Hot spot activity and tectonic settings near Amsterdam-St. Paul plateau (Indian Ocean)

Abstract : The Amsterdam-St. Paul (ASP) plateau is located in the central part of the Indian Ocean and results from the interaction between the ASP hot spot and the Southeast Indian Ridge (SEIR). It is located near the diffuse boundary between the Capricorn and Australian plates. The seamount chain of the Dead Poets (CDP) is northeast of the ASP plateau and may represent older volcanism related to the ASP hot spot; this chain consists of two groups of seamounts: (1) large flat‐topped seamounts formed 8-10 Ma and (2) smaller conical seamounts formed during the last 2 Myr. The ASP hot spot has produced two pulses of magmatism that have been ponded under the ASP plateau and erupted along the divergent boundary between the Capricorn and Australian plates. The N65° orientation of the CDP as well as the seamount's elongated shapes support an opening motion between the Capricorn and Australian plates along a suture oriented in the N155° direction. This motion compared to the Antarctic plate amounts to an apparent velocity of 7.7 cm/yr northeastward for the Capricorn‐Australian block. This motion does not fit with a fixed plume model. We suggest, therefore, that the ASP plume experienced a motion of about 1-2 cm/yr to the SW, which is opposite to the asthenospheric flow in this region and suggests a deep‐seated plume.