Magnetic signature of three Oceanic Core Complexes at the Southwest Indian Ridge

Abstract:

Oceanic Core Complexes (OCC) are widespread along the ultraslow-spreading Southwest Indian Ridge (SWIR). However, OCCs observed in different segments show varying characters possibly reflecting irregular magma supply during different phases of their emplacement. We collected near-bottom magnetic and bathymetry data by using an Autonomous Underwater Vehicle (AUV) over three OCCs on the SWIR at 49.25, 49.65 and 51.75°E, respectively. The bathymetry suggests that these OCCs are at different stages of exhumation, with the one at 49.65°E in its initial phase with a steep detachment fault, not clear corrugated surface and few mantle rocks, whereas the one at 51.75°E is more mature with a flat detachment surface and more ultramafic rocks. These different stages are also reflected in magnetic anomalies, where reversed polarity seems to be present and low anomalies are dominant over the more mature OCCs. We are using suitable inversion method to obtain equivalent magnetization and Reduced-to-the-Pole (RTP) anomalies before proceeding with further interpretation. The standard operator for RTP in the Fourier domain cannot be readily applied, because the magnetic anomalies have been collected at uneven altitude, about 100 m above the seafloor. Any attempt to upward-continue them to an even datum plane would result in a loss of resolution and is therefore not considered. RTP is therefore achieved by forward modeling from the equivalent magnetization, assuming the same magnetic layer geometry used in the inversion and vertical magnetization and geomagnetic field vectors.