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Luciano?Cortesogno Laura?GaggeroEmail author Ausonio?Ronchi Slavcho?Yanev 《International Journal of Earth Sciences》2004,93(4):500-520
The orogenic Balkanid belt, which developed between the Moesian Plate and the Moravian-Rhodopi-Thracian Massifs, was affected by the Late Carboniferous and Early Permian opening of W-E oriented graben structures. The progressive tectonic rejuvenation of the basins is demonstrated by the deposition of repeated regional sedimentary cycles, associated with volcanism that was mostly localised along the tectonic boundaries, in an intramontane setting.The Late Carboniferous volcanism is represented by rhyodacitic explosive products and hyaloclastites, and by andesitic flows. During the Early Permian, subvolcanic rhyodacitic and rhyolitic bodies and the explosive products prevailed in the western sectors, whereas rhyolitic ignimbrites occur to the east.The tectonically active basins are interpreted due to late orogenic collapse, and the alternation of extensional tectonics and minor compressional phases is consistent with the regional transtensional regime, active along the Variscan suture of Pangaea. The volcanic activity associated with the evolution of the basins matches the petrogenetic features and the evolution from early dacitic – andesitic to late rhyolitic activity in the Southern European segment of the Variscan system.These Late Carboniferous-Early Permian sedimentary and tectono-magmatic events in Bulgaria are characterized, and compared with the homologous Permo-Carboniferous sequences along some western European segments of the Variscan belt. 相似文献
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Peter Nozharov Nikolai Petkov Slavcho Yanev Vladimír Kropáček Miroslav Krs Petr Pruner Reviewer J. Pícha 《Studia Geophysica et Geodaetica》1980,24(3):252-284
Summary In order to obtain basic palaeomagnetic data on Upper Carboniferous, Permian and Triassic sediments collected from the NW Bulgaria, laboratory stability tests were extended from A.C. and thermal treatments to studies of mineral phase changes and to investigations of changes of magnetic anisotropy during laboratory procedures. Laboratory criteria were found which permitted to distinguish samples suitable for palaeomagnetic analyses from those representing rocks totally or almost totally chemically reworked during their history. Palaeomagnetic directions and pole positions derived from Stephanian, Lower Permian and Triassic rocks from the southern margin of the Moesian Platform are compatible with the values obtained for the tectonically stable North-European Platform. 相似文献
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Tertiary collision-related volcanic rocks of the Eastern Rhodopes (37–25.5 Ma) display calc-alkaline and shoshonitic affinities, with (A) intermediate to basic and (B) acid compositions. (A) Latites, andesites, also shoshonites and basaltic andesites and scarce basalts, absarokites and ultrapotassic latites were emitted through different eruptive styles: lava flows often autobrecciated, domes, ash and scarce pumice falls and flows. Lahars are frequent. K2 O contents of intermediate volcanics decrease from North to South towards the collision suture. (B) Rhyolites, trachyrhyolites and trachydacites show explosivity progressively decreasing with time. Several eruptive types can be distinguished: pyroclastic flows (weakly and strongly welded ignimbrite deposits), ash and lapilli falls, domes and lava flows. The large (30×10 km) Borovitza caldera is the result of a paroxysmic explosive phase.
All rocks are characterized by high contents of Rb, Th and Y. Conversely, negative Ba and Ta–Nb anomalies are typical of collision-related magmatism.
Intense hydrothermal episodes, contemporaneous with the volcanic activity, have converted large amounts of explosive products into bentonite and zeolites deposits. Typical metallogeny is associated with this collision-related volcanism: large Pb, Zn with Cu and Ag deposits and small U or Au deposits are exposed. 相似文献
All rocks are characterized by high contents of Rb, Th and Y. Conversely, negative Ba and Ta–Nb anomalies are typical of collision-related magmatism.
Intense hydrothermal episodes, contemporaneous with the volcanic activity, have converted large amounts of explosive products into bentonite and zeolites deposits. Typical metallogeny is associated with this collision-related volcanism: large Pb, Zn with Cu and Ag deposits and small U or Au deposits are exposed. 相似文献
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Five natural acid volcanic glasses (perlites) from the Eastern Rhodope mountains, Bulgaria, have been studied by X-ray diffraction. The quantity of the microlites varies from 1–3.5 weight percent. It is higher in the glasses from the rhyolite-perlite transition zone. Total pair correlation functions have been calculated for three of the glasses with less than 2 weight percent microlites. All total pair correlation functions are quite similar and have six well defined peaks up to 8 Å. Beyond 8 Å they are practically featureless. The general form of the curves and peak positions suggests that the short-range order in all the three glasses is compatible with a 6-membered tetrahedral ring polymerization scheme with some contribution of fourmembered rings. The T-01 (T=Si, Al) distance shows linear correlation with the weight percent ratio Al2O3/SiO2. The averaged first nearest neighbour distances T-01, O-01 and T-T1 are 1.615±0.005 Å, 2.66±0.02 Å and 3.16±0.02 Å, respectively. The mean T-O-T bond angle is 157±4°. Energy minimization and topology considerations of the possible distribution of different tetrahedral rings are discussed. 相似文献
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Time-resolved luminescence spectra of natural and synthetic hydrous volcanic glasses with different colors and different
Fe, Mn, and H2O content were measured, and the implications for the glass structure are discussed. Three luminescence ranges are observed
at about 380–460, 500–560, and 700–760 nm. The very short-living (lifetimes less than 40 ns) blue band (380–460 nm) is most
probably due to the 4T2(4D) →6A1(6S) and 4A1(4G) →6A1(6S) ligand field transitions of Fe3+. The green luminescence (500–560 nm) arises from the Mn2+ transition 4T1(4G) →6A1(6S). It shows weak vibronic structure, short lifetimes less than 250 μs, and indicates that Mn2+ is tetrahedrally coordinated, occupying sites with similar distortions and ion–oxygen interactions in all samples studied.
The red luminescence (700–760 nm) arising from the 4T1(4G) →6A1(6S) transition of Fe3+ has much longer lifetimes of the order of several ms, and indicates that ferric iron is also mainly tetrahedrally coordinated.
Increasing the total water content of the glasses leads to quenching of the red luminescence and decrease of the distortions
of the Fe3+ polyhedra.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
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