南岭西山多斑花岗斑岩矿物化学及其对岩浆过程的启示  

Mineral chemistry of the Xishan granite porphyry in the Nanling Range,and its implication of magma processes

作　　者：陈子龙 闫峻[1] 李全忠[1] 汪志杰 陶克勤 CHEN Zilong;YAN Jun;LI Quanzhong;WANG Zhijie;TAO Keqin(School of Resource and Environmental Engineering,Hefei University of Technology,Hefei,Anhui 230009,China)

机构地区：[1]合肥工业大学资源与环境工程学院,安徽合肥230009

出　　处：《矿物岩石》2024年第4期11-29,共19页Mineralogy and Petrology

基　　金：国家自然科学基金项目(批准号:42030801)。

摘　　要：西山火山—侵入杂岩体位于南岭地区九嶷山复式岩体东部,区内主要出露岩石单元为高硅花岗岩、多斑花岗斑岩以及流纹岩等火山岩。本次研究从矿物化学角度探讨了西山杂岩体多斑花岗斑岩中多斑聚集的成因,以及流纹岩、多斑花岗斑岩和高硅花岗岩三者之间的成因关系。结果表明,西山多斑花岗斑岩晶体含量约为55%,铁橄榄石、铁辉石多呈聚集团块出现,属于早期形成后被携带到近地表的超镁铁质捕掳体;黑云母均为原生黑云母,结晶温度为742~769℃,压力为3.45~4.81MPa,水含量在1.43%~1.75%,形成于中等氧逸度环境下;斜长石An在32~48,为中长石;斜长石粗晶颗粒的MgO含量和An之间呈负相关,暗示斜长石和熔体之间是平衡的;计算的与斜长石平衡熔体中w(MgO)(0.06%~1.27%)、w(Sr)(34×10^(-6)~61×10^(-6))含量变化范围不大,暗示这些斜长石具有相同的形成环境。以上特征表明,岩浆房经历了斜长石、黑云母等矿物的结晶,还携带了深部结晶的铁橄榄石和铁辉石,晶体达到了近55%的体积比例,这些富晶体的晶粥可以快速侵入到近地表环境,指示含有约55%晶体的粥状岩浆仍然具有运移的能力。西山多斑花岗斑岩基质主量元素的估算结果w(SiO_(2))约71.13%、w(TFe_(2)O_(3))约2.48%、w(MgO)约0.55%,暗示多斑花岗斑岩可能是岩浆房中长石等晶体结晶到约55%时岩浆挤出上侵形成,而流纹岩是与高硅花岗岩相同的残余岩浆直接喷发到地表所形成。The Xishan volcano-intrusive complex is located in the eastern part of the Jiuyishan complex in the Nanling region.The dominant rock units in the area include high-silica granite,granite porphyry,rhy-olite,and other volcanic rocks.This paper examines the genesis of multi-spot aggregation in the Xishan granite porphyry from a mineralogical-chemical perspective,as well as the genesis of the relationship be-tween rhyolite,granite porphyry,and high-silica granite.The results show that the crystal content of the Xishan Granite Porphyry is about 55%,with fayalite and ferrosilite primarily occurring in aggregated clus-ters.These minerals are part of ultramafic enclaves that were transported to near-surface levels after early formation;the biotite are of magmatic origin,with crystallization temperatures ranging from 742 to 769℃,pressures ranging from 345-481 MPa,and the water contents ranging from 1.43%to 1.75%.These micas formed in an environment of intermediate oxygen fugacity;the plagioclase An is in a range of 32-48;A reverse correlation exists between the MgO contents of the plagioclase coarse-crystalline parti-cles and An,suggesting an equilibrium between plagioclase and melt;the calculated zw(MgO)(0.06%-1.27%)and w(Sr)(34×10^(-6)-61×10^(-6))contents of the melts equilibrated with the plagioclase vary in a narrow range,implying that the plagioclase might have formed under a similar environment.Petrography and mineral geochemistry indicate that porridge-like magma,containing approximately 55%crystals still retains mobility.Estimations of the major elements of the matrix of the Xishan granite porphyry are about 71.13%SiO_(2),2.48%TFe_(2)O_(3),and 0.55%MgO.These results suggest that the granite porphyry likely formed through the extrusion and upward intrusion of magma,where feldspars and other crystals in the magma chamber were crystallized up to around 55%.Additionally,rhyolite may have generated as a result of eruption of the same residual magma that produced the high-silica granite.

关 键 词：南岭西山 多斑花岗斑岩 岩浆房 斜长石 间隙熔体 

分 类 号：P581[天文地球—岩石学] P588.11.4[天文地球—地质学]