Ductile deformation in limestone of the Bükk Mts.

What is it about?

In the Paleozoic and Mezozoic rocks of the Bükk Mountains the imprints of a polyphase deformation and an anchi-epizonal metamorphism were observed. The physical conditions of this metamorphism were the same as that of the earliest, ductile deformation phase. The imprints of later deformation phases can be distinguished in general by their tectonic style. Our investigation was focused on the style of folding and on the different textural elements of limestones which developed during the early deformation phase. According to the lithologic conditions and the geographical position, the folds show a certain style variety. The multilayer fold geometry depends on the thickness ratio and the competence contrast between the layers. In the occurrence of different textural patterns the position inside a fold and the predeformational grain size plays an important role. The main deformation mechanism in the fine-grained matrix was the pressure solution while coarse-grained crystal aggregates show signs of dynamic recrystallization which leads in some cases as far as to the development of milonitic texture and strong lattice preferred orientation. The spatial style differences of the same rock types provide a base to define tectofacial units in the eastern part of the Bükk Mts.

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Why is it important?

The Bükk Mts. is an elevated part of the Pre-Cenozoic basement of the Pannonian Basin. The structure comprises several fault sheets between large scale strike-slip faults. Stratigraphy is uncertain because ductile deformation and alteration features overprinted and in several cases erased the original textural elements of the rocks, and boundaries of the rock blocks are sheared, contacts are mostly tectonic. Ductile deformation style elements are characteristic for fault blocks and can serve as basis for defining tectofacial units.