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Three-dimensional gravity modeling has been performed for the Eastern Mediterranean including the northeastern Egyptian off-shore area. The gravity models and seismic profiles indicate that a transition from two layer continental crust to a simple layer oceanic crust takes a place along the Levantine margin. The transition along three profiles is located beyond the north African continental margin and it is quite gradual. The crust under the Levantine basin is typically oceanic and slightly thin with 13 km thickness, however it is typical continental under the Egyptian off-shore and having 30 km thickness. The obtained results reflect a large sedimentary sequence of 14 km under the Levantine basin. Since the sediments recovered by the Oceanic Drilling Program Leg160 in the eastern Mediterranean ranged from Pleistocene to Cretaceous, this reflects fairly high sedimentation rate. Distribution of recent earthquake foci indicates that almost all earthquakes occurred along the western and central segments of the Cyprean arc while they completely disappear along the eastern segment. This means that collision between Cyprus and the Eratosthenes seamount is marked by seismic activity and clearly affects the shape of the Cyprean arc. This collision represents a transition zone between active compression and probable subduction in the western segment and diffuse transtension through the eastern part of the arc. Incipient collision between Cyprus and Eratosthenes seamount probably began in Pleistocene time.

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253 278 White, R., D. McKenzie 1989: Magmatism at rift zones: The generation of volcanic continental margins and flood basalts. - J. Geophys. Res., 94, pp. 7685

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The Variscan metamorphic basement of the Great Hungarian Plain (Tisza Block, E Hungary) consists of deeply buried crystalline highs comprising several types of gneiss and metabasic rocks. A common gneiss type is an orthogneiss variety that can be followed across the basement from Jánoshalma northeastward within the Tisza Block. We believe the Jánoshalma High to be a uniform orthogneiss block of peraluminous composition; this is suggested by the presence of idiomorphic accessory phases (apatite needles, zircon), polygonal feldspar texture, occurrence of rock bodies of exotic origin, xenoliths (amphibolite, eclogite) and xenocrysts (feldspar megacrysts, amphibole, garnet) of varying composition and metamorphic evolution. The peculiar features of the orthogneiss body are indicative of processes that may have taken place in an ancient Alaskan-type orogenic belt (subduction-accretionary complex). In these situations, because of the continuous ample sediment supply, the accretionary prism retreats oceanward, forming structures of increasing steepness with depth, accreting against the continental margin. Thereafter, this causes oceanward retreat of the subduction trench as well. For this reason mantle-derived magmas do not penetrate the continental margin but the accretionary prism itself, resulting in the melting of its material. In the case of the Jánoshalma High, following the emplacement of the onetime granodioritic body at shallower crustal levels, it metamorphosed via to a two-stage overprint. An early high-temperature (HT) and a succeeding medium-temperature (MT) event formed orthogneiss from the ancient intrusive rock. This is the first detailed investigation of the Jánoshalma high that has been published.

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Abstract

Analysis of continental-scale lithostratigraphic data may facilitate an understanding of global sedimentary processes. The number of carbonate-bearing formations established in northern Eurasia (430 in total), northern Africa and Arabia (47 in total), and India (98 in total) is calculated per epochs for the last 145 Ma. The results show maxima in the Late Cretaceous, the Eocene, and the Miocene and minima in the Paleocene, the Oligocene, and the Pliocene. The Quaternary records are somewhat ambiguous. The similarity of the patterns established in the three regions argues for a single globalscale mechanism of carbonate accumulation. The noted patterns also coincide well with some modeled changes in the global amount of carbonates accumulated by epoch. Moreover, increases in the amount of carbonates in the Late Cretaceous and the Eocene, and a decrease in the Paleocene, reflect true changes in the accumulation rates. The global process of carbonate accumulation might have been controlled, at least, by eustatic changes (sea-level rise led to broad transgressions on continental margins and consequently to expansion of shelfal paleoenvironments) and climate dynamics (warm water facilitated carbonate production). Interestingly, no dependence between the global carbonate accumulation and marine biodiversity dynamics is established.

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Upper Carboniferous (Westphalian) coal-bearing fluvial sediments (Téseny Sandstone Formation) of the Slavonian-Drava Unit and their reworked pebbles and cobbles occurring in the western part of the Mecsek Mountains in Miocene conglomerate sequences (Szászvár Formation) were studied.  Based on the petrographic and geochemical characteristics, the sandstone studied consists of arkose, subarkose, litharenite and sublitharenite. The main clastic source was a recycled orogenic area (collision suture and fold-thrust belt) dominated by metamorphic rocks. It was associated with a probably Variscan magmatic arc as indicated by the volcanic rock fragments. The original source area of these clastic sediments was felsic and the analyzed sandstone could correspond to a continental arc/active margin tectonic suite.  The pebble and cobble-sized clasts of the conglomerate were predominantly derived from acidic and intermediate volcanic rocks, low-grade regional metamorphic rocks (different types of schist, metasandstone, mylonite, metagranitoid, gneiss, quartzite, and metaquartzite) and siliceous sedimentary rocks. Among the sedimentary clasts, reworked black siltstone and fine-grained sandstone from older (possibly Carboniferous) deposits are common. Chert and contact metamorphic rocks are present in minor quantity. The extracted volcanic clasts consist of andesite, trachyandesite, dacite and rhyolite. Their geochemistry suggests convergent, active continental margin affinity. Upper Carboniferous siliciclastic successions are widely known at the southeastern margin of the European Variscides. In the area of the Upper Silesian Coal Basin, the Cracow Sandstone Series (Westphalian C and D) shows a similar petrographic composition to that of the Téseny Sandstone Formation. Additionally, volcanic clasts of the Upper Carboniferous conglomerate from southern Transdanubia and the calc-alkaline volcanites from the Intra-Sudetic Basin can be characterized by similar geochemical patterns.

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O'Brien, G. W., J. R. Harris, A. R. Milnes, H. H. Veeh 1981: Bacterial origin of East Australian continental margin phosphorites. - Nature, 294, pp. 442 - 444 . Bacterial origin of East Australian continental margin

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White, R., S., D. McKenzie 1989: Magmatism at rift zones: the generation of volcanic continental margins and flood basalts. - J. Geophys. Res., 94, pp. 7685 - 7730 . Magmatism at rift zones: the generation of volcanic

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.K. Bird A.K. Pedersen 1997 Timing and structural relations of regional zeolite zones in basalts of the East Greenland continental margin

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M.H. Khalil 1994 Rejuvenation of the eastern Mediterranean passive continental margin in northern and central Sinai: new data from the Themed Fault Geol. Mag

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