engleski

Clay minerals as indicators of thermal alterations in rocks from the western part of the Papuk Mt. (Slavonian Mts., NE Croatia): preliminary results

Mount Papuk is located in the north-eastern Croatia within the Pannonian Basin (PB), the Neogene backarc basin formed within the Alpine- Carpathian-Dinaric orogenic system. Pre-Neogene basement of the PB is divided into two major tectonic units. The eastern one, the Tisia unit, consists of Variscan crystalline complexes and post-Variscan Alpine (PV) overstep sequences both exposed on the Papuk. For a long time, Papuk PV rocks were considered unmetamorphosed. However, Biševac et al. (2010) studied Late Permian and Triassic clastic-carbonate sedimentary succession in the eastern part of the Papuk Mountain and revealed the existence of Eoalpine (Cretaceous) metamorphism. The observed Kübler (KI) and Árkai (ÁI) indices indicated that these rocks passed through a high-anchizonal to epizonal thermal alteration. This is consistent with previous observations (Árkai, 2001 and references therein) that large areas of pre-Neogene PB basement were metamorphosed during the Eoalpine event. In order to better constrain the metamorphic conditions that prevailed in this area, new samples of PV rocks (Permo-Triassic, Triassic, and Jurassic) from the western part of Papuk Mt. were investigated in this study using X-ray methods. KI and ÁI were measured simultaneously on air-dried samples according to the recommendations of Kisch (1991). The majority of KI (values ranging from 0.25 to 0.42) and ÁI values measured on PV rocks (previously classified mainly as siltstones, sandstones, conglomerates, shales and a limestone) from the western part of the Papuk showed that the majority of the rocks studied were thermally altered by anchizonal metamorphism. The measured KI and ÁI are mostly in good correlation, deviations were only observed in samples with lower chlorite content and containing other clay minerals like corrensite and kaolinite. Only one sample, from a layer of shale occurring in dolomites, was according to KI (0.62) altered in the diagenetic zone. Thus, this preliminary investigation indicate that rocks sampled from the western Papuk Mt. were also affected by a PV metamorphic event most probably corresponding to the one described in the eastern part of the mountain.

Croatia, Papuk, Kübler index, Árkai index, anchizone

nije evidentirano