MOHO AND PETROLOGIC CRUST-MANTLE BOUNDARY COINCIDE UNDER SOUTHEASTERNAUSTRALIA

New seismic data from the Lake Bullen Merri area of southeastern Austr alia indicate strongly that there are no large differences between the depth to the crust-mantle boundary defined by petrological and geoche mical parameters and the depth to the Moho defined by seismic methods, contrary to previous seminal work on crustal and upper-mantle xenolit hs. These data are in agreement with interpretations from extensional basins on other continents where similar information is available. Und er the northern margin of the Otway basin in southeastern Australia, t he Moho depth of 31 km and the upper-mantle velocity of 7.8 km/s inter preted from seismic data are in good agreement with laboratory measure ments reported by other workers on spinel lherzolites in xenoliths fro m this same area; the laboratory data give an average P-wave velocity of 7.88 km/s at 1 GPa and 850-degrees-C, the physical conditions thoug ht to apply in the uppermost mantle at 30 km depth.