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. 1. Variation diagram of the basic dike-rocks after NlGGU. granite. This can be also demonstrated by the ratios of K

2

0 to Na2Û and K

2

0 + Na

2

0 to CaO (Table 2). Table 2. The ratios K

2

0/Na

2

0 and K

2

0 + Na

2

0/CaO K

2

0/Na

s

O K

s

O + Na

2

0/CaO Sárhegy 0.72 1.44 Csala forest 0.77 3.29 Székesfehérvár quarry 0.98 3.99 Granite pophyry 1.23 11.12 Granite (BUDA 1969) 1.60 Hence we are concerned here with a series of rocks the most basic member of which, the Sárhegy dike-rock (composed essentially of plagioclase and hornblende with minor orthoclase, biotite and quartz) may at best regarded as a spessartite. It is not easy to account for the origin of the lamprophyres and the difficulties arise even more if we are faced with the problem of a rock series having a range of composition somewhere between the lamprophyres and granites. Probably mixing of basic and acid magmas seems to be the best explanation. Acid dike-rocks In contrast to what has been said about the basic dikes, acid dikes are very frequent in the Velence granite pluton. Essentially they can be qualified as aplites and granite porphyries. Both granite porphyries and aplites can be divided into two well-defined types : 1. granite porphyry of Pátka type 2. granite porphyry of Sukoró type 3. aplite of dilatation-injection type 4. aplite of replacement type The first type is characterized by the dominance of a fine-grained groundmass in which phenocrysts of plagioclase, quartz, orthoclase and biotite "swim".