Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 66. (Budapest 1974)
Embey-Isztin, A.: Petrochemistry of the dike-rocks in the Velence Hills (Hungary)
Table 5. The ratio Or /Ab + An in aplites of dilatation-injection type Or : Ab + An Ördöghegy I. Mélyszeg I. Ráchegy I. Mélyszeg II. Pákozd W Gécsihegy Szöllőhegy Kisfalud Ráchegy II. Mélyszeg III. Tomposhegy Ördöghegy II. 63 37 92 8 75 25 66 34 61 39 69 31 63 37 57 43 62 38 60 40 64 36 60 40 Table 6. Normative mineral composition of the acid dike-rocks Granite Granite porphyry (Sukoro type Granite porphyry (Pátka type) Aplite (dilatation-injection type) Aplite (replacement type) Q 35 28 26 42 38 Or 30 28 25 34 30 Ab 24 29 35 17 27 An 4 2 3 1 2 total 93 87 89 94 97 more Or and Q, less Ab in respect to the ferner eutectic composition. Considering the experimental work on the system NaAlSigOs-KAlSigOs-H^O at 500 bars by TUTTLE & BOWEN (1958), it seems reasonable to deduce that crystallization started with a potassium-rich feldspar that was followed by a more sodium-rich phase. Similarly SAVOLAHTI (1956) thinks that in potassium-rich rapakivi granites potash feldspar was first to crystallize and sodium-rich feldspar and mafic minerals developed at some later stage. The early crystallization of potash feldspar in the Velence granite have been recorded by GOKHALE (1965). Additional results have been given by BTJDA (1969). Using the method of BARTH'S two feldspar geothermometer he found 600 °C for the temperature of origin of orthoclase and only 520 °C for that of plagioclase. Now, if we take into consideration all these facts, as well as the normative composition of the dike-rocks, and the results of experimental work, we can establish that the differentiation of granitic magma in the Velence pluton may have at least some analogous features to that of rapakivi granites. In both cases a more sodic and basic differentiate has been generated. The analogies may be the result of similarities in the physico-chemichal conditions. Since the latter one depends on the geological environment, we may think that geological circumstances have been also similar. Indeed the emplacement of the Velence granite like that of rapakivi granites has been thought to have taken place in peaceful conditions in the postkinematic stage.
