Hot and cold zones of the Southeast Indian Ridge and their influence on the peculiarities of its structure and magmatism (Numerical and Physical Modelling)

Abstract

The paper describes the specific features of the bottom topography and morphostructural segmentation along the strike of the Southeast Indian Ridge (SEIR) and in the zones of influence of the Amsterdam–St. Paul hot spot and the anomalous zone of the relatively cold mantle in the area of the Australian–Antarctic discordance. Numerical estimates of changes of thermal state and strength of the crust in axial and off-axial zones of the SEIR were performed. Сorrelation between the thermal–rheological settings in the axial zone of the ridge with the seabed topography and the morphostructural segmentation and magmatism has been established. The numerical modelling results make it possible to assume the presence of along-axis asthenospheric flows under the axial zone of the SEIR. One of them, which was initiated by the Amsterdam–St. Paul point and the Kerguelen plume, is oriented from west to east, and the second, located east of the Australian–Antarctic discordance, is oriented from east to west. Taking into account the numerical modelling results of the thermal regime and the change in thickness of the brittle layer of the axial lithosphere, we performed a physical modelling of the influence of temperature anomalies in the mantle on the peculiarities of crustal deformation in the axial zones of the ridge. The experimental modelling showed that the presence of a thermal anomaly in the sublithosphere mantle in the form of a local heat source (hot spot) will noticeably influence the geometry of the rift axis and its position in relation to the hot spot. An area of anomalous topography forms under the influence of the hot spot, traces of which are preserved in the off-axis spreading flank zones, as in the case of the Amsterdam–St. Paul hot spot. More contrasting and dissected topography forms in zones with a relatively low typical mantle temperature in the process of crustal accretion.