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listelement.badge.dso-typeЭлемент, ARRIVAL OF EXTREMELY VOLATILE-RICH HIGH-Mg MAGMAS CHANGES EXPLOSIVITY OF MOUNT ETNA(2007) Kamenetsky V.S.; Pompilio M.; Métrich N.; Sobolev A.V.; Kuzmin D.V.; Thomas R.The volcanic hazard potential of Mount Etna volcano is currently nourished by long-lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world's largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (FS) basalts ejected violently 4 k.y. ago. The FS primitive magmas (13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H2O and 3300 ppm CO2), and bear a trace element signature of a garnet-bearing, metasomatized source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo91), clinopyroxene (Mg# 92.5), and Cr spinel deep in the plumbing system (>5 kbar), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the FS fallout, provides a good explanation for major compositional and eruptive features of Mount Etna. published 255-258 2.4. TTC - Laboratori di geochimica dei fluidi JCR Journallistelement.badge.dso-typeЭлемент, ON "BIRTHMARKS" IN RARE-METAL GRANITES OF THE LOSEVKA PLUTON, NORTHERN KAZAKHSTAN(2007) Letnikov F.A.; Levin A.V.; Letnikova A.F.The Losevka pluton of rare-metal albite granite, which was explored as a possible source of columbite-zircon-malacon ore, is composed of quartz, sodic plagioclase, potassium feldspar, annite, protolithionite, lepidomelane, and Li-muscovite. The average chemical composition of this rock is as follows, wt %: 74.14 SiO2, 0.04 TiO2, 14.07 Al2O3, 1.05 Fe2O3, 0.78 FeO, 0.15 MnO, 0.09 MgO, 0.47 CaO, 4.65 Na2O, 4.11 K2O, and 0.03 P2O5. The accessory minerals are zircon, malacon, and cyrtolite (874 ppm); apatite (18 ppm); ilmenite (114 ppm); xenotime and monazite (119 ppm); and Nb-columbite (463 ppm). The black inclusions up to 15 cm in size, which are observed in this granite and called “birthmarks” by local geologists, consist of the same rock-forming minerals as the surrounding granite, but are enriched in MnO, MgO, CaO, TiO2, and F and depleted in SiO2 relative to the light granite. The black granite is also distinguished by much higher Sr and Ba contents and lower La, Rb, Y, Nb, REE, Cs, Ta, Th, and U contents. The black color is caused by enrichment in manganese oxides, manganoilmenite, and Mn-annite. All rock-forming minerals are pervaded by thin veinlets of Mn-oxides. In addition, bastnaesite, Y-and Th-fluorides, zircon, and malacon have been identified. Aggregates of black-colored minerals are not the products of the fractionation of the initial magma or immiscibility effects, because the structure of the albite-potassium feldspar-quartz-mica matrix is the same both in black and light granites. The percolation of a deep-sourced fluid enriched in Mn and F into a granitic melt might be a more probable origin.listelement.badge.dso-typeЭлемент, COMPARATIVE TAPHONOMY OF VENDIAN GENERA BELTANELLOIDES AND NEMIANA: TAXONOMY AND LIFESTYLE(2007) Leonov M.V.Taphonomic analysis of new material from Verdian sequences of the White Sea and southwestern Ukraine provides data for a better definition of both the widely distributed fossil taxa of Beltanelloides and Nemiana. A new type of Beltanelloides preservation is described, so it is now possible to attribute some sandstone imprints to this taxon. Nemiana simplex seems to have a lifestyle and level of body organization comparable with that of sponges. The narrow range of facies in which Nemiana occurs, when compared to the much broader range of Beltanelloides, is compelling evidence for a benthic lifestyle of Nemiana.listelement.badge.dso-typeЭлемент, SPECIFICITY OF PYROMETAMORPHIC MINERALS OF THE ELLESTADITE GROUP(2007) Zateeva S.N.; Sokol E.V.; Sharygin V.V.Numerous rare and new mineral species are synthesized during the process of pyrometamorphism (Gross, 1977; Chesnokov et al., 1987; Chesnokov and Shcherbakova, 1991; Chesnokov, 1999), including silicooxides, chloride-, fluoride, and sulfate-silicates, carbonate-sulfides, chloride-oxides, etc. Having made sense of numerous findings of compounds of this type, Chesnokov (1999) set forth the concept of the crystallochemical transition at extreme temperatures attaining 1200–1450°C in pyrogenic systems. First of all, intertype transitions (oxygen-bearing-oxygen-free) and interclass transitions (chloride-silicate, carbonate-sulfide, chlorideoxide) are realized. The specificity of pyrometamorphic mineral assemblages consists in the abundance of silicates with additional anions (F−, Cl−, (CO3)2−) (Sokol et al., 2005). Minerals of the ellestadite group Ca10(SiO4)3 − x (SO4)3 − x (PO4)2x (OH,F,Cl)2 are a spectacular example of these features. In the general case, they are silicate-sulfate-phosphate-hydroxide-chlorides-fluorides. The detailed description of these minerals based on the study of the original collection of pyrometamorphic minerals is presented in this paper.listelement.badge.dso-typeЭлемент, ELASTIC MODULI OF ANISOTROPIC CLAY(2007) Bayuk I.O.; Ammerman M.; Chesnokov E.M.Clay minerals are important components in shales, controlling their elastic properties and anisotropy. The elasticity of crystalline clay minerals differs significantly from that of clay in situ because of the ability of clay particles to bind water. In the majority of published works, only isotropic moduli for in situ clays are reported. However, anisotropy is inherent in the clay elasticity. We develop an inversion technique for determination of the stiffness tensor of in situ clay from the shale's stiffness tensor. As an example, we obtain the stiffness tensor of a "water-clay" composite from the data on the water-saturated Greenhorn shale sample, whose clay composition consists of almost equal amounts of illite and smectite and comparable amounts of kaolinite and chlorite. The stiffness tensor of the water-clay composite is found for the Greenhorn shale with step-by-step inversion based upon an effective medium theory. The inversion uses a nonlinear optimization technique with bounds imposed on the estimated parameters. In the inversion, we apply different approaches of the effective medium theory using a published method referred to here as the generalized singular approximation (GSA). The GSA method makes it possible to take into account the microstructure of shales. The resulting elasticity constants of the anisotropic (transversely isotropic) in situ clay composite are C-11 = 23.7, C-33 = 8.5, C-44 = 0.8, C-66 = 5.7, and C-13 = 3.1 (in GPa); and the density equals 2.17 g/cm(3). The Thomsen parameters for the clay composite are epsilon = 0.89, gamma = 3.10, and delta = -0.34. The elasticity constants found for this clay composite can be used in the theoretical analysis of shales that have a similar composition of clay but with different mineral compositions. The inversion technique developed can be used for general shale water-clay composites when the mineral composition and orientation of the clay platelets are known.