Topographical Characteristics of Seafloor Spreading and Ocean Core Complexes (OCCs) at the Middle Part of the Central Indian Ridge

Abstract

The middle portion of the Central Indian Ridge (MCIR) is located between 8°S and 18°S and consists of six first order segments that are offset by transform faults. The ocean core complexes (OCCs) occur at nearly all segment ends. OCC is an exposed mantle rocks uplifted through long-lived detachment fault processes which can also lead to extensive hydrothermal circulation. We analyzed seafloor morphology of OCCs in MCIR using high-resolution bathymetry and backscattered data recorded on the Deep-Tow Side-Scan Sonar system (IMI-30 and IMI-120, UH). Because new oceanic crust generated by spreading center has a complex morphology, we calculated the slope-gradient variations from the high-resolution bathymetry to examine the topographic change near the spreading zone. In slopes greater than 30° areas, the normal faults including the detachment faults were observed generally with high backscattered intensities that reflect more topographic effects than acoustic medium variation, while the gentle slopes less than 10° areas tend to show the relative low backscatter intensities reflecting the acoustic medium variation. To estimate the initial angle of the OCC detachments, we reveal the outward and inward dips of a breakaway zone and show 60° of initial dip, suggesting that the detachment faults exposing the OCCs are initiated with high-angle normal faults. In order to examine the changes in magma supply of OCC in MCIR, we calculated map-view M factor (MVM), which is defined as the fraction of total seafloor spreading accommodated by magma accretion, using the slope-gradient and down-slope direction variations. Currently, we are preparing to compare the MVM with other geophysical anomalies (e.g. gravity anomaly and magnetic anomaly). Although further study on the MVM should be carried out, other results provide that the topographical characteristics of seafloor spreading and OCC structures. Thus, we expect that the combination of the results (after M factor study) indicates a strong link among cold mantle sources, limited magma supply, and development of OCCs in MCIR.