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Co-operative study of the oldest rocks of the Earth : essentials for the whole Earth history

地球最古老岩石的合作研究：整个地球历史的要点

基本信息

批准号：
04302021
负责人：
MASUDA Toshiaki
金额：
$ 6.02万
依托单位：
SHIZUOKA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

Strain analysis of the conglomerate showed that axial ratios of the strain ellipsoid is 3.73 and 1.23 in the XZ and YZ planes, respectively. The conglomerate before the deformation was restored by the de-straining technique, and found to be a pebbly mudstone. The deposition of the conglomerate is presumed to have taken place in deeper water environment than that previously considered. Five different lithologies are discriminated in the banded cherts : green, white, black gray and brown layrs. Anomalously large amount of lr was detected in a black layr by the INAA technique. Such high lr content suggests that anomalously large amount of extraterrestrial materials were accumulated in the early Archaean ocean. The banded iron formations were divided into five different lithologies : black, red, white, green and gray layrs, They commonly consists of quartz, magnetite, amphibole and carbonate. Their component are different from layr to layr. The depositional rhythm has not yet found out from the banded iron formation. Metamorphic zonation in the lsua region was proposed ; the region is divided into three zones on the basis of metamorphic mineral assemblages : amphibolite, amphibolite/greenschist and greenschist facies in the ascending order of metamorphic grade. Pyroxenes in the peridotite is found to be linearly arranged and boudinaged. These structures strongly indicate that the mantle convection in the early Archaean was much faster that that in Phanerozoic. The pillow lave conformably overlain by cherts has been discovered by the Japanese group. The pillow lava-chert assemblage is the same as the top of the present-day oceanic crust. This discovery suggests that the tectonic processes in the early Archaean is very similar to the plate tectonics active in the phanerozoic.

应变分析表明，应变椭球在XZ和YZ平面上的轴比分别为3.73和1.23。用去应变技术恢复了变形前的砾岩，发现为含卵石的泥岩。据推测，该砾岩的沉积发生在比之前认为的更深的水环境中。条带状硅质岩可区分为绿色、白色、黑色、灰色和棕色五种岩性。通过INAA技术在黑色层中检测到异常大量的LR。如此高的LR含量表明，太古代早期大洋中聚集了异常大量的地外物质。带状铁建造分为黑、红、白、绿、灰五种不同的岩层，通常由石英、磁铁矿、角闪石和碳酸盐组成。它们的成分因层而异。条带状铁建造的沉积韵律尚未找到。提出了伊苏阿地区的变质分带，根据变质矿物组合将该区划分为角闪岩、角闪岩/绿片岩相和绿片岩相三个变质带。橄榄岩中的辉石呈线形排列，呈束状分布。这些结构强烈表明早太古宙的地幔对流比显生宙的快得多。被硅质岩覆盖的枕状熔岩已被日本小组发现。枕状熔岩-硅质岩组合与今天洋壳的顶部相同。这一发现表明，太古宙早期的构造作用与显生宙活动的板块构造非常相似。