江苏宁镇花岗岩体中暗色岩脉的岩浆包裹体研究

A Study on Magmatic Inclusions of Dark Dikes of Ningzhen Granitic Body in Jiangsu

江苏宁镇花岗岩体中的辉长岩脉和方沸碱煌岩脉中的辉石、橄榄石斑晶中含有大量的原生岩浆包裹体,多数为发育良好的含有辉石、钛铁矿、黑云母和钾长石等子晶矿物的演化 型岩浆包裹体,此外,还含有一定数量的C02流体包裹体。岩浆包裹体的均一温度为1220—1270℃。均一化包裹体电子探针分析结果显示,早期结晶的辉石斑晶所捕获的岩浆的酸性程度明显高于全岩。结合其它资料,认为包裹体的这一成分特点代表了岩脉成岩过程中的液态不混溶作用,同时为解释逆向岩浆活动的层状岩浆房假说提供了微观上的证据。

The Ningzhen granitic body is situated between Nanjing and Zhenjiang, formed in the Late Yanshanian period and belongs genetically to syntectic granitoids. Its major rock types are granodiorite porphyry, granodiorite, quartz diorite-porphyry and so on. This paper deals with the magmatic inclusions developed in two dark dikes—olivine gabbro dike and monchiquite dike intruding into the granitic body. These inclusions are enclosed in clino-pyroxene and olivine phenocrysts. Most of them are well-developed primary magtactic inclusions of evolution type, consisting of daughter minerals such as pyroxene, ilmenite, biotite and potassium feldspar. Some CO_2 fluid inclusions axe also observed. The homogenized temperatures of the magmatic inclusions are between 1220-1270℃. The results of electron microprobe analyses of homogenized inclusions indicate that magmas trapped in the early crystallized pyroxene phenocrysts are evidently more acidic than host rocks. Combined with other evidences it suggests liquid immiscibility took place during the formation of the dikes, thus providing an evidence for the hypothesis of layered magma chamber to explain reversed magmatic activity.