Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 12. 1985. (Budapest, 1985)

of good quality are also available (MAURITZ 1948). It seems now firmly established that the Badacsony olivine basanites, quite rich in normative nepheline, are chemically and minéralogie ally rather homogenous. Their D.I. and S.I. values indicate that these rocks are rather differentiated and they were probably originated by a restricted rate of partial fusion (Fig. 6). The normative olivine content varies between 9.68-12.55 % and the range of mg-value is very restricted (59.68-60.99) reflecting the homogenous nature of the basalt of Badacsony. Only two chemical analyses are available from the small basalt neck of Szigliget (EMBEYISZTIN & SCHARBERT, unpublished) according to which the rock would be an olivine basanite much poorer in normative nepheline (5.35 and 6.06 %) and richer in normative olivine (15.35 and 15.31 %) than the basalt of Badacsony. Their higher S.I. (36.0--35.

75) and mg-value (61.49 and 61.48) as well as their lower D.I. (35.95 and 37.01) clearly show that they are less differentiated. Also less differentiated, though only slightly, are the olivine basanites of Gulâcs

. The normative nepheline content varies between 6.05 and 10.74, olivine content between 9.91 and 11.07 % (EMBEY-ISZTIN & SCHARBERT, unpublished). The S.I., D.I. and mg-values are as follows: 32.9934.45, 40.59-42.57 and 60.03-61.11, respectively. The basalts of Szentgyörgyhegy (2.87±0.34 m.y., BALOGH 1984) seem to represent an exception among the basaltic rocks of the Balaton Highland in that they are markedly less undersaturated in silica (EMBEY-ISZTIN & SCHARBERT, unpublished). A part of them, the olivine tholeiites, have normative hypersthene (up to 8.94 %) and the more undersaturated rocks carry only restricted amounts of normative nepheline, falling therefore in the field of alkali olivine basalts. The maximum content of normative olivine in these latter rocks is 14.50 %, mg-value varies between 59.75-60.97. S.I. between 33.04-35.71, D.I. between 38.25 and 44.86 attesting that these rocks are also differentiated. The basalts of Halyagoshegy (3.94Í0.26 m.y., BALOGH 1984), near the village of Diszel have recently been studied and an important number of analyses have been performed (EMBEY-ISZTIN & SCHARBERT, unpublished). A few of the rocks studied, plot In the alkali olivine basalt field of Fig. 5, but most of them are olivine basanites with a considerable amount of normative nepheline (up to 13.33 %). The mg-value and S.I. are relatively higher: 60.65-63.32 and 34.01-37.89, as well as the normative olivine content (up to 17.89 %) indicating that the basalt of Diszel is the least differentiated one in the basaltic area of the Balaton Highland. Good outcrops and quarries are lacking in a number of volcanoes of the Balaton Highland and from these a very restricted number of analyses are available (MAURITZ 1948, JUGOVICS 1976). On the basis of the analyses only uncertain conclusions can be made. Hence, the rock of Tótihegy is probably an alkali olivine basalt or a nepheline poor olivine basanite. Similarly, the large basalt area of Királykö-Boncostető-Feketehegy may probably be composed of not too undersaturated basalts. The basalts of the Southern Bakony In this area small isolated volcanoes, e.g. Haláp and Hegyesd as well as large lava flows, e.g. Agárteto and Kabhegy, are known. Recent chemical analyses (EMBEY-ISZTIN & SCHARBERT, unpublished) have revealed that two kinds of basalt are present in the Haláp (2.94±0.34 m.y.); a silica-rich, Mg-poor variety that is slightly nepheline normative (alkali olivine basalt) or hypersthene normative (olivine tholeiite) and a silica-poor and Mg-rich basanite that is moderately enriched in normative olivine content (about 10-15 %, mg-value between 61.0-62.2). Sufficient petrochemical data are now available from the basalt of Hegyesd which is the smallest volcano of the Carpathian Basin (EMBEY-ISZTIN & SCHARBERT, unpublished). Most of the samples analysed yielded normative nepheline content: 0-5 % (alkali olivine basalt) but some fall into the field of olivine basanite. The normative olivine content and mg-value are between 8-11 % and 58.9-62.0, respectively, while S.I. varies between 32.45-35.33 and D.I. between 38.20-39.74. Both the new analyses (EMBEY-ISZTIN & SCHARBERT, unpublished) and the old ones published by JUGOVICS (1976) show that the basalt of Bondoróhegy is unusually rich in MgO. This rock is an olivine basanite with considerable amounts of normative nepheline (12-14 %) and huge quantities of normative olivine (up to 26.32 %). The mg-value and S.I. are consequently very high, up to 72.85 and 47.26, respectively. However, the value of D.I. is relatively high (Fig. 6). It seems probable that the high concentration of MgO is a consequence of contamination by harzburgite and lherzolite nodules that are unusually frequent in the basalt of Bondoróhegy (EMBEY-ISZTIN 1978). Nevertheless, the basaltic magma was probably primitive, since basalts carrying large amounts of mantle xenoliths had no time to differentiate.