Eastern Australia - 4000 kilometres of mantle samples

In eastern Australia there is possibly the greatest concentration of xenolith localities in the world, only approached in extent by those from E China. Xenoliths described include those from nephelinites, basanites, mugearites and trachytes which were erupted through the Phanerozoic Tasman fold belt from 80 m.y. to Recent times. Thus, the xenoliths reflect the development of a large segment of mantle from the Mesozoic onwards. In addition to the classical suites, Cr-diopside (Type I) and Al-augite (Type II), Fe-rich Cr-diopside, composite xenolith and megacryst suites are dealt with. The Cr-diopside suites (usually spinel lherzolites) are samples of both unmetasomatized and metasomatized (with apatite and hydrous minerals) mantle wall-rock. The Al-augite suite is subdivided into three; the wehrlite series commonly shows cumulate textures, and in places spectacular fluid inclusions and vugs. The metapyroxenite series is interpreted to have formed by cooling of rocks of the wehrlite series within the mantle from igneous to ambient T. The amphibole/apatite series is considered to represent fractionation products of a magma enriched in incompatible elements. The Fe-rich Cr-diopside suite is compositionally intermediate between the Cr-diopside and Al-augite suites and appears to have resulted from interaction of lherzolite wall-rock with basaltic liquids. -J.M.H.School of Earth Sciences, Macquarie Univ., North Ryde, NSW 2113, Australia.