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Fundamental study on behavior of fluids during high-temperature metamorphisms

高温变质作用过程中流体行为的基础研究

基本信息

批准号：
02640619
负责人：
SHIBA Masatoshi
金额：
$ 1.47万
依托单位：
Hirosaki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1992
项目状态：
已结题

项目摘要

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.

在该基金的资助下，进行了三年（1990、1991和1992）的研究，取得了以下成果。日高变质岩是在绿片岩相至麻粒岩相条件下进行递进变质作用形成的。利用多种地温计和气压计估算了该地区的P-T条件为450 ℃，2kbar ~ 900 ℃，5 kbar。根据K-Ar法测年，推测变质作用的年龄为56-40 Ma（始新世）.变质作用明显。变质作用可分为韧性糜棱岩化阶段和脆性脉状岩形成阶段。前一阶段变质条件对应于角闪岩相和绿片岩相。后者为绿片岩相，经历了钠闪石-阳起石相和钠闪石-钠闪石-沸石相。前者的P-T条件为600-400 ℃，2 kbar，后者为450-150 ℃，2-1.5 kbar。变质作用的时代前者为40-18 Ma（始新世-中新世），后者为18-10 Ma（中新世）.通过对脉体矿物组合、矿物成分的分析和矿物流体包裹体的观察，可以估算脉体形成阶段变质流体的成分及其变化。揭示了日高带变质作用中流体成分由贫Ca、Mg向富Na转变的过程，提出了变质流体压力-温度-时间-变形-成分变化的途径。