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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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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
10.
Mineralogy, Chemistry, and Genesis of the Boninite Series Volcanics, Chichijima, Bonin Islands, Japan 总被引：12，自引：1，他引：11
TAYLOR REX. N.; NESBITT ROBERT W.; VIDAL PHILLIPE; HARMON RUSSELL S.; AUVRAY BERNARD; CROUDACE IAN W. 《Journal of Petrology》1994,35(3):577-617
The Bonin archipelago represents an uplifted fore-arc terrainwhich exposes the products of Eocene supra-subduction zone magmatism.Chichijima, at the centre of the chain, represents the typelocality for the high-Mg andesitic lava termed boninite. Therange of extrusives which constitute the boninite series volcanicsare present on Chichijima, and are disposed in the sequenceboninite-andesite-dacite with increasing height in the volcano-stratigraphy.Progression to evolved compositions within the Chichijima boniniteseries is controlled by crystal fractionation from a boniniteparental magma containing 15% MgO. Olivine and clinoenstatiteare the initial liquidus phases, but extraction of enstatiticorthopyroxene, followed by clinopyroxene and plagioclase, isresponsible for the general evolution from boninite, throughandesite, to dacite. Some andesites within the overlying MikazukiyamaFormation are petrographically distinct from the main boniniteseries in containing magnetite phenocrysts and a high proportionof plagioclase. As such, these andesites have affinities withthe calc-alkaline series. Major and trace element data for 74 boninitic series rocks fromChichijima are presented. Although major element variation isdominantly controlled by high-level crystal fractionation, thelarge variations in incompatiable trace element concentrationsat high MgO compositions cannot be explained by this mechanism.Nd, Pb, and Sr isotopic data indicate the following: (1) a strongoverprint on 87Sr/86Sr by seawater alteration; (2) Pb isotopeslie above the northern hemisphere reference line (NHRL) andare thus similar to the <30-Ma are and basin lavas of theIzu—Bonin system, and (3) Nd(40 Ma) ranges between 2.8and 6.8 within the boninite series volcanics. Differences inrare-earth elements (REE), Zr, Ti, and 143Nd/144Nd at similardegrees of fractionation can be explained by the addition ofa component of fixed composition from the down-going oceaniccrustal slab to a variably depleted source region within theoverlying wedge. Data presented for Sm/Zr and Ti/Zr indicatethat boninite series volcanics are characterized by low valuesfor both of these ratios. In particular, boninites appear tohave uniquely low Sm/Zr ratios. These characteristics may bethe result of slab melting in the presence of residual amphibole;the resultant melt could combine with typical slab dehydrationfluids and infiltrate the overlying mantle wedge. Such a fluid—meltcomponent could mix either with shallow mantle or directly withprimitive melts from depleted mantle. Trace elements, REE, andisotope data thus point to a model for boninite genesis whichrequires tightly constrained pressure—temperature conditionsin the slab combined with melting of a variably depleted sourcein the overlying wedge. Such constraints are rarely met exceptduring the subduction of juvenile oceanic crust beneath a young,hot overriding plate. 相似文献