Study of the Evolutional History of the Earth based on the Paleomagnetic Observations of the Archean Geomagnetic variations

基于太古代地磁变化的古地磁观测研究地球演化史

基本信息

批准号：
06452076
负责人：
HAMANO Yozo
金额：
$ 4.67万
依托单位：
the University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06452076/
关键词：
Paleomagnetism Archean Geomagnetic Variation Western Austraria Earth's Core growth of the inner core Geomagneti Reversal Paleointensity 地球史古地磁気学 BIF 地球進化

项目摘要

Observational and theoretical investigations were made, aiming for the evolutional history of the Earth. Observational study includes the paleomagnetic study of Archean rocks sampled from Pilbara district, Western Australia. Rock sampling was made during July-August, 1995, and sedimentary rocks (Banded lron Formation, chert, etc) and igneous rocks (pillow basalts, bastlt flows, komatiite, dacite, etc) with the Archean ages (3.3-2.5 by) were sampled from 4 areas (Cleaverville, Marble Bar, North Pole, and Beaseley River) at the Western Australia. Paleomagnetic study of the banded iron formation (BIF) revealed a reversal sequence of the geomagnetic field during the Archean period, although the frequency of the reversals are not clear yet. Paleointensity study of the igneous rocks indicates that the strength of the geomagnetic field during ca. 33 by ago is much higher than the present field, and the filed strength decreases around the archean-Proterozoic boundary (-2.5 by ago). Results of the simulation study on the growth of the inner core due to secular cooling of the earth, indicate some relations between the physical properties of the inner core (heterogeneity and anisotorpy of the seimic P wave, radial distribution of the density, etc) and the cooling rate of the core, which can be used to infer the evolution of the earth's core from the seismic observations.

针对地球的演化历史进行了观测和理论研究。观测研究包括对西澳大利亚皮尔巴拉地区采样的太古代岩石进行古地磁研究。 1995年7月至8月进行了岩石采样，对太古宙年龄（3.3-2.5年）的沉积岩（带状铁矿层、燧石等）和火成岩（枕状玄武岩、玄武岩流、科马提岩、英安岩等）进行了取样。采样自西澳大利亚州的 4 个地区（Cleaverville、Marble Bar、North Pole 和 Beaseley River）。带状铁地层（BIF）的古地磁研究揭示了太古代时期地磁场的反转序列，尽管反转的频率尚不清楚。火成岩的古强度研究表明，大约在大约 10 年间地磁场的强度。 33年前远高于现在的磁场，并且在太古宙-元古代边界附近磁场强度减小（-2.5年前）。对由于地球长期冷却而导致的内核生长的模拟研究结果表明，内核的物理特性（地震 P 波的不均匀性和各向异性、密度的径向分布等）和地核的冷却速率，可用于从地震观测中推断地核的演化。