Ion microprobe analysis of oxygen isotope ratios in quartz from Skye granite: healed micro-cracks,fluid flow,and hydrothermal exchange   总被引：4，自引：0，他引：4  

J. W. Valley  Colin M. Graham 《Contributions to Mineralogy and Petrology》1996,124(3-4):225-234

 Quartz grains in hydrothermally altered granites from the Isle of Skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 μm scale. Ion microprobe analysis of one grain shows a gradient of 13‰ over 400 μm and a greater range in δ ¹⁸O than all quartz previously analyzed on the Isle of Skye. Other crystals from the same outcrop are homogeneous. Digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable. The ion probe analysis correlates low δ ¹⁸O values on a micro-scale to one set of healed cracks. Thus, quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures, in contrast to more reactive feldspar that appears to exchange from the grain boundary inward. Macroscopic models of isotope exchange are not realistic for these rocks; the flow of hydrothermal fluids was heterogeneous, anisotropic and crack controlled. Received: 23 October 1995/Accepted: 9 April 1996  相似文献   

Reply to: Comment on ‘A case example of near-surface correction for multicomponent VSPS’ by Gildas Omnes     

Colin MacBeth 《Geophysical Prospecting》1997,45(4):723-724

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Measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel     

Colin D. Rennie  Robert G. Millar 《地球表面变化过程与地形》2004,29(10):1173-1193

Maps are presented of the spatial distribution of two‐dimensional bedload transport velocity vectors. Bedload velocity data were collected using the bottom tracking feature of an acoustic Doppler current pro?ler (aDcp) in both a gravel‐bed reach and a sand‐bed reach of Fraser River, British Columbia. Block‐averaged bedload velocity vectors, and bedload velocity vectors interpolated onto a uniform grid, revealed coherent patterns in the bedload velocity distribution. Concurrent Helley‐Smith bedload sampling in the sand‐bed reach corroborated the trends observed in the bedload velocity map. Contemporaneous 2D vector maps of near‐bed water velocity (velocity in bins centered between 25 cm and 50 cm from the bottom) and depth‐averaged water velocity were also generated from the aDcp data. Using a vector correlation coef?cient, which is independent of the choice of coordinate system, the bedload velocity distribution was signi?cantly correlated to the near‐bed and depth‐averaged water velocity distributions. The bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress. Published in 2004 by John Wiley & Sons, Ltd.  相似文献   

Soft X-ray spectroscopic studies of the reaction of fractured pyrite surfaces with Cr(VI)-containing aqueous solutions     

Colin S. Doyle  Tom Kendelewicz  Gordon E. Brown Jr 《Geochimica et cosmochimica acta》2004,68(21):4287-4299

We have used synchrotron-based soft X-ray core-level photoemission and adsorption spectroscopies to study the reaction of aqueous sodium chromate solutions with freshly fractured pyrite surfaces. Pyrite surfaces were reacted with 50 μM sodium chromate solution at pH 7 for reaction times between 1 min and 37 hr. Additional experiments were performed at pH 2 and pH 4 with 50 μM sodium chromate solutions and at pH 7 with 5 mM solutions. At chromate concentrations of 50 μM, all chromium present on the pyrite surface was in the form of Cr(III), while at 5 mM, both Cr(III) and Cr(VI) were present at the pyrite surface. Minor quantities of oxidized sulfur species (sulfate, sulfite, and zero-valent sulfur) were identified as reaction products on the pyrite surface. The amount of oxidized sulfur species observed on the surface was greater when pyrite was reacted with 5 mM Cr(VI) solutions because the rate of chromium deposition exceeded the rate of dissolution of pyrite oxidation products, effectively trapping Cr(VI) and oxidized sulfur species in an overlayer of iron(III)-containing Cr(III)-hydroxide. This work shows that pyrite, an extremely cheap and readily available waste material, may be suitable for the removal of hexavalent chromium from acidic to circumneutral waste streams. The reduced chromium ultimately forms a coating on the pyrite surface, which passivates the pyrite surface towards further oxidation.  相似文献   

An experimental study of phase equilibria in the systems H2O–CO2–CaCl2 and H2O–CO2–NaCl at high pressures and temperatures (500–800?°C, 0.5–0.9?GPa): geological and geophysical applications     

Kirill I. Shmulovich  Colin M. Graham 《Contributions to Mineralogy and Petrology》2004,146(4):450-462

Phase equilibria in the ternary systems H₂O–CO₂–NaCl and H₂O–CO₂–CaCl₂ have been determined from the study of synthetic fluid inclusions in quartz at 500 and 800 °C, 0.5 and 0.9 GPa. The crystallographic control on rates of quartz overgrowth on synthetic quartz crystals was exploited to prevent trapping of fluid inclusions prior to attainment of run conditions. Two types of fluid inclusion were found with different density or CO₂ homogenisation temperature (T_h(CO₂)): a CO₂-rich phase with low T_h(CO₂), and a brine with relatively high T_h(CO₂). The density of CO₂ was calibrated using inclusions in the binary system H₂O–CO₂. Mass balance calculations constrain tie lines and the miscibility gap between brines and CO₂-rich fluids in the H₂O–CO₂–NaCl and H₂O–CO₂–CaCl₂ systems at 500 and 800 °C, and 0.5 and 0.9 GPa. The miscibility gap in the CaCl₂ system is larger than in the NaCl system, and solubilities of CO₂ are smaller. CaCl₂ demonstrates a larger salting-out effect than NaCl at the same P–T conditions. In ternary systems, homogeneous fluids are H₂O-rich and of extremely low salinity, but at medium to high concentrations of salts and non-polar gases fluids are unlikely to be homogeneous. The two-phase state of crustal fluids should be common. For low fluid-rock ratios the cation compositions of crustal fluids are buffered by major crustal minerals: feldspars and micas in pelites and granitic rocks, calcite (dolomite) in carbonates, and pyroxenes and amphiboles in metabasites. Fluids in pelitic and granitic rocks are Na-K rich, while for carbonate and metabasic rocks fluids are Ca-Mg-Fe rich. On lithological boundaries between silicate and carbonate rocks, or between pelites and metabasites, diffusive cation exchange of the salt components of the fluid will cause the surfaces of immiscibility to intersect, leading to unmixing in the fluid phase. Dispersion of acoustic energy at critical conditions of the fluid may amplify seismic reflections that result from different fluid densities on lithological boundaries.Editorial responsibility: I. Parsons  相似文献   

Nickel speciation in Sebertia acuminata,a plant growing on a lateritic soil of New Caledonia     

Nicolas Perrier  Fabrice Colin  Tanguy Jaffré  Jean-Paul Ambrosi  Jérôme Rose  Jean-Yves Bottero 《Comptes Rendus Geoscience》2004,336(6):567-577

Nickel speciation in a nickel hyperaccumulating plant (Sebertia acuminata) and its associated soil of southern New Caledonia was studied using various analytical methods. The soil is formed of iron oxides (goethite, hematite), which contain almost all the nickel. The available nickel is probably linked to the organic matter in the litter. Sebertia acuminata, acts as a nickel pump, and concentrates the metal in its leaves. It partitions nickel and silica; nickel is concentrated in the cells (probably in the vacuoles) as organometallic complexes, whereas silica forms the framework of the cells, and the phytolithes. A thorough study of these plants seems essential in order to define the soil–plant relations, and to propose appropriate ways for ecological restoration. To cite this article: N. Perrier et al., C. R. Geoscience 336 (2004).  相似文献   

Primary aragonite and high‐Mg calcite in the late Cambrian (Furongian). Potential evidence from marine carbonates in Oman          下载免费PDF全文

Joyce E. Neilson  Alexander T. Brasier  Colin P. North 《地学学报》2016,28(5):306-315

Transient aragonite seas occurred in the early Cambrian but several models suggest the late Cambrian was a time of calcite seas. Here, evidence is presented from the Andam Group, Huqf High, Oman (Gondwana) that suggests a transient Furongian (late Cambrian) aragonite sea, characterized by the precipitation of aragonite and high‐Mg calcite ooids and aragonite isopachous, fibrous, cements. Stable carbon isotope data suggest that precipitation occurred just before and during the SPICE (Steptoean Positive Carbonate Isotope Excursion). Aragonite and high‐Mg calcite precipitation can be accounted for if mMg:Ca ratios were around 1.2 given the very high atmospheric CO₂ at that time and if precipitation occurred in warm waters associated with the SPICE. This, together with reported occurrences of early Furongian aragonite ooids from various locations in North America (Laurentia), suggests that aragonite and high‐Mg calcite precipitation from seawater may have been more than just a local phenomenon.  相似文献   

Joggins Cliff on Nova Scotia: the most spectacular view into Upper Carboniferous time     

Wolf-Christian Dullo  Colin Devey 《International Journal of Earth Sciences》2016,105(2):581-582

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Interaction between scale and scheduling choices in simulations of spatial agents     

Tyler R. Bonnell  Colin A. Chapman  Raja Sengupta 《International journal of geographical information science》2016,30(10):2075-2088

Spatial simulations are a valuable tool in understanding dynamic spatial processes. In developing these simulations, it is often required to make decisions about how to represent features in the environment and how events unfold in time. These spatial and temporal choices have been shown to significantly alter model outcomes, yet their interaction is less well understood. In this paper, we make use of a simple group foraging model and systematically vary how features are represented (cell size of the landscape) as well as how events unfold in time (order in which foragers take action) to better understand their interaction. Our results show similar nonlinear responses to changes in spatial representation found in the literature, and an effect of the order in which agents were processed. There was also a clear interaction between how features are represented and how events unfold in time, where, under certain environmental representations results were found to be more sensitive to the order in which individuals were processed. Furthermore, the effects of feature representation, scheduling of agents, and their interaction were all found to be influenced by the heterogeneity of the spatial surface (food), suggesting that the statistical properties of the underlying spatial variable will additionally play a role. We suggest that navigating these interactions can be facilitated through a better understanding of how these choices affect the decision landscape(s) on which agents operate. Specifically, how changes to representation affect aggregation and resolution of the decision surface, and thereby the degree to which agents interact directly or indirectly. We suggest that the challenges of dealing with spatial representation, scheduling, and their interaction, while building models could also present an opportunity. As explicitly including alternate representations and scheduling choices during model selection can aid in identifying optimal agent–environment representations. Potentially leading to improved insights into the relationships between spatial processes and the environments in which they occur.  相似文献   

Erratum to: The oceanic cycles of the transition metals and their isotopes     

Derek Vance  Corey Archer  Susan H. Little  Michael Köbberich  Gregory F. de Souza 《中国地球化学学报》2018,37(1):151-151

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