北秦岭西段宽坪杂岩的地球化学、年代学研究及其构造地质意义

发布时间：2018-05-15 03:07

本文选题：宽坪岩群 + 碎屑岩　；参考：《西北大学》2015年硕士论文

【摘要】：北秦岭造山带主要由宽坪岩群、二郎坪岩群、秦岭岩群和丹凤岩群四个岩石地层单元组成,准确限定各个组成单元的形成时代和构造背景,对于研究和重建北秦岭造山带的形成和演化过程具有重要意义。本文在大量文献阅读和野外考察的基础上,选择北秦岭西段甘肃天水-陕西宝鸡地区的宽坪杂岩为研究对象,对研究区东岔、固川沟、斜峪关和大镇沟多条剖面出露的浅变质碎屑岩、变镁铁质岩和片麻状花岗岩进行了详细的野外地质、岩石学、地球化学和锆石U-Pb年代学研究,获得了以下初步认识：1、北秦岭西段宽坪杂岩主要由浅变质的碎屑岩、变镁铁质岩和片麻状花岗岩体组成。其中,碎屑岩主要为成熟度较高的长石石英砂岩,形成于被动大陆边缘环境；变镁铁质岩石的原岩为中基性火成岩,形成于大陆裂谷环境；东岔花岗岩显示了A型花岗岩的特征,而固川沟花岗岩为一套强过铝的S型花岗岩。2、锆石年代学研究结果显示,研究区宽坪杂岩浅变质碎屑岩的形成时代530Ma；变镁铁质岩石原岩的形成时代为1771±15Ma；东岔和固川沟花岗岩的形成时代分别为1775±14Ma和2197±19Ma。变镁铁质岩石原岩以及花岗质岩石的结晶年龄远大于宽坪碎屑岩的沉积年龄,说明它们并不构成一个统一岩石地层单位,这些古老的火成岩体应该是卷入造山带的华北板块南缘物质,应从宽坪岩群中剔除。3、碎屑锆石的定年结果显示,北秦岭西段宽坪岩群碎屑岩主要存在～600-800Ma、～950-1100Ma、-2500Ma和～3400Ma四组年龄峰值,其中-2500Ma和～3400Ma与华北板块的年龄谱系吻合,-950-1100Ma与北秦岭的岩浆事件吻合,～600-800Ma与南秦岭/扬子板块的年龄分布一致,指示宽坪碎屑岩同时接受了华北板块、北秦岭以及扬子板块北缘的碎屑物质,也间接证明,宽坪碎屑岩沉积环境应该是在华北地块和北秦岭陆块之间的一个裂陷盆地。
[Abstract]:The North Qinling orogenic belt is mainly composed of four lithostratigraphic units: Kuanping rock group, Erlangping rock group, Qinling rock group and Danfeng rock group. It is of great significance to study and reconstruct the formation and evolution of the North Qinling orogenic belt. Based on a large number of literatures and field investigations, this paper selects the Kuanping complex in Tianshui-Baoji area of Gansu Province in the western part of the North Qinling Mountains as the research object, and studies the Dongcha and Guchuan gully in the study area. The shallow metamorphic clastic rocks, metamorphic mafic rocks and granitic granites from several sections of Xiaoyuguan and Dazhenggou have been studied in detail in field geology, petrology, geochemistry and zircon U-Pb chronology. It is shown that the Kuanping complex in the western part of the North Qinling Mountains is mainly composed of shallow-metamorphic clastic rocks, metamorphic mafic rocks and granitic bodies. Among them, clastic rocks are mainly feldspar quartz sandstone with high maturity, which are formed in passive continental margin environment, and metamorphic mafic rocks are intermediate basic igneous rocks formed in continental rift environment. The Dongcha granite shows the characteristics of A-type granite, while the Guchuanggou granite is a set of S-type granite. The age of formation of shallow metamorphic clastic rocks in Kuanping complex, Kuanping complex is 530Ma. the age of formation of metamorphic rocks is 1771 卤15Ma. the age of formation of Dongcha and Guchuangou granites is 1775 卤14Ma and 2197 卤19Marespectively. The age of crystallization of metamorphic mafic rocks and granitic rocks is much greater than that of clastic rocks, indicating that they do not constitute a unified lithostratigraphic unit. These ancient igneous bodies should be the material in the southern margin of the North China plate involved in the orogenic belt, and should be excluded from the Kuanping rock group. The dating results of the detrital zircon show that the clastic rocks of the Kuanping rock group in the western part of the North Qinling Mountains mainly have the age peaks of Y600-800 Mahuan950-1100Ma-2500Ma and 3400Ma. The age spectrum of -2500Ma and Yi-3400Ma coincides with the age distribution of the North China plate from -950-1100Ma to the North Qinling magma event, indicating that the Kuanping clastic rocks accept the North China plate at the same time, and the age distribution of the South Qinling / Yangtze plate is the same as that of the North Qinling Plate. The detrital materials of the northern Qinling and the northern margin of the Yangtze plate also indirectly prove that the depositional environment of the clastic rocks in Kuanping is a rift basin between the North China block and the North Qinling continental block.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P597.3;P548

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