| Summary: | The Tasman Sea and the southeastern Indian Ocean are situated at the interface between the Indian and Pacific oceans mantle domains. Even though the present location of the boundary between these two reservoirs at the Australian Antarctic Discordance (AAD) is well constrained by geochemical data, its dynamic behaviour is less well understood. Here, we investigate the relationship between volcanism in and south of the Tasman Sea, absolute plate motion, spreading asymmetries and microcontinent formation. We test three hypotheses: since 90 Ma, the upper mantle east of the AAD and west of the Macquarie Triple Junction was attached to 1) the Indian-Atlantic hotspot reference frame, 2) the Pacific hotspot reference frame 3) to the Pacific hotspots from 90 to 40 Ma, and subsequently to the Atlantic-Indian hotspots, due to partial separation of the two mantle domains by subducting slabs. We find that hostspot tracks in this area are best modeled using a Pacific hotspot reference frame, confirming hypothesis (2). If a hotspot is now located close to the Balleny Islands, it could not have produced the Tasmanian seamount chain irrespective of which reference fame is chosen, contrary to previous suggestions. Seafloor spreading asymmetries and microcontinent formation in the Tasman Sea are best accounted for by plume-ridge interactions, rather than the absolute motion of the spreading ridge relative to the mantle. The short-lived nature of most hotspot volcanism in this area, as well as its geochemistry, points to a paleo-superswell in the upper mantle as its source, rather than deep seated plumes, with the exception of the Tasmantid seamounts.
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