Analysis of formation conditions for microcracking with fluid inclusions

基金资助的研究主要以分布在山梨县北角马区木川村的中中新世Momonoki亚群为样板田进行。得到的结果如下：(1)在研究区Momonoki亚群的地层学和褶皱构造方面取得了许多新的发现。(2)六叠花岗岩沿线存在源自Momonoki亚群的糜棱化接触光环，可能代表了花岗岩侵入后围岩的塑性变形。(3)利用石英碎屑颗粒中的变形微结构，即变形片层、扭结带和愈合微裂纹，推断了Momonoki亚群砂岩的古应力场。古应力场可能是指Momonoki亚群褶皱时期的应力场（Takeshita, 1995, in press）。(4)微裂纹愈合过程中包裹体的均一化温度在200 ~ 260℃之间。当对均匀化温度进行适当的压力校正时，表明石英在约300℃时发生变形。进一步研究了截断三巴川变质岩褶皱构造的阶梯式石英脉中流体包裹体的变形显微结构和均一温度。得到了以下结果：(1)愈合微裂纹的优先取向呈正交模式，每个优先取向均垂直于其中一个主应力轴。(2)石英脉的均质温度范围为150 ~ 350 C，最高温度组为300 ~ 330 C，表明流体被困在约400 C。高温流体可能预示着三巴川变质带抬升后出现了新的热源。

The research supported by the grant has mainly been conducted on the Middle Miocene Momonoki Subgroup distributed in the Mukawa village, Kitakoma district, Yamanashi prefecture as a model field. The obtained results are following.(1) I have obtained many new findings concerning the stratigraphy and fold structure in the Momonoki Subgroup in the studied area.(2) A mylonitized contact aureole originated from the Momonoki Subgroup exisits along the Yakegizo granite, which presumably represents plastic dcformation of the wall rock associated with the intrusion of the granite.(3) Paleostress field in the sandsones from the Momonoki Subgroup has been inferred with deformation microstructures in the quartz detrital grains, namely defrormation lamellae, kink bands and healed microcracks. The paleostress field perhaps indicates that the one during the folding of the Momonoki Subgroup (Takeshita, 1995, in press).(4) Homogenization temperatures of the fluid inclusions along the healed microcracks range between 200-260ﾟC.When an appropriate pressure correction is applied to the homogenization temperatures, it is suggested that the quartz deformed at ca.300ﾟC.Furthermore, I investigated the deformation microstructures and homogenization temperatures of fluid inclusions in echelon quartz veins from the Sambagawa metamorphic bets, which truncated its fold structures. The following results have been obtained.(1) The preferred orientations of healed microcracks are characterized by orthogonal pattern, where each preferred orientation is normal to one of the principal stress axs.(2) The hmogenization temperatures in the quartz veins range from 150 to 350ﾟC,and the highest temperature group, 300-330ﾟC suggests that the fluid was trapped at ca.400ﾟC.The high temperature fluid could indicate the emergence of a new heat source after the elevation of the Sambagawa metamorphic belts.