A comprehensive lithological and biostratigraphic investigation into diatoms and chrysophycean stomatocysts was conducted on two boreholes from the central zone of the Kostenets Neogene Basin. The diatom flora consists of 105 species, varieties, and forms. The results of these different analyses presented herein indicate three successive stages in the palaeoenvironmental development of the Kostenets Basin, at the end of the Miocene and the beginning of the Pliocene.
No abstract is available for this article.
A combination of methods is applied in the present study to define the exact age of the Petrohan and Mezdreya plutons and trace their magma evolution. Field, petrological, and geochemical studies of the Petrohan pluton revealed its complex evolution and emphasized the role of magma mingling and mixing, complementary to the normal assimilation and fractional crystallization (AFC) processes. Using high-precision conventional U-Pb (CA)-ID-TIMS zircon and titanite dating in combination with CA-LA-ICP-MS zircon dating and tracing, we suggest an incremental growth of a common Petrohan-Mezdreya pluton. It was assembled over minimum 4.5 Ma from 311.14±0.48 Ma to 307.54±0.54 Ma. The younger age of the gabbro (308.12±0.33 Ma), compared with the age of granodiorites (311.14±0.48 Ma), provides numerical proofs for magma replenishment during the assembling of the Petrohan pluton. Whole-rock strontium-neodymium (initial 87Sr/86Sr ratios of 0.70521–0.70527 to 0.70462 and 143Nd/144Nd of 0.51221 to 0.51210) and Hf-zircon isotope data (ε-Hf from –5.8 to +3.6) argue for interaction of mantle derived magma with crustal melts but also mixing and mingling and transfer of zircon grains between the gabbroic and granitic melts. Possible petrogenetic scenario includes melting of subcontinental mantle lithosphere and crust and evolution trough AFC, FC and mingling/mixing processes. Considering the Petrohan-Mezdreya pluton as part of the Variscan orogeny in SE Europe, our new data support the accretion/collision of both the Balkan and Sredna Gora/Getic units with Moesia in the Early Carboniferous followed by syn- and post-collisional Carboniferous and Permian magmatism.
The Botevgrad basin is one of the numerous Late Pliocene–Quaternary basins developed over the Balkanide orogen. The basin is developed in the West Balkan tectonic zone and on the northern slopes of the Stara Planina Mountain along the Plakalnitsa fault zone, the front of the orogen. The basin was interpreted as half-graben formed on the SW block of the Dragoybalkan fault, considered as the Plakalnitsa fault zone’s extensionally reactivated roots. Our data suggest that the basin formation is more complicated and all basin boards are fault predestined. The boards are morphologically well prominent and their geometry is a result of the reactivated older faults’ segmentation, combined with the different rheology of the basement lithologies, mainly Palaeozoic low-grade metamorphites and intruded into them syn- to post-metamorphic granitoids. The distribution of the numerous depocentres, the orientation of drainage systems, watershed shape and depositional system migration indicate polyphasic basin evolution. The basin shape and other data, such as criteria for sense of shearing, and intrabasinal push-up blocks’ rotation, suggest that the Botevgrad basin should be interpreted as pull-apart basin.
No abstract is available for this article.
No abstract is available for this article.
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