The geomorphic evolution of the Tasmantid Seamount Chain

Oceanic volcanoes develop distinct post-eruptive morphologies depending on the geomorphic conditions they experience. Submerged, truncated, flat-topped volcanoes, known as guyots, result from marine erosion and subsidence, whereas on reefs or carbonate-capped volcanoes, carbonate accretion veneers the summit. New and existing bathymetric data are utilised to identify different geomorphic forms of oceanic volcanoes in the Tasmantid Seamount Chain, a hotspot chain off the east coast of Australia, dated from ∼6 Ma in the south to >50 Ma in the north. Profiles and slope calculations across long and short axes provide morphometric values on the basis of which four morphologic forms are identified: seamount, guyot, modern reef, and carbonate-capped guyot. Volcanoes which erupted on oceanic lithosphere are estimated to have subsided at an average rate of 46.5 mMyr −1 , faster than the subsidence rate of volcanoes that erupted on continental lithosphere (33.0 mMyr −1 ). The guyots are estimated to have eroded at an average rate of 1.9 ± 0.5 kmMyr −1 . Substantial carbonate accretion has formed on the summits of eleven volcanoes, ranging in thickness from 1146 m in the north to 93 m in the south. The geomorphic evolution of the Tasmantid Seamount Chain, since the Oligocene, is synthesised into a conceptual model. This study finds that the post-eruptive morphology of each volcano in the chain is a product of the combined influence of the northward movement of the Australian Plate, erosion, subsidence, and carbonate accretion. • High-resolution bathymetry enables morphometric characterisation of Tasmantid seamounts. • Four morphological types of volcanoes are discriminated along the chain. • Processes involve plate movement, subsidence, erosion and carbonate accretion. • A conceptual model is proposed for the evolution of 21 volcanoes.