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

对元古界基性侵入岩进行了古地磁和岩石磁学分析。对南极东部恩德比地的里瑟-拉森地区进行了古地磁研究，以获取古地磁信息，阐明超大陆的形成过程。NE向和N-S向侵入岩的放射性年龄分别为1.9Ga和1.2Ga。渐进退磁和热磁实验结果表明，贫钛钛磁铁矿中存在高稳定性磁性组分。在57个站点中的21个站点上确定了稳定磁分量的站点平均方向。还对样品进行了磁化率各向异性（AMS）测量和薄片显微观察。具有变形结构的样品一般表现出大于1.3的各向异性度和扁圆形的AMS组构。在21个测点中，有15个测点的AMS度低于1.3，磁面理与稳定分量的平均方向之间的方向关系不大。因此，这15个测点的稳定成分可能是侵入岩形成时获得的原始磁性成分。由15个测点的平均方向确定了3个平均方向：南北向侵入岩：倾角=-44.4°，倾角=66.0°，α <95>=48.5°;北东向侵入岩：倾角=-119.5°，倾角=-36.4°，<95>α =34.8°<95>;推测东冈瓦纳大陆（包括东南极洲和澳大利亚）在1.2和1.9Ga可能不存在。

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.