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

terrestrial (rocky) planets, but also in the interior of those bodies. It is well known that the proportion of olivine in the upper mantle peridotites of the Earth is generally greater than 50 per cent. Olivine should also be a major constituent in the mantles of other terrestrial planets, moreover, its stability field may encompass greater depths compered to the Earth, because of the lower ambient pressures in the interior of these bodies, due to their smaller size. In a number of regions (Nógrád county, Central Range, Little Hungarian Plain, Burgenland and Graz Basin), in the western and northern part of the Pannonian Basin (Fig. 1), alkali basaltic lavas (olivine tholeiites, alkali basalts, basanites and nephelinites) as well as tuffs erupted from the late Miocene to Pleistocene times (for details see EMBEY-ISZTIN & SCHARBERT 1981, EMBEY-ISZTLN et al. 1993, EMBEY-ISZTIN & DOBOSI 1995, DOBOSI 1989, DOBOSI et al. 1991, 1995). The basaltic magmas originated by partial melting of an ascending mantle diapir below the basin area, and at some localities they brought olivine-rich mantle-derived peridotite xenoliths onto the surface (EMBEY-ISZTIN et al. 1989, KURAT et al. 1991, DOWNES et al 1992, SZABÓ et al. 1995, DOBOSI et al. 1999, EMBEY-ISZTIN et al 2001). Fig. 1. Geological sketch map of the western and northern part of the Pannonian Basin showing alkali basalt occurrences (black spots). LHP = Little Hungarian Plain. Modified after DOBOSI et al. (1999)