ALBERT

Description: An ascorbic acid extraction at pH 7.5 has been examined to assess the influence of reaction conditions (pH, ascorbic acid concentration) on the dissolution of Fe from synthetic 2-line ferrihydrite and from other Fe-bearing minerals. The method was highly selective for Fe in ferrihydrite with only small amounts of Fe extracted from other (oxyhydr)oxides or clays. The labile Fe extracted from the synthetic 2-line ferrihydrite stored as a slurry decreased with time, and high resolution microscopy showed that the older materials formed networked aggregates that slow down the dissolution. The apparent rate constant for the dissolution of fresh 2-line ferrihydrite (similar to 10(-3) s(-1)) was an order of magnitude larger than that for aged suspensions (similar to 10(-4) s(-1)). Fresh 2-line ferrihydrite that was filtered, freeze-dried, frozen and freeze-dried, and stored in the dry was even less readily dissolved (apparent rate constants similar to 10(-6) s(-1)). These ferrihydrites also contained networked aggregates and, additionally, appear to occur as granular aggregates (visible to the naked eye) during the early stages of dissolution. Storage of filtered, freeze-dried, and frozen and freeze-dried ferrihydrites, whether in water or air, produced similar dissolution behaviour because aggregation caused by de-watering decreases the labile Fe content and is not reversed by re-hydration. The determination of labile Fe in ferrihydrite requires that natural samples should be collected, stored and extracted wet. The most aged samples dissolved by parabolic dissolution kinetics indicate that the rates of dissolution were controlled by the diffusion of reactant into the internal porosity of aggregates. (C) 2010 Elsevier B.V. All rights reserved.

Description: The transformation of ferrihydrite (5Fe(2)O(3)center dot 9H(2)O) to hematite (alpha-Fe2O3) under alkaline condition in the presence and absence of lead was for the first time investigated using in situ, time-resolved synchrotron-based energy dispersive X-ray diffraction combined with off-line chemical characterization and imaging. The results showed that the crystallization of hematite occurred via a two-stage process with goethite (alpha-FeOOH) as an intermediate phase. The presence of lead enhanced the formation of hematite and reduced the induction times (similar to 20-30%) but had little effect on the mechanism of the transformation reactions. The reaction rates for the two systems (with and without lead) ranged from 12 to 259 x 10(-4) s(-1) and 19 to 461 x 10(-5) s(-1) for the first and second stage, respectively. The activation energies of nucleation of the two systems were 16(+/- 3) and 9(+/- 2) kJ/mol, while the activation energies for crystallization ranged from 41(+/- 7) to 77(+/- 14) kJ/mol. During the hematite crystallization, the majority of the lead in the system was rapidly and irreversibly incorporated into the final hematite, while only minor amounts of lead were released back into solution.

Description: The time has come to exploit the full richness of broadband, three-component waveforms. The inversion of full seismograms leads to a tremendous improvement in imaging resolution due to the ability to map structures that are smaller than the seismic wavelength. In addition, it provides important constraints on density and attenuation. State-of-the-art software for full waveform tomography is available in scientific environments but is not yet accessible to the practitioner. The Toolbox for Applied Seismic Tomography (TOAST) will open a new window to seismic inversion. Due to advances in available computational resources and recent developments in high performance and parallelized computing, 3D inversion of full seismograms is within reach. By combining tested code collections for waveform modelling and the solution of large inverse problems, complemented by experience in the management of large software projects and by sound expertise in the inversion of elastic waves from the centimeter to the kilometer scale, the cooperation of the TOAST project partners will provide a unique knowledge base for implementing flexible and efficient tools for full waveform tomography and to transfer the knowledge to industrial practice. The TOAST project pursues the concept of modularization. It will provide modules that interact through standardized interfaces and thereby can be re-combined in application-specific and efficient ways. The Toolbox for Applied Seismic Tomography will prove its worth through application to surveys from commercial practice. Existing data from seismic experiments at different scales (e.g., monitoring of embankments, CO2 sequestration studies) and newly aquired shallow seismic and ultrasonic data will serve as case studies to validate the functionality of the toolbox.

Description: HOTSPOT is an international collaborative effort to understand the volcanic history of the Snake River Plain (SRP). The SRP overlies a thermal anomaly, the Yellowstone-Snake River hotspot, that is thought to represent a deep-seated mantle plume under North America. The primary goal of this project is to document the volcanic and stratigraphic history of the SRP, which represents the surface expression of this hotspot, and to understand how it affected the evolution of continental crust and mantle. An additional goal is to evaluate the geothermal potential of southern Idaho. Project HOTSPOT has completed three drill holes. (1) The Kimama site is located along the central volcanic axis of the SRP; our goal here was to sample a long-term record of basaltic volcanism in the wake of the SRP hotspot. (2) The Kimberly site is located near the margin of the plain; our goal here was to sample a record of high-temperature rhyolite volcanism associated with the underlying plume. This site was chosen to form a nominally continuous record of volcanism when paired with the Kimama site. (3) The Mountain Home site is located in the western plain; our goal here was to sample the Pliocene-Pleistocene transition in lake sediments at this site and to sample older basalts that underlie the sediments. We report here on our initial results for each site, and on some of the geophysical logging studies carried out as part of this project.

Description: Iron-rich (ferruginous) conditions were a prevalent feature of the ocean throughout much of Earth's history. The nature of elemental cycling in such settings is poorly understood, however, thus hampering reconstruction of paleoenvironmental conditions during key periods in Earth evolution. This is particularly true regarding controls on nutrient bioavailability, which is intimately linked to Earth's oxygenation history. Elemental scavenging during precipitation of iron minerals exerts a major control on nutrient cycling in ferruginous basins, and the predictable nature of removal processes provides a mechanism for reconstructing ancient ocean chemistry. Such reconstructions depend, however, on precise knowledge of the iron minerals formed in the water column. Here, we combine mineralogical and geochemical analyses to demonstrate formation of the mixed-valence iron mineral, green rust, in ferruginous Lake Matano, Indonesia. Carbonated green rust (GR1), along with significant amounts of magnetite, forms below the chemocline via the reduction of ferrihydrite. Further, we show that uptake of dissolved nickel, a key micronutrient required for methanogenesis, is significantly enhanced during green rust formation, suggesting a major control on methane production in ancient ferruginous settings.

Description: Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M w = 8.2) and 1995 (M w = 8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42 ± 2 by 56 ± 2 km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Nábělek (1984) inversion procedure is: (strike, dip, rake) = (277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20 ± 2 s, a stress drop of 5.4 ± 2.5 MPa and a seismic moment of 2.7 ± .7 × 1020 Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54 km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2 m, a source duration of 30 s and a seismic moment of 1.88 × 1020 Nm.