Multiple episodes of volcanism in the Southern Austral Islands: Flexural constraints from bathymetry, seismic reflection, and gravity data

Abstract

At the southeastern end of the Cook-Austral Island chain, in the vicinity of the currently active Macdonald Seamount, multiple episodes of volcanism have left a diverse population of seamounts. Multichannel seismic reflection and shipboard gravity data provide observational constraints on the magnitude and wavelength of flexure, and multibeam bathymetry obtained by R/V Ewing and F/S Sonne within the study area provides full spatial coverage of all volcanic loads. Three-dimensional flexural modeling of closely spaced loads emplaced at discrete times, performed both with analytical models of idealized loads and with fourier domain solutions of the observed volcanic loads partitioned into the younger and older seamounts, is compared with seismic and gravity data. This modeling provides a more complete view of the volcanic history than radiometric dating and geochemical analysis of sparse dredge samples alone. Wide-angle seismic refraction data from ocean bottom hydrophones (OBHs) and expendable sonobuoys are also consistent with the flexural modeling results. Volume estimates of the different volcanic episodes show that one-half to two-thirds of the material added to the abyssal seafloor by midplate volcanic processes is due to older volcanism that erupted on young lithosphere, while the younger, higher seamounts contributed the remainder. Copyright 2004 by the American Geophysical Union.