Surface complexation modeling for predicting solid phase arsenic concentrations in the sediments of the Mississippi River Valley alluvial aquifer, Arkansas, USA   总被引：1，自引：0，他引：1  

Md. Salah U. Sharif  Ralph K. DavisKenneth F. Steele  Burmshik KimPhillip D. Hays  Tim M. KresseJohn A. Fazio 《Applied Geochemistry》2011,26(4):496-504

The potential health impact of As in drinking water supply systems in the Mississippi River Valley alluvial aquifer in the state of Arkansas, USA is significant. In this context it is important to understand the occurrence, distribution and mobilization of As in the Mississippi River Valley alluvial aquifer. Application of surface complexation models (SCMs) to predict the sorption behavior of As and hydrous Fe oxides (HFO) in the laboratory has increased in the last decade. However, the application of SCMs to predict the sorption of As in natural sediments has not often been reported, and such applications are greatly constrained by the lack of site-specific model parameters. Attempts have been made to use SCMs considering a component additivity (CA) approach which accounts for relative abundances of pure phases in natural sediments, followed by the addition of SCM parameters individually for each phase. Although few reliable and internally consistent sorption databases related to HFO exist, the use of SCMs using laboratory-derived sorption databases to predict the mobility of As in natural sediments has increased. This study is an attempt to evaluate the ability of the SCMs using the geochemical code PHREEQC to predict solid phase As in the sediments of the Mississippi River Valley alluvial aquifer in Arkansas. The SCM option of the double-layer model (DLM) was simulated using ferrihydrite and goethite as sorbents quantified from chemical extractions, calculated surface-site densities, published surface properties, and published laboratory-derived sorption constants for the sorbents. The model results are satisfactory for shallow wells (10.6 m below ground surface), where the redox condition is relatively oxic or mildly suboxic. However, for the deep alluvial aquifer (21-36.6 m below ground surface) where the redox condition is suboxic to anoxic, the model results are unsatisfactory.  相似文献   

极隙区Pc3频段脉动的传播特性   总被引：1，自引：0，他引：1       下载免费PDF全文

刘勇华  刘瑞源  杨少峰  贺龙松  BJ Fraser 《极地研究》2000,12(2):121-128

南极中山站和戴维斯站 (不变磁纬 74.5°S)白天中午位于磁层极隙区 ,夜间位于极盖区或极光带的极向边沿。两站均安装了完全相同的感应式磁力计。选择两站 1 997年 3月和 1 996年 6、9、1 2月的数据 ,运用快速傅立叶变换和波形检查方法选择 Pc3频段脉动事件 ,然后用信号互谱技术进行统计分析 ,结果如下 :在中山站 -戴维斯站 ,Pc3频段脉动主要出现于白天中午 /磁中午和磁午夜附近 ;白天 ,Pc3频段脉动振幅、出现率和出现的时间范围均有一定的季节变化 ,冬季最小 ,但在夜间 ,Pc3频段脉动没有这种变化 ;夜间 ,Pc3频段脉动振幅比在白天大许多 ;Pc3频段脉动传播方向 ,白天主要向西 ,夜间不太规则。这些可能反映了电离层电导率和日侧电离层电流系统对 Pc3频段脉动的影响。  相似文献   

Watson: A new link in the HE iron chain     

Edward Olsen  Andrew Davis  Roy S. Clarke  Ludolf Schultz  Hartwig W. Weber  Robert Clayton  Toshiko Mayeda  Eugene Jarosewich  Paul Sylvester  Lawrence Grossman  Ming-Sheng Wang  Michael E. Lipschutz  Ian M. Steele  James Schwade 《Meteoritics & planetary science》1994,29(2):200-213

Abstract— Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the HE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new HE iron. Whole rock Watson silicate shows an enrichment in K and P (each ～2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa₂₀), opx (Fs₁₇Wo₃), capx (Fs₉Wo₄₁) (with very fine exsolution lamellae), antiperthite feldspar (An_1–Or₅) with <1 μm exsolution lamellae (An_1–3Or_>40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of ～300X and 100–150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or₁₃, and in the presence of antiperthite. Whole rock trace element data for the silicate mass support the petrography. Watson silicate was an H-chondrite engulfed by metal and melted at > 1550 °C. A flat refractory lithophile and flat REE pattern (at ～1x average H-chondrites) indicate that melting took place in a relatively closed system. Immiscible metal and sulfide were occluded into the surrounding metal host. Below 1100 °C, the average cooling rate is estimated to have been ～1000 °C/Ma; Widmanstätten structure formed, any igneous zoning in the silicates was equilibrated, and feldspar and pyroxene exsolution took place. Cooling to below 300 °C was completed by 3.5 Ga B. P. At 8 Ma, a shock event took place causing some severe metal deformation and forming local melt pockets of schreibersite/metal. This event likely caused the release of Watson into interplanetary space. The time of this event, 8Ma, corresponds to the peak frequency of exposure ages of the H-chondrites. This further confirms the link between HE irons and the H-chondrites, a relationship already indicated by their common oxygen isotope source. Watson metal structures are very similar to those in Kodaikanal. Watson, Kodaikanal and Netschaëvo form the young group of HE meteorites (ages 3.7 ± 0.2 Ga). They appear to represent steps in a chain of events that must have taken place repeatedly on the HE parent body or bodies from which they came: chondrite engulfed in metal (Netschaëvo); chondrite melted within metal (Watson); and finally melted silicate undergoing strong fractionation with the fractionated material emplaced as globules within metal (Kodaikanal). Watson fills an important gap in understanding the sequence of events that took place in the evolution of the IIE-H parent body(ies). This association of H-chondrite with HE metal suggests a surface, or near surface process-a suggestion made by several other researchers.  相似文献   

The Wilhelmøya Formation (Upper Triassic-Lower Jurassic) at Bohemanflya, Spitsbergen     

HENNING DYPVIK  SVEN HVOSLEF  TOR BJ/ERKE  EGIL FINNERUD 《Polar research》1985,3(2):155-165

An 18.5 m thick shale sequence of Norian-Rhaetian age is described from the Bohemanfiya-Syltoppen area (north of Isfjorden, central Spitsbergen). Lithological, petrographical and palynological analyses show that the sequence represents a marginal development of the lower part of the Wilhelmeya Formation. The depositional history at the Triassic-Jurassic transition is discussed in the light of this new evidence. The Wilhelmøya Formation was probably deposited during a weak marine transgression over an area of low relief. Low sediment supply and current and wave reworking of the sediments characterized the depositional conditions.  相似文献   

Geochemical Transformations and Modeling of Two Deep-Well Injected Hazardous Wastes     

W. R. Roy  B. Seyler  J. D. Steele  S. C. Mravik  D. M. Moore  I. G. Krapac  J. M. Peden  R. A. Griffin 《Ground water》1991,29(5):671-677

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Liverpool telescope 2: a new robotic facility for rapid transient follow-up     

C. M. Copperwheat  I. A. Steele  R. M. Barnsley  S. D. Bates  D. Bersier  M. F. Bode  D. Carter  N. R. Clay  C. A. Collins  M. J. Darnley  C. J. Davis  C. M. Gutierrez  D. J. Harman  P. A. James  J. H. Knapen  S. Kobayashi  J. M. Marchant  P. A. Mazzali  C. J. Mottram  C. G. Mundell  A. Newsam  A. Oscoz  E. Palle  A. Piascik  R. Rebolo  R. J. Smith 《Experimental Astronomy》2015,39(1):119-165

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Comprehensive imaging and Raman spectroscopy of carbonate globules from Martian meteorite ALH 84001 and a terrestrial analogue from Svalbard     

A. Steele  M. D. Fries  H. E. F. Amundsen  B. O. Mysen  M. L. Fogel  M. Schweizer  N. Z. Boctor 《Meteoritics & planetary science》2007,42(9):1549-1566

Abstract— We report a comprehensive imaging study including confocal microRaman spectroscopy, scanning electron microscopy (SEM), and 3‐D extended focal imaging light microscopy of carbonate globules throughout a depth profile of the Martian meteorite Allan Hills (ALH) 84001 and similar objects in mantle peridotite xenoliths from the Bockfjorden volcanic complex (BVC), Svalbard. Carbonate and iron oxide zoning in ALH 84001 is similar to that seen in BVC globules. Hematite appears to be present in all ALH 84001 carbonate‐bearing assemblages except within a magnesite outer rim found in some globules. Macromolecular carbon (MMC) was found in intimate association with magnetite in both ALH 84001 and BVC carbonates. The MMC synthesis mechanism appears similar to established reactions within the Fe‐C‐O system. By inference to a terrestrial analogue of mantle origin (BVC), these results appear to represent the first measurements of the products of an abiotic MMC synthesis mechanism in Martian samples. Furthermore, the ubiquitous but heterogeneous distribution of hematite throughout carbonate globules in ALH 84001 may be partly responsible for some of the wide range in measured oxygen isotopes reported in previous studies. Using BVC carbonates as a suitable analogue, we postulate that a low temperature hydrothermal model of ALH 84001 globule formation is most likely, although alteration (decarbonation) of a subset of globules possibly occurred during a later impact event.  相似文献   

Ni partitioning between diopside and silicate melt: A redetermination by ion microprobe and recognition of an experimental complication     

Ian M. Steele  David J. Lindstrom 《Geochimica et cosmochimica acta》1981,45(11):2177-2183

The ion probe is uniquely suited for measurement of element partitioning between phases in experimental and natural systems. A redetermination of the partitioning of Ni between diopside and quenched silicate melt using samples previously measured by β-track mapping gives 1.87 (weight ratio of ⁶²Ni in diopside/melt), slightly lower than the β-track value of 2.05. Critical to the accurate determination of distribution coefficients are: (1) a secondary ion signal that is linear with concentration in the range measured, and (2) a calibration using known concentrations to correct for differential secondary ion yields from different phases. In the present case the secondary ion signal is linear with Ni concentrations below ~ 1 wt% in both diopside and glass, but nonlinear above. Differential yields were corrected by calibrating the secondary ion signal against compositions determined by electron microprobe.Partition coefficients measured using ⁵⁸Ni and ⁶⁰Ni, in contrast to ⁶²Ni, are not constant with concentration in these samples probably due to Ni migration during crystallization. Measurements using these isotopes (or bulk Ni) show a change of partition coefficient with Ni concentration.  相似文献   

The late Pleistocene geomagnetic field as recorded by sediments from Fargher Lake,Washington, U.S.A.     

Seong-Jae Doh  William K. Steele 《Earth and Planetary Science Letters》1983,63(3):385-398

Measurement of the remanent magnetization of a 6.88-m oriented core of soft sediments and tephras from Fargher Lake near Mount St. Helens in southwestern Washington State shows that no significant geomagnetic reversals were recorded in the sediments of the lake. Radiocarbon and palynological dating of the tephra layers from the lake bed indicates deposition during the interval 17, 000–34, 000 years B.P. although geochemical correlation of a prominent tephra layer in the core with tephra set C of Mount St. Helens could mean that the maximum age of the sediments may be at least 36, 000 years B.P. The core was divided into specimens 0.02 m long, each representing approximately 55 years of deposition assuming a constant rate of sedimentation. Pilot alternating field demagnetization studies of every tenth specimen indicated a strong, stable remanence with median destructive field of 15 mT, and the remaining specimens were subsequently demagnetized in fields of this strength. The mean inclination for all specimens exclusive of the unstably magnetized muck and peat from near the surface is 56.1° which is 8° shallower than the present axial dipole field at this site, perhaps because of inclination error in the detrital remanent magnetization of the sediments, although because of the variability in the data, this departure from the axial dipole field may not be significant. The ranges of inclination and declination are comparable to those of normal secular variation at northern latitudes. Although three isolated specimens have remanence with negative inclination, these anomalous directions are due to sampling and depositional effects. Measurement of a second core of 6.86 m length also revealed only normal magnetic polarity, but this result is of little stratigraphic value as this core failed to penetrate the distinctive tephra found near the base of the former core.Studies of a concentrate of the magnetic minerals in the sediments by optical microscopy and X-ray diffraction indicate that the primary magnetic constituent is an essentially pure magnetite of detrital origin. The magnetite occurs in a wide range of grain sizes with much of it of sub-multidomain size (< 15 μm).As a whole, this study provides substantial evidence against the existence of large-scale worldwide geomagnetic reversals during the time interval of Fargher Lake sedimentation, a segment of geological time for which many excursions and reversals have been reported elsewhere.  相似文献   

Advanced argillic lithocaps in the Bolivian tin-silver belt   总被引：2，自引：0，他引：2  

R. H. Sillitoe  G. B. Steele  J. F. H. Thompson  J. R. Lang 《Mineralium Deposita》1998,33(6):539-546

Zones of advanced argillic alteration constituting lithocaps are commonplace in the shallow parts of porphyry copper systems. Similar lithocaps are also recognized in the shallowly eroded southern part of the Bolivian tin-silver belt, where mineralization typically is centred on felsic volcanic domes. A well-preserved lithocap at Potosí is dominated by vuggy residual quartz and contained the world's largest silver resource, whereas the basal remnant of a lithocap at Pulacayo is composed of barren quartz-alunite. Minor gold occurs in the structurally controlled roots of a lithocap at Tasna. The mineralization in these lithocaps is of high-sulphidation type and was generated in the epithermal environment. In contrast, the tin- and base metal-bearing massive sulphide veins and associated sericitic and quartz-tourmaline alteration that underlie the Bolivian lithocaps are typified by sulphides of low sulphidation state, but are dominantly mesothermal rather than epithermal in character. Magma chemistry is believed to account for the characterization of Bolivian lithocaps by silver-tin-antimony and porphyry copper lithocaps by gold-copper-arsenic. Low-grade, bulk-tonnage silver mineralization within Bolivian lithocaps and high-grade tin-bearing veins concealed beneath them both constitute attractive exploration objectives. Received: 13 February 1998 / Accepted: 11 March 1998  相似文献