Petrology and Geochemistry of Boninite Series Volcanic Rocks,Chichi-jima, Bonin Islands, Japan

An Eocene submarine boninite series volcanic center isexposed on the island of Chichi-jima, Bonin Islands, Japan. Five rocktypes, boninite, bronzite andesite, dacite, quartz dacite, and rhyolite,were distinguished within the boninite volcanic sequence on the basis ofpetrographic and geochemical observations. Boninite lavas contain highmagnesium, nickel, and chromium contentsindicative of primitive melts,but have high silica contents relative to other mantle-derived magmas.All boninite series lavas contain very low incompatible elementconcentrations, and concentrations of high-field strength elements inprimitive boninite lavas are less than half of those found in depletedmid-ocean ridge basalts. Abundances of large-ion lithophile elements arerelatively high in boninite series lavas, similar to the enrichmentsobserved in many island arc lavas. Trends for both major and traceelement data suggest that the more evolved lavas of the boninite magmaseries were derived primarily through high-level fractionalcrystallization of boninite. Textural features, such as resorption andglomeroporphyrocrysts, and reverse chemical zonations suggest that magmamixing contributed to the development of the quartz dacitelavas

The influence of rice husk ash addition on the properties of metakaolin-based geopolymers

This paper investigates the replacement of metakaolin (MK) with rice husk ash (RHA) in the production of alkali-activated binders or geopolymers. The influence of the RHA addition on compressive and flexural strength, as well as water absorption and apparent porosity were determined, in terms of the percentage of RHA in the mixture and molar ratios of the mixes. Fourier Transform Infrared (FTIR) spectroscopy and Energy Dispersive spectroscopy (EDS) were carried out to assess the changes in the microstructure of the geopolymer matrices with the RHA addition. Results have shown that RHA may be a supplementary precursor for geopolymers. The composition of the geopolymer matrices containing 0-40% RHA is very similar, which indicates that the additional Si provided by RHA is not incorporated to the geopolymer matrix. In addition, geopolymers with RHA content higher than 40% present a plastic behavior, characterized by extremely low strength and high deformation, which can be attributed to the formation of silica gel in formulations containing variable Si/Al ratio

Investigations of water-rock interaction in geothermal systems of Japan and Taiwan. Final report

Separate abstracts were prepared for individual papers. (MHR

Petrology and Geochemistry of Boninite Series Volcanic Rocks, Chichi-jima, Bonin Islands, Japan

An Eocene submarine boninite series volcanic center is exposed on the island of Chichi-jima, Bonin Islands, Japan. Five rock types, boninite, bronzite andesite, dacite, quartz dacite, and rhyolite, were distinguished within the boninite volcanic sequence on the basis of petrographic and geochemical observations. Boninite lavas contain high magnesium, nickel, and chromium contents indicative of primitive melts, but have high silica contents relative to other mantle-derived magmas. All boninite series lavas contain very low incompatible element concentrations, and concentrations of high-field strength elements in primitive boninite lavas are less than half of those found in depleted mid-ocean ridge basalts. Abundances of large-ion lithophile elements are relatively high in boninite series lavas, similar to the enrichments observed in many island arc lavas. Trends for both major and trace element data suggest that the more evolved lavas of the boninite magma series were derived primarily through high-level fractional crystallization of boninite. Textural features, such as resorption and glomeroporphyrocrysts, and reverse chemical zonations suggest that magma mixing contributed to the development of the quartz dacite lavas

Petrology and Geochemistry of Boninite Series Volcanic Rocks, Chichi-jima, Bonin Islands, Japan

An Eocene submarine boninite series volcanic center is exposed on the island of Chichi-jima, Bonin Islands, Japan. Five rock types, boninite, bronzite andesite, dacite, quartz dacite, and rhyolite, were distinguished within the boninite volcanic sequence on the basis of petrographic and geochemical observations. Boninite lavas contain high magnesium, nickel, and chromium contents indicative of primitive melts, but have high silica contents relative to other mantle-derived magmas. All boninite series lavas contain very low incompatible element concentrations, and concentrations of high-field strength elements in primitive boninite lavas are less than half of those found in depleted mid-ocean ridge basalts. Abundances of large-ion lithophile elements are relatively high in boninite series lavas, similar to the enrichments observed in many island arc lavas. Trends for both major and trace element data suggest that the more evolved lavas of the boninite magma series were derived primarily through high-level fractional crystallization of boninite. Textural features, such as resorption and glomeroporphyrocrysts, and reverse chemical zonations suggest that magma mixing contributed to the development of the quartz dacite lavas

Mineral chemistry of garnet peridotites from Paleozoic and Cenozoic lithosphere and Mesozoic UHP terrain: constraints on lithospheric evolution, east China

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Petrogenesis of eclogites enclosed in mantle-derived peridotites from the Sulu UHP terrane: constraints from trace elements in minerals and Hf isotopes in zircon

Garnet clinopyroxenite and eclogite lenses are widespread in mantle-derived garnet peridotites from the Sulu UHP terrane, eastern China. In order to constrain their origin, major and trace element compositions of minerals from 6 eclogites and one garnet clinopyroxenite, and Hf isotopes of zircons from one eclogite, were analyzed by electron probe, LA-ICP-MS and LA- (MC) ICP-MS, respectively. Eclogitic garnets show a large variation in composition (Alm20-48Prp24-50Grs15-38Sps 1), weakly correlated with garnets in their host peridotites. Garnets show LREE depletion and flat HREE patterns, with Lan of 0.02-0.52 and Lun of 5-75. Some garnets show zoning in HREE and Y with a U-shaped, concave-downward profile, but locally exhibit positive sharp variations in HREE and Y contents; such feature reflects disturbance in chemical-physical conditions during garnet growth. Clinopyroxene exhibits humped (mostly) or sinusoidal REE patterns, with Lan of 0.3-6.0, Ndn of 2-14 and (La/Lu)n of 1.8-113 with a few exceptions. Partition coefficients of REE (D) between coexisting clinopyroxene and garnet in eclogite show a large variation: DLREE and DHREE ranging from 10 to100 and from 0.1 to 0.01, respectively, similar to DREE values of the natural systems at 800-1100°C. The D values (0.1-1) of HREE between Cpx and Grt from Grt clinopyroxenite and one eclogite differ distinctly from the other eclogites, which are consistent with high-T experimental data on garnet lherzolites. Zircons from the Xugou eclogite have no inherent core, which have low U/Th (most < 0.20) and 176Lu/177Hf (0.000008-0.0000637), and relative high 176Hf/177Hf (0.28241-0.28262) ratios. These features indicate a metamorphic signature, and document that metasomatism affected the eclogite protolith. The model ages (TDM1) of zircons mostly cluster around 1.0-1.1 Ga, which probably reflects the metasomatic source. Bulk compositions of eclogite and Grt clinopyroxenite differ from those of Sulu eclogites in gneiss and MORB. The protoliths of these rocks may reflect the intrusion of asthenosphere-derived melts in Proterozoic. Eclogites with convex REE pattern and garnet clinopyroxenite were formed by high-pressure crystal accumulation whereas the LREE-enriched eclogites may represent crystallized melt; both eclogite and clinopyroxenite together with their host peridotite were metamorphosed at 700-965°C and ≥ 4 GPa during the Triassic northward subduction of the Yangtze craton.17 page(s