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

The volcano of Kabhegy (4.39-5.23 m.y., BALOGH 1984) yielded the largest volume of basalt in Hungary. However, good outcrops are lacking and the basalt is exposed only in an old quarry (Tormarét)

, so it is difficult to obtain fresh samples. Samples originating from the Tormarét quarry have only recently been analysed (EMBEY-ISZTIN& SCHARBERT, unpublished) and in addition, a very restricted number of analyses was published from the area of Kabhegy by MAURITZ (1948) and JUGOVICS (1976). It can be deduced from the available data that the Kabhegy basalt is tholeiitic in character. Nepheline, if it is present in some samples, does not reach the amount of 1 %. The olivine tholeiites and olivine basalts are differentiated rocks with low mg-values (57.6-59-1) (Figs 5 and 6). The data indicate that the Kabhegy basalt was originated probably by a higher amount of partial melting. Analyses published by JUGOVICS (1976) indicate that the rock of Doboshegy

, part of the second largest basalt flow (Agârteto) is similar to the Kabhegy lavas, i.e. it is also hypersthene normative (olivine tholeiite, mg-value: 55-63). Basalts of the Nógrád region (North Hungary

) A considerable number of recent analyses (EMBEY-ISZTIN & SCHARBERT, unpublished) from the basalt of Medves clearly show that these rocks are strongly differentiated. However, the large volume of the Medves lava flow is not homogenous, samples originating from the quarry of Magyarbánya (2.76Í0.34 m.y., BALOGH 1984) indicate an extremely high rate of differentiation as opposed to the basalt of the quarry of Eresztvény (2.59±0.65 m.y., BALOGH 1984). So the D.I. can be as high as 51.57 in the basalt of Magyarbánya while the maximum value of D.I. is 44.7 in the case of Eresztvény. The rock of Magyarbánya (olivine basanite) is very rich in normative nepheline (19-22%) but poor in normative olivine (6-10 %) with mg-value as low as 56.4-58.0. The olivine basanite of Eresztvény is poorer in normative nepheline (11-18 %) but not richer in olivine (7-8 %). The mgvalue is 58-60. Only a very few analyses are available from the smaller basaltic occurrences in the Nógrád area, according to which the basalts of Somoskö, Korlát, Kissalgó and Ragacs would also be highly differentiated nepheline-rich olivine basanites, while the basalts of Kővár and Péc s ko seem to be less undersaturated alkali olivine basalts. The basalt of Bár (South Hungary

) (2.17Î0.17 m.y., BALOGH 1984). A peculiar basalt-like rock was described by VICZIAN (1965). The samples originated from boulders. Later on a small basic body was discovered by deep drilling at shallow depth and this material was analysed by SZEDERKÉNYI (1980). The rocks are unusually rich in alkali, especially in potassium (KgO up to 8.2 %). They occupy quite a distinct position in the field of tephrophonolite of the TAS-diagram (Fig. 7). The Si0

2 content is too high (48-50 %) for an alkali-rich basalt, Fe

2

03/FeO and H2O contents are also high and the pétrographieal description suggests that these rocks may be altered. If so, the determination of absolute age may be of questionable value. We also think that a secondary process such as potash metasomatism may have been responsible for the enrichment of potassium. In spite of the very high KgO concentration, the rocks do not have leucite in their norms because of the high SÍO2 content and partly owing to the high ratio of Fe20g/FeO. So, the rocks should be classified as orthoclase-rich olivine basanites (nepheline: 411 %; albite: 4-33 %; olivine: 9-15 % and orthoclase: 26-50 %). Basalts of Banska Stiavnica (Selmecbánya) area (8.29± 0.65 m.y., BALOGH 1984) Small basaltic bodies are closely associated with huge volumes of andesitic rocks. The analyses referred to here were taken from the data collection of POKA (1981), (FIALA 1962, F ORG AO & KUPCO 1974). In the TAS-diagram they plot far away from the field of alkali basalts (high Si0

2 and low total alkali content). They are strongly hypersthene normative olivine tholeiites and partly quartz tholeiites with mg-values between 54-64. These basalts clearly belong to the calc-alkaline volcanic series of the Intra-Carpathian Mountain Range. Basalts of Sárospatak (Tokaj Mts

) Also situated in a calc-alkaline andesitic environment, the deep drilling near the town of Sárospatak showed the existence of a basaltic body (GYARMATI 1977). The rocks are 9.4Í0.5 m.y. old (BALOGH 1984). Nevertheless, the analyses yielded poor totals probably because of secondary alteration that can seriously affect age determination. In spite of this, it can be safely stated that the basalts of Sárospatak are somewhat more undersaturated rocks than the basalts of the Banska Stiavnica area. Some of them are olivine tholeiites, medium-rich in normative hypersthene, while