Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 13. 1987. (Budapest, 1987)

like or isometric grains are shown in Fig. 6. These garnet clasts with normal (bell-shaped) zoning were not equilibrated with the surrounding matrix, as it can be deduced from the unreal (improbably high) P-T data obtained by the method of GHENT and STOUT (1981) for the sample Kaba-D-4.

1. Contrasting with the Kaba-S region on the eastern margin of the Derecske Depression, the metamorphic basement escaped this overprint. In these cases the features of the first event could be reconstructed without any difficulties, not being disturbed by younger effects. The mostly very weak and irregular sericitization of staurolite and plagioclase and chloritization of garnet and biotite may be attributed either to the late (low temperature, completing) phase of the second, retrograde metamorphic event or to near-surface weathering as well. Fissure fillings with prehnite-quartz or laumontite+quartz suggest low Xçq^ in the hydrothermal fluids circulated in the fractured rock masses. Summarizing the characteristics discussed above, it can be concluded that the metamorphic overprint proved to be generally of low-pressure type, partly prograde, mostly retrograde, locally preceded by mylonitization. CONCLUSIONS, THE PROBLEMS OF CORRELATION Having applied textural, petrochemical, mineral paragenetic, and thermobarometric methods, the following metamorphic evolution model can be outlined. The organic matter bearing pelitic-silty (subordinately psammitic) sediments containing presumed basic magmatic intercalations were subjected to a medium-grade, mediumpressure (Barrovian) regional dynamothermal metamorphism. Two syntectonic, and between them one post-tectonic episodes could be separated within the first metamorphic cycle characterized by continuous changes in P-T and deformational state. In certain places and rock types the crystallization went on after reaching the thermal climax (retrograde phase directly related to the prograde phase). Concordant P-T values obtained by using the isograde system of WINKLER (1979), the thermobarometers of GHENT and STOUT (1981) and PLYUSNINA (1981, 1982) indicate maximal pressure of 6.8-7.9 kbar and maximal temperature of 517-525°C, corresponding to intermediate metamorphic gradient (18-26°C/km). The features of the second metamorphic event separated by distinct time (P-T, and deformational state) differences from the first one proved to be considerably variable. Near to the late-kinematic granite intrusion prograde (increasing T, decreasing P), in other places retrograde (greenschist facies, chlorite-, biotite-, garnet-zones), low-pressure type overprint is characteristic, while other parts of the basement escaped the second event. In the Kaba-S region the overprint was preceded by mylonitization. This two-step metamorphic evolution model illustrated schematically in Fig, 5 is very similar to those established in other parts of the Great Plain (Danube-Tisza Interfluve), and in Southwest Transdanubia (Somogy-Drava Basin) studied by the same methods (ÁRKAI,NAGY and DOBOSI 1985). Taking into account the Hercynian age of the granitic magmatism in the Great Plain and in the Mecsek Mts. (Transdanubia), (KOVÁCH in SZÁDEC

ZKY-KARDOSS et al, 1969; BUDA 1985) as well as the Hercynian Rb/Sr whole rock isochron ages (330-338 Ma) of the South Hungarian metamorphites (KOVÁCH, SVINGOR and SZEDERKÉNYI 1985), the Hercynian age of the second, low-pressure type, partly prograde, mostly retrograde metamorphism seems to be the most probable. The age of the first event is uncertain. Considering the lack of the Caledonian granitoid magmatism, postorogene volcanism and sedimentation, its Early Hercynian or Caledono-Hercynian age might be supposed. There are no data supporting Precambrian metamorphic ages. This Hercynian or Caledono-Hercynian plurifacial model delineated in detail by ÁRKAI, NAGY and DOBOSI (1985) is in good agreement with the Eastern Alps too (see FRANK, PURTSCHELLER et al. 1978; LELKES-FELVÁRI and SASSI 1981), but contradicts the model elaborated by the Roumanian authors for the Transylvanian Central (Apuseni) Mts., part of which (Plopis = Réz Mts.) is in close geographic relation with the basement of the Derecske Depression. The crystalline basement of the latter may be correlated with the Somes (Szamos) series of the Biharia autochthonous unit (also see SZEPESHÁZY 1973). According to recent opinions (GIUSCA et al. 1969; DUMITRESCU, 1981; KRÄUTNER 1981) the Somes series was metamorphosed from Middle Proterozoic complex during the Dalslandian orogeny ( ~800 Ma). This model, however, having been elab-