Fundamental study on behavior of fluids during high-temperature metamorphisms

本基金资助的三年研究(1990、1991和1992年)取得了以下成果。东高变质岩是在绿片岩相-麻粒岩相条件下进行递进变质作用形成的。用几种地温计和地质压力计估算的P-T条件为450kbar，2kbar~900kbar℃，5kbar。根据K-Ar年龄推算变质作用的年龄为56-40 Ma(始新世)。变质岩经历了明显的退变质作用。变质作用可分为两个阶段：糜棱岩化阶段(韧性阶段)和脉状形成阶段(脆性阶段)。前一阶段的变质条件对应于角闪岩相和绿片岩相。后者为绿片岩相，由前驱体-阳起岩相、前驱体-孔雀石相到沸石相。前者的P-T条件为600-400ﾟC，2kbar，后者为450-150ﾟC，2-1.5kbar。前者变质年龄为40~18 Ma(始新世至中新世)，后者为18~10 Ma(中新世)。通过对矿脉的矿物组合和矿物成分的分析，以及对矿物流体包裹体的观察，可以估计成脉期变质流体的组成及其变化。由此可以预见，在日达卡带变质作用过程中，变质流体的压力-温度-时间-变形-成分的变化轨迹。

Following results have been obtained by the three-year research (1990, 1991 and 1992) supported by this grant.1. The Hidaka metamorphic rocks were formed by progressive metamorphism under the conditions of the greenschist facies to the granulite faces. The P-T conditions are estimated to have been 450ﾟ,2 kbar to 900ﾟC,5 kbar by means of several kinds of geothermometor and geobarometor. The age of the metamorphism are estimated to have been 56-40 Ma (Eocene) on the basis of by K-Ar dating.2. The metamorphic rocks were obviously suffered retrograde metamorphism. The metamorphism can be divided into two stages:the stage of mylonitization (ductile stage) and vein-foming stage (brittle stage). The metamorphic conditions of the former stage correspond to the amphibolite facies and greenschist facies. These of the latter are to have been the greenschit facies, through the prehnite-actinolite faceis and prehnite-pupmpellyite facies to the zeolite facies. The P-T conditions of the former are to have been 600-400ﾟC,2 kbar, the latter to have been 450-150ﾟC,2-1.5 kbar. The ages of the metamorphisms are to have been 40-18 Ma(Eocene to Miocene) of the former and 18-10 Ma(Miocene) of the latter.3. Compositions and their changes of metamorphic fluid during the vein-forming stage can be estimated by means of analysis of the mineral assemblages and mineral compositions of the veins and observation of fluid inclusions of the minerals. These revealed that the compositions of fluids had became Ca- and Mg-poorer and Na- richer.We can envisage the paths of pressure- temperature- time- deformation- compositional changes of metamorphic fluids during the metamorphism of the Hidaka belt.