Basic and Ultrabasic Xenoliths from Volcanic Rocks of New South Wales

Basic and ultrabasic xenoliths found in Tertiary basaltic and lamprophyric volcanic rocks from New South Wales are predominantly peridotites, but mineralogical gradations between these and associated pyroxenites and gabbros also occur. The xenoliths are unstable in their host rocks and show marked marginal reactions. Evidence of xenocrystal material derived from such xenoliths has been observed in 40 per cent of other basaltic rocks in the New South Wales Tertiary volcanic province. A review of evidence from New South Wales and that available in the literature favours the hypothesis that such xenoliths represent portions of the earth's mantle incorporated in magmas originating from within that zone. Analyses of xenoliths and host rocks, and seven new analyses of clinopyroxenes from xenoliths are presented.