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

为了了解地球的进化史，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的太古宙岩石进行古地磁研究。1995年7 - 8月，在西澳大利亚Cleaverville、Marble Bar、North Pole和Beaseley River 4个地区采集了太古宙（3.3-2.5 by）的沉积岩（带状铁组、燧石组等）和火成岩（枕玄武岩、玄武岩流、科马地岩、英安岩等）。古地磁研究揭示了太古宙地磁倒转序列，但倒转频率尚不清楚。火成岩的古强度研究表明，约33亿年前的地磁场强度远高于现在，在太古宙-元古代边界附近（-2.5亿年前）地磁场强度减弱。对地球长期冷却导致的地核生长的模拟研究结果表明，地核的物理性质（地震P波的非均质性和各向异性、密度的径向分布等）与地核的冷却速率之间存在一定的关系，可用于从地震观测中推断地核的演化。

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.