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721.
Gualtiero Badin Jörn Behrens Christian Franzke Jens Rademacher 《地球物理与天体物理流体动力学》2019,113(5-6):425-427
722.
723.
Gold and palladium have been determined in 42 geological reference samples with graphite furnace AAS after aqua regia digestion and SnCl2 -Hg extraction. A brief discussion on the quality of these analyses also is presented. 相似文献
724.
Isotopic and Geochemical Constraints on the Origin and Evolution of the Columbia River Basalt 总被引:13,自引:6,他引:13
New major and trace element data on over 70 samples are combinedwith a wider knowledge of the regional stratigraphy, and ofthe tectonic evolution of the boundary between the ColumbiaPlateau and the northern margin of the Basin and Range province,to distinguish three subgroups within the Columbia River BasaltGroup (CRBG): the Picture Gorge Basalt; the main sequence ofColumbia River flood basalts, here named the Clarkston Basalt;and the Saddle Mountains Basalt. The subgroups are characterizedby different incompatible element and Sr-, Nd-, and Pb-isotoperatios, and they are interpreted in terms of different sourceregions mobilized under different tectonic conditions. The majordifferences between the subgroups are consistent with partialmelting processes in the upper mantle, and it is argued thatthey reflect previous partial melting episodes which resultedin source regions that were variably enriched and depleted inincompatible elements. The major variations within the PictureGorge and Clarkston Basalt subgroups include increases in theabundances of large ion lithophile elements (LILE) and increasesin the ratios of LILE/high field strength elements (HFSE) whichare interpreted as the addition of a lithospheric/subduction-relatedcomponent. The Picture Gorge Basalt has a depleted isotopic and chemicalsignature on which is superimposed an enrichment of LILE toproduce a trace element pattern similar to that of other 170-Mabasalts erupted south of the Olympic Wallowa Lineament. Thispattern is characteristic of volcanism associated with the Basinand Range extensional province, and others have attributed itto a source component derived from an enriched subcontinentallithospheric mantle (SCLM). Of the Clarkston Basalts, the Imnaha and Grande Ronde Basaltsform chemical and isotopic arrays which indicate mixing of componentsfrom two distinct source regions. One had high ratios of LILE/HFSEand light rare earth elements (LREE)/HFSE, and as these arenot common in oceanic basalts, this component is thought tohave been derived from the continental mantle lithosphere. Itsisotope ratios are more enriched (older?) than those of thePicture Gorge Basalt, and its Rb/Sr ratios are much higher thanthose in its source rocks, consistent with preferential mobilizationof LILE at the time of magmatism. The second component was derivedfrom an asthenospheric source similar to that of Hawaii basaltsand is most obviously attributed to mantle plume activity. Basaltsof the Eckler Mountain and Wanapum Formations (smaller, separateformations of the Clarkston Basalt as redefined in this paper)fit this mixing model less well and may represent mixing betweenmore than two components. Flows of the third CRBG subgroup,the Saddle Mountains Basalt, also carry a lithospheric geochemicalsignature and have long been recognized as having more radiogenicisotopic signatures than the other two subgroups. Thus, SaddleMountains flows appear to require a lithospheric source enrichedin LILE at an even earlier time, and we concur with other workersthat the isotopic and chemical evidence implies their derivationfrom subcontinental lithospheric mantle enriched at {small tilde}2000Ma. Within each subgroup, the chemical effects of partial melting,fractional crystallization, and magma mixing processes can allbe distinguished within particular flow sequences. In the ImnahaBasalt variable degrees of partial melting during the generationof the CRBG magmas, and gabbro fractionation within the lowercrust, played major roles in their evolution. In the GrandeRonde Basalt fractional crystallization appears to be restrictedto >10%. The chemical and isotopic data for each CRBG subgroup, and thedifferent sources which those data imply, can be accommodatedin a tectonic model which includes the passing of the Yellowstonehotspot south of the center of the CRBG eruption before significantBasin and Range extension had moved north of the Brothers Faultzone at 15 Ma. 相似文献
725.
Oceanic crust west of North America at the beginning of the Jurassic belonged to the Kula plate. The development of the western margin of North America since the Jurassic reflects interaction with the Kula plate, the Kula-Farallon spreading center and the Farallon plate. The Kula plate ceased to exist in the Paleocene and later developments were caused by interaction of the Farallon plate and, subsequently, collision with the East Pacific Rise.At the beginning of the Jurassic, when spreading between North and South America began, the Kula-Farallon-Pacific triple junction moved to the north relative to North America, and the eastern end of the Kula-Farallon spreading center swept northwards along the continental margin.During the Paleocene, Kula-Pacific spreading ceased and the Kula plate fused to the Pacific plate. Throughout the Mesozoic, subduction of the Kula plate took place along the Alaskan continental margin. When the Kula plate joined the Pacific plate a new subduction zone formed along the line of the present Aleutian chain.Wrangellia and Stikinia, anomalous terrains in Alaska and northwestern Canada respectively, were emplaced by transport on the Kula plate from lower latitudes. Hypotheses which require transport of these plates in the Mesozoic from the “far reaches of the Pacific” ignore the problem of transport across either the Kula-Pacific or Kula-Farallon spreading centers. The interaction of the Kula plate and western North America throughout the Jurassic and the Cretaceous should result in emplacement of these terrains by motion oblique to the continental margin. Tethyan faunas in Stikinia must come from the western end of Tethys between North and South America, not the Indonesian region at the eastern end of Tethys.As the northeastern end of the Kula-Farallon ridge moved northward, the sense of motion changed from right lateral shear between the Kula and North American plates to collision or left lateral shear between the Farallon and North American plates. Left lateral shear along zones analogous to the Mojave-Sonora megashear may have been the means by which anomalous terrains were transported to the southeast into the gap between North and South America forming present day Central America. Such a model overcomes the overlap difficulties suffered in previous attempts to reconstruct the Mesozoic paleogeography of Central America. 相似文献
726.
H.V. Warren S.J. Horsky A. Kruckeberg G.H.N. Towers J.E. Armstrong 《Journal of Geochemical Exploration》1983,18(3):169-173
Summary of biogeochemical prospecting for mercury mineralization in the Pinchi Fault is given. One thousand two hundred and eight plant samples were collected and analyzed for mercury. In mineralized areas the typical mercury content of dried plants was not less than 0.2 and 0.4 μg/g and even concentrations between 0.6 and 1.6 μg/g were observed. In nonmineralized zones at least 90% of the plants contained no more than 0.15 μg/g of mercury. Analytical and sampling procedures are described. 相似文献
727.
728.
The standard enthalpies of formation of FeS (troilite), FeS2 (pyrite), Co0.9342S, Co3S4 (linnaeite), Co9S8 (cobalt pentlandite), CoS2 (cattierite), CuS (covellite), and Cu2S (chalcocite) have been determined by high temperature direct reaction calorimetry at temperatures between 700 K and 1021 K. The following results are reported: $$\Delta {\rm H}_{f,FeS}^{tr} = - 102.59 \pm 0.20kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,FeS}^{py} = - 171.64 \pm 0.93kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_{0.934} S} = - 99.42 \pm 1.52kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_9 S_8 }^{ptl} = - 885.66 \pm 16.83kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Co_3 S_4 }^{In} = - 347.47 \pm 7.27kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,CoS_2 }^{ct} = - 150.94 \pm 4.85kJ mol^{ - 1} ,$$ $$\Delta {\rm H}_{f,Cu_2 S}^{cc} = - 80.21 \pm 1.51kJ mol^{ - 1} ,$$ and $$\Delta {\rm H}_{f,CuS}^{cv} = - 53.14 \pm 2.28kJ mol^{ - 1} ,$$ The enthalpy of formation of CuFeS2 (chalcopyrite) from (CuS+FeS) and from (Cu+FeS2) was determined by solution calorimetry in a liquid Ni0.60S0.40 melt at 1100 K. The results of these measurements were combined with the standard enthalpies of formation of CuS, FeS, and FeS2, to calculate the standard enthalpy of formation of CuFeS2. We found \(\Delta {\rm H}_{f,CuFeS_2 }^{ccp} = - 194.93 \pm 4.84kJ mol^{ - 1}\) . Our results are compared with earlier data given in the literature; generally the agreement is good and our values agree with previous estimates within the uncertainties present in both. 相似文献
729.
Dependence on pressure of conduction by hopping of small polarons in minerals of the Earth's lower mantle 总被引:1,自引:0,他引:1
Electrical conductivity of the lower mantle-like assemblage (Mg,Fe)SiO3 perovskite-(Mg,Fe)O magnesiowüstite is usually analyzed using the quasi-chemical Arrhenian approach of diffusion. The conductivity
of this assemblage has often been attributed to hopping of small polarons, because of the low value of the activation energy
and the small negative activation volume. However, the solid-state physics approach can provide more arguments, for or against
conduction by polarons. We have tried to bridge the gap between the two approaches and identify the physical quantities entering
the phenomenological activation parameters. In particular, we have investigated the pressure dependence of the activation
energy, and the physical meaning of the activation volume. Hopping is controlled by the binding energy of the polaron and
by the value of the exchange integral, which increases with pressure causing the observed decrease of the activation energy.
From the physical theory and the results of experiments at pressures up to 40 GPa and temperatures up to 400 ∘C, we have estimated the values of parameters characteristic of polarons: radius, mobility, time between jumps and adiabaticity.
These values are compatible with conduction by small adiabatic polarons. The consequences for extrapolations to lower mantle
conditions of the presence of a temperature dependent preexponential term in the expression for conductivity have been examined.
It was found that the extrapolations are not significantly different from those using the Arrhenius equation.
Received: 5 November 1998 / Revised, accepted: 4 May 1999 相似文献
730.
W. L. F. Brinkmann Dr. H. Hahn H. Schick J. W. Fachbereich Geowissenschaften 《GeoJournal》1987,14(3):331-338
Two lakes, Lake Gänseweiher (LGW) and Lake Fechenheimer Weiher (LFW) occupy groundwater filled abandoned gravel pits which serve as fishing grounds and are part of recreational areas, respectively.Both lakes are cut into a near-surface groundwater aquifer, which is located in the pleistocene River Main gravel terrace t6. They are sealed at the base by miocene clays and above by overlying flood deposits of the River Main. The latter provide protection from pollutants derived from wet and dry deposition of atmospheric contaminants.Groundwater chemistry determines the pool of dissolved constituents in lake water. The temporal and spatial distribution patterns of chemical compounds in lake water are brought about by endo-biogenic processes, of which the indicators are nitrate-nitrogen and dissolved silica. The latter illustrates an instantaneous response to pulses of diatom blooms.Both lakes are eutrophic (polytrophic) according to the classification guidelines presented in literature. 相似文献