Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 99. (Budapest 2007)

Embey-Isztin, A. ; Dobosi, G.: Composition of olivines in the young alkali basalts and their peridotite xenoliths from the Pannonian Basin

textures, and these are mainly responsible for the low degree of correlation in Fig. 12. The Ca content of olivines, and hence the equilibrium temperatures are also texture dependent (Fig. 13). Olivines in xenoliths having undeformed protogranular and poikilitic textures show higher Ca than their deformed equigranular and mosaic equivalents. As the increase of pressure and temperature is intimately linked in the interior of Earth, the range of 400 °C shown by our xenoliths indicate that the shallowest samples come from a depth of about 25-30 km (10 > kbar pressure) and the deepest ones were equilibrated at a depth of about 70 km (20 kbar). Since the lithosphère is thin below the region, it is possible that our xenoliths encompass the whole thickness of the lithosphère. The alkali basalts of the Pannonian Basin have been formed by partial melting in the ascending astenosphere. The degree of partial melting varied from a few per cent to about 15% bringing about a spectrum of lava rocks from the highly silica undersaturated nephelinites (low degree of partial melting) to the olivine tholeiites (high degree of melting) through basanites and alkali basalts (EMBEY-ISZTIN et al. 1993). The majority of basalt lavas are slightly differentiated, but a few primitive rocks, having Mg-values of 67-68 have been identified. Fig. 13. Variation of the CaO content of olivines with the temperature of equilibration. After EMBEY-ISZTIN et al. (2001), slightly modified by DOBOSI (2003)