冀北赤城燕山期火山作用及其与深成岩浆活动的成因关系

发布时间：2018-03-08 17:40

本文选题：火山作用　切入点：深成岩浆活动　出处：《成都理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：赤城地区火山岩主要包括火山熔岩和火山碎屑岩,其中以火山熔岩为主,其次为火山碎屑岩,主要分布于该地区北部、东部及南部的一部分岩石。本文通过岩相学、矿物学、地球化学、LA-ICP-MS锆石U-Pb测年等方法,对该地区火山岩进行了岩石类型划分、地球化学特征、岩浆物质来源、形成的构造环境以及形成时代的确定等研究,在此基础上,与该地区花岗岩浆作用进行对比,推断赤城地区构造演化过程。根据岩石主量元素数据,利用火山岩岩石类型图解,对所采的火山岩样品进行岩石类型的划分,主要为流纹岩、粗面岩、粗安岩。根据A/CNK值划分,赤城地区火山岩属于过铝质,与同时期的花岗岩属于同一系列的岩石。微量元素采用原始地幔标准化蛛网图和稀土元素球粒陨石标准作图,流纹岩具有轻稀土富集而重稀土亏损,岩浆分异程度较高的特征;具有钙碱性演化趋势。对火山岩进行成因类型的划分,由于岩石中的SiO2、Na2O和K2O含量较高,而且CaO、MgO、TiO和P2O5值较低,Sr、Rb值较低,Zr、Nb、Ce值较高,比较符合A型花岗岩的特征,并且在K2O-Na2O图中也证明了这一推断。对构造环境投图发现,赤城地区火山岩全部形成于碰撞后构造环境中。对火山岩εHf(t)值进行计算并投图发现,其εHf(t)值全部为负值,表明赤城地区火山岩岩浆的物质源区来自于下地壳。根据火山岩的二阶段模式年龄分析赤城地区火山岩岩浆的形成年龄为1896Ma和1763Ma,即形成于古元古代。而造成源岩年龄的不一致,可能是由于形成火山岩岩浆的物源不同。LA-ICP-MS锆石U-Pb技术获得的火山岩年龄为(137.91±0.95)Ma和(141.03±0.95)Ma,属于燕山期。本文通过对赤城地区燕山期火山岩与燕山期花岗岩的对比,发现两者之间存在一些联系与差异。燕山期花岗岩主要为I型花岗岩类型,与火山岩呈现的A型花岗岩特征有所区别。火山岩与花岗岩的εHf(t)值全部为负值,说明两者均为壳源,两者的二阶段模式年龄(tDM2)平均值为1838Ma~1763Ma、1940Ma。表明两赤城地区火山岩与花岗岩的物质来源均为古老的下地壳。形成于同碰撞挤压环境下的花岗岩与形成于碰撞后拉张环境下的火山岩,两者之间存在构造转换事件,其时限为(143.9±2.2)Ma~(141.03±0.95)Ma,持续时间约为2.87Ma。
[Abstract]:The volcanic rocks in Chicheng area mainly include volcanic lava and pyroclastic rocks, among which volcanic lava is the main rock, followed by pyroclastic rock, mainly distributed in the northern, eastern and southern parts of the area. Geochemical LA-ICP-MS zircon U-Pb dating method has been used to study the classification of volcanic rocks, geochemical characteristics, source of magmatic material, tectonic environment of formation and determination of forming age in this area. The tectonic evolution process of Chicheng area is inferred by contrasting with granite magma in this area. According to the data of rock principal elements and the diagram of volcanic rock types, the rock types of volcanic rock samples collected are classified mainly as rhyolite. The volcanic rocks in the Chicheng area belong to peraluminous rocks and belong to the same series of rocks as the granite of the same period. Trace elements are mapped using the primitive mantle standardized spider web map and the standard rare earth element chondrites. The rhyolite is characterized by light rare earth enrichment, heavy rare earth depletion, high magma differentiation, calc-alkaline evolution trend. For the classification of volcanic rocks, the content of Sio _ 2N _ 2O and K _ 2O in the rocks is relatively high. In addition, the values of CaOO _ (MgO) _ (TIO) and P _ 2O _ (5) are lower, and the values of Sr _ 2O _ (RB) are lower than that of zirconia, which is consistent with the characteristics of A-type granite, and this inference is also proved in the K _ 2O-Na _ 2O diagram. The volcanic rocks in Chicheng area were all formed in the post-collision tectonic environment. This indicates that the source of volcanic magma in Chicheng area comes from the lower crust. According to the two-stage model age of volcanic rocks, the age of formation of volcanic magma in Chicheng area is 1896 Ma and 1763 Ma, that is, formed in ancient Gu Yuan, which results in the inconsistent age of source rocks. It may be due to the different provenance of volcanic magma. LA-ICP-MS zircon U-Pb technique has obtained volcanic rocks of 137.91 卤0.95Ma and 141.03 卤0.95Ma. which belong to Yanshanian period. This paper compares Yanshanian volcanic rocks with Yanshanian granites in Chicheng area. It is found that there are some relations and differences between them. The Yanshanian granites are mainly I-type granite types, which are different from the A-type granite features of volcanic rocks. The 蔚 Hftt values of volcanic rocks and granites are all negative, indicating that both of them are crust-source. The average two-stage model age (tDM2) is 1838 Ma, 1763 Ma, 1940 Ma. it shows that the material sources of volcanic rocks and granites in the two Chicheng areas are both ancient lower crust, which are formed in the same collision compression environment and the volcanic rocks formed in the post-collision extensional environment. There is a tectonic transition event between them, the time limit is 143.9 卤2.2 Ma, 141.03 卤0.95Ma, and the duration is about 2.87 Ma.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P317;P588.1

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