 1) for the Xianggongshan dolomite Z2? 1x) and Linjiang formation? It is determined that the siliceous rocks of the Linjiang formation have the geochemical characteristics of the deep water environment on the continental margin, indicating that there may be no oceanic basin in the early Paleozoic study area. The tectonic evolution of the Mianliao tectonic belt and its adjacent area is discussed. It is considered that the time limit for the existence of the Mianliao oceanic basin is mainly in the early and middle Neoproterozoic, and it subducted under the Qinling microplate and the Yangtze plate in both directions at the middle and early Neoproterozoic times. The assemblage of the two plates was completed at about 800Ma, forming a large area of oceanic crustal volcanic rocks and arc volcanic rocks distributed in the Mianluo tectonic belt and the northwest margin of the Yangtze plate. In the region, there are rift-valley volcanic rocks distributed in the area, which may correspond to the global Rodinia supercontinent pyrolysis events, and the late Neoproterozoic pyrolysis stopped slightly during the Sinian period, and the pyrolysis occurred in the late Neoproterozoic period, and in the late Neoproterozoic period, the pyrolysis occurred during the Sinian period. During the Cambrian period, it entered a new process of continental margin pyrolysis, and formed a slightly rift trough in Silurian, and then experienced the late Paleozoic stable platform basin-platform deposits, and closed the trough in the early Middle Triassic and entered a new stage of intra-continental evolution.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542

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