New early winter f_CO2 data reveal continuous uptake of CO₂ by the Weddell Sea     

M. H. C. STOLL  H. J. W. DE BAAR  M. HOPPEMA  E. FAHRBACH 《Tellus. Series B, Chemical and physical meteorology》1999,51(3):679-687

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Relict Majoritic Garnet Microstructures from Ultra-Deep Orogenic Peridotites in Western Norway   总被引：9，自引：1，他引：9  

VAN ROERMUND  H. L. M.; DRURY  M. R.; BARNHOORN  A.; DE RONDE  A. 《Journal of Petrology》2001,42(1):117-130

Protogranular, porphyroclastic and equigranular (or equant-polygonal)garnet microstructures from Mg–Cr type orogenic garnetperidotites, Otrøy, Western Gneiss Region, Norway, havebeen studied using naked eye, light-optical, electron-opticaland confocal laser (fluorescence) microscopy techniques. Protogranularand porphyroclastic garnets contain microstructural evidencefor the former existence of majoritic (or super-silicic) garnet.The microstructural evidence consists of exsolution texturesinvolving pyroxene. Two types of exsolution microstructuresoccur—needles parallel to <111>_grt and interstitialgrains. The maximum volume percentage for intra-crystallinepyroxene exsolution is 2·7, and 3·6 for inter-crystallinepyroxene exsolution. The maximum pyroxene total volume percentagemeasured in one single protogranular or porphyroclastic garnetis 4·0. This value, at 1200°C, corresponds to minimumpressures of 6·4 GPa (  相似文献   

COMMENT ON 'SECONDARY SHEAR WAVES FROM SOURCE BOREHOLES’ BY J. A. MEREDITH,M. N. TOKSÖZ AND C. H. CHENG1     

J. A. DE BRUIN 《Geophysical Prospecting》1993,41(8):1067-1069

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Basin inversion: some consequences for drainage evolution and alluvial architecture   总被引：1，自引：0，他引：1  

ANNE E. MATHER 《Sedimentology》1993,40(6):1069-1089

ABSTRACT Sedimentary basins developed in tectonically active areas commonly display dramatic changes in sedimentation rates, styles and spatial organization of alluvial facies. When deformation rates are relatively high these changes are frequently attributed to deflection and/or ponding of the fluvial systems. This paper examines the indirect modifications that less intense, epeirogenic uplift may instigate, during the latter stages of basin inversion, in the context of a fluvial system adjusting to the deformation. Field evidence is taken from the Sorbas Basin of south-east Spain and data are employed from both the current drainage pattern and ancient (Plio-Quaternary) sedimentary sequence. Major provenance and sedimentation changes in the ancient record (in terms of both rates and styles) are attributed to river capture. Intrinsic controls to the system (fan progradation and trenching) and the prevailing (semi-arid) climate provided the overall framework of fan development (general coarsening upwards sequence and change from sheetflood to braided conditions in the lower part of the sequence). This sedimentation trend was then substantially modified (a change to small meandering channels and a change in provenance) by the capture of the fan feeder by an aggressive subsequent stream. This cut off the connection with the former source area and reduced sediment and water input into the system. Initially the sedimentation rates declined and minor incision was stimulated by the increase in the water to sediment ratio as a result of the reduction in easily erodible sand to the system that resulted from the source area change. This minor incision stimulated a rejuvenation of the streams sourcing the fan, temporarily increasing sediment supply and choking the small channels, leading to a return to unconfined flow conditions. The system rapidly exhausted the sediment from the reduced catchment area leading to a fining upwards and abandonment of the system. This was followed by incision of the modern drainage network stimulated by base level changes in the main Sorbas Basin drainage network, to which the study area was tributary.  相似文献   

Trace Element Data on Geostandards by Mass Spectrometric Isotope Dilution Technique     

J. R. DE  LAETER K. O. R. ROSMAN 《Geostandards and Geoanalytical Research》1977,1(1):35-38

The stable isotope dilution technique using solid source mass spectrometry is described. The method is capable of high sensitivity, and can yield accurate determinations of elements in trace quantities. The method enjoys freedom from interference effects and systematic errors, and because of its high absolute accuracy it is ideal for the determination of trace elements in geochemical reference samples. A compilation of isotope dilution analyses on ten trace elements in a number of international standard rock samples carried out at the Western Australian Institute of Technology is presented.  相似文献   

Wind tunnel and field testing of a simple sand catcher for sampling inhomogeneously saltating sand in desertified environments     

A. E. MOHAMMED  O. D. VAN DE VEER†  H. J. OLDENZIEL†  C. J. STIGTER‡ 《Sedimentology》1996,43(3):497-503

Problems of vertical alignment and vibrations of disposable coffee cups used in a modified version of the De Ploey saltating sand catcher were solved. The new version was tested in a sediment wind tunnel. Its catches appeared linearly related to amounts of eroded sand, largely independent of wind speed and wind direction, and depended logarithmically on height. The catch efficiency may therefore be taken to be approximately independent of wind speed and direction. The instrument performed well under conditions of inhomogeneously saltating sand in a strongly desertified environment in Central Sudan. Use and results show the improved simple catcher to be easy to assemble, reproducible and cheap, suitable for multipoint use to cover all inhomogeneities in outdoor saltating sand fields.  相似文献   

CEMPS: A prototype spatial decision support system to aid in planning emergency evacuations     

MICHAEL PIDD  RICHARD EGLESE  F NISHAKUMARI DE  SILVA 《Transactions in GIS》1996,1(4):321-334

CEMPS is a prototype spatial decision support system which links the topographical support and analysis provided by a geographic information system, ARC/INFO, with the ability to simulate the dynamics of an evacuation process. CEMPS has been designed to enable emergency planners to experiment with different emergency evacuation plans in order to devise a plan which meets their requirements. ARC/INFO is used to parameterize a dynamic simulation with topographical information and to display its results. The prototype runs on a Sun SPARCStation cluster but could be modified to run on other hardware and software.  相似文献   

COMPUTING FIELD STATICS WITH THE HELP OF SEISMIC TOMOGRAPHY*     

W.N. DE AMORIM  P. HUBRAL  M. TYGEL 《Geophysical Prospecting》1987,35(8):907-919

Field static corrections in general need be applied to all onshore seismic reflection data to eliminate the disturbing effects a weathering layer or near-surface low velocity zone has on the continuity of deep seismic reflections. The traveltimes of waves refracted at the bottom of the low velocity zone (or intermediate refracting interfaces) can often be observed as first breaks on shot records and used to develop a laterally inhomogeneous velocity model for this layer, from which the field static corrections can then be obtained. A simple method is described for computing accurate field statics from first breaks. It is based on a linearization principal for traveltimes and leads to the algorithms that are widely and successfully applied within the framework of seismic tomography. We refine an initial model for the low velocity layer (estimated by a standard traveltime inversion technique) by minimizing the errors between the observed first arrivals on field records and those computed by ray theory through an initial model of the low velocity layer. Thus, one can include more lateral velocity variations within the low velocity layers, which are important to obtain good field static corrections. Traditional first break traveltime inversion methods cannot, in general, provide such refined velocity values. The technique is successfully applied to seismic data from the Amazon Basin. It is based on a simple model for the low velocity layer that consists of an undulating earth surface and one planar horizontal refractor overlain by a laterally changing velocity field.  相似文献   

Shallow subsurface diagenesis of Pleistocene periplatform ooze: northern Bahamas   总被引：2，自引：0，他引：2  

HENRY T. MULLINS  SHERWOOD W. WISE ANNE F. GARDULSKI  EDWARD J. HINCHEY  PHILIP M. MASTERS  D.I. SIEGEL 《Sedimentology》1985,32(4):473-494

Previous studies on early submarine diagenesis of periplatform carbonates have implied that these originally polymineralic (aragonite, magnesian calcite, calcite) sediments are susceptible to early diagenesis only in current-swept open seaways or where surficially exposed by erosion on the seafloor. It has also been proposed that while in the shallow subsurface, periplatform oozes retain their original mineralogy for at least 200,000–400,000 yr and remain unlithified for tens of millions of years. Evidence is reported here for extensive calcitization and selective lithification of periplatform oozes of late Pleistocene age in two piston cores collected from water depths of ～ 1,000 m north of Little Bahama Bank. It is shown that shallow (<30 m) subsurface diagenesis can significantly alter the original mineralogy of periplatform oozes to predominantly calcite in less than 440,000 yr, and that cementation by calcite can produce chalk-ooze sequences within the same time-frame. Periplatform oozes that originally contain a high percentage of bank-derived magnesian calcite appear to have a higher diagenetic potential than those originally low in magnesian calcite. Shallow subsurface calcitization and fithification greatly reduce the diagenetic potential of periplatform carbonates, and chalk-ooze sequences apparently can persist for tens of millions of years and to burial depths of at least 300 m. Shallow subsurface diagenesis, at water depths > 1,000 m, proceeds via dissolution of magnesian calcite and aragonite and reprecipitation of calcite as allochem fillings, exterior overgrowths and cement. It is speculated that density-driven ‘Kohout convection‘, where seawaters under-saturated with respect to magnesian calcite and aragonite and saturated/supersaturated with respect to calcite flow through the margins of carbonate platforms, is the primary driving mechanism for shallow subsurface diagenesis. Removal of Mg during early stages of deep seafloor and shallow subsurface diagenesis should increase the Mg content of interstitial waters which is likely to increase the ‘dolomitizing potential’ of Kohout convection fluid flow.  相似文献   

The Lithospheric Mantle beneath Continental Margins: Melting and Melt-Rock Reaction in Canadian Cordillera Xenoliths   总被引：3，自引：0，他引：3  

PESLIER  ANNE H.; FRANCIS  DON; LUDDEN  JOHN 《Journal of Petrology》2002,43(11):2013-2047

Seven alkali basalt centers in the southern Canadian Cordilleracontain mantle xenolith suites that comprise spinel Cr-diopsideperidotites, spinel augite-bearing wehrlites and orthopyroxene-poorlherzolites, and minor pyroxenites. The Cr-diopside peridotitesappear to be residues of the extraction of Mg-rich basalts byup to 15% partial melting (median 5–10%) of a pyrolite-likesource in the spinel stability field. The xenoliths are similarto other mantle xenolith suites derived from beneath convergentcontinental margins, but are less depleted, less oxidized, andhave lower spinel mg-number than peridotites found in fore-arcsettings. Their dominant high field strength element depletedcharacter, however, is typical of arc lavas, and may suggestthat fluids or melts circulating through the Canadian Cordilleralithosphere were subduction related. Modeling using MELTS isconsistent with the augite-bearing xenoliths being formed byinteraction between crystallizing alkaline melts and peridotite.Assimilation–fractional crystallization modeling suggeststhat the trace element patterns of liquids in equilibrium withthe augite xenoliths may represent the initial melts that reactedwith the peridotite. Moreover, the compositions of these meltsare similar to those of some glasses observed in the mantlexenoliths. Melt–rock interaction may thus be a viablemechanism for the formation of Si- and alkali-rich glass inperidotites. KEY WORDS: Canadian Cordillera; mantle xenolith; peridotite; wehrlite; melt–rock reaction  相似文献