Detailed petrographic studies on marbles are rare in the Hungarian geological literature. Determination of the mineral phases and their grain size, examination of the grain boundaries as well as deformation microstructures, however, can provide a comprehensive information about the metamorphic evolution and the deformation history of a marble unit.The metamorphic basement block near the village of Dorozsma contains a few-meter-thick marble zone within the Békés-Codru Zone. A petrographic study of archive thin sections representing this marble zone was carried out from the boreholes Dorozsma-4, Dorozsma-7 and Dorozsma-54.The fine-grained marble samples show heteroblastic texture with a composition of carbonate + quartz + muscovite + Mg-chlorite ± talc. The carbonate crystal boundaries are dominantly sutured, embayed and rarely curved. All the morpho logical types of deformation twins appear in the samples, but dominantly twin types II and IV are present. The characteristic features of the samples are small dissolution cavities filled with fine crystalline carbonate, blocky quartz and, in some cases, with saddle dolomite. In the samples from the borehole Dorozsma-4 small inclusion free carbonate grains substitute the deformation twins of the large carbonate crystals. In addition, small carbonate neoblasts and Mgchlorite flakes can be found among the large carbonate crystals. Characteristic microstructures of the samples from the well Dorozsma-7 are large sigmoid carbonate clasts in a very fine-grained matrix. The deformation twins of the carbonate clasts can be easily identified and show the signs of recrystallization. These samples beside the carbonate clasts also contain irregularly shaped polycrystalline quartz grains with dissolved edges, undulose extinction and signs of incipient dynamic recrystallization.The microstructures presented above suggest a polyphase deformation. The D 1 deformation event took place above 250 °C based on the relict microstructures. The subsequent D 2 ductile deformation event was a low-temperature dynamic recrystallization with a simple shear component, which could be the result of a hydrolitic weakening effect of hydrothermal fluids during deformation of the Dorozsma marble.Keywords: Dorozsma, marble, petrography, ductile deformation, metasomatism Összefoglalás A márványok petrográfiai vizsgálata napjainkig alárendelt szerepet kapott a hazai földtani szakirodalomban. A már -ványt felépítő ásványfázisok, valamint azok szemcsemérete és a szemcsehatár jellegének meghatározása (kőzetszövet), illetve a deformációs bélyegek feltárása és értelmezése révén azonban átfogó képet kaphatunk a kőzet metamorf fejlő dé -séről és deformációtörténetéről, ami független bizonyítékokkal szolgálhat a befoglaló metamorf kőzettest korreláció -jához.A Békés-Codrui-egységen belül elhelyezkedő, Dorozsma környéki kristályos aljzatban egy maximum néhányszor tíz mé ter vastagságú, markáns töréses deformációt szenvedett márványzóna található. Tanulmányunkban az e zónát mintázó Dorozsma-4, -7 és -54 fúrá...

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