Kostoula, Thomai; (2000) The petrography, mineralogy and geochemistry of a mantle xenolith suite from the carbonatitic and alkaline volcano Mt. Vulture, southern Italy. Masters thesis (M.Phil), UCL (University College London).

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Abstract

The Vulture peridotites represent mantle material comprised of olivine [plus-minus] orthopyroxene, clinopyroxene and spinel with similar composition to those from the 'typical spinel lherzolite'. Rare garnet is present. Lherzolites and wehrlites are the most common rock types. The Vulture peridotites show mantle metamorphic textures slightly modified by pyrometamorphic textures. The peridotites have been derived from the lower part of the spinel stability field in the upper mantle. They record variable degrees of partial melting and subsequent enrichment. The fertile peridotites are enriched in Ba, Th, U, LREE, and Sm, while the refractory peridotites in Ba, La and Sm. All of them are depleted in Nb, Ti and Ta. A few fertile peridotites are also enriched in Rb, K and Sr, consistent with their containing of modal phlogopite and alkali-rich silicate glass. The Sr- and Nd-isotopic ratios for clinopyroxene from the Vulture peridotites, the first isotopic data on mantle xenoliths from Italy, show a slight enrichment relative to the Bulk Earth and the European mantle peridotites. The Vulture peridotites are type IB xenoliths and only a single wehrlite belongs to type IA. They have an unmetasomatised signature resembling more closely the Ray Pic (Massif Central) enriched Iherzolites rather than metasomatised peridotites from world-wide and also show some similarity with garnet peridotites from South Africa. The mantle beneath Vulture is heterogeneous and OIB-like with isolated MORB-like mantle segments. It has had a complex evolution; a possible model could be the following: asthenospheric melts/fluids migrating upwards into a thinned lithosphere that has already experienced partial melting and also might have been affected by dehydration of subducted slab remnants before the tectonic setting changed to an extension-guided.

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