This chapter presents study on zeolitized tuffs from the Eastern Rhodopes Paleogene volcanic area... more This chapter presents study on zeolitized tuffs from the Eastern Rhodopes Paleogene volcanic area. Sodium (Na)-mordenite and calcium (Ca)-clinoptilolite are the main products of the acid glass alteration. Erionite, analcime, and stilbite are also identified. Opal and adularia are most abundant at the base of tuff succession. Zeolite content increases upward. Compared with flesh perlite, zeolitized tuffs are depleted in sodium oxide (Na2O), Y, rubidium (Rb), barium (Ba), and manganese (Mn) and enriched in calcium oxide (CaO) and strontium (Sr). C.E.C. coefficient ranges from 60.66 to 94.53 meq/100g. Low-temperature hydrothermal solutions, heated by the initially hot pyroclastic material are the inferred cause of the zeolite formation.
Paleogene Eastern Rhodopes Volcanic Area (ERVA) is part of a more than 2000 km long magmatic belt... more Paleogene Eastern Rhodopes Volcanic Area (ERVA) is part of a more than 2000 km long magmatic belt in SE Europe extending from the Inner Dinarids (West Bosnia-Herzegovina) to Western Anatolia (European Turkey). Volcanic activity occurred during the Late Eocene-Early Oligocene and was spatially related to extensional Paleogene shallow marine basins underlain by a high-grade metamorphic basement. The volcanism is bimodal in character, with minor mafic (basalts) and major intermediate (mainly andesites) to acid (mainly rhyolites) volcanics present in similar volumes. This work focuses on Maritsa volcanic group (36-32 Ma) located in the NE part of the ERVA, S Bulgaria. The volcanic group comprises Lozen volcano composed of dacites, rhyodacites, and rhyolites, St Marina rhyolite dome, and Sheinovets rhyolite dome-cluster located within a caldera with the same name. Measured present day 87Sr/86Sr of the rhyolites range from 0.7075 to 0.7180, however on a plot 87Rb/86Sr vs 87Sr/86Sr the data form an errorchron (MSWD=21) with 30.5 +/-3.6Ma age and 87Sr/86Sr initial equal to 0.7074. Pb isotopic compositions in all of the volcanoes show similar values ranging from 18.712 to 18.768 in 206Pb/204Pb, 15.643 to 15.687 in 207Pb/204Pb, and 38.790 to 38.922 in 208Pb/204Pb. Nd isotopes show also little variations with 143Nd/144Nd ranging from 0.51242 to 0.51249. The similarity in the isotopic compositions between the volcanoes suggests common, homogeneous magmatic source. Crustal origin of the rhyolites as a result of melting of the metamorphic basement is not plausible because the rhyolites have different Sr and Nd isotopic compositions from the gneisses in the ERVA. Sr and Nd isotopic data for the rhyolites differ also from the basalts (i.e. possible mantle melts) in the Eastern Rhodopes region. Rhyolites have higher 87Sr/86Sr and lower 143Nd/144Nd ratios compared to the basalts, thus suggesting involvement of crustal component in the magma generation, most probably the metamorphic basement that underlies the volcanoes. On 143Nd/144Nd vs 87Sr/86Sr diagram the rhyolites plot on a mixing curve between the basalts and the gneisses from the metamorphic basement indicating about 70% mafic and 30% basement component involved in their genesis. Lead concentrations in the mantle is relatively low compared to the upper crust and the Pb isotopic signature in lavas generated in continental volcanic arcs is often completely dominated by crustal components. The rhyolites have more radiogenic 207Pb/204Pb and 208Pb/204Pb isotopic compositions than the basalts and plot entirely within the field defined by the metamorphic rocks in the ERVA suggesting that any mantle derived Pb was completely swamped by crustal Pb. Our isotopic results provide evidence for extensive crustal contamination of the felsic magmas in the region. Mafic melts, generated either during subduction or delamination ascended in the mantle wedge until they become stalled at a level of neutral buoyancy. Crustal melting and assimilation occurred at that level accompanied by homogenisation and crystal fractionation in large magma chambers until the evolving magmas reached the required density to re-establish buoyant ascent. The observed isotopic homogeneity in the felsic volcanoes in the region suggests that large zone of MASH at crustal levels existed during the Paleogene beneath the ERVA.
This chapter presents study on zeolitized tuffs from the Eastern Rhodopes Paleogene volcanic area... more This chapter presents study on zeolitized tuffs from the Eastern Rhodopes Paleogene volcanic area. Sodium (Na)-mordenite and calcium (Ca)-clinoptilolite are the main products of the acid glass alteration. Erionite, analcime, and stilbite are also identified. Opal and adularia are most abundant at the base of tuff succession. Zeolite content increases upward. Compared with flesh perlite, zeolitized tuffs are depleted in sodium oxide (Na2O), Y, rubidium (Rb), barium (Ba), and manganese (Mn) and enriched in calcium oxide (CaO) and strontium (Sr). C.E.C. coefficient ranges from 60.66 to 94.53 meq/100g. Low-temperature hydrothermal solutions, heated by the initially hot pyroclastic material are the inferred cause of the zeolite formation.
Paleogene Eastern Rhodopes Volcanic Area (ERVA) is part of a more than 2000 km long magmatic belt... more Paleogene Eastern Rhodopes Volcanic Area (ERVA) is part of a more than 2000 km long magmatic belt in SE Europe extending from the Inner Dinarids (West Bosnia-Herzegovina) to Western Anatolia (European Turkey). Volcanic activity occurred during the Late Eocene-Early Oligocene and was spatially related to extensional Paleogene shallow marine basins underlain by a high-grade metamorphic basement. The volcanism is bimodal in character, with minor mafic (basalts) and major intermediate (mainly andesites) to acid (mainly rhyolites) volcanics present in similar volumes. This work focuses on Maritsa volcanic group (36-32 Ma) located in the NE part of the ERVA, S Bulgaria. The volcanic group comprises Lozen volcano composed of dacites, rhyodacites, and rhyolites, St Marina rhyolite dome, and Sheinovets rhyolite dome-cluster located within a caldera with the same name. Measured present day 87Sr/86Sr of the rhyolites range from 0.7075 to 0.7180, however on a plot 87Rb/86Sr vs 87Sr/86Sr the data form an errorchron (MSWD=21) with 30.5 +/-3.6Ma age and 87Sr/86Sr initial equal to 0.7074. Pb isotopic compositions in all of the volcanoes show similar values ranging from 18.712 to 18.768 in 206Pb/204Pb, 15.643 to 15.687 in 207Pb/204Pb, and 38.790 to 38.922 in 208Pb/204Pb. Nd isotopes show also little variations with 143Nd/144Nd ranging from 0.51242 to 0.51249. The similarity in the isotopic compositions between the volcanoes suggests common, homogeneous magmatic source. Crustal origin of the rhyolites as a result of melting of the metamorphic basement is not plausible because the rhyolites have different Sr and Nd isotopic compositions from the gneisses in the ERVA. Sr and Nd isotopic data for the rhyolites differ also from the basalts (i.e. possible mantle melts) in the Eastern Rhodopes region. Rhyolites have higher 87Sr/86Sr and lower 143Nd/144Nd ratios compared to the basalts, thus suggesting involvement of crustal component in the magma generation, most probably the metamorphic basement that underlies the volcanoes. On 143Nd/144Nd vs 87Sr/86Sr diagram the rhyolites plot on a mixing curve between the basalts and the gneisses from the metamorphic basement indicating about 70% mafic and 30% basement component involved in their genesis. Lead concentrations in the mantle is relatively low compared to the upper crust and the Pb isotopic signature in lavas generated in continental volcanic arcs is often completely dominated by crustal components. The rhyolites have more radiogenic 207Pb/204Pb and 208Pb/204Pb isotopic compositions than the basalts and plot entirely within the field defined by the metamorphic rocks in the ERVA suggesting that any mantle derived Pb was completely swamped by crustal Pb. Our isotopic results provide evidence for extensive crustal contamination of the felsic magmas in the region. Mafic melts, generated either during subduction or delamination ascended in the mantle wedge until they become stalled at a level of neutral buoyancy. Crustal melting and assimilation occurred at that level accompanied by homogenisation and crystal fractionation in large magma chambers until the evolving magmas reached the required density to re-establish buoyant ascent. The observed isotopic homogeneity in the felsic volcanoes in the region suggests that large zone of MASH at crustal levels existed during the Paleogene beneath the ERVA.
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