Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 66. (Budapest 1974)
Embey-Isztin, A.: Petrochemistry of the dike-rocks in the Velence Hills (Hungary)
Fig. 3. Variation diagram of the acid dike-rocks after NIGGLI. region. The controlling factors are the shape and size of the magmatic body, composition, temperature gradient, etc. Differentiation of granitic magma in the light of petrochemical evidences In order to show the conditions of differentiation a variation diagram after NIGGLI (Fig. 3) and a differentiation index (DI), oxide percentage diagram proposed by THORNTON & TTJTTLE (1960), have been prepared (Figs. 4a, 4b). In both diagrams it is revealed that the two types of granite porphyry have greater basicity as compared with the granite, that is they have a lower value of DI and si. The oxides vary regularly with the exception of CaO, so the value of c decreases with decreasing si. On the other hand, both types of aplite have much lower basicity, that is a higher value of DI. The. ratio of potash to soda varies characteristically (Table 3). Table 3. The ratio of K 2 0/Na 2 0 and K 2 0 + Na 2 0/CaO K 2 0/Na 2 0 K 2 0 + Na 2 0/ CaO granite (GOKHALE 1965) granite pophyry (Sukoro type) granite porphyry (Pátka type) aplite (dilatation-injection type) aplite (replacement type) 1.80 1.45 1.02 2.81 1.62 10.57 11.46 10.79 32.87 19.74 In comparison with the granite K20/Na20 decreases in granite porphyries but it considerably increases in aplites of dilatation-injection type, whereas it does not change much in aplites of replacement type. It is obvious therefore that the two types of aplite differ from each other not only in structural and mineralogical features, but in chemical composition too (Table 4). This is apparent if we regard the ratio K 2 0 +Na 2 0/CaO or if we plot the Sr+Ba in ppm. against K 2 0/Na 2 0 (Fig. 5). In this diagram the rock types form separate groups which can be accounted for as follows: aplites of dilatation-injection type have greater values of K 2 0/Na 2 0
