Dampier Ridge, Tasman Sea, as a stranded continental fragment∗

A more comprehensive version of Table 1 is a Supplementary Paper, lodged with the National Library of Australia (Manuscript Section); copies may be obtained from the Business Manager, Geological Society of Australia.

Dredging of the Dampier Ridge recovered small fragments of granite, gabbro and sandstone. Dating of the igneous samples by the U‐Pb, K‐Ar and Rb‐Sr methods yielded precise ages mainly in the range 250 to 270 Ma, mid‐Permian. An imprecise Sm‐Nd mineral age of ∼ 310 Ma might reflect slightly earlier emplacement of the gabbro. A granitic fragment has a composition approximating that of a minimum melt. Taken together with the Late Palaeozoic emplacement ages and other geochemical and geophysical data, the evidence strongly supports the conclusion that the Dampier Ridge is a continental fragment, formerly part of eastern Australia, with its present location a consequence of continental rifting and opening of the Tasman Basin by sea‐floor spreading.

Key words:

• Dampier Ridge
• geochemistry
• geochronology
• isotopic dating
• magmatism
• Tasman Basin

Notes

A more comprehensive version of Table 1 is a Supplementary Paper, lodged with the National Library of Australia (Manuscript Section); copies may be obtained from the Business Manager, Geological Society of Australia.

Present address: Department of Geology, University of Dar‐es‐Salaam, Dar‐es‐Salaam, Tanzania.