Geodynamic Conditions of Formation of the Modern Structure of the Andrew-Bain Transform Fault (South–West Indian Ocean): Experimental Modeling

The Andrew-Bain transform fault separates two parts of the Southwest Indian Ridge (Indian Ocean), different in their structure and evolution. It stands out among other transform faults by its complex structure, which includes troughs and areas of oblique extension. To identify the geodynamic conditions of formation of the modern structural pattern of the Andrew-Bain transform fault, experimental modeling was carried out, which reproduced the formation of the modern structure of the transform fault. In experiments, we obtained several strike-slip zones, which changed their position, and also were obtained overlapping strike-slip zones and extension axes, corresponding to the currently inactive area of the oblique extension of the transform fault eastern part. The main factors that determined the formation of the structural pattern of the fault zone are (i) the obliquity of the adjacent spreading segments relative to the spreading direction, and (ii) the initially specified lens-like shape of the transform domain. The formation of the lens-like shape was reproduced in a separate experimental series. It is assumed that the thermal influence of the Marion plume under transtension conditions could have led to local compression in the area of the northeastern edge of the transform fault. These conditions differ significantly from other similar examples, where the formation of a complex structural pattern occurred exceptionally under the influence of kinematic reorganization of the boundaries of lithospheric plates without a significant influence of thermal anomalies. The combined influence of these two factors and, as a consequence, the formation of the lens-shaped structure for the Andrew-Bain transform fault was possible in the period 52‒40 Ma ago during a change in the spreading direction on the Southwestern Indian Ridge, which coincided with the pulse of magmatic activity of the Marion plume.