engleski

Middle Miocene Extension at the Southwestern Corner of the Pannonian Basin: Surface data on faults and paleostress field

Middle Miocene (Badenian-Sarmatian) is a period of broad extension in the Pannonian Basin system when numerous basins opened or widened to accommodate convergence in the outer East Carpathians. Most of the basins were generated along large NE-SW trending strike-slip fault zones or master normal faults and generally acquire elongated, variably deep, half-graben shape. At some places low-angle normal faulting contributed to exhumation of basement rocks and to the formation of metamorphic core complexes (e.g. Rechnitz metamorphic core complex). Basin opening was accompanied by considerable calc-alcaline volcanism dispersed almost across the entire Basin system. During the same period several basins opened or re-opened at the southwestern corner of the Pannonian Basin, southwestward of the Periadriatic and the Drava Lineament, as marginal basins or troughs which terminate to the southwest at the Pannonain Basin – Dinarides boundary. These basins are recently parts of two larger Neogene basins in Croatia, i.e. Hrvatsko Zagorje and Sava Basin that experienced quite complex tectonic history since Late Cretaceous-Paleogene times. This work analyses two fault populations thought to be responsible for the opening of basins in the Middle Miocene time. Both are recorded in the highest structural unit of pre-Neogene tectonic assemblage at Samoborsko gorje Mt., a moderately (up to 900 m) high mountain elevated at the southwestern edge of the Pannonian Basin. One comprises a system of NE-SW striking, normal faults characterized by a set of smoothly curving, listric surfaces. It generates major rotated fault blocks, often dissected into smaller blocks by a set of high-angle, planar, antithetic faults. This fault system creates a series of half-grabens filled with Middle Miocene rocks. At one location faulting was accompanied by extrusion of volcanic dacite-andesite rocks of the same age. Computed paleostress axis orientation indicate that these faults accommodate NW-SE directed extension, mostly perpendicular to their strike. The other fault population is characterized by two sets of moderate to high angle strike-slip NE and NW-striking faults, generally accommodating N-S directed compression. The relative age between these events is still ambiguous. Overprinting relations suggesting that early normal-sinistral and normal-dextral movement is followed by sinistral slip on the same fault plane (i.e. earlier NE-SE extension is followed by N-S compression) are observed only on two locations. Comparison with data recorded in other parts of the Pannonian Basin as well as with some results obtained from experimental models leaves the possibility that both populations acted more or less synchronously.

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