Interaction of thin-skinned detached faults and basement-involved strike-slip faults on a transform margin: the Moattama Basin, Myanmar

Abstract

Abstract The Sagaing Fault (SF), one of the world's most active strike-slip faults, defines a plate boundary on the eastern West Burma Block margin, from the Andaman Spreading centre, northwards for >1600 km to the eastern Himalayas. In the Northern Andaman Sea the SF traverses the Late Miocene–Recent Moattama Basin. There, 2D and 3D seismic reflection data show highly unusual fault patterns, that overall resemble a giant (area >33 000 km 2 ) horsetail structure. A horsetail pattern typically implies loss of displacement at a fault tip, which is potentially incompatible with the SF forming a transform margin. In the thinner, northern part of the Late Miocene–Recent basin three branches of the SF can be identified. These become lost in the thickest (>7 km), central part of the basin, and two branches emerge to the south where the basin thins. The fault patterns are interpreted to represent a previously unknown interaction of thin- and thick-skinned styles, where relatively shallow detached structures and sediment loading have interacted with basement-involved strike-slip faults that form a releasing bend geometry at the basement level. The Moattama Basin demonstrates how very thick sedimentary basins can produce fault patterns that differ from classic structural models.