Geochemical controls on sediment reactivity and buffering processes in a heterogeneous aquifer     

Carlos Descourvières  Niels Hartog  Bradley M. Patterson  Carolyn Oldham  Henning Prommer 《Applied Geochemistry》2010

The injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short- and long-term imbalance between freshwater supply and demand. The extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection, storage and recovery. Water–sediment interactions within the most permeable parts of the aquifer, where the bulk of the injectant will penetrate, may dominate, however, water quality may also be impacted by interactions within the finer-grained, less permeable but potentially highly reactive media. In this study, the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised, the amount, type and reactivity of the sedimentary reductants present determined, and the relationship between reductive capacity and sedimentary lithologies quantified. The average potential reductive capacities (PRC_TOT), based on total organic C and pyrite concentrations of the sediment, were quantified for sands (382 μmol O₂ g⁻¹), clays (1522 μmol O₂ g⁻¹), and silts (1957 μmol O₂ g⁻¹). Twenty-seven samples, spanning the three different lithologies, were then incubated for 50 days and the measured reductive capacities (MRC) determined for the sands (29.2 μmol O₂ g⁻¹), silts (136 μmol O₂ g⁻¹), and clays (143 μmol O₂ g⁻¹). On average, the MRC were 10% of the PRC_TOT. The main consumers of O₂ were pyrite (20–100%), sedimentary organic matter (SOM; 3–56%), siderite (3–28%) and Fe(II)-aluminosilicates (8–55%). The incubation data plus hydrogeochemical modelling, indicated that pH-buffering was controlled firstly by dissolution of trace level carbonates, followed by dissolution of feldspars. Zinc, Co, Ni, Cd and Pb were readily mobilized during incubation.  相似文献   

Integrated exploration workflow in the south Middle Magdalena Valley (Colombia)     

Isabelle Moretti  German Rodriguez Charry  Marcela Mayorga Morales  Juan Carlos Mondragon 《Journal of South American Earth Sciences》2010,29(2):187-197

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Role of cryptic amphibole crystallization in magma differentiation at Hudson volcano, Southern Volcanic Zone, Chile   总被引：1，自引：0，他引：1  

David J. Kratzmann  Steven Carey  Roberto A. Scasso  Jose-Antonio Naranjo 《Contributions to Mineralogy and Petrology》2010,159(2):237-264

Hudson volcano (Chile) is the southern most stratovolcano of the Andean Southern Volcanic Zone and has produced some of the largest Holocene eruptions in South America. There have been at least 12 recorded Holocene explosive events at Hudson, with the 6700 years BP, 3600 years BP, and 1991 eruptions the largest of these. Hudson volcano has consistently discharged magmas of similar trachyandesitic and trachydacitic composition, with comparable anhydrous phenocryst assemblages, and pre-eruptive temperatures and oxygen fugacities. Pre-eruptive storage conditions for the three largest Holocene events have been estimated using mineral geothermometry, melt inclusion volatile contents, and comparisons to analogous high pressure experiments. Throughout the Holocene, storage of the trachyandesitic magmas occurred at depths between 0.2 and 2.7 km at approximately ~972°C (±25) and log fO₂ −10.33–10.24 (±0.2) (one log unit above the NNO buffer), with between 1 and 3 wt% H₂O in the melt. Pre-eruptive storage of the trachydacitic magma occurred between 1.1 and 2.0 km, at ~942°C (±26) and log fO₂ −10.68 (±0.2), with ~2.5 wt% H₂O in the melt. The evolved trachyandesitic and trachydacitic magmas can be derived from a basaltic parent primarily via fractional crystallization. Entrapment pressures estimated from plagioclase-hosted melt inclusions suggest relatively shallow levels of crystallization. However, trace element data (e.g., Dy/Yb ratio trends) suggests amphibole played an important role in the differentiation of the Hudson magmas, and this fractionation is likely to have occurred at depths >6 km. The absence of a garnet signal in the Hudson trace element data, the potential staging point for differentiation of parental mafic magmas [i.e., ~20 km (e.g., Annen et al. in J Petrol 47(3):505–539, 2006)], and the inferred amphibolite facies [~24 km (e.g., Rudnick and Fountain in Rev Geophys 33:267–309, 1995)] combine to place some constraint on the lower limit of depth of differentiation (i.e., ~20–24 km). These constraints suggest that differentiation of mantle-derived magmas occurred at upper-mid to lower crustal levels and involved a hydrous mineral assemblage that included amphibole, and generated a basaltic to basaltic andesitic composition similar to the magma discharged during the first phase of the 1991 eruption. Continued fractionation at this depth resulted in the formation of the trachyandesitic and trachydacitic compositions. These more evolved magmas ascended and stalled in the shallow crust, as suggested by the pressures of entrapment obtained from the melt inclusions. The decrease in pressure that accompanied ascent, combined with the potential heating of the magma body through decompression-induced crystallization would cause the magma to cross out of the amphibole stability field. Further shallow crystallization involved an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the Hudson suite.  相似文献   

“Invisible” silver and gold in supergene digenite (Cu_1.8S)     

Martin Reich  Stephen L. Chryssoulis  Carlos Palacios  Magdalena Weldt 《Geochimica et cosmochimica acta》2010,74(21):6157-6173

Despite its potential economic and environmental importance, the study of trace metals in supergene (secondary) Cu-sulfides has been seriously overlooked in the past decades. In this study, the concentration and mineralogical form of “invisible” precious metals (Ag, Au) and metalloids (As, Sb, Se, Te) in supergene digenite (Cu_1.8S) from various Cu deposits in the Atacama Desert of northern Chile, the world’s premier Cu province, were determined in detail using a combination of microanalytical techniques. Secondary ion mass spectrometry (SIMS) and electron microprobe analyzer (EMPA) measurements reveal that, apart from hosting up to ∼11,000 ppm Ag, supergene digenite can incorporate up to part-per-million contents of Au (∼6 ppm) and associated metalloids such as As (∼300 ppm), Sb (∼60 ppm), Se (∼96 ppm) and Te (∼18 ppm). SIMS analyses of trace metals show that Ag and Au concentrations strongly correlate with As in supergene digenite, defining wedge-shaped zones in Ag-As and Au-As log-log spaces. SIMS depth profiling and high-resolution transmission electron microscopy (HRTEM) observations reveal that samples with anomalously high Ag/As (>∼30) and Au/As (>∼0.03) ratios plot above the wedge zones and contain nanoparticles of metallic Ag and Au, while samples with lower ratios contain Ag and Au that is structurally bound to the Cu-sulfide matrix. The Ag-Au-As relations reported in this study strongly suggest that the incorporation of precious metals in Cu-sulfides formed under supergene, low-temperature conditions respond to the incorporation of a minor component, in this case As. Therefore, As might play a significant role by increasing the solubility of Ag and Au in supergene digenite and controlling the formation and occurrence of Ag and Au nanoparticles. Considering the fact that processes of supergene enrichment in Cu deposits can be active from tens of millions of years (e.g. Atacama Desert), we conclude that supergene digenite may play a previously unforeseen role in scavenging precious metals from undersaturated (or locally slightly supersaturated) solutions in near-surface environments.  相似文献   

Toward improved operational surge and inundation forecasts and coastal warnings     

Ming Ji  Frank AikmanIII  Carlos Lozano 《Natural Hazards》2010,53(1):195-203

Coastal regions are vulnerable to storm surge and flooding due to tropical and extratropical storms. It is necessary to build robust resiliency of the coastal communities to these hazards. The main objectives of operational surge and inundation forecast and coastal warning systems are to protect life and to sustain economic prosperity. The National Oceanic and Atmospheric Administration of the United States has initiated an integrated effort through pilot demonstration projects, and model-based ocean and coastal forecasting systems, to build improved operational warnings and forecasts capability for storm surge and inundation. This note describes the overall strategy and progress to date, with an emphasis on forecasting extratropical storm surge.  相似文献   

Antigorite equation of state and anomalous softening at 6 GPa: an in situ single-crystal X-ray diffraction study   总被引：1，自引：0，他引：1  

Fabrizio Nestola  Ross J. Angel  Jing Zhao  Carlos J. Garrido  Vicente López Sánchez-Vizcaíno  Giancarlo Capitani  Marcello Mellini 《Contributions to Mineralogy and Petrology》2010,160(1):33-43

The compressibility of antigorite has been determined up to 8.826(8) GPa, for the first time by single crystal X-ray diffraction in a diamond anvil cell, on a specimen from Cerro del Almirez. Fifteen pressure–volume data, up to 5.910(6) GPa, have been fit by a third-order Birch–Murnaghan equation of state, yielding V ₀ = 2,914.07(23) Å³, K _T0 = 62.9(4) GPa, with K′ = 6.1(2). The compression of antigorite is very anisotropic with axial compressibilities in the ratio 1.11:1.00:3.22 along a, b and c, respectively. The new equation of state leads to an estimation of the upper stability limit of antigorite that is intermediate with respect to existing values, and in better agreement with experiments. At pressures in excess of 6 GPa antigorite displays a significant volume softening that may be relevant for very cold subducting slabs.  相似文献   

Competition effects in cation binding to humic acid: Conditional affinity spectra for fixed total metal concentration conditions     

Calin David  Carlos Rey-Castro  Encarnació Companys  José Salvador  Joan Cecilia  Francesc Mas 《Geochimica et cosmochimica acta》2010,74(18):5216-18046

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Field exploration of coupled hydrological and biogeochemical catchment responses and a unifying perceptual model   总被引：3，自引：0，他引：3  

Carlos J. Ocampo  Murugesu SivapalanCarolyn E. Oldham 《Advances in water resources》2006

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Simulating the value of El Niño forecasts for the Panama Canal     

Nicholas E. Graham  Konstantine P. Georgakakos  Carlos Vargas  Modesto Echevers 《Advances in water resources》2006

The Panama Canal relies on rain-fed streamflow into Gatun Lake, the canal’s primary storage facility, for operations—principally ship passage and hydropower generation. Precipitation in much of Panama has a strong negative relationship with eastern tropical Pacific sea surface temperature (SST) and this relationship is reflected in Gatun Lake inflows. For example, the correlation coefficient between wet season (July–December) inflow and NINO3 SST is −0.53 over the period 1914–1997. Operational capabilities to predict tropical Pacific SSTs have been demonstrated by several forecast systems during the past decade, and (as we show) such SST forecasts can be used to reduce the uncertainty of estimates of future inflows (compared with climatological expectations). Because substantial reductions in lake inflow negatively impact canal operations, we wondered whether these forecasts of future inflows, coupled with a method for translating that information into effective operational policy, might result in more efficient canal management. A combined simulation/optimization/assessment “virtual” canal system was implemented and exercised using operational El Niño forecasts over the period 1981–1998. The results show the following main points:

(i)

At current demand levels, the canal system is relatively robust (insensitive to flow forecasts) unless flows are substantially reduced (i.e., during El Niño episodes) or forecasts are extremely accurate.  相似文献   

“The ESA XMM-Newton Science Operations Centre: Making Basic Space Science Available to the Whole Scientific World”     

Carlos Gabriel  Matteo Guainazzi  Leo Metcalfe 《Astrophysics and Space Science》2006,305(3):315-320

XMM-Newton is a major X-ray observatory of the European Space Agency (ESA). Its observing time is open to astronomers from the whole scientific community on a peer reviewed competitive basis. The Science Operations Centre, located at ESA’s premises in Villafranca del Castillo, Spain, is responsible for the instrument operations, as well as for all the tasks related to facilitating the scientific exploitation of the data which the mission has been producing since its launch in December 1999. Among them, one may list:

•	distribution of scientific data in different formats, from raw telemetry, up to processed and calibrated high-level science products, such as images, spectra, source lists, etc;
•	development and distribution of dedicated science analysis software, as well as of continuously updated instrument calibration;
•	regular organisation of training workshops (free of cost), for potential users of XMM-Newton data, where the procedures and techniques to successfully reduce and analyze XMM-Newton data are introduced;
•	access to the data through state-of-the-art, in-house-developed archival facilities, either through the Internet or via CD-ROM;
•	continuously updated documentation on all aspects of spacecraft and instrument operations, data reduction and analysis;
•	maintenance of a comprehensive set of project web pages;
•	a competent and responsive HelpDesk, providing dedicated support to individual XMM-Newton users.

Everyone can be an XMM-Newton observer. So far, astronomers from 36 countries submitted observing programs. Public data can be accessed by every scientist in the world through the XMM-Newton Science Archive (XSA).Despite all these efforts, one can’t help noticing an asymmetric level of scientific exploitation in the realm of X-ray astronomy between developing and developed countries. The latter have traditionally enjoyed the comparative advantage of deeper know-how, deriving from direct experience in hardware and mission development. The XMM-Newton Science Operations Centre’s efforts act to alleviate this situation through, for example, increasing the usage of the web for data and information dissemination, as well as by supporting actively such initiatives as the COSPAR Capacity-Building Workshops, specifically designed to create long-lasting bridges between researchers in developing and developed countries.  相似文献