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Tectonic suture of the meliata (Jaklovce) occurences - mezostructural and microstructural research application

Zakrsmidova B., Nemeth Z., Jacko S.

Geology, Geophysics and Environment

2014

Vol. 40, no. 1

147

The study presents new paleopiezometric data of calcite marbles, contributing to a solution of principal geological and tectonic problems of autochthonous vs. allochthonous position of a carbonate succession north of Jaklovce village in the eastern part of the Northern-Gemeric zone. The Triassic-Jurassic sequences in the Kurtova skala hill are since the 1970s linked with the Meliaticum, so-called Jaklovce succession, but direct tectonic and structural evidences of its allochthonous position were not demonstrated as yet. However, due to the corresponding appearance of both, autochthonous and allochthonous carbonates, the boundary between both complexes was not clearly determined, or even both sequences were considered to be in the autochthonous position with primary lithological transitions towards the Permian bedrock. The dymanic recrystallization of the whole volume of allochthonous calcite marbles was shown by our research. The origin of deformation twins was found in nearly each calcite grain (twinning incidence is almost to 100%). The high number of deformation twins per 1 mm of perpendicular diameter of the grain (D = 173.05-646.25) at the very small size of grains (23.7-42.7 µm) resulted from their recrystallization at high differential stresses 6 = 347.49-429.55 MPa. This differs the allochthonous bodies of the Meliaticum from those of autochthonous Permo-Triassic cover of the Northern Gemericum, which does not exhibit deformation twins and ductile overprint. This difference simultaneously indicates that the total plastic recrystallization of allochthonous marbles should have occurred in the conditions of subduction zone, but their post-exhumation transport occurred with kinematics of the superficial nappe and did not cause any whole-volume recrystallization. The exhumed suite (besides carbonates, radiolarites, mafic, and ultramafic rocks) was overprinted by the two principal Alpine deformation phases AD1 and AD3 of tectonic imbrication and horizontal shearing, causing the origin of brittle-ductile and brittle disjunctive structures. Despite the overprint, the primary bedding (gen. So 330/55°) of allochthonous carbonates remained preserved, and contrasts to general NW-SE trending bedding and secondary foliation of autochthnous sequences.

The tectonometamorphic evolution of the marbles in the Lądek-Śnieżnik Metamorphic Unit, West Sudetes

Jastrzębski M.

Geologia Sudetica

2005

Vol. 37

1-26

Together with the adjacent rocks, the marbles of the Lądek-Śnieżnik Metamorphic Unit (LSMU), West Sudetes, SW Poland underwent a polyphase structural evolution that occurred in metamorphic conditions changing from medium-grade to low-grade and in deformation regimes changing from ductile to semi-brittle. The structural evolution of the marbles began with E-W subhorizontal shortening resulting in the tilting of the Cal-Dol layering (which had generally originated as a pre-tectonic and pre-metamorphic feature) and its transposition to a steeply dipping metamorphic S1 foliation. The subsequent vertical flattening occurred at the temperature peak of regional metamorphism and produced the N-S trending tight, recumbent F2 folds. This event is also documented by the subhorizontal S2 axial-plane carbonate grain shape fabric and the parallel alignment of Phl-MsšTršCzo in the marbles, and the S2 axial-plane schistosity in the adjacent mica schists. The temperature increase was associated with the progressive mineral sequence Phl › Tr › Di in the dolomite-bearing marbles, which probably initially equilibrated at low to moderate X(CO2). Under peak temperatures, the observed arrangement of the metamorphic zonation of the Stronie formation developed, overprinting the folded planes. Subsequently, under retrogressive conditions, younger deformations were localised in the dynamically recrystallised shear zones that mostly reactivated the S2 planes and were associated with a late top-to-the-N (NE) directed tectonic transport. The D3 mylonitisation was associated with the elongation and size reduction of carbonate grains within the S-C' or S-C mylonites. It produced the S3 planes and the N-S trending L3 stretching lineation. Both groups of the tectonic structures and D2-established mineral isograds (Tr-in and Di-in) were together reoriented during the late compressional stages D4 and D5, related respectively to the SW-NE (WSW-ENE) and NW-SE (NNW-SSE) directed tectonic shortenings. This is visible in the large scale F4 folds, the diversity of the D2-and D3-related mineral assemblages, and the temperature estimations related to both tectonic stages, which indicate decreasing metamorphic conditions from ? 600°C in the SE to ? 490°C in the NE of the LSMU during D2, and from ca. 510°C to 430°C for the respective domains during D3. The incomplete pattern of the Di-in and Tr-in isograds, which still refers to the geometry of gneiss-schist boundary, confirms that the macrostructures of the LSMU mainly developed in tectonic event(s) following the temperature peak of metamorphism.