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.

我们在加拿大的Acasta Granite Complex进行了实地调查，这是世界上最古老的火成岩体，该体系是4 GA形成的。我们根据锆石的日期和地质证据揭示了火成岩复合体形成的顺序和时机。我们也在澳大利亚的Pilbara Craton进行了野外工作，这是最古老的花岗岩绿石地形之一，形成为2.8-3。 5 GA。我们调查了山脊中部山脊的火成岩活动，并在该年龄段转换了边缘。结果表明，大将海水包括大量的二氧化碳，并且通过热液活动形成了海洋壳中碳酸盐矿物质的大量比例。这种碳酸壳俯冲在收敛边缘，将大量碳带入深内部。此外，津巴布韦的3.5 Ga komatiites的融化研究表明，当时的李子披风包括大量水。我们还使用kawai型设备进行了高P-T实验，以研究下地幔中的熔化过程。确定了黄铁矿和玄武岩组成的熔融相关系，并研究了痕量元素分配。这些实验结果表明，casio_3-玻璃岩石在较低地幔中的痕量元素分配中起主要作用，包括核心掩体边界的熔化过程。预期通过在地幔底部熔化形成的痕量元件的特征模式在夏威夷和南太平洋的李子地幔的异洛石斜角乙烯中发现，这表明它们起源于该地区。我们进一步使用激光加热的钻石砧细胞进行了超高的P-T实验。我们透露，二氧化硅相在下层中两次进行相变，并且在最低地幔条件下α-PBO_2型相位稳定。