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101.
John M. Ferry Laurence J. Mutti Gregory J. Zuccala 《Contributions to Mineralogy and Petrology》1987,95(2):166-181
Alkali olivine basalts from Skye were simultaneously contact metamorphosed by Tertiary gabbro and granite intrusions and altered by the hydrothermal convection system that the plutons induced. Four metamorphic zones were mapped around the plutons. Furthest from the intrusions, in the primary olivine zone, metabasalts are composed of combinations of igneous olivine, augite, plagioclase, titaniferous magnetite, ilmenite, zeolites, gyrolite, sulfides, and chlorite-smectite intergrowths. Closer to the plutons, in the smectite zone, saponite and carbonate appear, primary olivine and gyrolite disappear, and zeolites decrease dramatically in abundance. Still closer to the plutons, in the amphibole zone, actinolite, edenite, chlorite, sphene, epidote, andradite, and quartz appear and saponite and chlorite-smectite intergrowths disappear. Along parts of the contact between gabbro and basalt, in the orthopyroxeneolivine zone, orthopyroxene, metamorphic olivine, and biotite appear and amphibole, chlorite, sphene, epidote, andradite, carbonate, and quartz disappear. Whole-rock chemical data indicate only minor change in the major-element chemical composition of the metabasalts during progressive metamorphism/hydrothermal alteration. Two-pyroxene eothermometry and various mineral-fluid equilibria suggest the range of peak temperatures attained in the metamorphic zones: orthopyroxene-olivine zone, 900°1, 030° C; amphibole zone, 400°–900° C; smectite and primary olivine zones, < 400° C. Mineralogical and oxygen isotopic alteration of the metabasalts were closely coupled: Basalts from the primary olivine zone with nearly unaltered igneous mineralogies have normal or near-normal wholerock
18O>+5 (SMOW); mineralogically more altered basalts from the smectite zone have whole-rock
18O=+2 to +5; still more mineralogically altered basalts from the amphibole zone (with one exception) have
18O<+ 2; completely recrystallized hornfelses from the orthopyroxene-olivine zone have
18O<0. The principal mechanism of isotope exchange between basalt and metamorphic/ hydrothermal fluid probably was heterogeneous mineralfluid reaction.Metabasalts from the orthopyroxene-olivine zone are mineralogically fresh pyroxene hornfelses that record crystallization temperatures > 1,000° C yet have highly altered whole-rock oxygen isotope compositions,
18O<0%. The hornfelses chemically interacted with metamorphic/hydrothermal fluids either at very high temperatures or while they were heated to > 1,000° C or both. Their mineralogy, however, rules out significant water-rock interaction after they cooled below 900° C. Hydrothermal convection on Skye was a two-stage process: (a) fluid flow through wall rocks initially was pervasive while they are heated; (b) fluid flow after the thermal peak in the wall rocks was sufficiently channelized that rocks such as those in the orthopyroxeneolivine zone were isolated from further fluid-rock interaction during all or almost all of the cooling history of the hydrothermal system. 相似文献
102.
南堡凹陷位于渤海湾盆地黄骅坳陷北部,新近系馆陶组是该凹陷的重要勘探层段。馆陶组以辫状河沉积为主,中段发育曲流河沉积。其油气勘探的首要问题是优质储集砂体的精确对比及有利盖层分布预测。根据高分辨率层序地层学理论以及录井和测井资料,对馆陶组的层序地层样式、沉积特征和储盖组合进行了分析。研究结果表明,该地层具有两种短期旋回和四个中期旋回。在两种短期旋回中,一种是低可容纳空间的非对称旋回,另一种是高可容纳空间的对称旋回。四个中期旋回中,两个以上升半旋回为主体(MSC1、MSC2),一个是对称旋回(MSC3),一个以下降半旋回为主体(MSC4)。短、中期旋回均以非对称旋回为主。该地层的长期基准面具有缓慢上升而后快速下降的特点。从MSC1到MSC4旋回,沉积相呈现出冲积扇-辫状河→辫状河-曲流河→曲流河-辫状河相组合的演化过程。自北向南,各中期旋回的可容纳空间增大,沉积主体由砾质河道渐变为砂质河道。由于受基准面中期旋回格架控制,南堡凹陷馆陶组发育上、中、下三套储盖组合。上部储盖组合,因其储、盖层条件最好,应是馆陶组最重要的油气勘探层系。 相似文献
103.
Andrew Swales R. Bruce Williamson Laurence F. Van Dam Morag J. Stroud Matt S. McGlone 《Estuaries and Coasts》2002,25(1):43-56
Cores were collected from the length of Pakuranga estuary, a small urban estuary in Auckland, New Zealand, to determine sedimentation
and contaminant history, and in particular the impact of urbanization. Catchment sediment loads for the most recent history
(1953–1995), including urbanization since 1960, were reconstructed using the landcover history and soil erosion modeling.
Pollen and14C dating and pre-urban landcover history were used to reconstruct early estuary sedimentation (i.e., post-3000 yr BP to 1960).
Heavy metal concentrations, particle size,137Cs, pollen, and catchment sediment loads were all needed to disentangle the complex estuarine response to urbanization.137Cs profiles did not reflect the historical fallout pattern, but deposition of137Cs-labelled eroded catchment soil, coinciding with peaks in urban construction. Temporal variations in stormwater137Cs concentrations are likely due to varying contributions from137Cs-rich topsoil and137Cs-poor subsoils. A similar pattern was observed in heavy-metal concentrations and attributed to street runoff rather than
topsoil being diluted by metal-poor subsoils. Dating of the sediment profiles showed that during urbanization sedimentation
rates in the tidal creek and estuary were higher than sedimentation rates associated with past agricultural landuse and the
original forest landcover. Urbanization has brought about substantial environmental changes in the upper estuary through continued
infilling of shallow, intertidal areas, contamination by heavy metals to levels of ecological concern, sediment textural changes,
and rapid mangrove colonization of formerly bare intertidal sediments. 相似文献
104.
Application of geochemical and stable isotopic tracers to investigate groundwater salinity in the Ochi-Narkwa Basin,Ghana 总被引:1,自引:1,他引:0
Samuel Y. Ganyaglo Shiloh Osae Tetteh Akiti Thomas Armah Laurence Gourcy Tomas Vitvar 《水文科学杂志》2017,62(8):1301-1316
Rainwater, groundwater and soil-water samples were analysed to assess groundwater geochemistry and the origin of salinity in the Ochi-Narkwa basin of the Central Region of Ghana. The samples were measured for major ions and stable isotopes (δ18O, δ2H and δ13C). The Cl? content in rainwater decreased with distance from the coast. The major hydrochemical facies were Na-Cl for the shallow groundwaters and Ca-Mg-HCO3, Na-Cl and Ca-Mg-Cl-SO4 for the deep groundwaters. Groundwater salinization is caused largely by halite dissolution and to a minor extent by silicate weathering and seawater intrusion. Stable isotope composition of the groundwaters followed a slope of 3.44, suggesting a mixing line. Chloride profiles in the soil zone revealed the existence of salt crusts, which support halite dissolution in the study area. A conceptual flow model developed to explain the mechanism of salinization showed principal groundwater flow in the NW–SE direction.
EDITOR D. KoutsoyiannisASSOCIATE EDITOR K. Heal 相似文献
105.
The importance of characterizing the ecohydrological interactions in natural, damaged/drained, and restored bogs is underscored by the importance of peatlands to global climate change and the growing need for peatland restoration. An understudied aspect of peatland ecohydrology is how shallow lateral flow impacts local hydrological conditions and water balance, which are critical for peatland restoration success. A novel method is presented using microcosms installed in the field to understand the dynamics of shallow lateral flow. Analysis of the difference in water table fluctuation inside and outside the microcosm experimental areas allowed the water balance to be constrained and the calculation of lateral flow and evapotranspiration. As an initial demonstration of this method, a series of four microcosm experiments were set up in locations with differing ecological quality and land management histories, on a raised bog complex in the midlands of Ireland. The timing and magnitude of the lateral flow differed considerably between locations with differing ecological conditions, indicating that shallow lateral flow is an important determining factor in the ecohydrological trajectory of a recovering bog system. For locations where Sphagnum spp. moss layer was present, a slow continuous net lateral input of water from the upstream catchment area supported the water table during drought periods, which was not observed in locations lacking Sphagnum. Consistent with other studies, evapotranspiration was greater in locations with a Spaghnum moss layer than in locations with a surface of peat soil. 相似文献
106.
Abigail McQuatters-Gollop Alison J. Gilbert Laurence D. Mee Jan E. Vermaat Yuri Artioli Christoph Humborg Fred Wulff 《Estuarine, Coastal and Shelf Science》2009,82(4):583-596
Anthropogenic eutrophication affects the Mediterranean, Black, North and Baltic Seas to various extents. Responses to nutrient loading and methods of monitoring relevant indicators vary regionally, hindering interpretation of ecosystem state changes and preventing a straightforward pan-European assessment of eutrophication symptoms. Here we summarize responses to nutrient enrichment in Europe's seas, comparing existing time-series of selected pelagic (phytoplankton biomass and community composition, turbidity, N:P ratio) and benthic (macro flora and faunal communities, bottom oxygen condition) indicators based on their effectiveness in assessing eutrophication effects. Our results suggest that the Black Sea and Northern Adriatic appear to be recovering from eutrophication due to economic reorganization in the Black Sea catchment and nutrient abatement measures in the case of the Northern Adriatic. The Baltic is most strongly impacted by eutrophication due to its limited exchange and the prevalence of nutrient recycling. Eutrophication in the North Sea is primarily a coastal problem, but may be exacerbated by climatic changes. Indicator interpretation is strongly dependent on sea-specific knowledge of ecosystem characteristics, and no single indicator can be employed to adequately compare eutrophication state between European seas. Communicating eutrophication-related information to policy-makers could be facilitated through the use of consistent indicator selection and monitoring methodologies across European seas. This work is discussed in the context of the European Commission's recently published Marine Strategy Directive. 相似文献
107.
Two-dimensional continuous wavelet transform of simulated spatial images of waves on a slowly varying topography 总被引:1,自引:0,他引:1
Laurence Zsu-Hsin Chuang Li-Chung Wu Dong-Jiing Doong Chia Chuen Kao 《Ocean Engineering》2008,35(10):1039-1051
The wavelet transform (WT) is now recognized as a useful, flexible, and efficient technique to analyze intermittent, non-stationary and inhomogeneous signals as well as images which are obtained from experimental or in situ measurements. In this study, the two-dimensional continuous wavelet transform (2-D CWT) was introduced to analyze the spatial image of waves. The numerical algorithm of 2-D CWT was developed and testified in simulated wave field of regular and random waves. Some more simulated wave fields of various wave conditions and sea bed slopes were then assumed to verify the analytical accuracy of this new technique. The comparisons of estimations to theoretical values for several wave parameters show that the 2-D CWT is capable of identifying the directional spectra and wave properties in shallow water. 相似文献
108.
Laurence A. Coogan Craig E. Manning Robert N. Wilson E.I.M.F 《Earth and Planetary Science Letters》2007,260(3-4):524-536
Millimeter-scale amphibole veins in the lower oceanic crust record fracture-controlled fluid flow at high-temperatures but the importance of this fluid flow for the thermal and chemical evolution of the lower oceanic crust is unclear. In the section of lower oceanic crust recovered at Hess Deep from ODP Hole 894G, which formed at the fast-spreading East Pacific Rise, these veins are randomly distributed with an average spacing of 1 m. We unravel the history of fluid flow through one of these veins by combining in situ O-isotope analyses of wall-rock plagioclase with major element analyses, geothermometry and diffusion modeling. Thermometry indicates vein sealing by amphibole at 720 °C over a narrow temperature interval (± 20 °C). In situ O-isotope analyses by ion microprobe, with a precision of < 0.5‰, reveal zoning of O-isotopes in plagioclase adjacent to the vein. The zoning profiles can be reproduced using a diffusion model if the duration of O-isotope exchange was ≤ 100 yr. A similar interval of fluid–rock exchange is suggested by modeling potassium depletion in plagioclase adjacent to the vein. If representative of fracture controlled fluid flow in the lower oceanic crust the limited duration of fluid flow, and its occurrence over a narrow temperature interval, suggest that high-temperature fluid flow in this porosity network does not transport significant heat. 相似文献
109.
MUHAMMAD SHARAF GARY ARROY RON PERKINS Spectra-Physics Inc. North First Street San Jose CA U.S.A. 《地理学报(英文版)》1991,(3)
Ratio measurements are commonly used to address a variety of analytical problems in environmental,forensic and pharmaceutical laboratories.In absorbance ratioing techniques,analytical chemists rely onthe spectral features of the analyte(s)of interest.The absorbances at two wavelengths are monitored andthe ratio of these two absorbances is computed.This ratio is then used to confirm the identity of theanalyte(s)of interest,the purity of a product or the overlap of chromatographic peaks.These decisionsoften have far-reaching consequences(e.g.the identification of the source,biogenic or petrogenic,ofhydrocarbons in biological tissues or water).Given the cost and the liabilities associated with suchdecisions,it is unfortunate that these ratios are seldom reported with any statistical confidence.Thepurpose of this study is to delineate the parameters that affect absorbance ratio measurements.Themodels that can be used to estimate the statistical confidence in these measurements are derived andevaluated experimentally.The results show that these models can estimate the relative standard deviationsin absorbance ratios accurately.They can also estimate the effect of signal-to-noise ratio and the choiceof wavelengths on the precision of absorbance ratios. 相似文献
110.
Nicholas R. Bates Liliane Merlivat Laurence Beaumont A. Christine Pequignet 《Marine Chemistry》2000,72(2-4)
The ocean is an important sink for carbon and heat, yet high-resolution measurements of biogeochemical properties relevant to global climate change are being made only sporadically in the ocean at present. There is a growing need for automated, real-time, long-term measurements of CO2 in the ocean using a network of sensors, strategically placed on ships, moorings, free-drifting buoys and autonomous remotely operated vehicles. The ground-truthing of new sensor technologies is a vital component of present and future efforts to monitor changes in the ocean carbon cycle and air–sea exchange of CO2.A comparison of a moored Carbon Interface Ocean Atmosphere (CARIOCA) buoy and shipboard fugacity of CO2 (fCO2) measurements was conducted in the western North Atlantic during two extended periods (>1 month) in 1997. The CARIOCA buoy was deployed on the Bermuda Testbed Mooring (BTM), which is located 5 km north of the site of the US Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time-series Study (BATS). The high frequency of sampling revealed that temperature and fCO2 responded to physical forcing by the atmosphere on timescales from diurnal to 4–8 days. Concurrent with the deployments of the CARIOCA buoy, frequent measurements of surface fCO2 were made from the R/V Weatherbird II during opportunistic visits to the BTM and BATS sites, providing a direct calibration of the CARIOCA buoy fCO2 data. Although, the in situ ground-truthing of the CARIOCA buoy was complicated by diurnal processes, sub-mesoscale and fine-scale variability, the CARIOCA buoy fCO2 data was accurate within 3±6 μatm of shipboard fCO2 data for periods up to 50 days. Longer-term assessments were not possible due to the CARIOCA buoy breaking free of the BTM and drifting into waters with different fCO2-temperature properties. Strategies are put forward for future calibration of other in situ sensors. 相似文献