Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 13. 1987. (Budapest, 1987)
tablished the following genetic model: 1) amphibolite facies regional metamorphism and synkinematic granitoid formation from the Proterozoic sequences; 2) local greenschist facies retrograde metamorphism, mylonitization; 3) prograde greenschist facies metamorphism of the Paleozoic rocks, metasomatism, late-kinematic granites in the polymetamorphic sequences. METHODS In addition to the macroscopic and light-microscopic (textural, mineral paragenetic) investigations of the core samples, the following methods were used: - X-ray diffractometric studies aimed the determination and refinement of the mineral composition. The X-ray work was done with help of a Philips PW- 1730 type diffractometer with CuK^radiation, 45 kV/35 mA, proportional counter, graphite monochromator, divergency and detector slits: 1°, goniometer speed: 1/2°/min and 2°/min, time constant of 2 sec, and paper speed of 2 cm/ min; - bulk chemical analyses of rock samples (made by J. LEFLER and Gy. HANGYÁS) by a Carl Zeiss AAS1M type atomic absorption spectrophotometer, combined with the traditional gravimetric, photometric, and chromatographic methods; - determination of chemical composition and its variations (zoning) in rock forming and accessory minerals by means of a JEOL Superprobe733, using the JEOL-ZAF program for corrections. The electron probe investigations were carried out by Dr. G. NAGY and Dr. G. DOBOSI. From the mineral chemical data cation numbers per unit cell were calculated and used for characterization of the P-T conditions (and trends) of the metamorphic events applying different geothermometers and geobarometers. Moreover, emission spectroscopic and organic geochemical analyses were also carried out, but the evaluation of these results falls far beyond the interest of the present interpretation (for details see ÁRKAI 1979, 1980, 1981). ROCK TYPES, PREMETAMORPHIC LITHOFACIES On the eastern margin of the Derecske Depression (Álmosd area, see Fig. 2) gneiss, plagioclase-mica schist, and mica schist are the main constituents of the basement. There are continuous transitions between these rock types, the gneiss (samples Aim1.9, 10; Álm2.4; Alm6. 4; Aim11. 4, 5) being more frequent than the mica schist (samples Aim3. 9; Álm-10.5, 6; Álm-9.2; Alm13. 4. ). Mylonite and blastomylonite formed from the gneiss-mica schist group by cataclastic metamorphism and subsequent (retrograde) recrystallization are subordinate in the Álmosd area (Álm-4. 4; Kism-3.2. ) but dominant in the Kaba-South area (on the western rise of the depression). On the northern and southern slopes of the Kaba-S structure mainly gneisses (bores Kaba-D- 3, -2,-5.), in the central part mostly mica schists (bores Kaba-D- 4,-6.) were transformed into blastomylonites, the transitions being frequent here too. Biotite or epidote bearing amphibolites occur in the Álmosd area (samples Álm-9. 1. and Aim13. 4. , respectively) as well as in the bore Mezőpeterd Mp-1. south of the area of Fig. 2 (see Fig. 1). The gneiss - mica schist and the mylonite - blastomylonite groups were metamorphosed from carbonate-poor or carbonate-free pelitic- silty (aleuritic), subordinately psammitic sediments. Graphite flakes with preferred orientation forming continuous, thin bands in the matrix and in the helicitic garnet and staurolite porphyroblasts (Plate 1:2-4) indicating the direction of the sedimentary layering and the first schistosity, the frequent occurrence of Al-rich minerals and the lack or minor quantity of kalifeldspar all provide pétrographie evidence for para-origin of these rocks. Calculating the ACF and ÁKF values from the chemical compositions (Table 1), and comparing them with the projections of the main rock types given by WINKLER (1979) the majority of these rocks corresponds to the carbonate-free or carbonate-poor marine pelites and graywackes (Fig. 3). (Sample Aim6. 4. having higher F values shows graywacke-affinity.
