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Eocene-Oligocene volcanic rocks drilled at Site 786 in the Izu-Bonin forearc cover a wide range of compositions from primitive boninites to highly evolved rhyolites. K-Ar dating reveals at least two distinct episodes of magmatism; one at 41 Ma and a later one at 35 Ma. The early episode produced low-Ca boninites and bronzite andesites that form an oceanic basement of pillow lavas and composite intrusive sheets, overlain by flows and intrusive sheets of intermediate-Ca boninites and bronzite-andesites and a fractionated series of andesites, dacites, and rhyolites. The later episode produced high-Ca boninites and intermediate-Ca boninites, exclusively as intrusive sheets.Trace element data indicate that all of the evolved chemical groups at Site 786 can be related by fractionation and/or accumulation of the observed mineral phases back to the three boninite groups, which represent distinct parental magmas. The boninites have very low abundances of Ti, Y, and HREE relative to MORB, consistent with an origin from a depleted source, and consideration of Cr-Y-Ti melting systematics and major element data indicates that the low-Ca boninites came from a source more depleted than the high-Ca boninite source. The boninites show enrichment in LIL elements, LREE and selected HFS (Zr, Hf) relative to Ti, Y, HREE which reflect the addition of a "subduction" component to the boninite source region. The distinctive enrichment of Zr is a feature not found in typical arc-related volcanics, but it has been recognized in several other boninite suites. The fractionation of Zr from Sm and Ti suggests an important role for amphibole in any petrogenetic model to explain the genesis of these boninites. Possibilities include the addition of a melt derived from subducted amphibolitized ocean crust and the interaction of an OIB-like melt with amphibole stabilized in the mantle wedge.The multiple episodes of boninite magmatism at Site 786 imply a recurrence of conditions for boninite genesis over an extended period of time (at least 7 m.y.). This refutes the idea that boninites are generated solely at the initiation of subduction. However, the predominance of LREE and Zr, Ta, Nb enrichment in the Eocene boninite groups does imply a genetic relationship with the onset of subduction and may be explained by early hydrous melting of amphibolitized forearc lithospheric mantle combined with mobilization of a pre-existing OIB-like component. 1 Fryer, P., Pearce, J. A., Stokking, L. B., et al., 1992. Proc. ODP, Sci. Results, 125: College Station, TX (Ocean Drilling Program).

The assignments of Raman bands in the spectra of silicate and germanate glasses, including SiO2, GeO2, Rb2Si4O9, NaFe3+Si3O8, anhydrous and hydrous albite (NaAlSi3O8) and anhydrous and deuterated Ge‐albite (NaAlGe3O8) and Ge‐jadeite (NaAlGe2O6), were re‐examined in the light of new information from Raman measurements at high pressures and temperatures. On the basis of polarized Raman spectra of single‐component (e.g. SiO2 and GeO2) glasses, it is demonstrated that the νas(T–O–T) mode (where T represents tetrahedrally coordinated cations, Si or Ge) gives rise to LO–TO splitting. The depolarized nature of the νas(T–O–T) LO–TO doublet in the Raman spectra of SiO2 and GeO2 glasses reflects the fact that the local site symmetry of T cations is close to Td. Persistence of the νas(T–O–T) LO–TO doublet slightly above the melting temperature demonstrates that significant intermediate range order exists even in the high‐temperature liquids. Likewise, in the spectra of NaFe3+Si3O8 and NaFe3+Si2O6 glasses, the high‐wavenumber νas(T–O–T) bands exhibit a depolarized character characteristic of a three‐dimensional network. The depolarized nature of the νas(T–O–T) bands indicates that the local site symmetry of the T cation is close to Td and that the triply degenerate (F) character of the νas(T–O–T) is preserved. Additionally, a significant shift in the position of the νas(T–O–T) mode on substituting NaFe3+ for Si4‐ reflects strong vibrational coupling of FeO4 and SiO4 tetrahedra in the glass. In the hydrated and deuterated aluminosilicate and ‐germanate glasses, it is proposed that the degeneracy of the νas(T–O–T) bands is lifted because of structural distortion caused by the presence of H3O+ (D3O+) ions. © 1997 John Wiley & Sons, Ltd.

Abstract:The spectral imaging (SI) approach is used in analytical electron microscopy for determining chemical compositions in materials at the microscale. A major challenge is how to efficiently unlock microspatially resolved chemical information in large SI data cubes. Tata Steel has developed an in-house software approach called PhAse Analysis, Recognition and Characterization (PARC). PARC combines automated phase recognition with flexible user-defined refinement functions to create phase allocation models. These models may be used in automated batch processing on multiple SI fields, enabling the visualization of complex microstructures, and the quantification of phase proportions and chemistry, at length scales up to several millimeters. The approach bridges the gap between microanalysis and bulk analysis and lends itself to cross-validation with independent bulk analytical techniques such as X-ray fluorescence (XRF) and X-ray diffraction (XRD).

The effect of curing conditions (sealed and unsealed) on the pore solution composition and carbonation resistance of different binary alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes is investigated in this study. The studied mixtures were with FA/GBFS ratios of 100:0, 70:30; 50:50, 30:70, 0:100. Ordinary Portland cement (OPC) and Cement III/B (70 wt.% of GBFS and 30 wt.% OPC) pastes with the same precursor content were also studied to provide a baseline for comparison. Accelerated carbonation conditions (1% (v/v) CO2, 60% RH for 500 days) were considered for evaluating the carbonation resistance of the pastes.