PETROLOGY AND GEOCHEMISTRY OF SPINEL PERIDOTITE XENOLITHS FROM THE WESTERN PANNONIAN BASIN (HUNGARY) - EVIDENCE FOR AN ASSOCIATION BETWEEN ENRICHMENT AND TEXTURE IN THE UPPER MANTLE

Twenty spinel peridotite xenoliths from Pliocene alkali basaltic tuffs and lavas of the western Pannonian Basin (Hungary) have been analysed for bulk rock major and trace elements, electron probe mineral compositions, and REE and Sr, Nd isotopes on separated and leached clinopyroxenes. The xenoliths are texturally diverse, including protogranular, porphyroclastic, equigranular and poikilitic textures which can generally be correlated with geochemical features. Protogranular xenoliths are relatively undepleted in Ca, Al, Ti and Na, whereas poikilitic xenoliths are more refractory. LREE-depleted patterns and MORB-like espilon(Nd) and epsilon(Sr) values are associated with protogranular peridotites. In contrast, xenoliths with complex textures are generally LREE-enriched. Much of the isotopic variation in the suite (epsilon(Sr) = - 20.4 to +10.4, epsilon(Nd) = +1.8 to +13.7) can be related to interaction between protogranular mantle and melts resembling the host alkali basalts, but a third (high epsilon(Sr) component may be due to Miocene subduction beneath the region.