Merkl O. Szerk.: A Magyar Természettudományi Múzeum évkönyve 92. (Budapest 2000)
Embey-Isztin, A. ; Scharbert, H. G.: Glasses in peridotite xenoliths from the western Pannonian Basin
ANNALES HÏSTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Volume 92 Budapest, 2000 pp. 5-20. Glasses in peridotite xenoliths from the western Pannonian Basin A. EMBEY-ISZTIN' & fH. G. SCHARBERT 'Department of Mineralogy and Petrology, Hungarian Natural History Museum, Ludovika tér 2, H-1431 Budapest, Pf. 137, Hungary e-mail: embey@ludens.elte.hu 'Endemann Gasse 6-18 1238 Vienna, Austria EMBEY-ISZTIN, A. & SCHARBERT, H. G (2000): Glasses in peridotite xenoliths from the western Pannonian Basin. - Annls hist.-nat. Mus. natn. hung. 92: 5-20. Abstract - A few peridotite xenoliths originating from the alkali basaltic rocks of the western Pannonian Basin contain small amount of glasses. The composition of these glasses is highly enriched in alumina and alkalis, however, they have lower Mg and Fe abundances than typical alkali basalts of the region. It has been concluded that hydrous phases did not play an essential role in the formation of glasses. Mass balance requirements suggest, however, the involvement of metasomatic enrichment processes affecting mostly alkali elements. The partial melting process may have taken place at mantle depth as a consequence of the metasomatism. On the contrary, similar glass pockets occurring in lower crustal granulite xenoliths have been produced by the combined effect of sudden decompression and heating in rapidly ascending host lavas. With 9 figures and 4 tables. INTRODUCTION Several workers reported sporadic small-scale melting phenomena in mantle xenoliths from alkali basalts involving the formation of glass films along grain boundaries as well as discrete melt pockets (e.g. FREY & GREEN 1974, IRVING 1974, MCRAE 1979, STOSCH & SECK 1980, JONES et al. 1983). The melting has been widely ascribed to decompression effects and heating of the xenoliths during rapid ascent and eruption whereby the more fusible phases (amphibole, mica, pyroxene, spinel or garnet) disintegrate and melt. Following this interpretation, the melting process is secondary in nature, i.e. it is unrelated to processes in the mantle source regions of the xenoliths. However, JONES et al. (1983), SCHIANO et al. ( 1992) and IONOV et al. ( 1994) have proposed that the small-scale melting of man- 3