[S-CG67_1PM1] Ocean Floor Geoscience

[SCG67-07] Magnetic Anomalies in the Southern Indian Ocean Revisited

*Yoshifumi NOGI¹, Taichi SATO², Tomoko HANYU³ (1.National Institute of Polar Research, 2.National Institute of Advanced Industrial Science and Technology, 3.Graduate University for Advanced Studies)

Keywords:magnetic anomaly, Indian Ocean, Gondwana, continental crust

Magnetic anomalies in the Southern Indian Ocean are vital to understanding initial breakup process of Gondwana. However, seafloor age estimated from magnetic anomalies still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the initial breakup process of Gondwana, vector magnetic anomaly data as well as total intensity magnetic anomaly data obtained in the Enderby Basin, Southern Indian Ocean, are used. The strikes of magnetic structures are deduced from the vector magnetic anomalies.Magnetic anomaly signals, most likely indicating Mesozoic magnetic anomaly sequence, are obtained almost parallel to WNW-ESE trending lineaments just to the south of Conrad Rise inferred from satellite gravity anomalies. Most of the strikes of magnetic structures indicate NNE-SSW trends, and are almost perpendicular to the WNW-ESE trending lineaments. Mesozoic sequence magnetic anomalies with mostly WNW-ESE strikes are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and Gunnerus Ridge. Magnetic anomalies originated from Cretaceous normal polarity superchron are found in these profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. However, Mesozoic sequence magnetic anomalies are only observed in the west side of theWNW-ESE trending lineaments just to the south of Conrad Rise and not detected to the east of Cretaceous normal superchron signals. These results show that counter part of Mesozoic sequence magnetic anomalies in the south of Conrad Rise would be found in the East Enderby Basin, off East Antarctica. NNE-SSW trending magnetic structures, which are similar to those obtained just to the south of Conrad Rise, are found off East Antarctica in the East Enderby Basin. However, some of the strikes show almost E-W orientations.Moreover, the thickness of the crust increase just to the north of the Conrad Rise and clear magnetic anomaly signals considered to be magnetic anomaly C34 in this region may indicate continental-ocean boundaries while taking dredged continental origin rock samples at the Ob seamount into account. Therefore, magnetic anomaly C34 identified in the Indian Ocean must be reconsidered. These suggest complicated ridge reorganization occurred during initial breakup of Gondwana in the Indian Ocean.