Three-phase tectonic evolution of the Andaman backarc basin

摘要

A three-phase evolutionary scheme since Late Oligocene for the Andaman backarc basin is proposed based on the multibeam swath bathymetry, magnetic and seismological data. A SW-NE trending spreading ridge bisects the basin. The tectonic evolution of the Andaman basin with special reference to the formation of oceanic crust within the backarc basin encompassing the backarc spreading, suggests a phase of ridge propagation. Swath bathymetry data documented topographic fabric of the ridge propagation and reveal several morphotectonic features that divide the basin into a complex western part comprising arc-parallel seamount chains, N-S trending fault systems and a relatively smooth eastern part. Spreading centre jump during Late Oligocene, rifting and extension during Middle Miocene to Early Pliocene followed by the recent true seafloor spreading since last 4 Ma define the three-phase tectonic evolution of the Andaman backarc basin. The recent phase has experienced westward propagation of the spreading centre. It is suggested that ridge propagation modulated the crust. A schematic evolutionary sequence of the Andaman backarc basin is presented.