太行山南段教场闪长岩矿物学特征及其地质意义

Mineralogical Characteristics of Jiaochang Diorite in Southern TaihangMountains and Geological Significance

太行山南段中生代杂岩体的成因与演化是近几十年来探索的热点话题之一.基于野外调研和电子探针分析,对教场闪长岩的矿物学特征及其意义进行了研究.该闪长岩主要由斜长石、普通角闪石、黑云母、少量单斜辉石和橄榄石组成.SiO2含量为52.91%~53.39%,具有高Mg#[100×Mg/(Mg+Fe2+)]值(60.28~62.39)、富Na(Na2O/K2O=1.18~1.40)特征.斜长石An介于36~60,属于中长石和拉长石,具正环带结构,含量约50%.角闪石具有高CaO(>10%)、MgO(>18%)特征,属富镁普通角闪石,含量约30%.黑云母Mg#[Mg/(Mg+Fe2++Fe3++Mn)]值为0.564~0.582,属镁质黑云母,含量约12%.单斜辉石均属Ca-Mg-Fe辉石族,含量约5%,为幔源岩浆在由深部向浅部运移过程中逐步结晶的产物.橄榄石Fo在76~91,为贵橄榄石和镁橄榄石,含量约2%,属地幔捕虏晶.通过单斜辉石温压计计算获得其岩浆结晶温度为1060~1094℃,压力为0.24~0.55 GPa.结果表明,岩浆源区壳幔混源特征,在岩浆上升侵位过程中,发生了弱结晶分异作用.教场闪长岩体现古太平洋板块俯冲及华北克拉通内部伸展的叠加构造背景.

The petrogenesis and evolution of Mesozoic complex in the southern Taihang Mountains have been one of hot topics explored since last several decades. Based on field investigation and Electron Probe Microanalysis(EPMA), in the paper, it studies the mineralogy and its significance of Jiaochang diorite. The Jiaochang diorite is mainly composed of plagioclase,amphibole, biotite, and few clinopyroxene and olivine. The SiO2 contents of the rocks range from 52.91% to 53.39% with high Mg#[100×Mg/(Mg+Fe2+)](60.28-62.39) and Na(Na2 O/K2 O=1.18-1.40). The plagioclases(about 50%) present An number of 36 to 60 with normal zoning, and belong to andesine and labradorite. The amphiboles(about 30%) has high CaO(>10%) and MgO(>18%), belonging to magnesial amphibole. With [Mg/(Mg+Fe2++Fe3++Mn)] of 0.564-0.582, the biotite(about 12%)is magnesial. The clinopyroxenes(about 5%) belong to Ca-Mg-Fe pyroxene series, which were produced by gradual crystallization of mantle-derived magma during its upwelling from deep to shallow. The olivines(about 2%) as xenocrysts are composed of chrysolite and forsterite with Fo from 76 to 91. The crystallized temperature and pressure of the diorite by clinopyroxene geothermobarometry range from 1 060 ℃ to 1 094 ℃ and from 0.24 GPa to 0.55 GPa respectively. These characteristics suggest that the diorite formed by mantle derived materials from the magma sources. The magma had almost no differentiation during the upward process and the diorite reflects the dual tectonic background of the subduction of the ancient Pacific plate and the extension of North China craton.