Interaction of Plate, Mantle, core and the magmatism in the earth's history

地球历史上板块、地幔、地核与岩浆作用的相互作用

基本信息

批准号：
12126202
负责人：
KAWAMURA Katsuyuki
金额：
$ 27.84万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

We made a fieldwork at Acasta granitic complex in Canada, which is the oldest igneous body in the world formed at 4 Ga. We revealed the sequence and timing of formation of igneous complex on the basis of zircon dating and geological evidences. We made a fieldwork also at Pilbara craton in Australia, which is one of the oldest granite-greenstone terrain formed at 2.8-3. 5 Ga. We investigated igneous activities both at mid-oceanic ridges and convergent margins at that age. Results indicate that Archean seawater included large amounts of carbon-dioxide, and it formed significant proportions of carbonate minerals in oceanic crust through hydrothermal activities. Such carbonated crust subducted at convergent margins carrying large amount of carbon into the deep interior. In addition, melt inclusion studies of 3.5 Ga komatiites from Zimbabwe revealed that plume mantle included lots of water at that time. We also performed high P-T experiments using Kawai-type apparatus in order to investigate the melting processes in the lower mantle. Melting phase relations both of pyrolite and basalt compositions were determined, and trace element partitioning were investigated. These experimental results suggest that CaSiO_3-perovskite plays predominant roles in the partitioning of trace elements in the lower mantle including melting process at the core-mantle boundary. The characteristic pattern of trace elements expected to be formed by melting at the bottom of the mantle is found in the xenolith clinopylroxenes in the plume mantle at Hawaii and south Pacific, suggesting that they originated from that region. We further performed ultra-high P-T experiments using laser-heated diamond anvil cell. We revealed that silica phase undergoes phase transition twice in the lower mantle, and α-PbO_2-type phase is stable at the lowermost mantle conditions.

我们对加拿大的阿卡斯塔花岗岩杂岩进行了实地考察，这是世界上最古老的火成岩体，形成于 4 Ga。我们还根据皮尔巴拉克拉通的锆石测年和地质证据揭示了火成岩杂岩的形成顺序和时间。位于澳大利亚，是最古老的花岗岩-绿岩地形之一，形成于 2.8-3 Ga。我们调查了大洋中部的火成岩活动。结果表明，太古宙海水含有大量二氧化碳，通过热液活动，在洋壳中形成了相当大比例的碳酸盐矿物，这种碳化地壳在汇聚边缘俯冲，将大量碳带入海洋。此外，对津巴布韦 3.5 Ga 科马提岩的熔体包裹体研究表明，当时地幔中含有大量的水。我们还利用 Kawai 型进行了高 P-T 实验。实验结果表明，CaSiO_3-钙钛矿在下地幔中的微量元素分配中起主导作用。在包体中发现了下地幔，包括地核-地幔边界处的熔融过程，预计地幔底部熔融会形成微量元素的特征模式。在夏威夷和南太平洋的地幔柱中发现了单斜烯，表明它们起源于该地区，我们使用激光加热的金刚石砧室进一步进行了超高 P-T 实验，揭示了二氧化硅相在下地幔中经历了两次相变。 α-PbO_2型相在最低地幔条件下是稳定的。