Abstract

New seismic data from the Lake Bullen Merri area of southeastern Australia indicate strongly that there are no large differences between the depth to the crust-mantle boundary defined by petrological and geochemical parameters and the depth to the Moho defined by seismic methods, contrary to previous seminal work on crustal and upper-mantle xenoliths. These data are in agreement with interpretations from extensional basins on other continents where similar information is available. Under the northern margin of the Otway basin in southeastern Australia, the Moho depth of 31 km and the upper-mantle velocity of 7.8 km/s interpreted from seismic data are in good agreement with laboratory measurements reported by other workers on spinel Iherzolites in xenoliths from this same area; the laboratory data give an average P-wave velocity of 7.88 km/s at 1 GPa and 850 °C, the physical conditions thought to apply in the uppermost mantle at 30 km depth.

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