山西浑源中庄铺中生代火山岩岩石学特征及其构造意义

发布时间：2018-03-01 05:10

本文关键词： 中庄铺中生代火山岩地球化学火山断陷盆地　出处：《太原理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：浑源中庄铺地区是山西东北部中生代火山岩出露最全的地区,是研究中生代火山岩的理想场所。笔者通过火山岩的野外详细观察、剖面实测,并采集火山岩新鲜样品,在火山岩岩相学特征研究基础上,结合主量元素、微量元素、稀土元素等地球化学特征研究,对中庄铺地区中生代火山岩岩浆物质特征及来源、岩浆形成构造环境及动力学背景主要得出以下认识：1、中庄铺地区火山岩始于中侏罗世晚期,终于早白垩世后期,形成四个火山喷发旋回。各旋回火山岩岩性特点表现在早期为碱性的中基性火山岩类,晚期为钙碱性的酸性火山岩类,早期多以溢流一喷溢相熔岩为主,晚期多以强烈爆发相碎屑岩为主。2、主量元素地球化学研究表明,中庄铺火山岩总体上为一套以准铝质、钾玄岩系列为主,个别为高钾钙碱性系列的火山岩,随着火山岩岩浆酸性程度的逐渐增强,碱性程度逐渐减弱,呈现出碱性向钙碱性过渡演化的特点。3、通过与晋东北地区灵丘太白维山、塔地、左云旧高山火山盆地对比,发现不同地区同时期火山岩岩性、主量元素、稀土及微量元素具有相似性,稀土微量元素配分曲线与微量元素蛛网图均为右倾型且近于平行,反映在不同地区同时期火山岩岩浆物质来源与岩浆作用具有一致性。早白垩世张家口早期各地区抢风岭段火山岩富集Rb、Ba等大离子亲石元素,亏损Nb、Y等高场强元素,可能是壳幔物质混染的结果。张家口晚期岩浆作用发生了斜长石结晶分异作用,各地区向阳村段火山岩稀土元素配分曲线均显示负Eu异常。中庄铺地区早白垩世张家口早期与义县晚期、左云旧高山地区早白垩晚期玄武岩的Th/Ta、Ta/Hf、Nb/Zr等特征微量元素比值,反映山西北东部中生代火山岩形成于大陆板内拉张裂谷环境。4、中庄铺地区火山岩的形成受控于古太平洋板块向欧亚板块的俯冲碰撞作用,中侏罗晚期到早白垩晚期中庄铺一带上地幔和下地壳物质部分熔融的混合,构成中庄铺地区火山活动的岩浆物质来源。在区域拉张应力作用下,浑源中庄铺一带发生裂谷作用。在中侏罗世早期,起初在断陷盆地中首先形成了陆相砂砾堆积,随着拉张作用的进一步加强,已形成的岩浆沿盆地边缘断裂上侵,喷出地表,形成了四个早期以碱性的中基性岩浆溢流作用为主,晚期以钙碱性酸性岩浆爆发作用为主的旋回的火山岩。
[Abstract]:The Zhongzhuangpu area of Hunyuan is the most exposed area of Mesozoic volcanic rocks in northeastern Shanxi, and is an ideal place to study Mesozoic volcanic rocks. Based on the study of the petrographic characteristics of volcanic rocks and the geochemical characteristics of major elements, trace elements and rare earth elements, the material characteristics and sources of Mesozoic volcanic magma in Zhongzhuangpu area are studied. The tectonic environment and dynamic background of magmatic formation are as follows: 1. The volcanic rocks in Zhongzhuangpu area began in the late Middle Jurassic and finally in the late early Cretaceous. Four volcanic eruptive cycles were formed. The lithologic characteristics of volcanic rocks in each cycle were characterized by alkaline volcanic rocks in the early stage, acidic volcanic rocks in the later period, and overflow and spillage facies lava in the early stage. In the late period, the main element geochemical study showed that Zhongzhuangpu volcanic rock was a set of volcanic rocks with quasialuminite, potash series and high potassium calc-alkaline series, and the main element geochemical study showed that the volcanic rocks in the late period were mainly explosive facies clastic rocks. With the increasing acidity of volcanic magma and the weakening of alkalinity, it shows the characteristics of transition from alkalinity to calc-alkalinity. It is compared with the old alpine volcanic basins of Lingqiu Taibai Wei Mountain, Tadi and Zuoyun in northeast Shanxi. It is found that the lithology, principal elements, rare earth elements and trace elements of volcanic rocks in different regions are similar at the same time. The distribution curves of rare earth elements and cobwebs of trace elements are all right-tilted and nearly parallel. The source of magmatic material and magmatism are consistent in different regions. In early Cretaceous Zhangjiakou early Zhangjiakou volcanic rocks enriched in large ion lithophile elements, such as Rbnb Ba and so on, and depleted high field strength elements, such as NbGY, and the volcanic rocks in the early Cretaceous Zhangjiakou area were rich in large ion lithophile elements. It may be the result of the mixing of crust and mantle materials. The plagioclase crystallization differentiation occurred in the late Zhangjiakou magmatism. The REE distribution curves of volcanic rocks in Xiangyangcun section showed negative EU anomalies. The ratios of Th/ Ta-Ta-Ta-Hfnb / Zr in the early Cretaceous Zhangjiakou early Cretaceous and the late Yixian and Zuo Yun Old Alpine basalts in Zhongzhuangpu area, etc. The results show that the Mesozoic volcanic rocks in the eastern part of Shanxi Province were formed in the extensional rift environment of continental plate, and the formation of volcanic rocks in Zhongzhuangpu area was controlled by the subduction and collision between the paleo-Pacific plate and the Eurasian plate. The partial melting of the mantle and the lower crust in the Zhongzhuang Pu belt from the late Middle Jurassic to the late Cretaceous constitutes the source of magmatic material for volcanic activity in the Zhongzhuang Pu area. In the early Middle Jurassic, the continental sandstones were first formed in the faulted basin. With the further strengthening of the extensional process, the magma formed along the margin of the basin and ejected out of the surface. Four cycles of volcanic rocks were formed in the early stage and in the late period were mainly calc-alkaline acid magmatic eruptions mainly by alkaline intermediate basic magma spillage and in the late stage by calc-alkaline acid magma eruption.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P588.14

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