... Descrizione del metodo analitico ... uno coassiale al Ge(Li) per i fotopicchi privi di interf... more ... Descrizione del metodo analitico ... uno coassiale al Ge(Li) per i fotopicchi privi di interferenze e uno intrinseco a maggiore risolu-zione per quelli che presentano problemi di sovrapposizione. ... Il tempo di misura è stato scelto in maniera da avere una buona statistica di conteggio. ...
Abstract Upper Cretaceous volcaniclastic sedimentary rocks from the Srednogorie Zone of the Balka... more Abstract Upper Cretaceous volcaniclastic sedimentary rocks from the Srednogorie Zone of the Balkanides have been investigated by the study of eight measured sections thought to be most typical of the flysch sedimentary environment. Two main sedimentary cycles have been recognized: (1) earlier Turonian deposits that are mineralogically mature, of mainly metamorphic origin, and with basin trends and palaeocurrent directions similar to those of the younger cycle; and (2) Senonian deposits consisting primarily of outer-fan lobes deposited adjacent to the eruptive centers. Volcanic detritus comprises a major part of the Senonian sediments, although they also contain metamorphic fragments (except in the eastern part of the Srednogorie Zone). The sedimentary and petrographic features point to an intra-arc setting at an early evolutionary stage.
The Srednogorie zone of Bulgaria was the site of extensive Late Cretaceous calc-alkalic and shosh... more The Srednogorie zone of Bulgaria was the site of extensive Late Cretaceous calc-alkalic and shoshonitic magmatism. The calc-alkalic volcanism developed mainly in the central and western parts, whereas shoshonitic volcanism was the predominant magmatic feature of the eastern part. Leucitic basanites, limburgites, and picrites occur in minor amounts in eastern Srednogorie. The shoshonitic volcanic rocks are intermediate to silicic in composition and are characterized by high K 2 O, K 2 O/Na 2 O around unity, high Rb, Sr, and Ba, and low TiO 2 contents. They are associated with calc-alkalic rocks less strongly enriched in K and incompatible elements. Petrographically, the calc-alkalic rocks are characterized by the presence of hydrous mineral phenocrysts that are not present in the shoshonitic rocks. Shoshonitic and calc-alkalic rocks have some common chemical characteristics such as low TiO 2 , lack of absolute iron enrichment, and large overlap in many trace-element abundances. These are considered evidence for a genetic relationship between their primary magmas, which may have undergone different degrees of enrichment in incompatible elements. The eastward increase of K-rich volcanic rocks relative to calc-alkalic rocks in the Srednogorie zone is believed to be related to distension tectonics connected with the opening of the Black Sea.
In Central Europe, Early Cretaceous alkaline igneous rocks (lamprophyres, basanites, phonolites) ... more In Central Europe, Early Cretaceous alkaline igneous rocks (lamprophyres, basanites, phonolites) occur in the Moravian-Silesian Beskidy area (northern Czech Republic and southern Poland) and in the Mecsek-Alfold Zone (southern Hungary). Presently they are located at about 400 km distance of each other. These alkaline igneous rocks show close similarities in their mineral, chemical, and bulk rock compositional data, implying similar petrogenesis and suggesting that these two regions could have been much closer during the Early Cretaceous; they could belong to the same rift zone in the European continental margin. Their trace element distribution and Sr and Nd isotopic ratios suggest that the parental magmas derived from an enriched, HIMU OIB-like asthenospheric mantle by different degrees (3-6%) of partial melting at the depth of spinel-garnet transitional and garnet stabilization zone (about 60-80 km depth). This mantle source appears to be akin to that thought to have supplied the Tertiary to Quaternary ...
ABSTRACTFifty‐three samples from D.S.D.P. Sites 127, 128 (Hellenic Trench), 130 (Mediterranean Ri... more ABSTRACTFifty‐three samples from D.S.D.P. Sites 127, 128 (Hellenic Trench), 130 (Mediterranean Ridge) and 131 (Nile Cone) ranging in size from clayey silt to sand were submitted to grain‐size and compositional analyses. The former confirmed the evidences obtained from the visual observation of the sedimentary features as to the presence of turbidites (Sites 127, 128, 131) and fluxoturbidites (Site 131). The cumulative frequency distributions of the latter are closely similar to those obtained from ancient deposits of the same type.The X‐ray quantitative analyses of the total samples showed that at both Site 127 and Site 128 calcite and phyllosilicates make up together, on average, about two‐thirds of the total composition. Quartz averages about 20%. Dolomite, plagioclase and K‐feldspars are present subordinately in this order; the former, observed in all samples, is both detrital and authigenic. In the Nile Cone quartz comprises, on average, about 70% of the composition. Phyllosilicates, plagio‐clases and K‐feldspars were observed in minor quantities.The four samples of the Mediterranean Ridge, although Nile derived, show a composition closer to the Hellenic Trench samples than to the Nile Cone. This is due to the strong control exerted by the grain size on the quantitative mineralogical composition. The microscopic analyses carried out on both light and heavy minerals of the sand fraction and the clay mineralogy clearly differentiate between the Hellenic Trench and all the Nile derived sediments (Sites 130 and 131) and exclude an intermixing of even the finest fractions. Each group is well clustered in the compositional diagrams. The Hellenic Trench sediments could be classified as lithic arenites (Crook, 1960) or greywackes (Malesani & Manetti, 1970) and the Nile Cone sediments as sublabile lithic feldspathic arenites or feldspathic subgrey‐wackes.The semi‐quantitative clay mineralogy showed that, on average, almost 50% of the Nile derived clay sized sediments is montmorillonite. Mixed layer minerals make up a relevant part of the remaining fraction. In contrast, the Hellenic Trench sediments show lower quantities of montmorillonite (about 10%) and prevailing percentages of illite and chlorite. Kaolinite is present only in the latter samples and not in the Nile Cone sediments.The lack of relevant changes in the composition of the Nile Cone sediments along the cored sections of the holes suggests that the present hydrography of the Nile River dates from at least the Lower Pleistocene.
... Descrizione del metodo analitico ... uno coassiale al Ge(Li) per i fotopicchi privi di interf... more ... Descrizione del metodo analitico ... uno coassiale al Ge(Li) per i fotopicchi privi di interferenze e uno intrinseco a maggiore risolu-zione per quelli che presentano problemi di sovrapposizione. ... Il tempo di misura è stato scelto in maniera da avere una buona statistica di conteggio. ...
Abstract Upper Cretaceous volcaniclastic sedimentary rocks from the Srednogorie Zone of the Balka... more Abstract Upper Cretaceous volcaniclastic sedimentary rocks from the Srednogorie Zone of the Balkanides have been investigated by the study of eight measured sections thought to be most typical of the flysch sedimentary environment. Two main sedimentary cycles have been recognized: (1) earlier Turonian deposits that are mineralogically mature, of mainly metamorphic origin, and with basin trends and palaeocurrent directions similar to those of the younger cycle; and (2) Senonian deposits consisting primarily of outer-fan lobes deposited adjacent to the eruptive centers. Volcanic detritus comprises a major part of the Senonian sediments, although they also contain metamorphic fragments (except in the eastern part of the Srednogorie Zone). The sedimentary and petrographic features point to an intra-arc setting at an early evolutionary stage.
The Srednogorie zone of Bulgaria was the site of extensive Late Cretaceous calc-alkalic and shosh... more The Srednogorie zone of Bulgaria was the site of extensive Late Cretaceous calc-alkalic and shoshonitic magmatism. The calc-alkalic volcanism developed mainly in the central and western parts, whereas shoshonitic volcanism was the predominant magmatic feature of the eastern part. Leucitic basanites, limburgites, and picrites occur in minor amounts in eastern Srednogorie. The shoshonitic volcanic rocks are intermediate to silicic in composition and are characterized by high K 2 O, K 2 O/Na 2 O around unity, high Rb, Sr, and Ba, and low TiO 2 contents. They are associated with calc-alkalic rocks less strongly enriched in K and incompatible elements. Petrographically, the calc-alkalic rocks are characterized by the presence of hydrous mineral phenocrysts that are not present in the shoshonitic rocks. Shoshonitic and calc-alkalic rocks have some common chemical characteristics such as low TiO 2 , lack of absolute iron enrichment, and large overlap in many trace-element abundances. These are considered evidence for a genetic relationship between their primary magmas, which may have undergone different degrees of enrichment in incompatible elements. The eastward increase of K-rich volcanic rocks relative to calc-alkalic rocks in the Srednogorie zone is believed to be related to distension tectonics connected with the opening of the Black Sea.
In Central Europe, Early Cretaceous alkaline igneous rocks (lamprophyres, basanites, phonolites) ... more In Central Europe, Early Cretaceous alkaline igneous rocks (lamprophyres, basanites, phonolites) occur in the Moravian-Silesian Beskidy area (northern Czech Republic and southern Poland) and in the Mecsek-Alfold Zone (southern Hungary). Presently they are located at about 400 km distance of each other. These alkaline igneous rocks show close similarities in their mineral, chemical, and bulk rock compositional data, implying similar petrogenesis and suggesting that these two regions could have been much closer during the Early Cretaceous; they could belong to the same rift zone in the European continental margin. Their trace element distribution and Sr and Nd isotopic ratios suggest that the parental magmas derived from an enriched, HIMU OIB-like asthenospheric mantle by different degrees (3-6%) of partial melting at the depth of spinel-garnet transitional and garnet stabilization zone (about 60-80 km depth). This mantle source appears to be akin to that thought to have supplied the Tertiary to Quaternary ...
ABSTRACTFifty‐three samples from D.S.D.P. Sites 127, 128 (Hellenic Trench), 130 (Mediterranean Ri... more ABSTRACTFifty‐three samples from D.S.D.P. Sites 127, 128 (Hellenic Trench), 130 (Mediterranean Ridge) and 131 (Nile Cone) ranging in size from clayey silt to sand were submitted to grain‐size and compositional analyses. The former confirmed the evidences obtained from the visual observation of the sedimentary features as to the presence of turbidites (Sites 127, 128, 131) and fluxoturbidites (Site 131). The cumulative frequency distributions of the latter are closely similar to those obtained from ancient deposits of the same type.The X‐ray quantitative analyses of the total samples showed that at both Site 127 and Site 128 calcite and phyllosilicates make up together, on average, about two‐thirds of the total composition. Quartz averages about 20%. Dolomite, plagioclase and K‐feldspars are present subordinately in this order; the former, observed in all samples, is both detrital and authigenic. In the Nile Cone quartz comprises, on average, about 70% of the composition. Phyllosilicates, plagio‐clases and K‐feldspars were observed in minor quantities.The four samples of the Mediterranean Ridge, although Nile derived, show a composition closer to the Hellenic Trench samples than to the Nile Cone. This is due to the strong control exerted by the grain size on the quantitative mineralogical composition. The microscopic analyses carried out on both light and heavy minerals of the sand fraction and the clay mineralogy clearly differentiate between the Hellenic Trench and all the Nile derived sediments (Sites 130 and 131) and exclude an intermixing of even the finest fractions. Each group is well clustered in the compositional diagrams. The Hellenic Trench sediments could be classified as lithic arenites (Crook, 1960) or greywackes (Malesani & Manetti, 1970) and the Nile Cone sediments as sublabile lithic feldspathic arenites or feldspathic subgrey‐wackes.The semi‐quantitative clay mineralogy showed that, on average, almost 50% of the Nile derived clay sized sediments is montmorillonite. Mixed layer minerals make up a relevant part of the remaining fraction. In contrast, the Hellenic Trench sediments show lower quantities of montmorillonite (about 10%) and prevailing percentages of illite and chlorite. Kaolinite is present only in the latter samples and not in the Nile Cone sediments.The lack of relevant changes in the composition of the Nile Cone sediments along the cored sections of the holes suggests that the present hydrography of the Nile River dates from at least the Lower Pleistocene.
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