安徽城安岩体地球化学特征及成因研究

发布时间：2018-06-22 20:57

  本文选题：花岗闪长岩 + 二长花岗岩　； 参考：《合肥工业大学》2015年硕士论文

【摘要】：安徽祁门地区城安复式岩体位于扬子板块东南缘,江南隆起带内。前人对城安复式岩体研究程度薄弱,尤其是内部发育的二长花岗岩与正长花岗岩。本文通过该复式岩体中的岩石学、同位素年代学、地球化学等方面的研究,初步取得以下认识：1、城安复式岩体主要由花岗闪长岩体、二长花岗岩体和正长花岗岩体组成。主体岩性花岗闪长岩体内部分带较为明显。二长花岗岩体和正长花岗岩体分别与花岗闪长岩呈脉动侵入接触关系。2、高精度锆石U-Pb年代学测试结果表明,城安花岗闪长岩、剪刀卡二长花岗岩、刘家正长花岗岩的成岩年龄分别在151.0±2.8Ma,131.2±2.0Ma,129.4±1.5Ma。继承锆石年龄集中在800Ma左右,说明有大量成岩物质可能来源于元古代褶皱基底。结合前人研究,本文获得了城安花岗闪长岩体为皖南地区燕山期成岩年龄最老的岩体。3、通过电子探针测试结果并采用黑云母压力计和二长石温度计,对城安复式岩体形成的温压条件进行估算：花岗闪长岩中T=560℃, P=0.22-0.30Gpa,形成深度在5-8 km,二长花岗岩中,T=580℃, P=0.6Gpa,正长花岗岩中T=513-520℃, P=0.23-0.24GPa,形成深度在5-8km。由于受到挥发分的影响,该估算结果会低于实际值。4、花岗闪长岩体和剪刀卡二长花岗岩均属高钾钙碱性系列,碱度率较低,具有钙碱性特征,为过铝质岩石。复式岩体内部,正长花岗岩体轻重稀土分异作用最弱,花岗闪长岩体则最为强烈。右倾轻稀土富集模式与下地壳相同。该复式岩体内LILE元素浓度高,HFSE元素浓度低。微量元素原始地幔标准化图解为右倾型。5、城安花岗闪长岩体为I型花岗岩的特征,岩浆主要源于地壳,可能混有少量的地幔物质,在挤压向拉伸的转折环境中产生。剪刀卡二长花岗岩体具有A型花岗岩特点,岩浆基本源于地壳,主要形成在转换的动力学背景下产生。城安复式岩体的形成过程,记录了皖南地区燕山期挤压-转换-伸展的地球动力学演化过程。6、城安复式岩体演化过程较为完全,可能是源区部分融熔与分异结晶共同作用而成。其侵位机制也较为复杂,可能为先岩墙扩展上侵,随后发生顶蚀作用。
[Abstract]:The Chengan complex in Qimen area, Anhui Province is located in the southeast margin of Yangtze plate and in the Jiangnan uplift belt. The previous studies on the Chengan complex are weak, especially the interior-developed monzogranites and syenomorphic granites. Based on the petrology, isotopic chronology and geochemistry of the complex rock mass, the authors have obtained the following preliminary understanding: 1. The Chenan complex rock body is mainly composed of granodiorite, monzogranite and syenite. Part of the main lithologic granodiorite is obvious. The relation between the two granitic bodies and granodiorite is pulsating intrusive contact. The high precision zircon U-Pb geochronology test results show that the Chenan granodiorite, the shisset card monzogranite, the granodiorite, the shisset monzogranite, the granodiorite and the shisset monzodiorite. The diagenetic age of Liujiazheng feldspar granite is 151.0 卤2.8 Ma, 131.2 卤2.0 Ma, 129.4 卤1.5 Ma, respectively. The inherited zircon age is about 800 Ma, indicating that a large amount of diagenetic material may have originated from the Proterozoic fold basement. Combined with previous studies, the authors obtained that the Chengan granodiorite is the oldest rock mass of Yanshanian diagenetic age in southern Anhui. The results were measured by electron probe and biotite pressure gauge and anamite thermometer were used. The temperature and pressure conditions for the formation of Chenan complex granodiorite are estimated as follows: the formation depth of granodiorite is 560 鈩，

本文编号：2054204