极性转换期间地球磁场形态学研究

本文对采自中国黄土高原西峰（35.7°N,107.6°E）和段家坡（34.2°N,109.2°E）两个剖面中黄土层L8和古土壤层S8的1281块定向古地磁样品做了详细的岩石磁学和古地磁学研究.证实了Matuyama-Brunhes（M-B）极性转换带位于L8的中下部.提出了下列观点:1.M-B极性转换过程与地球磁场方向变化相联系的持续时间为3600-4500a,而与地球磁场强度变化相联系的持续时间则为8000-9000a,即强度变化存在“超前和滞后” 效应;2.M-B转换场的形态是由三次快速倒转和一次不成功的倒转构成,或者说,转换场具有快速变换极性的振荡特征;3.M-B转换过程中地球磁场并不是以轴对称的非偶极子场为主,而是偶极子场至少与非偶极子场相当;4.中国黄土-古土壤沉积物所含磁性矿物的主要成分是磁铁矿,它是研究极性转换期间地球磁场详细结构的良好物质.

MORPHOLOGY OF THE EARTH'S MAGNETIC FIELDS DURING THE TRANSITION

The paleomagnetism of the loess unit L8 and soil unit S8 in two sections located in Xifeng （35.7°N, 107.6°E） and Duanjiapo （34.2°N, 109.2°E） has been studied. A total of 1281 oriented specimens has been measured to determine the behavior of magnetic minerals in the specimens and the morphology of the geomagnetic fields during the Matuyama-Brunhes （M-B） transition. Time-scale has been constructed based on the SPECMAP δ18O time scale. Five results have been obtained: 1. The M-B transition is located in the low part of L8. 2. The duration of the M-B transition defined by direction changes is estimated to be about 3600-4800 years, whereas the intensity changes are of the characteristics of the "pre-effect" and "lag-effect" as compared wirh the directional changes. 3. The morphology of the M-B transition field is characterized not by a single reversal course, but at least by three reversals and one aborted reversal course. 4. The VGP paths obtained are not consistent with a non-dipole axisymmetric field. The geomagnetic fields during this transition seem to have the configurations that dipole field component is at least comparable to the non-dipole ones in magnetude. 5. The dominant magnetism minerals in loess and soil of the Chinese Loess Plateau is magnetite.