Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 57. (Budapest 1965)

Csalogovits, I. J.: Geological and petrological conditions of the Szanda - Bercel area

bottles sealed with glass plugs for making possible the investigation of changes in water content (transvaporization) appearing along the contact surface. The samples were subjected to the measuring of drying (at 105 C°) and heating (1000 C°) losses, chemical analysis, differential-thermal tests, and microscopical examination. The values of water content as calculated at distances from the contact surface (sediment — the magmatic side) are shown in Table I. It was found that the differential-thermal test revealed montmorillonite contents in the rocks of the area and few ferrichydroxidic minerals : moving away from the contact, continuously and rapidly decreasinglimonitization was noted up to 3.6 m in the andésite under the microscope. The maximum of heating loss was noted in andésite at 60 cm: at 3.6 m this value was 1.6 times below the average water content of andésite. Practically it may be presumed that the water content of andésite in a band of 0.60—1 m thickness along the contact is 3.96 times higher if compared to fresh rock. It should be noted however that at pulverization — which is necessary for the analyses — the heat effect and the presence of adsorption water from the air in case of overpulverization influence the results and may cause considerable errors in case of material quantities ranging from 0.5 to 4%. The endocontacts of the vulcanites occurring here show no considerable chemical, mineral or textural changes. No increase in the degree of crystallization — resulting from a decrease in viscosity that is caused by presumable water intake — can be shown here as concerns texture: Unionization showing on the edges of mineral components, the plagioclase porphyries surrounded by Iimonitic aureoles, with their abovementioned crushed structure and inclusion characteristics, can all clearly be qualified as intratelluric minerals already crystallized at the time the contact was formed. Slight limonization elicited by transvaporization processes affected these on the edges only. The thickness of the belt affected by contact processes is negligible on the andésite side beyond 1 m and lies within the limits of analysis errors. Post-magmatic formations Dealing with the post-magmatic formations described in the Cserhát area, NOSZKY mentions occasional slight traces of chalcedony and opal. In the course of petrologicai examinations we have found in the andésites (especially in those of Mt. Bercel) decomposition in several places: their character and intensity, especially in case of samples taken from the interior of the andésite mass, cannot be explained as the effect of metavulcanitic phenomena. Later on it was possible to detect in the area several hydrothermal veins that were considerable as to thickness. Hydrothermal formations occur in belts that are under heavy tectonic stress and whose trend is in most cases identical with that of the main structural trends. The trend of these structural lines goes NNE — SSW, and is nearly vertical to the trend of the three vulcanite units which are separated from one another: it can be traced along the trend in each of them. If we follow the trend of the veins between Mt. Szanda and Mt. Bercel, and between Mt. Bercel and Istenhegy, they are absent from the Chattian country rock everywhere, but if we proceed along the trend they reappear in andésite. The cause of this phenomenon is that the rock-mechanical manifestations of the structural line are different in the two formations (this