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首页> 外文期刊>Contributions to Mineralogy and Petrology >Episyenite formation in the Toki granite, central Japan
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Episyenite formation in the Toki granite, central Japan

机译：日本中部的土岐花岗岩中的高效地层

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Episyenite is a quartz-depleted vuggy rock resulting from hydrothermal alteration of granitic rocks. This is the first report of its existence in an island arc, which is identified in a deep drill core of the Toki Cretaceous granite distributed in central Japan. In order to understand the petrographical features of the episyenite, neutron porosity measurement, geochemical analysis, microscopic observation, and X-ray computed tomography scanning were carried out. The results show remarkably high porosity (35.4 %) due to interconnecting vugs and the removal of quartz, plagioclase, and biotite. The Rb-Sr isotopic results and the paragenetic sequence of secondary minerals in the vugs suggest that the hydrothermal alteration process can be divided into an episyenitization stage and a later hydrothermal stage. At the episyenitization stage (70.6 it 3.1 Ma) ca. 6 million years after the emplacement of the unaltered granite (76.3 ±1.5 Ma), dissolution of quartz, biotite, and plagioclase occurred and was followed by the precipitation of albite, vermicular chlorite, and platy calcite. The episyenitization is considered as a local alteration of the Toki granite in an isoto-pically closed system. At the later hydrothermal stage, illite and secondary quartz precipitated from circulating meteoric-derived water in the dissolution vugs. Superimposing alteration at the later hydrothermal stage is limited, which results in the preservation of the episyenite in an almost primitive condition.
机译：钠长石是一种石英贫化的蓬松岩石，是由花岗岩岩石的热液蚀变产生的。这是它存在于岛弧中的第一份报告，在分布于日本中部的土岐白垩纪花岗岩的深层钻探岩心中发现了该弧。为了了解方钠石的岩石学特征，进行了中子孔隙率测量，地球化学分析，显微镜观察和X射线计算机断层扫描。结果表明，由于相互连接的孔洞以及石英，斜长石和黑云母的去除，孔隙率非常高（35.4％）。 Rb-Sr同位素结果和岩心中次生矿物的共生序列表明，热液蚀变过程可以分为上表观硝化阶段和随后的热液阶段。在表观晶化阶段（70.6，3.1 Ma）。放置未改变的花岗岩（76.3±1.5 Ma）后的600万年，石英，黑云母和斜长石发生溶解，随后钠长石，蠕虫亚氯酸盐和板状方解石沉淀。表观析晶化被认为是Toki花岗岩在同位素封闭系统中的局部变化。在随后的热液阶段，伊利石和次生石英从溶蚀孔洞中循环的陨石源水中沉淀出来。在随后的热液阶段叠加变化是有限的，这导致在几乎原始的条件下保持了方钠石的保存。

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