Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 72. (Budapest 1980)
Embey-Isztin, A.: Major element patterns in Hungarian basaltic rocks: an approach to determine their tectonic settings
ably a zeolitization, since according to MAURITZ (1913) the phonolites and intermediate rocks con- • tain a great amount of natrolite and analcite, both minerals being poor soda-zeolites 100 Mg:Mg+Fe 2+ (Mg-values) are generally too low except for the cumulative rocks, consequently even the most "primitive" basalts have been modified by olivine fractionation No xenoliths of peridotite was described from these rocks Po 2 of the crystallizing magma was probably high, leading to an early separation of iron ore, which is thought to be the first phase to separate on textural grounds (see MAURITZ 1913) Concluding the discussion we can say that evidence from the discriminant analysis as well as from different differentiation diagrams suggest that the basaltic members of the Mecsek alkaline series belong to the WPB-basalts. The high differentiation rate of this rock series is in sharp contrast with the non-differentiated young alkali basalts discussed in the preceding section. Analyses of diabases have been plotted on the discriminant function diagrams in Figs. 1 and 7. Both diagrams reveal that the analyses have clear OFB (ocean-floor basalt) affinities. The gabbros plot as within-plate basalts in Fig. 1 and island arc tholeiites (LKT) in Fig 7, and this inconsistency proves that the original constraints must be respected and the use of the discriminant diagrams should be restricted to lava rocks. The means and standard deviations of the eight oxides are given in Table 2. The low potassium content is remarkable and this is one of the characteristics of ocean-floor basalts. Since potassium has the highest score (+0.70) on the discriminant function F 2 , ocean-floor basalts plot on the lowest part of the diagram. Other chemical features however show certain differences between the Bükk diabases and average ocean-floor basalts. Notably the high MgO and CaO concentrations of oceanfloor basalts are contrasted with relatively low concentrations in the diabases. On the other hand, the diabases are higher in total Fe than are ocean-foor basalts. We may think that the Bükk diabases were modified by olivine and clinopyroxene fractionation. Mg-values are indeed rather small (52-61). The separated olivine and clinopyroxene crystals accumulated at lower levels of the igneous mass forming small peridotite bodies. Evidence for the presence of cumulative texture in the largest peridotite body was given by NOSKE-FAZEKAS & EMBEYISZTIN (1978). The calculated CIPW-norms (Table 3) show that we are dealing with a hy-ol rockDiabase-gabbro-opereridotite series of the Bükk Mts. Fig. 6. Na-K-Ca diagram. Symbols are the same as in Fig. 5
