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

According to the different diagrams of the major element distribution, these basaltic rocks are represented by basanites, nepheline basalts, olivine basalts and basaltic andésites (Figs 2, 3, 4). Among these, the most widespread are the basaltic andésites, less widespread are the olivine basalts, basanites and nepheline basalts (PELTZ & al. 1972a, 1972b, 1973). Basalts of the Western Part of the Carpathian Basin The petrochemical features of these basalts can be studied by the total alkali-silica (TAS) as well as the differentiation index - solidification index (D.I. - S.I.) and the normative mineral indices (indicating the grade of undersaturation in the silica) - S.I. diagram (Figs 5, 6, 7). The differentiation index (D.I.) of THORNTON & TJTTLE (1960) is a sensitive indicator of the rate of differentiation but it also depends on the amount of partial melting of the parental peridotite.The higher the D.I. the more evolved the basalt should be considered, alternatively, small D.I. values are characteristic of undifferentiated rocks and or of those originated by high amounts of partial melting of the parental mantle material. Similarly, the solidification index (S.I.j KUNO 1960) is also a good measure for judging the rate of differentiation or that of partial melting. High values of S.I. indicate primitive rocks and/or important quantities of partial melting. As to the normative mineral indices used in Fig. 5, they are based on a nomenclature as given below: Quartz tholeiite: basalt with normative hypersthene and quartz; Olivine tholeiite

: basalt with normative hypersthene and olivine, hypersthene < 3 %. Olivine basalt: with normative olivine and with 0-3 % normative hypersthene, no normative nepheline; Alkali olivine basalt: with normative olivine and nepheline, nepheline < 5 %. Olivine basanite: basalt with normative olivine, nepheline and albite, nepheline > 5 %, albite < 2 %. Olivine nephelinite

: basalt-like composition with major normative olivine and nepheline, albite > 2 %, normative orthoclase and/or leuclte, no normative larnite. Olivine melilite nephelinite

: basalt-like composition with normative olivine, nepheline, leucite and larnite. Basalts of the Basin of Graz The volcanic rocks of Klöch

. Steinberg and Stradner Kogel have been throughly studied by POULTIDIS (1981) and high quality minor and major element analyses are available. The only absolute age data known to the authors were performed by BALOGH (unpublished measurements). According to these, the basalts of the Basin of Graz would be younger than those of Transdanubia (Klöch: 2.28Í0.22 m.y.; Steinberg: 2.20Î0.11 m.y.). In the TAS diagram (Fig. 7) they plot in the field of tephrite and basanite except for the rocks of Stradner Kogel that plot as foidites.Their most primitive rocks are those of Klöch

. However, they are fractionated to some

1 extent (normative olivine content is between 6.0-9.3 %, mg-value (lOOMg

/Mg+S

Fe) lies between 62.0-63.0). In addition, the Klöch basalts are nepheline-rich olivine basanites (see Fig. 5), and they could have been originated by a relatively small degree of partial melting of garnet peridotite at a considerable depth. The olivine basanites of Steinberg are extremely rich in normative nepheline, they have lower S.I. and higher D.I. values than the basalts of Klöch, therefore an even smaller degree of partial melting and/or a stronger fractionation should be assumed in their genesis. The lower normative olivine content (2.48-8.65 %) and mg-value (54.0-59.9) also stress this interpretation. The most under satu rated basalts of the whole Carpathian Basin are those of Stradner Kogel nephelinite and melilite nephelinites. Their mg-value is small (53.3-54.3). Because of their very high Ca/Mg ratios, all the Mg and Fe should be allotted to form diopside so there is no normative olivine in these rocks. This fact, coupled with the very low S.I. and very high D.I. values displayed by the rocks suggest that an important olivine fractionation must have taken place during the formation of these basalts. Of course, a very low percentage of partial melting must be assumed in this case. Basalts of Burgenland Three basaltic eruption centers are known in this area that have been studied pétrographie ally by POULTIDIS (1981). In addition, a great number of high quality,unpublished analyses have been per-