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.

砾岩应变分析表明，应变椭球在XZ和YZ平面上的轴比分别为3.73和1.23。通过去应变技术对变形前的砾岩进行了恢复，发现其为卵石泥岩。据推测，砾岩的沉积发生在比之前认为更深的水环境中。带状燧石有五种不同的岩性：绿色、白色、黑灰色和棕色层。 INAA 技术在黑层中检测到异常大量的 lr。如此高的lr含量表明早期太古宙海洋中积累了异常大量的外星物质。带状铁地层分为五种不同的岩性：黑色、红色、白色、绿色和灰色层，它们通常由石英、磁铁矿、角闪石和碳酸盐组成。它们的成分因层而异。条带状铁矿的沉积韵律尚未查明。提出了lsua地区的变质分带；根据变质矿物组合，该地区分为三个区域：按变质程度由高到低依次为角闪岩、角闪岩/绿片岩和绿片岩相。橄榄岩中的辉石被发现呈线性排列和布丁状。这些结构有力地表明，太古宙早期的地幔对流比显生宙快得多。日本研究小组发现了由燧石均匀覆盖的枕形熔岩。枕状熔岩-燧石组合与当今洋壳的顶部相同。这一发现表明，太古宙早期的构造过程与显生宙活跃的板块构造非常相似。