Dr. Nagy I. Zoltán szerk.: Fragmenta Mineralogica Et Palaentologica 6. 1975. (Budapest, 1975)
Another striking phenomenon in the fine-grained aplite is the relict structure. Large relict crystals of biotite or potash feldspar are not at all rare. Evidences in favor of a submagmatic, metasomatic replacement of feldspar by quartz in the fine-grained aplites were given earlier (EMBEY-ISZTIN 1973). In cotrast, the porphyry aplite and the granite porphyry clearly indicates a high temperature of crystallization e.g. quartz dihexaedra, magmatic resorption etc. All the above mentioned field evidences and textures features speak for a dilatation-injection emplacement of the granite porphyry and porphyry aplite, while in the case of fine-grained aplite a replacement origin seems much more probable. The same conclusion may be drawn from the investigation of the degree of order in feldspars. As a matter of fact potash feldspars of all the acid dike-rock types optically show monoclinic symmetry, but it is the potash feldspar of the fine-grained aplite which proved the greatest triclinicity . The values of optic axial angle show the greatest spreding again in the case of these feldspars. In the case of the potash feldspars of the granite porphyry and porphyry aplite the spreading is slighter and the smaller axial angle can be found in the porphyry aplite . In accordance with this, the plagioclase in the porphyry aplite represents the high temperature form and the spherulitic matrix suggests an earlier vitreous state. In the other rock types the plagioclase is invariably the low temperature form. According to earlier investigations (EMBEY-ISZTIN 1974) the two kind of aplite show constant chemical diffei-ences as well. First of all the alkali content has to be mentioned, but there are differences also in the minor elements especially in the case of Ba and Sr. It can be argued that the chemical differences are due to and in accordance with the twofold genetic hystory of the fine-grained and the porphyry aplite as outlined in this paper. IRODALOM - REFERENCES BARTH, T. F. W. (1952): Theoretical petrology . - New York - London (1-387). BUDA, Gy. (1969): Genesis of the granitoid rocks of the Mecsek and Velence Mountains on the basis of the investigation of the feldspars. - Acta Geol. Ac. Sei. Hung., 13 (131-155). BUDDINGTON, A. F. (1959): Granite emplacement with special reference to North America. -Bull. Geol. Soc. Am., 70 (671-748). BURRY, C. PARKER, L. R. - WENK, E. (1967): Die optische Orientierung der Piagioklase. - Basel, pp. 334. DERRY, D. R. (1931): The genetic relationship of pegmatites, aplite s and tin veins. Geol. Mag., 68 (454-475). DRESCHER-KADEN, F. K. (1969): Granitprobleme. - Akademie Berlin, pp. 586. EMBEY-ISZTIN, A. (1972): A study of lamprophyric dike rocks of the Velence Hills (Hungary), - Fragm. Min. Pal., 3 (5-24). EMBEY-ISZTIN, A. (1973): On the problem of graphic intergrowth and normal granitic structure. - Ann. Hist.-nat. Mus. Nat. Hung., 65 (19-29).
