安徽省休宁县鄣源基性混杂岩地质地球化学特征及成因

发布时间：2018-08-02 08:48

【摘要】：鄣源基性混杂岩带分布于安徽省休宁县内,呈北东-南西向展布,沿瑶里-鹤城-江潭一线以构造碎片或碎块形式产于木坑岩组二、三岩段中,主要岩石组成为块状辉长岩、辉绿岩和枕状玄武岩。本次工作对其中的辉长岩进行了年代学研究并对三种岩性分别做了岩相学研究,主量、微量和稀土元素研究,判断了其大地构造环境并与伏川蛇绿岩套进行了对比研究。三种岩石均遭受较强的蚀变和构造变形,薄片中可见岩石中斜长石普遍钠黝帘石化、绿泥石化和绢云母化,辉石具钠黝帘石化、绿泥石化和纤闪石化,并可见绿泥石旋转碎斑。在主量元素TAS图中,岩石大部分落入玄武岩区域,属亚碱性岩石系列,拉斑玄武岩系列。在微量元素研究中,岩石富大离子亲石元素,相容元素Ci、Ni强烈亏损,岩石中Zr/Hf比值平均值为36.11,与洋岛玄武岩(平均35.9)相同。岩石稀土元素与球粒陨石标准化图中,呈现Eu负异常的右倾型,轻稀土含量比富集轻稀土的E-MORB还要高,更高于轻稀土亏损的N-MORB,推断其可能为岛弧或大陆边缘玄武岩。通过对鄣源混杂岩中辉长岩进行了锆石LA-ICP-MS U-Pb定年,得到其成岩年龄为998±5.6Ma,通过对岩石抗蚀变微量元素进行大地构造环境和成因研究,得出其形成环境为岛弧,岩浆来源于原始地幔并受到地壳的弱同化混染作用。最后将其与伏川蛇绿岩进行了地质特征对比,主微量元素、稀土元素和形成年龄以及构造环境的对比,认为其与伏川蛇绿岩并不是一条构造混杂岩带。
[Abstract]:The Zhangzhan-source and basic melange belt is distributed in Xiuning County, Anhui Province, and distributes in the NE-SW direction. Along the Yaoli-Hecheng Jiangtan line, it occurs in the form of tectonic fragments or fragments in the second and third member of the Mukengyan formation. The main rock composition is massive gabbro. Diabase and pillow basalt. In this work, the pyroxene has been chronologically studied, and the lithology, principal quantity, trace and rare earth elements have been studied respectively. The geotectonic environment has been judged and compared with the Fuchuan ophiolite suite. The three kinds of rocks are all subjected to strong alteration and structural deformation. The plagioclase is generally characterized by sodium tetrahedronitization, chlorite and sericite, and pyroxene is characterized by sodium tetrahedronitization, green mud petrification and fibro diortization, and chlorite rotational spots can be seen in the thin sheet. In the principal element TAS diagram, most of the rocks fall into the basalt area and belong to the subalkaline series and tholeiite series. In the study of trace elements, the rock is rich in large ion lithophile elements, and the compatible element Cigni Ni is depleted strongly. The average value of Zr/Hf ratio in the rocks is 36.11, which is the same as that of the oceanic island basalt (average 35.9). In the normalized diagram of rare earth elements and chondrites, there is a negative EU anomaly in the right-dip type. The content of light rare earth is higher than that of E-MORB enriched with light rare earth, and higher than that of N-MORBB, which is depleted of light rare earth. It is deduced that it may be island arc or continental margin basalt. Based on zircon LA-ICP-MS U-Pb dating of gabbro in Zhangyuan melange, the diagenetic age is 998 卤5.6 Ma.The tectonic environment and genesis of altered trace elements are studied, and the formation environment is island arc. The magma originated from the primitive mantle and was influenced by the weak assimilation of the crust. Finally, the geological characteristics, main trace elements, rare earth elements, age of formation and tectonic environment of Fuchuan ophiolite are compared, and it is considered that it is not a tectonic melange belt with Fuchuan ophiolite.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P588.36

【相似文献】