Magnesian igneous enclave in the Ohmine Granitic Rocks of Kii Peninsula
Magnesian igneous enclave in the Ohmine Granitic Rocks of Kii Peninsula
复制标题
纪伊半岛大峰花岗岩中的镁质火成岩包体
DOI：
10.2465/gkk.34.15
复制
发表时间：
2005
影响因子：
--
通讯作者：
T. Sumii
中科院分区：
文献类型：
--
作者：
H. Shinjoe;G. Shimoda;T. Fukuoka;T. Sumii
在日本西南部纪伊半岛大峰花岗质岩体最北端的Dorogawa岩体中发现了一个最大尺寸达2 m的次棱角状镁质火成岩包体。火成岩包体主要由作为斑晶的斜长石和角闪石以及作为基质矿物的斜长石、角闪石、石英和黑云母组成。它们还含有含水镁铁质矿物集合体，由镁铁质、阳起石和黑云母组成，并含有罕见的铬尖晶石微晶。它们的全岩成分的特征在于高MgO含量（5.8-7.0重量%）、低FeO*/MgO比（0.80-0.92）、高Cr（256-346 ppm）和Ni（81-138 ppm）含量。微量元素丰度的模式是接近的Setouchi火山岩的高镁安山岩（HMA）。含水镁铁质矿物集合体中铬尖晶石微晶的组成范围与Setouchi HMA中橄榄石或斜方辉石斑晶中的组成范围相似。岩浆包体的这些地球化学和矿物学特征表明，HMA岩浆的活动与Dorogawa岩体的侵入在时空上密切相关。
Magnesian igneous enclaves showing sub-angular shape and up to 2 m in the maximum dimension were found from granodiorite in the Dorogawa pluton, the northernmost pluton of the Ohmine granitic rocks in Kii peninsula, southwest Japan. Igneous enclaves are composed mainly of plagioclase and hornblende, as phenocrysts, and of plagioclase, hornblende, quartz, and biotite as groundmass minerals. They also contain hydrous mafic mineral aggregates consisting of chlorite, actinolite, and biotite with rare chromian spinel microcrystals. Their whole rock compositions were characterized by high MgO content (5.8-7.0 wt%), low FeO*/MgO ratio (0.80-0.92), high Cr (256-346 ppm), and Ni (81-138 ppm) contents. Patterns of trace element abundances are close to those of the high-Mg andesite (HMA) of the Setouchi volcanic rocks. The compositional range of microcrystals of chromian spinel within hydrous mafic mineral aggregates is similar to those of included in olivine or orthopyroxene phenocrysts of the Setouchi HMA. These geochemical and mineralogical characteristics of the igneous enclaves suggest the activity of HMA magma closely in space-time with the intrusion of the Dorogawa pluton.