International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

DUCTILE DEFORMATION AND REVISED LITHOSTRATIGRAPHY OF THE MARTONYI SUBUNIT (TORNA UNIT, RUDABANYA MTS.), NORTHEASTERN HUNGARY

Pages: 355 - 369

Authors: LASZLO FODOR, BALAZS KOROKNAI

Abstract: New structural observations and mapping resulted in the reinterpretation of the Martonyi Subunit, part of the metamorphic Torna Unit, NE Hungary. This low-grade metamorphosed Triassic sequence contains lower Anisian Gutenstein Dolomite, a thin transitional pelagic sequence (Bódvarakó Formation?), Carnian Tornaszentandras Slate, late Carnian-Norian Pötschen Limestone. This stratigraphy is closer to the Bódvarakó windows than to any other Torna subunits. The original sedimentation area could be located on thinned continental crust, relatively close to the oceanic crust of the Meliata branch of the Neotethys. The whole sequence suffered three phases of ductile deformation during Alpine (Cretaceous?) tectogenesis. First, layer-parallel foliation developed (D1), most probably connected to first order nappe stacking. The second deformation phase (D2) is marked by upright, chevron-type folding (D2a). Detachment faults could form at the top of the Gutenstein Dolomite in order to accommodate space problems at fold hinges. The chevron folds were flattened later, during a progressive D2b phase associated with the development of axial plane cleavage and steep reverse faults. The structural style varies depending on locations within folds and on lithology suggesting strain partitioning during the D2b phase. Small kink folds with oblique axes can be related to reactivation of steep faults with oblique slip during the D3 phase, at the transition of brittle-ductile deformation field. The whole unit was thrust upon non-metamorphic unit(s) (D4 brittle phase) due to strike-slip displacement along the Darnó Zone sensu lato during the late Cretaceous and/or Tertiary.

Keywords: Mesozoic, Inner Western Carpathians, NE Hungary, Torna Unit, ductile deformation, folds, foliation, strain partitioning

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