Simple models of coupled fluid infiltration and redox reactions in the crust     

Jay J. Ague 《Contributions to Mineralogy and Petrology》1998,132(2):180-197

Simple one-dimensional numerical models are presented for coupled advection-hydrodynamic dispersion and kinetically controlled oxidatioin-reduction reactions in graphite-free porous media containing magnetite coexisting with silicate assemblages. Fluid-solid interactions involving either OH (O₂-H₂O-H₂) or COH (O₂-H₂O-H₂-CO₂-CO-CH₄) fluids are considered at ∼500 ^∘C and 5 kbar. The major implications of the modeling are as follows: (1) Regional (km scale) reduction of typical magnetite-bearing rocks originally at f _O2 near NNO may be possible during long-term metamorphic fluid flow if the infiltrating fluids have sufficiently low f _O2 and sufficiently large concentrations of CH₄ and/or H₂. Regional oxidation of such rocks by highly oxidized OH or COH fluids appears to be difficult to achieve. (2) Nearly identical mineral assemblages and modes may be produced by very different kinetic reaction pathways. The model implies that “equilibrium” assemblages preserved in rocks may not always reflect the true kinetic reaction path that evolved during fluid flow, and highlights the need for quantitative measurements of metamorphic reaction rates. (3) Preservation of sharp lithologic contacts between rocks of very different redox states containing accessory amounts of oxides may be unlikely if fluid-rock interaction times exceed 10³10⁴ years. Substantial contact disruption over these times scales is predicted even for oxide-rich rocks if redox contrasts between layers are large. Flow across lithologic contacts may produce asymmetric patterns of metasomatic mineral zonation that may prove useful for mapping flow directions in metamorphic sequences. (4) For fluid flow in typical T gradients through originally homogeneous rock, significant major element metasomatism (e.g., K, Na, Ca) may be possible without producing large changes in oxide abundances. Received:12 November 1997 / Accepted: 9 March 1998  相似文献   

Isotopic evidence for the source of Ca and S in soil gypsum, anhydrite and calcite in the Atacama Desert, Chile   总被引：1，自引：0，他引：1  

Jason A Rech  Jay Quade 《Geochimica et cosmochimica acta》2003,67(4):575-586

The origin of pedogenic salts in the Atacama Desert has long been debated. Possible salt sources include in situ weathering at the soil site, local sources such as aerosols from the adjacent Pacific Ocean or salt-encrusted playas (salars), and extra-local atmospheric dust. To identify the origin of Ca and S in Atacama soil salts, we determined δ³⁴S and ⁸⁷Sr/⁸⁶Sr values of soil gypsum/anhydrite and ⁸⁷Sr/⁸⁶Sr values of soil calcite along three east-west trending transects. Our results demonstrate the strong influence of marine aerosols on soil gypsum/anhydrite development in areas where marine fog penetrates inland. Results from an east-west transect located along a breach in the Coastal Cordillera show that most soils within 90 km of the coast, and below 1300 m in elevation, are influenced by marine aerosols and that soils within 50 km, and below 800 m in elevation, receive >50% of Ca and S from marine aerosols (δ³⁴S values > 14‰ and ⁸⁷Sr/⁸⁶Sr values >0.7083). In areas where the Coastal Cordillera is >1200 m in elevation, however, coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced. Most pedogenic salts from inland soils have δ³⁴S values between +5.0 to +8.0‰ and ⁸⁷Sr/⁸⁶Sr ratios between 0.7070 and 0.7076. These values are similar to average δ ³⁴S and ⁸⁷Sr/⁸⁶Sr values of salts from local streams, lakes, and salars (+5.4 ±2‰ δ³⁴S and 0.70749 ± 0.00045 ⁸⁷Sr/⁸⁶Sr) in the Andes and Atacama, suggesting extensive eolian reworking of salar salts onto the surrounding landscape. Ultimately, salar salts are precipitated from evaporated ground water, which has acquired its dissolved solutes from water-rock interactions (both high and low-temperature) along flowpaths from recharge areas in the Andes. Therefore, the main source for Ca and S in gypsum/anhydrite in non-coastal soils is indirect and involves bedrock alteration, not surficially on the hyperarid landscape, but in the subsurface by ground water, followed by eolian redistribution of ground-water derived salar salts to soils. The spatial distribution of high-grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt, supporting arguments for tropospheric nitrogen as the main source for soil nitrate.  相似文献   

Elasticity of pyrope and majorite-pyrope solid solutions to high temperatures     

Stanislav V. Sinogeikin  Jay D. Bass 《Earth and Planetary Science Letters》2002,203(1):549-555

Majorite-garnet solid solutions are major mineral phases in the Earth’s upper mantle and transition zone. Here we present the first Brillouin scattering measurements of the elasticity of majorite (Mj, Mg₄Si₄O₁₂)-pyrope (Py, Mg₃Al₂Si₃O₁₂) solid solutions (Mj₅₀Py₅₀ and Mj₈₀Py₂₀) and single-crystal elasticity of pure synthetic pyrope at temperatures up to 800°C. The temperature derivatives of the adiabatic bulk (K_S) and shear (μ) moduli for all compositions along the Mj-Py join are the same within the experimental uncertainties (−∂K_S/∂T=14.0-14.5(20) MPa/K, −∂μ/∂T=8.3-9.2(10) MPa/K). The temperature dependence of the acoustic velocities for Mj-Py solid solutions is about half that of other major transition zone minerals. This implies that temperature variations in the transition zone, inferred from lateral velocity heterogeneity, can be significantly underestimated if the properties of majoritic garnet are not taken into account.  相似文献   

Whither Geography?     

Jay R. Harman 《The Professional geographer》2003,55(4):415-421

I argue that scientific disciplines are esteemed, supported, and patronized largely to the degree to which they are perceived as providing a “return” on invested societal resources. This “return” takes the form of scholarly products that help answer deep human questions or otherwise materially benefit members of the society whose resources they are. Such a view implies that disciplines exist in a “market” in which members compete for these limited resources by delivering products seen as valuable. In such a market, disciplinary relevance and survival are ultimately tied to decisions individual scholars practicing within the disciplines make about which research they pursue, the greater the perceived “return” the better for the long‐term health of the discipline.  相似文献   

An archaeoseismic approach and method for the study of active strike-slip faults     

Jay Stratton Noller  Kent G. Lightfoot 《Geoarchaeology》1997,12(2):117-135

The use of archaeology to study earthquake hazards provides a human dimension to an issue of modern societal concern. We developed an archaeoseismic approach to the study of prehistoric earthquakes on active strike-slip faults. This approach employs a combination of standard archaeological and paleoseismic techniques. We have successfully applied this approach and its attendant methods to an archaeological site that straddles and has been offset by the San Andreas fault in northern coastal California. Resultant fault parameters, including cumulative rate of slip and timing of the penultimate event, are comparable to results of strictly paleoseismic investigations at other sites on this fault. The archaeoseismic approach furnishes a number of advantages over geologic studies in terms of the availability and number of potential study sites, the abundance of datable materials, and the array of potential piercing features with which to constrain fault history. © 1997 John Wiley & Sons, Inc.  相似文献   

Effects of iron limitation on intracellular cadmium of cultured phytoplankton: Implications for surface dissolved cadmium to phosphate ratios     

Erin S. Lane  David M. Semeniuk  Robert F. Strzepek  Jay T. Cullen  Maria T. Maldonado   《Marine Chemistry》2009,115(3-4):155-162

This study compares intracellular Cd content (Cd:C) of cultured marine phytoplankton grown under various Fe levels, with estimated particulate Cd:P ratios derived from regression slopes of Cd versus PO₄³⁻ relationships from a global dataset. A 66-fold difference in Cd:C ratios was observed among the seven species grown under identical Fe concentrations, with oceanic diatoms having the highest Cd quotas and prymesiophytes the lowest. Interestingly, all species significantly increased their Cd:C ratios under Fe-limitation (on average 2-fold). The global data set also showed that the mean estimated Cd:P ratio of surface water particulates in HNLC (high nutrient low chlorophyll) regions were approximately 2-fold higher than non-HNLC regions. A sequence of events are proposed to explain high Cd:P ratios in HNLC waters. First, the seasonal relief from Fe-limitation in HNLC regions leads to blooms of large chain forming diatoms with high intrinsic Cd:P ratios. These large blooms may, in theory, deplete surface water CO₂ and Zn concentrations, which ultimately, would result in increased Cd uptake. Eventually these blooms will run out of Fe, which has been shown to further increase intercellular Cd via growth biodilution and increased Cd uptake through non-specific Fe(II) transporters. Ultimately, Fe-limited diatoms with enhanced Cd quotas will sink out of surface waters leading to pronounced regional differences in Cd:P ratios between HNLC and non-HNLC waters in the global ocean.  相似文献   

Holographic in situ stress measurements   总被引：3，自引：0，他引：3  

Jay D. Bass  Douglas Schmitt  Thomas J. Ahrens 《Geophysical Journal International》1986,85(1):13-41

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Evidence for the silicate source of relict soils on the Edwards Plateau, central Texas     

M. Jennifer Cooke  Libby A. Stern  Jay L. Banner 《Quaternary Research》2007,67(2):275-285

Relict soils provide insights into Quaternary soil formation and erosion on the Edwards Plateau of central Texas and into soil-forming processes in karst terranes. Late Quaternary climate-driven soil erosion produced a mosaic of thick and thin soils on the Edwards Plateau landscape. Thick soils on uplands of the Edwards Plateau are interpreted to be relicts of a formerly more extensive soil cover that was eroded during the late Pleistocene to middle Holocene. The relict, thick soils are silicate-rich and most commonly overlie the relatively silicate-poor Cretaceous Edwards Limestone, which supports the idea that the thick soils did not form from weathering of the underlying limestone. Other potential sources of silicates for the relict soils include dust, alluvial sediments, and the Del Rio Clay, a stratigraphically higher but locally eroded clay-rich unit. Here we investigate the geographic distribution, texture, clay-sized mineralogy, rare earth element geochemistry, and neodymium isotope composition of the relict soils. We have found that the relict, thick soils are deeply weathered soils that occur dominantly over the Edwards Limestone and have a high clay content and a neodymium isotope composition that is similar to that of the Del Rio Clay. Thus, we propose that in situ weathering of the Del Rio Clay, along with partial weathering of the upper portion of the underlying Edwards Limestone produced thick chert- and clay-rich soils over resistant limestone. In areas like the Edwards Plateau, where pure limestones are interbedded with clay-rich strata, the overlying clay-rich strata must be considered as a possible silicate source to soils on pure limestone bedrock.  相似文献   

Reduction in organic contaminant exposure and resultant hepatic hydropic vacuolation in winter flounder (Pseudopleuronectes americanus) following improved effluent quality and relocation of the Boston sewage outfall into Massachusetts Bay, USA: 1987-2003     

Moore M  Lefkovitz L  Hall M  Hillman R  Mitchell D  Burnett J 《Marine pollution bulletin》2005,50(2):156-166

Effluent upgrades for metropolitan Boston have included toxicant reduction, primary and secondary treatment and outfall extension. Between 1992 and 2003 winter flounder at five stations were surveyed annually for liver and muscle burden and chronic hepatic sub-lethal impacts of polynuclear and halogenated aromatic hydrocarbons, and metals. Trends in flounder availability and fin condition were also examined. In 1988 12% of the adult winter flounder in Boston Harbor exhibited hepatic neoplasms and up to 80% had hepatic hydropic vacuolation (HV). Tumor prevalence fell to 0-2% and HV to <50% by 1996. Since then tumors have been absent, while a steady prevalence of HV has persisted, consistent with lower hydrocarbon loading and tissue levels. Contaminants and HV also fell with distance from the Boston outfall. After the outfall extension was activated in 2000, there has been no significant change in flounder liver health at the new outfall site.  相似文献   

Charged dust in the outer planetary magnetospheres     

Jay Roderick Hill  D. A. Mendis 《Earth, Moon, and Planets》1981,25(4):427-436

Interplanetary dust grains entering the Jovian plasmasphere become charged, and those in a certain size range get magneto-gravitationally trapped in the corotating plasmasphere. The trajectories of such dust grains intersect the orbits of one or more of the Galilean satellites. Orbital calculations of micron sized dust grains show that they impact the outermost satellite Callisto predominantly on its leading face, while they impact the inner three — Io, Europa and Ganymede — predominantly on the trailing face. These results are offered as an explanation of the observed brightness asymmetry between the leading and trailing faces of the outer three Galilean satellites. The albedo of Io is likely to be determined by its volcanism.  相似文献