Cryptic metasomatism in clino- and orthopyroxene in the upper mantle beneath the Pannonian region
Dobosi, G. and Jenner, G.A. and Embey-Isztin, A. and Downes, Hilary (2010) Cryptic metasomatism in clino- and orthopyroxene in the upper mantle beneath the Pannonian region. Geological Society, London, Special Publications 337 (1), pp. 177-194. ISSN 0305-8719.
Clino- and orthopyroxenes in anhydrous spinel peridotite xenoliths from Pliocene alkali basalts of the western Pannonian Basin have been analysed for trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Clinopyroxenes show highly variable mantle normalized REE (rare earth elements) patterns but basically can be classified into three major groups: LREE-depleted, LREE-enriched and U-shaped patterns. As the REE patterns of clinopyroxenes usually reflect the REE patterns of the host peridotite, the three major REE patterns define three geochemically different groups of xenoliths. LREE-depleted xenoliths generally have undeformed protogranular textures, while the more deformed xenoliths with porphyroclastic and equigranular textures have LREE-enriched trace element patterns. The U-shaped pattern is very distinctive and is generally associated with poikilitic textures. The HREE content of the clinopyroxenes suggest that most of the xenoliths experienced less than15% partial melting, with the lowest degree occurring in the LREE-depleted xenoliths, and the highest degree in LREE-enriched xenoliths. Cryptic metasomatism frequently accompanies deformation. Metasomatic enrichment of incompatible trace elements can be observed not only in clinopyroxenes but also in coexisting orthopyroxenes. The metasomatic agents were probably alkaline mafic melts of asthenospheric origin and some may relate to upper Cretaceous alkali lamprophyre magmatism. Geochemical signatures of subduction-related melts or fluids have not been found in the anhydrous LREE-enriched xenoliths, although poikilitic xenoliths with U-shaped normalized REE patterns may indicate the influence of subduction-related melts.
|School:||Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences|
|Date Deposited:||02 Dec 2011 13:49|
|Last Modified:||11 Oct 2016 11:59|
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