权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Serch for the Earth's ealiest life in Western Australia

在西澳大利亚寻找地球上最古老的生命

基本信息

批准号：
08041102
负责人：
ISOZAKI Yukio
金额：
$ 4.99万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Intensive 1/5000 scale field mapping in the North Pole area in Pilbara coupled with indoor analyzes has clarified the following new aspects of the 3.5 Ga greenstone belt. 1) The predominant basaltic greenstone (previously called the Mount Ada Basalt, Towers Formation and Apex Basalt by Hickman, 1983) form imbricated thrust sheets (Unit I-IV ; each composed of 1-2 km thick greenstones and thin chert), suggesting a layr-parallel shortening after the primary volcanism and sedimentation. 2) The absence of coarse-grained terrigenous clastics in the greenstone-chert units suggests a mid-oceanic rather than continental setting. 3) Numerous silica dikes called T-chert penetrated pillowed greenstones (particularly of the Unit I) to their stratigraphic top, suggesting an extensional regime prior to the contraction. 4) The gradual transition from T-chert to overlying bedded chert demonstrates a feeder and deposits relationship for silica. Bedded chert up to 60 m thick is a sum consequence of inte … More rmittent normal faulting with T-chert intrusion in several generations. 5) Bedded chert has slumping-dewatering structures, indicating a rapid and syn-deformational sedimentation. 6) Filamentous microorganisms (bacteria) from the bedded chert resemble to the known oldest ones (Schopf, 1993). 7) Eu-positive REE patterns of both T-chert and bedded chert suggest a hydrothermal origin of silica. 8) Barite vein and bedded barite in chert are also in a feeder and deposits relationship. The alleged oldest stromatolite associated with barite is of non-photosynthetic but hydrothermal origin. The non-terrigenous environment, extensional tectonic regime, and hydrothermal activity concordantly suggest a mid-oceanic ridge oprigin of these Early Archean rocks and fossils. The Archean life habitat appears analogous to modern deep-sea hydrothermal sites along MORs, although the Archean MOR depth is unknown. The layr-parallel shortening was probably resulted from subduction-accretion along an Archean trench. Less

密集的1/5000比例尺实地测绘在皮尔巴拉北极地区加上室内分析，澄清了以下新的方面的3.5 Ga绿岩带。1)主要的玄武质绿岩（以前被希克曼称为阿达山玄武岩，塔组和尖玄武岩，1983年）形成叠瓦状的逆冲岩席（单位I-IV ;每个由1-2公里厚的绿岩和薄燧石组成），表明在原始火山作用和沉积作用后，平行层缩短。2)粗粒陆源碎屑在绿岩燧石单位的情况下，建议洋中，而不是大陆设置。3)许多硅岩脉称为T-燧石穿透枕状绿岩（特别是第一单元），其地层顶部，这表明在收缩之前的伸展制度。4)从T-燧石到上覆层状燧石的逐渐过渡证明了硅的馈线和存款的关系。厚达60 m的层状燧石是由于 ...更多信息间歇性正断层作用，伴随着几代的硅质岩侵入。5)层状硅质岩具有滑塌-脱水构造，反映了快速的同变形沉积作用。6)层状燧石中的丝状微生物（细菌）与已知最古老的丝状微生物相似（Schopf，1993）。7)T-燧石和层状燧石的Eu正稀土模式表明二氧化硅的热液成因。8)硅质岩中的重晶石脉与层状重晶石也呈矿源-矿床关系。据称与重晶石有关的最古老的叠层石是非光合作用的，而是热液成因的。非陆源环境、伸展构造体制和热液活动一致地表明这些早太古代岩石和化石的洋中脊起源。太古代的生命栖息地似乎类似于现代深海热液网站沿着MOR，虽然太古代莫尔深度是未知的。这种平行缩短可能是沿太古代海沟沿着俯冲-加积作用的结果。少