Archean Tectonics of the Pilbara craton, Western Australia

西澳大利亚皮尔巴拉克拉通的太古代构造

基本信息

批准号：
06041038
负责人：
ISOZAKI Yukio
金额：
$ 2.88万
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：
1994
资助国家：
日本
起止时间：
1994 至无数据
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06041038/
关键词：
accretionary complex chert MORB BIF OIB hydrothermal activity plume orogenic belt

项目摘要

Archean (3.5-2.5 Ga) sedimentary rocks in the Pilbara craton, Western Australia, have been regarded as succesive sequences accumulated in situ on continetal crust. Present research project has clarified, however, that these Archean sedimentary complexes are ancient accretionary complexes formed at subduction zones. Detailed field research was conducted in the Cleaverville, North Pole, Marble Bar, Camel Creek, and Beasley River areas in the granite/greenstone belts of the Pilbara craton, and following results were newly obtained.Recognition of duplex structure and oceanic plate stratigraphy of component rocktypes proved the occurrence of Archean acrretionary complex. This find indicates that plate tectonics including subduction of oceanic plate was working already at 3.5 Ga (mid-Archean time), and that the Archean granite/greenstone belt represents subduction-related Cordilleran-type orogenic belt. Furthermore, it implies that Archean granite/greensone belts in other cratons can be all … More re-interpreted as Cordilleran-type orogenic belts.On the other hand, some peculiar characteristics of Archean accretionary complex can be documented as follows ; 1) Archean MORB in accretionary complex is fairly thicker than those in Phanerozoic equivalents, 2) occurence of komatiitic greenstones which is absent in Phanerozoic example, and 3) metalliferous pelagic sediments including barite deposits. What was also clarified is a considerable variation in Archean accretionary complexes including komattitic grenstone (probably of oceanic plateau origin) -dominant complex, and those with strong alteration by hydrothermal venting associated with barite units. In addition, the so-called oldest (3.5 Ga) stromotolite was revealed to be a deep-sea hydrothermal deposits associated with barite.The above-mentioned results are all new to this study field, and the present project team is now trying to publish these in international journals as soon as possible. We would like to appreciate the Ministry of education and culture of Japan for the support on this project. Less

西澳大利亚皮尔巴拉克拉通的太古代（3.5-2.5 Ga）沉积岩被认为是在大陆地壳上原位堆积的连续层序，然而，目前的研究项目已经澄清，这些太古代沉积杂岩是俯冲形成的古老增生杂岩。在克利弗维尔、北极、大理石吧、骆驼溪和比斯利河地区的花岗岩/绿岩地区进行了详细的实地研究。对皮尔巴拉克拉通带的复式结构和大洋板块地层的组成岩石类型的认识证明了太古代增生杂岩的存在，这一发现表明包括大洋板块俯冲在内的板块构造已经在3.5 Ga（太古代中期），太古代花岗岩/绿岩带代表了与俯冲相关的科迪勒拉型造山带。其他克拉通的花岗岩/绿岩带都可以重新解释为科迪勒拉型造山带。另一方面，太古宙增生杂岩的一些独特特征可以记录如下： 1) 增生杂岩中的太古宙 MORB 相当厚。与显生宙对应物相比，2）出现了显生宙中不存在的科马提质绿岩，以及 3）含金属还澄清了包括重晶石矿床在内的太古宙增生杂岩的相当大的变化，其中包括以科马提质粗岩（可能源自海洋高原）为主的杂岩，以及与重晶石单元相关的热液喷发强烈蚀变的杂岩。 - 被称为最古老（3.5 Ga）叠层石被发现是与重晶石伴生的深海热液矿床。上述结果全部这是该研究领域的新手，目前的项目团队正在努力尽快在国际期刊上发表这些内容，感谢日本教育和文化部对该项目的支持。