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

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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.