海南岛侏罗纪辉长岩—正长岩套地球化学特征与构造意义

发布时间：2018-07-28 21:41

【摘要】：辉长岩—正长岩套属于岩石圈伸展减薄有关的地质背景环境下的产物,本文通过对海南岛侏罗纪辉长岩—正长岩套的研究,可以为长期存在争议的华南晚中生代大地构造演化提供一定指示。海南岛侏罗纪(早燕山期)辉长岩-正长岩套分布陵水断裂带上的勤赛地区,面积约为1.5Km2,该岩套以成分演化跨度大为特点,由黑云母辉长岩、角闪二长岩、角闪正长岩等构成了一个演化系列。大致可分为里茂中粒黑云母辉长岩单元,黑栋中细粒二长岩单元,八宝坡巨粒角闪正长岩单元。运用LA-ICP-MS锆石U-Pb定年方法获得八宝坡正长岩年龄为165.2±1.6Ma;里茂辉长岩年龄为167.1±2.2Ma;该单元形成时代为中侏罗世。该单元SiO_2含量变化较大,从40.02%-65.09%,全碱含量变化较大,在硅-碱图中绝大多数落入碱性系列中,K2O/Na2O为0.55~1.32,该岩套为钾质碱性玄武岩系列。其稀土元素分配曲线呈中等斜率的右倾型,轻稀土分异中等—较明显,晚期单元轻稀土元素分馏变强,而重稀土元素除早期单元有分馏外,晚期单元则趋于平坦,该岩套岩石的初始锶比值都比较低,为0.70406-0.70493,εNd(t)较高,为1.6-4.1,具有OIB(洋岛玄武岩)的特点,其源区是亏损软流圈地幔与富集的岩石圈地幔混合的产物,相同的Sr、Nd同位素组成,暗示它们具有相同的岩浆起源。勤赛碱性玄武岩系列产于被动陆缘裂谷环境,该辉长岩-二长岩岩套岩浆起源于软流圈对岩石圈地幔的交代作用,玄岩浆成分主要来源于含金云母或角闪石的岩石圈部分熔融,熔融作用深度在60-80Km之间;岩浆在上升过程中,岩浆房周围受到地壳物质的混染先形成辉长岩,岩浆房内部的原生岩浆发生结晶分异作用,形成晚期的二长岩和正长岩。
[Abstract]:The gabbro-syenite suite is a product of the geological setting related to lithospheric extensional thinning. The Jurassic gabbro-syenite suite in Hainan Island is studied in this paper. It can provide a certain indication for the late Mesozoic tectonic evolution of South China, which has been disputed for a long time. The Jurassic (early Yanshanian) gabbro-syenite suite in Hainan Island is located in Qinsai area of the Lingshui fault zone with an area of about 1.5 km ~ 2. The suite is characterized by a large span of evolution, consisting of biotite gabbro and hornblende. The hornblende syenite constitutes an evolutionary series. It can be roughly divided into Limaozhong biotite gabbro unit, Heidong medium fine-grained monzonite unit and Babaopo giant hornblende syenite unit. The age of Babaopo syenite is 165.2 卤1.6 Mausing LA-ICP-MS zircon U-Pb dating method, and the age of gabbro is 167.1 卤2.2 Ma.The unit was formed in the Middle Jurassic. The SiO_2 content of the unit varies greatly from 40.02 to 65.09, and the total alkali content changes greatly. The K _ 2O _ 2O / Na _ 2O is 0.551.32 in the silicon-alkali diagram, which is a series of potash alkaline basalts. The distribution curve of rare earth elements is of the right inclined type with medium slope. The light rare earth elements are distinguished from medium to obvious. The fractionation of light rare earth elements in the late stage units becomes stronger, while the heavy rare earth elements tend to flatten except for the fractionation of the early units. The initial strontium ratios of these rocks are all relatively low, ranging from 0.70406-0.70493, and 蔚 Nd (t) is higher (1.6-4.1). It has the characteristics of OIB (oceanic island basalt), and its source region is a mixture of depleted asthenospheric mantle and enriched lithospheric mantle, with the same SRN ND isotopic composition. It suggests that they share the same magma origin. The Qinsai alkaline basalt series occurred in the passive continental margin rift environment. The gabbro-monzonitic mantle magma originated from the metasomatism of the lithospheric mantle in the asthenosphere. The metamorphic composition of the metamorphic rocks mainly originated from the partial melting of the lithosphere containing phlogopite or hornblende. The melting depth is between 60-80Km and the magma rises, the magma chamber is mixed by crustal material to form gabbro, the primary magma in the magma chamber is crystallized and differentiated, and the late monzonite and syenite are formed.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.1;P583

【相似文献】