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

皮尔巴拉（Pilbara）北极区域的密集1/5000比例场映射加上室内分析，已经阐明了3.5 GA Greenstone带的以下新方面。 1）主要的基底绿岩（先前称为Ada Mount Basalt，Towers Mountation towers towers和Hickman的Apex Basalt，由Hickman，1983）形成了覆盖的推力板（I-IV单元；每个组成1-2 km厚的绿色晶体和薄裂缝），表明在初级火山和沉降后均匀的平行途径。 2）在绿岩雪地单元中没有粗粒的陆原经典表明是偏移而不是连续的环境。 3）许多二氧化硅堤将T-Chert穿透的枕套绿色石（部分I单元）到它们的地层顶部，这表明收缩之前是一种延伸的状态。 4）从T-Chert到上覆盖的床的等级过渡表明了二氧化硅的收益和沉积关系。高达60 m厚的床头切口是Inte的总和。 5）床的缝隙具有倾斜的供电结构，表明迅速而综合的沉积物。 6）从床的chert裂（细菌）类似于已知最古老的微生物（Schopf，1993）。 7）T-Chert和床的cher的EU阳性REE模式都表明了二氧化硅的热液起源。 8）chert中的Barite静脉和床头bar骨也处于饲养和沉积关系中。所谓的最古老的与Barite相关的基质岩是非光合合成但热液起源的。非人造环境，外部构造制度和水热活动一致地表明了这些早期的大将岩石和化石的中山山脊中的山脊。天主生活栖息地似乎类似于沿MOR的现代深海热液遗址，尽管太古莫尔的深度尚不清楚。 Layr平行的缩短可能是由于沿着Archean Strench的俯冲 - 周期性产生的。较少的