海坨山岩体中黑云母的成分特征及其指示意义

Compositional Characteristics of Biotites in the Haituoshan Pluton and Its Implications for Magmatic Origin and Environment

海坨山岩体位于北京市延庆区与河北省怀来县的交界处,为一大型复式岩基,前人对于其成因类型及形成环境方面的研究程度较低。黑云母是花岗岩中最为常见的暗色造岩矿物之一,其化学成分对生长环境较为敏感,可提供熔体的物理化学条件等信息,反映岩浆演化和结晶条件,故研究岩体中黑云母的成分特征,对研究其岩浆物质来源,分析其岩浆形成环境,探讨其与成岩作用的关系具有很好的指示意义。本文通过电子探针方法,对海坨山岩体中黑云母的化学成分特征进行了分析和研究,并在此基础上,对该岩体的岩浆物质来源与形成环境条件进行了研究与探讨。研究显示,海坨山岩体中的黑云母,具有富铁、镁,贫硅、铝的特征,钛的含量较高,属于镁质黑云母。其成分特征表明,海坨山岩体属I型花岗岩,其岩浆物质来源于上地幔与下地壳,形成于相对高温高压的较深环境。

The Haituoshan pluton located in the border between Yanqing District of Beijing and Huailai County of Hebei Province,is a large composite plutonic batholith,which previous research on the genetic types and formation environment is not enough.The biotite is one of the most common dark rock-forming minerals of granite,and its chemical composition is more sensitive to the growth environment,which can provide the information such as physical and chemical conditions of the melt,and reflect the conditions of the magma evolution and crystallization.Therefore,researching the component characteristics of the biotite in the pluton has the indicative significance for studying the material source of magma,analyzing the formation environment of magma and discussing the diagenesis relationship.In this paper,we analyzed and studied the chemical composition characteristics of the biotite from the Haituoshan pluton via electron microprobe.And on this basis,we analyzed and studied the magma material source and the formation environment of the pluton.The analytical results show that the biotite is characteristized by high contents of Fe and Mg,low contents of Si and Al,and high Ti contents,indicating that it is belong to magnesia-biotite,The composition characteristics of the biotite show that it belongs to I-type granite,and the magma material derived from the upper mantle and lower crust,and it formed in relatively deep environment of high temperature and high pressure.