12 resultados para PETROCHEMISTRY

em Publishing Network for Geoscientific


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Collisional and post-collisional volcanic rocks in the Ulubey (Ordu) area at the western edge of the Eastern Pontide Tertiary Volcanic Province (EPTVP) in NE Turkey are divided into four suites; Middle Eocene (49.4-44.6 Ma) aged Andesite-Trachyandesite (AT), Trachyandesite-Trachydacite-Rhyolite (TTR), Trachydacite-Dacite (TD) suites, and Middle Miocene (15.1 Ma) aged Trachybasalt (TB) suite. Local stratigraphy in the Ulubey area starts with shallow marine environment sediments of the Paleocene-Eocene time and then continues extensively with sub-aerial andesitic to rhyolitic and rare basaltic volcanism during Eocene and Miocene time, respectively. Petrographically, the volcanic rocks are composed primarily of andesites/trachyandesites, with minor trachydacites/rhyolites, basalts/trachybasalts and pyroclastics, and show porphyric, hyalo-microlitic porphyric and rarely glomeroporphyric, intersertal, intergranular, fluidal and sieve textures. The Ulubey (Ordu) volcanic rocks indicate magma evolution from tholeiitic-alkaline to calc-alkaline with medium-K contents. Primitive mantle normalized trace element and chondrite normalized rare earth element (REE) patterns show that the volcanic rocks have moderate light rare earth element (LREE)/heavy rare earth element (HREE) ratios relative to E-Type MORB and depletion in Nb, Ta and Ti. High Th/Yb ratios indicate parental magma(s) derived from an enriched source formed by mixing of slab and asthenospheric melts previously modified by fluids and sediments from a subduction zone. All of the volcanic rocks share similar incompatible element ratios (e.g., La/Sm, Zr/Nb, La/Nb) and chondrite-normalized REE patterns, indicating that the basic to acidic rocks originated from the same source. The volcanic rocks were produced by the slab dehydration-induced melting of an existing metasomatized mantle source, and the fluids from the slab dehydration introduced significant large ion lithophile element (LILE) and LREE to the source, masking its inherent HFSE-enriched characteristics. The initial 87Sr/86Sr (0.7044-0.7050) and eNd (-0.3 to +3.4) ratios of the volcanics suggest that they originated from an enriched lithospheric mantle source with low Sm/Nd ratios. Integration of the geochemical, petrological and isotopical with regional and local geological data suggest that the Tertiary volcanic rocks from the Ulubey (Ordu) area were derived from an enriched mantle, which had been previously metasomatized by fluids derived from subducted slab during Eocene to Miocene in collisional and post-collisional extension-related geodynamic setting following Late Mesozoic continental collision between the Eurasian plate and the Tauride-Anatolide platform.

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New results on the petrochemistry and geochemistry of dolerites from the Schirmacher Oasis shed light on the development of the Karoo-Maud plume in Antarctica. The basalts and dolerites are petrologically identical to the rocks of western Dronning Maud Land (DML), which were previously studied and interpreted as a manifestation of the Karoo-Maud plume in Antarctica. The spatial distribution of the dikes suggests eastward spreading of the plume material, up to the Schirmacher Oasis for at least 10 Ma. The geochemical characteristics of magmas from the Schirmacher Oasis reflect the influence of crustal contamination, which accompanied both the ascent and spreading of the plume. The magmas of the initial stage of plume activity (western DML) appeared to be the most contaminated in crustal components. It was found that the geochemical characteristics of Mesozoic magmas from the Schirmacher Oasis are identical to those of enriched tholeiites from the Afanasy Nikitin Rise and the central Kerguelen Plateau (Hole 749), which indicates that their enrichment was related to the ancient material of the Gondwana continent. This was caused by the opening of the Indian Ocean under the influence of the Karoo-Maud plume. This process was peculiar in that it occurred in the presence of nonspreading blocks of varying thickness, for instance, Elan Bank in the central Kerguelen Plateau, and was accompanied by the formation of intraplate volcanic rises, which are documented in the seafloor relief of basins around Antarctica. The geochemical characteristics of igneous rocks from the resulting rises (Afanasy Nikitin, Kerguelen, Naturaliste, and Ninetyeast Ridge) indicate the influence of processes related to crustal assimilation. The magmatism that occurred 40 Ma after the main phase of the Karoo-Maud volcanism at the margins of the adjacent continents of Australia (Bunbury basalts) and India (Rajmahal trapps) could be generated by the Karoo-Maud plume flowing along the developing spreading zone. The plume moved subsequently and was localized at the Kerguelen Plateau, where it occurs at present as an active hotspot.

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The monograph has been written on the base of data obtained from samples and materials collected during the 19-th cruise of RV ''Akademik Vernadsky'' to the Northern and Equatorial Indian Ocean. Geological features of the region (stratigraphy, tectonic structure, lithology, distribution of ore-forming components in bottom sediments, petrography of igneous rocks, etc.) are under consideration. Regularities of trace element concentration in Fe-Mn nodules, nodule distribution in bottom sediments, and engineering-geological properties of sediments within the nodule fields have been studied. Much attention is paid to ocean crust rocks. The wide range of ore mineralization (magnetite, chromite, chalcopyrite, pyrite, pentlandite, and other minerals) has been ascertained.

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A petrologic-geochemical study (petrochemistry, contents of siderophile and certain lithophile elements, composition of rock-forming silicates and accessory chrome spinels) of ultrabasic rocks dredged from the arc side in the northern end of the Tonga deep-sea trench has been carried out. The ultrabasites included harzburgites and dunites. Peridotites show clearly manifested material characteristics of ultrabasic relicts strongly depleted in low-temperature basaltic components. It is suggested that they have arose in the high degree of partial melting (about 30%) of a matrix mantle source of the lherzolite type. Great similarity of the rocks studied with ultrabasites of many ophiolites that are widespread in folded belts indicates that young island arcs are among the most likely geodynamic environments of ophiolite generation.

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The Duolong porphyry Cu-Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au), which is related to the granodiorite porphyry and the quartz-diorite porphyry from the Bangongco copper belt in central Tibet, formed in a continental arc setting. Here, we present the zircon U-Pb ages, geochemical whole-rock, Sr-Nd whole-rock and zircon in-situ Hf-O isotopic data for the Duolong porphyries. Secondary ion mass spectrometry (SIMS) zircon U-Pb analyses for six samples yielded consistent ages of ~118 Ma, indicating a Cretaceous formation age. The Duolong porphyries (SiO2 of 58.81-68.81 wt.%, K2O of 2.90-5.17 wt.%) belong to the high-K calc-alkaline series. They show light rare earth element (LREE)-enriched distribution patterns with (La/Yb)N = 6.1-11.7, enrichment in large ion lithophile elements (e.g., Cs, Rb, and Ba) and depletion of high field strength elements (e.g., Nb), with negative Ti anomalies. All zircons from the Duolong porphyries share relatively similar Hf-O isotopic compositions (d18O=5.88-7.27 per mil; eHf(t)=3.6-7.3), indicating that they crystallized from a series of cogenetic melts with various degrees of fractional crystallization. This, along with the general absence of older inherited zircons, rules out significant crustal contamination during zircon growth. The zircons are mostly enriched in d18O relative to mantle values, indicating the involvement of an 18O-enriched crustal source in the generation of the Duolong porphyries. Together with the presence of syn-mineralization basaltic andesite, the mixing between silicic melts derived from the lower crust and evolved H2O-rich mafic melts derived from the metsomatizied mantle wedge, followed by subsequent fractional crystallization (FC) and minor crustal contamination in the shallow crust, could well explain the petrogenesis of the Duolong porphyries. Significantly, the hybrid melts possibly inherited the arc magma characteristics of abundant F, Cl, Cu, and Au elements and high oxidation state, which contributed to the formation of the Duolong porphyry Cu-Au deposit.

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The monograph presents results of comprehensive geological and geophysical studies carried out in 1973 and 1976 during Cruises 54 and 58 of R/V "Vityaz" in the Eastern Indian Ocean. On the base of obtained data a description of topography, magnetic and gravity fields, structure of the sedimentary series and deep crustal structure of the East Indian Ridge, Central, West Australian and Cocos Basins, the Sunda Trench has been done. Materials on petrography, petrochemistry and geochemistry of igneous rocks in the region have been summarized. New geological and geophysical information has been compared with with DSDP materials. Tectonics and geological history of the Eastern Indian Ocean are under consideration.