Paleomagnetic study of Proterozoic basic intrusive rocks in Enderby Land, East Antarctica

南极洲东部恩德比地元古代基性侵入岩的古地磁研究

基本信息

批准号：
15540434
负责人：
ISHIKAWA Naoto
金额：
$ 2.18万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

Paleomagnetic and rock-magnetic analyses were performed on Proterozoic basic intrusive rocks at the Mt. Riiser-Larsen area in Enderby Land, East Antarctica in order to obtain paleomagnetic information for clarifing the formation process of supercontinents. Radiometric ages of 1.9 Ga and 1.2 Ga were reported from samples of NE and N-S trending intrusive rocks, respectively. Results of progressive demagnetization and thermo-magnetic experiments indicated the presence of high-stability magnetic components carried by Ti-poor titanomagnetite. Site-mean directions of the stable magnetic components were determined at 21 sites out of 57 sites. Measurements of anisotropy of magnetic susceptibility (AMS) and microscopic observations of thin sections were also performed on the samples. Samples with deformation structure generally showed higher anisotropy degree than 1.3 and oblate shape of AMS fabrics. Out of the 21 sites, samples of 15 sites showed lower degree of AMS than 1.3 and little directional relationship between magnetic foliation and the mean directions of the stable components. The possibility was thus implied that the stable components of the 15 sites may have been primary magnetic components acquired at the formation of the intrusive rocks. The following three mean directions were determined from the mean directions of the 15 sites:N-S trending intrusive rocks : declination=-44.4°, inclination =66.0°, α_<95>=48.5°NE trending intrusive rocks : declination=-119.5°, inclination=-36.4°, α_<95>=34.8°declination=-119.8°, inclination =39.1°, α_<95> =17.0°Positions of paleomagnetic poles corresponding to the mean directions are not consistent with 1.9 and 1.2 Ga segments of an apparent polar wander path of Australia in the East Gondwanaland reference frame. It is possibly inferred that East Gondwanaland including East Antarctica and Australia might not have existed at 1.2 and 1.9 Ga.

在南极洲东部的Enderby Land山山山地山地的植物基本侵入性岩石上进行了古磁和岩石磁分析，以获得古磁信息，以阐明超强的形成过程。从NE和N-S趋势侵入性岩石的样品中报道了辐射年龄为1.9 GA和1.2 GA。进行性消灭和热磁性实验的结果表明，存在由Ti-Poor Titanomagnetite携带的高稳定性磁成分。在57个地点中的21个地点确定稳定磁成分的位置方向。在样品上还进行了磁化率（AMS）各向异性（AMS）和微观观察结果的测量。具有变形结构的样品通常显示出高于1.3的各向异性程度，并扁平的AMS织物形状。在21个地点中，15个位点的样品显示出比1.3的较低程度的AM级，并且磁叶与稳定组件的平均方向之间的方向关系很小。因此，这种可能性暗示，这15个位点的稳定组件可能是在侵入岩的形成下获得的主要磁成分。以下三个平均方向是从15个地点的平均方向确定的：N-S趋势侵入性岩石：偏斜= -44.4°，倾斜度= 66.0°，α__<95> = 48.5°Ne趋势趋势趋势侵入性岩石：偏斜= -119.5°，倾斜，倾斜= -36.4°，α__<95 = 34.84.8.8.8.8.8°= 34.8°= 34.8°= 34.8°= 34.8°°°°°°c = 34.8°°°c = 34.°°°°°°°°;倾斜度= 39.1°，α_<95> =与平均方向相对应的古磁极的17.0°位置与东冈瓦纳兰（East Gondwanaland）参考框架中澳大利亚明显的极性徘徊路径的1.9和1.2 GA段不一致。可以推断，包括东南极洲和澳大利亚在内的东冈瓦纳兰德可能不存在1.2和1.9 GA。