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KEVIN ROBERT GURNEY RACHEL M. LAW A. SCOTT DENNING PETER J. RAYNER DAVID BAKER PHILIPPE BOUSQUET LORI BRUHWILER YU-HAN CHEN PHILIPPE CIAIS SONGMIAO FAN INEZ Y. FUNG MANUEL GLOOR MARTIN HEIMANN KAZ HIGUCHI JASMIN JOHN EVA KOWALCZYK TAKASHI MAKI SHAMIL MAKSYUTOV PHILIPPE PEYLIN MICHAEL PRATHER BERNARD C. PAK JORGE SARMIENTO SHOICHI TAGUCHI TARO TAKAHASHI CHIU-WAI YUEN 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):555-579
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Metamorphic Evolution of the Seward Peninsula Blueschist Terrane 总被引:3,自引:0,他引:3
Blucschists and greenschists of the central Seward Peninsula(the Nome Group) crop out over an 8000 km2 area. The protolithpackage for the mid-Jurassic high P/T metamorphism consistedlargely of Cambrian, possibly also Precambrian, to Devoniansedimentary rocks (limestones, marls, pelites, carbonaceoussiltites, quartzites) of shallow water miogeoclinal origin,which maintained a coherent lithostratigraphy during metamorphismand concurrent high-strain, noncoaxial deformation. Several experimentally and empirically calibrated geothermobarometershave been integrated with textural and microstructural observationsin order to derive a pressure-temperature (P-T) path for themetamorphism of the Nome Group. These data, coupled with previouslyobtained Rb-Sr phengite-whole-rock isochron ages, yield a P-T-tpath showing a steep burial segment followed by a prolongedperiod ({small tilde}55 Ma) of isothermal decompression. Peakpressures, obtained from the jadeite content of clinopyroxenein rare, isofacial eclogites, and from the celadonite contentin phengite yield {small tilde}12 kb. Temperatures at this pressure,gained from garnet-clinopyroxene and microcline-plagioclasepairs, were 460?30?C. Decompression temperatures were essentiallythe same, as evidenced by calcite-dolomite and garnet-biotitethermometry. Uniformity of metamorphic conditions throughoutthe Seward Peninsula blueschist terrane coupled with the miogeoclinalnature of the protolith package indicate burial beneath a flat-lying(A-type) subduction zone. The derived P-T-t path is difficultto reconcile with one-dimensional thermal models of collisionalblueschists, where peak P and T are not generally coincident. 相似文献
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Kongsbreen, a tide-water glacier located in Kongsfjorden, is the most active calving glacier in Svalbard. Three SPOT images are used to determine its flow speed and calving rate. The position of fourteen reference points was determined on the coast or mountain sides, and the changes in position of 144 characteristic features on the glacier surface were calculated. The obtained speed profiles arc consistent with the findings from previous works from 1962-64 and 1983-86. When comparing the obtained longitudinal profile to the data from 1962–64. it is found that the flow velocity at a given distance from the front has been nearly constant.
The results from the SPOT images analysis are completed by using existing topographic works. The present study shows that SPOT images (panchromatic as well as multichannel), recorded with a periodicity of one year, can be used to determine precisely the annual flow speed and calving rate of active glaciers such as Kongsbreen. Images recorded with a periodicity of two, three or four weeks can allow identical determination on tide-water glaciers during a surging active phase. 相似文献
The results from the SPOT images analysis are completed by using existing topographic works. The present study shows that SPOT images (panchromatic as well as multichannel), recorded with a periodicity of one year, can be used to determine precisely the annual flow speed and calving rate of active glaciers such as Kongsbreen. Images recorded with a periodicity of two, three or four weeks can allow identical determination on tide-water glaciers during a surging active phase. 相似文献
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Experimental modelling of forearc basin development during accretionary wedge growth 总被引:1,自引:0,他引:1
CHRISTOPHE Larroque SYLVAIN Calassou† JACQUES Malavieille† FRANK Chanier‡ 《Basin Research》1995,7(3):255-268
We present results of three sand-box experiments that model the association between tectonic accretion and sedimentation in a forearc basin. Experimental sedimentation occurs step by step in the forearc basin during shortening of the sand wedge. In each experiment, the development of the accretionary wedge leads to the formation of a major backthrust zone. This major deformation zone accounts for the thickening in the rear part of the wedge. In natural settings this tectonic bulge dams sediments that are transported toward the trench from mountainous terrain behind the forearc. We test the variation of friction along the déollement and note the following: (1) shortening of a low-friction wedge involves a mechanical balance between forethrusts and backthrust propagation and this balance is recorded by the sedimentary sequence trapped in the forearc basin. Indeed, if most of the movement occurs along the backthrust, the deepening of the basin will be larger and consequently the thickness of the sedimentary sequence will be greater. (2) Such balance does not exist in the case of a high-friction wedge. (3) Variation of friction along the décollement during shortening of the sand wedge leads to modification in the forearc basin filling. Thus, for similar increments of convergence, the sequence deposited in the forearc basin shows relatively larger thickness when the wedge is shortened above a high-friction décollement. We suggest that contraction and thickening in the rear part of the wedge is an efficient mechanism to, initiate and develop a forearc basin. Thus, this kind of basin occurs in convergent settings, without collapse related to local extension or tectonic erosion. They represent a sedimentary trap on a passive basement, bounded by a tectonic bulge. The Quaternary Hikurangi forearc basin, southeast of the North Island of New Zealand, is bounded by two actively uplifting ridges. Thus, this basin is considered to be a possible example of the basins modelled in our experiments, and we suggest that the limit between the basin and the wedge could be a complex backthrust zone. 相似文献
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The Proterozoic Lindås Nappe, part of the Caledonidesof western Norway, was affected by penetrative Sveconorwegiangranulite-facies metamorphism, followed by a fluid-driven eclogite-and amphibolite-facies Caledonian overprint, spatially restrictedalong fractures and shear zones. In mafic granulites and amphibolites,a luminescent anhedral zircon overgrowth, which gives an averageage of 924 ± 58 Ma (Th/U = 0·52; secondary ionmass spectrometry data), surrounds a magmatic zoned core withan age of 952 ± 32 Ma (Th/U = 1·27). In the granulites,a continuous rim of zircon or a discontinuous corona of 相似文献
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Heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness. Distinct spatial zones in terms of grain size have been reported, for example sand ribbons and bedload sheets. The transition from areas of finer to coarser grained surface sediment is often abrupt. However, the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels. This paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistancé on the structure of the turbulent boundary layer. Measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river. Immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface, boundary shear stress and roughness length increase considerably. Downstream from this transition, velocity profiles become concave upwards. Downstream and upstream sections show significant differences in terms of near bed velocities (deceleration downstream of the transition), velocity gradient and turbulence intensity of the streamwise velocity component. Comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity (or shear stress) associated with the pressure drag produced by large and isolated obstacles. 相似文献
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Podiform Chromite Ore Bodies: a Genetic Model 总被引:3,自引:0,他引:3
This paper presents an attempt to interpret the formation ofpodiform chromite ore found in ophiolitic complexes from magmaticaccumulation inside cavities along the basalt conduits feedingthe main magma chamber. Two processes play a major role in chromite concentration: anactive upward magma flow in narrow dykes; and an active convectioninside the cavity, for which a numerical modelling has beenperformed. The physical conditions imposed by the model compare well withgeophysical and geological data. 相似文献
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Aluminous granulites of the Archean (2?8 Ga) Kasai craton (Zaire)consist of two main mineral assemblages: Grt-Opx and Sil?Grt?Crdrocks. The high-grade metamorphic conditions as deduced from Grt-Opxand Grt-Opx-Pl-Qtz equilibria are 720?C-6?7 kb. Consideringthe zoning of the same minerals, the slope of the P-T path isestimated at 15 b/?C. Thermobarometry involving Crd is consistentwith those P-T conditions. Three cordierite-forming reactions have been observed petrographically:
These equilibria are continuous reactions; end-member reactionshave slopes less than 15 b/?C; they are decompression reactionsoccurring after the metamorphic climax. Using available thermodynamic data, (R3) fixes the oxygen fugacityto a value below the QFM buffer (log10fO2 = 17?6 at720?C, 6?7 kb and in the graphite stability field. The absence of graphite in the rocks showsthat the end of the granulite facies metamorphism did not occurunder important CO2 streaming. The polymetamorphic history of this Archean craton is considered. 相似文献