广西燕山期马其岗二长斑岩的矿物学特征及其成因

MINERALOGICAL CHARACTERISTICS AND GENESIS OF YANSHANIAN MAGIGANG MONZONITE PORPHYRY IN GUANGXI PROVINCE

华南晚中生代侵入岩的成因与演化一直是地学界探索的焦点问题之一。本次对广西马其岗二长斑岩的斑晶矿物进行了矿物学特征及成因意义研究,查明该二长斑岩斑晶主要由斜长石、钾长石、斜方辉石和单斜辉石组成,基质主要由隐晶质、黑云母微晶和长石微晶等组成。斑晶斜长石属于中长石(An=30.17~49.36),发育韵律环带和正环带;钾长石属于正长石w(Qr)为63.70%~80.74%,发育条纹和环带;辉石全部属于Ca-Mg-Fe辉石族;斜方辉石的端元组分w(B)范围为Wo为2.85%~4.75%,En为38.29%~46.65%,Fs为49.09%~58.86%。单斜辉石的端元组分w(B)范围为Wo为41.45%~42.05%,En为32.67%~33.43%,Fs为24.52%~25.83%;辉石总体上均为低w(TiO2),w(Al2O3)和w(Na2O)的特点,斜方铁辉石具有拉斑系列的演化特征,普通辉石具有钙碱性系列的演化特征。依此认为:岩浆在由深部向浅部运移过程中发生了岩浆混合作用。

The genesis and evolution of Late Mesozoic intrusive rocks in South China have always been one of the key focuses in geosciences research. This paper studies the mineralogical characteristics and genetic significance of the porphyry minerals in the Maqigang monzonite porphyry in Guangxi Province. It is found that the porphyry is mainly composed of plagioclase, potassium feldspar, orthopyroxene and clinopyroxene, and the matrix is mainly composed of cryptocrystal, biotite microcrystal and feldspar microcrystal. The phenocrytic plagioclase belongs to andesine(An=30.17-49.36), with oscillatory zone. Potassium feldspar belongs to orthoclase w(Qr) 63.70%-80.74%, with stripes and zonal development. All pyroxenes belong to Ca-Mg-Fe pyroxene group, with the end component w(B) of orthopyroxene ranging from Wo: 2.85% to 4.75%, En: 38.29% to 46.65%, Fs: 49.09% to 58.86%. The end component w(B) of clinopyroxene ranges from Wo: 41.45% to 42.05%, En: 32.67% to 33.43%, Fs: 24.52% to 25.83%. In general, pyroxene is characterized by low w(TiO2), w(Al2O3) and w(Na2O). The ferrosilite shows the characteristics of tholeiite series and the augite shows the characteristics of calc-alkaline series. It is considered that magma mixing occurred during magma migration from deep to shallow part of the earth crust.