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1.
The seasonal variation in the trace metals’ concentrations (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were investigated in surface sediments of the Pandoh Lake. The horizontal distribution of TC, TN, and TP reflects spatial and temporal differences in sedimentary organic production. The chemical sequential extraction of heavy metals was carried out by seven-step fractionation scheme (Leleyter and Probst in Int J Environ Chem 73:109–128, 1999). The significant concentrations of Ni and Cd were associated with “water soluble (Eua)” fraction in the monsoon and winter, respectively, while “exchangeable (Exch)” and “carbonate-bound (Carb)” fractions for Ni and Cd were abundant in winter and summer. The Cd, Cu, and Pb associated with “Exch” fraction in the summer season support their availability on exchange sites due to oxidized nature of surface sediments. Enrichment of Co, Fe, Mn, and Zn in “AFeO” fraction showed poor bioavailability, while Cd, Cu, and Mn in the monsoon, Co in the winter and summer, and Zn in the winter season showed significant “organically bound (Org)” fraction. The ANOVA was significant for chemical fractions of trace elements except “Carb” fraction of Pb and Zn and “CFeO” fraction of Pb. Factor analysis revealed that the “Eua”, “Exch”, and “Carb” fractions together control the metal enrichment of “MnO”, “AFeO”, and “CFeO” fractions in the summer season.  相似文献   

2.
This work is a contribution to the understanding of the mechanical properties of non-cohesive granular materials in the presence of friction and a continuation of our previous work (Roul et al. 2010) on numerical investigation of the macroscopic mechanical properties of sand piles. Besides previous numerical results obtained for sand piles that were poured from a localized source (“point source”), we here consider sand piles that were built by adopting a “line source” or “raining procedure”. Simulations were carried out in two-dimensional systems with soft convex polygonal particles, using the discrete element method (DEM). First, we focus on computing the macroscopic continuum quantities of the resulting symmetric sand piles. We then show how the construction history of the sand piles affects their mechanical properties including strain, fabric, volume fraction, and stress distributions; we also show how the latter are affected by the shape of the particles. Finally, stress tensors are studied for asymmetric sand piles, where the particles are dropped from either a point source or a line source. We find that the behaviour of stress distribution at the bottom of an asymmetric sand pile is qualitatively the same as that obtained from an analytical solution by Didwania and co-workers (Proc R Soc Lond A 456:2569–2588, 2000).  相似文献   

3.
Sarah Gall 《GeoJournal》2009,74(6):525-540
The focus on ‘flexible specialisation’ in the 1980s and 1990s marked an important turning point in framings of economic agency and diversity within economic geography. This article deconstructs the ways in which subjects were framed as ‘flexible’ in both the flexible specialisation literature and later work on the Diverse Economy (Gibson-Graham 1996, 2002, 2006), seeking out particular examples of the ways in which different projects of subjection appear to frame different views of economic possibility. Drawing richly on a case study of residents in an inner-city neighbourhood of West End, Brisbane (Australia), this paper uses resident’s articulations of their everyday practices to reinvigorate some of the ideas of the flexible specialisation literature and challenge, defamiliarise and rework existing ideas of economic life in “First World”, urban contexts.  相似文献   

4.
Secondary soft-bottom dwellers evolved several times in the Arcoida. These include semi-infaunal endobyssate taxa and free-burrowing species. The Jurassic arcoid bivalve Grammatodon inaequivalvis (Goldfuss, 1837) is remarkable for showing different sculptures on its left and right valve. A functional analysis of the shell points to a reclining mode of life on soft bottoms. This interpretation is corroborated by the occurrence of this species in very fine-grained sediments, and by taphonomic patterns such as “butterflied” preservation. It is proposed here that this species was resting on its left valve on the sediment, probably without byssal attachment. This reclining mode of life of G. inaequivalvis was hitherto undescribed from soft-bottom dweller arcoid bivalves.  相似文献   

5.
Alfred E. Bergeat, originated from a family, who produced gold-glance in a factory (porcelain painting), studied mineralogy and geology at the University of Munich from 1886 to 1892. Due to the results of his habilitation work on the volcanism of island arcs, especially of the Stromboli volcanic island in the Tyrrhenian Sea, he became a recognized volcanologist and specialist in volcanic petrography. He further became an explorer of syngenetic, epigenetic and deuterogenic ore deposits at the mining academies (Bergakademien) of Freiberg (Saxony) and Clausthal (Harz mountains). He described these ore deposits in a two-volume manual (1904–1906) which was summarized again in 1913. After his early death in 1924, the two manuals “Die Vulkane” (1925) and “Vulkankunde” (1927) were posthumously published by his colleague and friend Karl Sapper (1866–1945).  相似文献   

6.
Based on the results of the Conference on Resource Assessment Techniques of IGCP Project 98 in Loen, Norway, 1976, the importance of mineral and energy inventories is demonstrated by their long-term objectives which aim at the solution of problems of quantitative and qualitative mineral and energy reserve and resource assessments, estimates of the exploration potential, supply analysis, future land-use planning, and national mineral policy. Prior to establishing a mineral and energy inventory it is essential to clearly define both the long-term and short-term objectives, because they control the scope of an inventory and determine the approach to and the method of constructing the data base. Only then can questions be answered as to the kind of data required, the advantages of regional-versus commodity-based inventories, the necessity of computer-processable data files, the availability of a user-oriented data base management system, and the usefulness of conducting a pilot project. Examples are given for simple and complex types of mineral and energy inventories. The “Mineral Deposit Inventory” of the Institute for Geosciences and Natural Resources, Hannover, Federal Republic of Germany, serves mainly as an information and reference system, whereas the mineral inventory of “Project Manitoba” of the Geological Survey of Canada forms the base for reserve and resource assessment as well as land-use planning of that province. For developing and industrialized countries alike, mineral and energy inventories are appropriate tools in planning new exploration activities and decisions on future national mineral policy. Used by the Regional Mineral Resources Development Centers of ESCAP and ECA, the United Nations economic commissions in Asia and Africa, these tools could be of great advantage and mutual benefit to the developing countries of those regions. This paper was presented at the International Geological Correlation Program (IGCP) Project 98: “Standards for Computer Applications in Resource Studies” held at Taita Hills, Kenya, November 8–15, 1977.  相似文献   

7.
The Proterozoic Deadhorse Creek volcaniclastic breccia complex was emplaced in Archean metasedimentary and metavolcanic rocks of the Schreiber-White River greenstone belt adjacent to the Proterozoic Coldwell alkaline complex. The western sub-complex of the Deadhorse Creek breccia consists of metasomatically-altered breccia, a U-Be-Zr-rich main mineralized zone and a Zr-Y-Th-rich carbonate vein. The main mineralized zone is enriched in beryllium, thorium, uranium, first and second row transition elements, and rare earth elements. The major minerals present include: albite; potassium feldspar; quartz; calcite; apatite; and phenakite. Accessory minerals include: aegirine-jervisite; aegirine-natalyite; allanite; barite; barylite; coffinite; Ca-Mn-silicate; magnetite; monazite-(Ce); niobian vanadian rutile; pyrite; thorite; thorogummite; thortveitite; uraninite; vanadian crichtonite; xenotime-(Y); zircon and hydrated zircon; and zircon-thorite-coffinite solid solutions. The carbonate vein consists of dolomite-ankerite and calcite with accessory zircon, xenotime, and monazite. Barite, baotite and Ba-rich feldspars, were formed during metasomatism of the earlier-formed and genetically-unrelated volcaniclastic breccia adjacent to the main mineralized zone. The complex mineral assemblage of the fault-controlled main mineralized zone is considered to have formed in three stages. An initial emplacement of a “granitic” melt/fluid was followed by introduction of CO2-bearing Cr-Nb-V-Ti-enriched alkaline fluids. The latter reacted with minerals which had crystallized from the “granitic” melt/fluid to produce the exotic V-, Sc- and Nb-bearing mineral assemblage. Subsequently, a supergene suite of minerals, consisting principally of calcite, thorogummite, hollandite and tyuyamanite, formed during post-Pleistocene alteration was superimposed onto the pre-existing Proterozoic age mineral assemblage. The major mineralogy of the main mineralized zone is essentially ‘granitic” and the melts/fluids are considered to be derived from an A-type granite source. However, the Deadhorse Creek mineralization is older (1129±6 Ma) than the A-type quartz syenites of the adjacent Coldwell complex (1108±1 Ma) which are the nearest potential sources of such melts. Thus, the source of the “granitic” melt together with that of the Cr-Nb-V-Ti-bearing alkaline fluids remains enigmatic.  相似文献   

8.
Chapman and Pollack (C and P)[2007, Int J Earth Sci] criticize Hamza et al. [2007, Int J Earth Sci] for using actual heat flux measurements in young oceanic crust instead of values from 1-D cooling models. The rationalization of C and P and previous authors is that hydrothermal circulation causes the discrepancy between model and measurement. However, the discrepancy between model values and measured heat flux exists over the entire ocean floor and is opposite to the perturbations that hydrothermal circulation would superimpose on a conductive system [Hofmeister and Criss (2005) Tectonophysics 409:199–203]. The error lies in force-fitting a 1-D cooling model to the 3-D oceanic crust [Hofmeister and Criss (2005) Tectonophysics 395:159–177]. Shortcomings of the 1-D model include mathematical errors, such as use of volumetric rather than linear thermal expansivity to describe contraction which, by assumption, is limited only to the Z -direction [Hofmeister and Criss (2006) Tectonophysics]. This 3× error, traceable to McKenzie and Sclater [1969, Bull Vocanol 33–1:101–118], accidentally provides good agreement of model values with globally averaged seafloor depths for young, but not old ages, and is the sole rationale for using the simplistic cooling model. There is no justification for selective substitution of erroneous 1-D model values for measurements only for the younger half of the 3-D oceanic crust, as stridently and arbitrarily promoted by C and P. Hamza et al. [2007, Int J Earth Sci], in contrast, use the scientific method, which calls for discarding models that do not well describe physical phenomena. The remainder of this report summarizes the shortcomings of cooling models, particularly the half-space cooling (HSC) model touted by C and P, and explains how hydrothermal circulation affects heat flux. We focus on the basics, as these have been misunderstood. With the key issues of C and P being erroneous, it is not necessary to address their remaining comments, many of which enumerate the vote for an imagined, gargantuan circulation of hot fluid through oceanic basins that is somehow warmed without removing heat from the rocks. The use of “consensus” to belittle valid challenge is the enemy of the scientific method.  相似文献   

9.
Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO2 from ?15 to ?20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H2O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions $ P_{H_2 O} Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO2 from −15 to −20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H2O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions ≥ 0.7 PS and = 0.01–0.3. The oxidation potential of the “external” fluid is close to that of the H2O-C system under carbon-saturated vapor conditions. Original Russian Text ? O.V. Avchenko, I.A. Aleksandrov, V.O. Khudolozhkin, M.A. Mishkin, 2009, published in Tikhookeanskaya Geologiya, 2009, Vol. 28, No. 4, pp. 3–15.  相似文献   

10.
Summary ?Results of experimental investigations in the dry system PtS-PdS-NiS at 1100°C, 1000°C, and 900°C are presented. The phases observed at 1100°C are “cooperite” and a melt, at 1000°C “cooperite”, “braggite”, and a melt and at 900°C “cooperite”, “braggite”, “vysotskite”, Ni1−xS, and a melt. At 1100°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 2.7 atomic per cent and the Pd-content limit in Ni-free “cooperite” is 12.8 atomic per cent. At 1000°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 3.3 atomic per cent and the Pd-content in Ni-free “cooperite” is 13.7 atomic per cent. The “braggite” composition ranges from Pt0.56Pd0.38Ni0.06S and Pt0.59Pd0.41S in a Ni-saturated and Ni-free environment respectively to Pt0.18Pd0.80Ni0.02S and Pt0.14Pd0.86S respectively. At 900°C the maximum Ni-content in ideal Pd-free “cooperite” is 3.1 atomic per cent and the Pd-limit in Ni-free “cooperite” is 12.5 atomic per cent. The “braggite” composition ranges from Pt0.59Pd0.29Ni0.12S and Pt0.60Pd0.40S for a Ni-saturated and Ni-free environment respectively, to Pd0.91Ni0.09S and PdS respectively. The Ni-content in “braggite” and “vysotskite” increases slightly with increasing Pt/Pd ratios and is higher at 900°C than at 1000°C. Comparison of experimental trends with cooperite, braggite, and vysotskite analyses from the literature implies high temperatures of formation for Pt-Pd-Ni sulphides in placers if Ni-saturation is assumed.
Zusammenfassung ?Synthetischer ,,Cooperit”, ,,Braggit” und “Vysotskit” im System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C Ergebnisse experimenteller Untersuchungen im trockenen System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C werden dargestellt. Bei 1100°C sind die Phasen “Cooperit” und Schmelze, bei 1000°C “Cooperit”, “Braggit” und Schmelze und bei 900°C “Cooperit”, “Braggit”, “Vysotskit”, Ni1−xS und Schmelze stabil. Bei 1100°C ist die maximale L?slichkeit von Ni in idealem, Pd-freiem “Cooperit” 2.7 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.8 Atomprozent. Bei 1000°C ist die maximale L?slichkeit von Ni in idealem, Pd-freien “Cooperit” 3.3 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 13.7 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.56Pd0.38Ni0.06S und Pt0.18Pd0.80Ni0.02S in einem Ni-ges?ttigtem und zwischen Pt0.59Pd0.41S und Pt0.14Pd0.86S in einem Ni-freien Umfeld. Bei 900°C liegt die maximale L?slichkeit von Ni in idealem Pd-freien “Cooperit” bei 3.1 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.5 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt0.59Pd0.29Ni0.12S und Pd0.89Ni0.08S in einem Ni-ges?ttigten und zwischen Pt0.59Pd0.40S und PdS in einem Ni-freien Umfeld. Der Nickelgehalt in “Braggit” und “Vysotskit” nimmt mit zunehmendem Pt/Pd Verh?ltnis zu und ist bei 900°C h?her als bei 1000°C. Ein Vergleich der experimentellen Trends mit Cooperit, Braggit und Vysotskit Analysen aus der Literatur weist auf eine Hochtemperaturbildung der Pt-Pd-Ni Sulfide in Seifenlagerst?tten hin, wenn man von Nickels?ttigung ausgeht.

Received October 1, 1998;/revised version accepted September 7, 1999  相似文献   

11.
This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.  相似文献   

12.
Recent work in political geography has emphasised how scale plays a role in constituting relationships and identities. Historically, the Canadian federal government has taken responsibilities for social services for First Nations people on reserves, leaving this responsibility to provinces for First Nations people in cities. This constitutes First Nations women as individuals with Aboriginal rights only on reserves, and as part of mainstream society in urban areas. First Nations women have challenged the definitions of their identities embedded in these scales of service provision. In presenting alternative geographies for organising the provision of services, they demonstrate the importance of paying attention to the diversity of women’s everyday geographies in the city. This is a phrase from Vicki English’s (1993) presentation to the Royal Commission on Aboriginal Peoples, where she argues that treaty rights to housing, education, medicare and other services should not be confined to the boundaries of reserves. I use the term “First Nations” to refer to people who identify themselves as such, including people who are and are not registered pursuant to the Indian Act. By “Aboriginal peoples” I mean the descendants of the indigenous people in Canada, including First Nations people, Métis and Inuit. The Census of Canada uses the term “North American Indian” to refer to First Nations people, and I employ this terminology for clarity in some cases.
  相似文献   

13.
Soil radon concentration levels in Deir Abu-Said District, Irbid, Jordan were measured for several depths using CR-39 detectors, in the summer 2004 for six geological formations, namely, Wadi umm ghudran (WG), Wadi esSir “massive” limestone, Amman silicified limestone (ASL), Al-Hisa phosphatic limestone (AHP), Muwaqqar chalky-marl (MCM), and Basalt. Using a model (Yakovleva in Ann Geophys 48(1):195–198, 2005) based on the solution of the diffusion equation in the quasi-homogenous approximation, the characteristics of radon transport were calculated. Radon flux density from the Earth’s surface, the depth Z eq, at which the equilibrium value of soil radon concentration is reached and the convective radon flux velocity (v) for the different soils are calculated and found to be consistent with similar values presented elsewhere. Calculations indicate that the soil covering WG has a low radon risk while, on the contrary, AHP has a higher radon risk as expected, since AHP has higher content of uranium. The other formations have intermediate values. The results of the present study confirm the statement by Yakovleva (Ann Geophys 48(1):195–198, 2005) that two measurements suffice in order to estimate the characteristics of soil radon transport.  相似文献   

14.
Summary The stoichiometry of pyroxenes {viiiX2+ viY2+ ivZ4+ 2 O6} and garnets {xiiX2+ 3 viY3+ 2 ivZ4+ 3 O12} is re-evaluated by a theoretical crystal-chemical approach that takes into account natural phenomena that do not fit with conventional anhydrous stoichiometric mineralogy: the existence in eclogites of microinclusions of other minerals that may have been exsolved from previous supersilicic or subsilicic UHPM pyroxene or garnet. Different definitions of supersilicic and subsilicic are discussed and the one based on the ability to exsolve SiO2 and leave behind a stoichiometric pyroxene or garnet is recommended for general adoption. The SHAND system (S = Si et al.; H = H; A = Al et al.; N = Na et al.; D = divalents) for projecting multivariate chemical space involving 23 cations and 104 selected natural or potential mineral species on to two essential diagrams (SAND and SHND) is described in full for the first time. Numerous possible chemical exchanges are considered and justified with respect to known mineral phenomena such as cation vacancies, octahedral silicon or protonation. Several new potential end-members are presented, in particular “supersilipyx”, “supersiligar” and “subsiligar”. It is suggested that small quantities of these end-members can be incorporated into UHPM solid-solutions and lead to various exsolution phenomena during eclogite exhumation.  相似文献   

15.
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16.
During the late Early Cretaceous, the shallow-water domains of the western Tethys are characterized by the widespread deposition of Urgonian-type carbonates rich in rudists, corals and other oligotrophic, shallow-marine organisms. In the Helvetic Alps, the Urgonian occurrences have been dated by ammonite biostratigraphy as Late Barremian and Early Aptian. For the more proximal occurrences in the western Swiss Jura, a recent age model based on bio-, chemo- and sequence stratigraphy has been proposed, which allows for an improved correlation with the Helvetic counterparts. In order to corroborate the recently proposed age model for the Jura, a set of well-preserved rhynchonellids collected from five different lithostratigraphical formations and members (“Marnes bleues d’Hauterive”, “Marnes d’Uttins”, basal marly layers within the “Urgonien Jaune”, “Marnes de la Russille”, “Urgonien Blanc”) has been analysed for its strontium–isotope ratios (87Sr/86Sr). In addition, K–Ar dating was performed on well-preserved glauconite grains from two different levels (“Marnes d’Uttins” and a basal layer within the “Urgonien Jaune”). The correlation of the Sr–isotope data set with a belemnite-based, ammonite-calibrated reference curve provides an age model which is coherent with recently published ages based on calcareous nannofossil biostratigraphy and the correlation of trends in chemo- and sequence stratigraphy. K–Ar dating on well-preserved glauconite grains from the “Marnes d’Uttins” and lowermost part of the “Urgonien Jaune” delivered ages of 127.5 ± 2.3 and 130.7 ± 2.6 Ma, respectively. Whereas the age of the glauconitic level near the base of the “Urgonien Jaune” is chronostratigraphically meaningful, the K–Ar age of the “Marnes d’Uttins” appears too young relative to the presently used time scale. This may be related to rejuvenation of the K–Ar chronometer due to post-depositional Ar loss, most likely during hardground formation. The ages obtained here confirm the Late Barremian age for the onset of the Urgonian platform, an age which is conform with ages obtained in the Helvetic Alps and elsewhere along the northern Tethyan margin.  相似文献   

17.
There is growing evidence that the budget of Pb in mantle peridotites is largely contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt) are very fast. Given the possibility that sulfide melt “wets” sub-solidus mantle silicates, and has very low viscosity, the implications for Pb behavior during mantle melting are profound. There is only sparse experimental data relating to Pb partitioning between sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of Pb behavior in sulfide may hold the key to several long-standing and important Pb paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all known mantle reservoirs lie to the right of the Geochron, with no consensus as to the identity of the “balancing” reservoir. We propose that long-term segregation of sulfide (containing Pb) to the core may resolve this paradox. Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB is greater than bulk earth, and constant at a value of 25. The constancy of this “canonical ratio” implies similar partition coefficients for Ce and Pb during magmatic processes (Hofmann et al. in Earth Planet Sci Lett 79:33–45, 1986), whereas most experimental studies show that Pb is more incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the sulfide melt/silicate melt partition coefficient for Pb has a value of ∼ 14. Modeling shows that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle sources for these basalts. Sulfide may play other important roles during magmagenesis: (1) advective/diffusive sulfide networks may form potent metasomatic agents (in both introducing and obliterating Pb isotopic heterogeneities in the mantle); (2) silicate melt networks may easily exchange Pb with ambient mantle sulfides (by diffusion or assimilation), thus “sampling” Pb in isotopically heterogeneous mantle domains differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an apparent “de-coupling” of these systems.  相似文献   

18.
The Dachang antimony deposit in Qinglong,Guizhou Province,is strictly controlled by the “Dachang Layer” which is a complex altered rock occurring at unconformity between the Permian Emeishan basalt and the Maokou limestone.Based on the studies of the hanging-and foot-wall rocks,the trace elements and REE contents of the rocks and ores and heavy placer minerals in the basalt,this paper is focused on the relations between these data and the “Dachang Layer”and its hanging- and oot-wall rocks.The author pointed out that the “Dachang Layer” and basalt are the source-beds of antimony;ilmenite and magnetite are the major mineral carriers of antimony.In the processes of halmyrosis and burial metamorphism of the “Dachang Layer” an basalt,antimony was mobilized along with the mobilization of iron and was preliminarily concentrated in the“ Dachang Layer”.  相似文献   

19.
We apply the logic of clinical epidemiological studies to quantify the accuracy of mapping sinkholes by ALSM in the 750 km2 Pinellas County. By such studies, a new diagnostic procedure is tested by comparing the diagnoses in a clinical trial to diagnoses on the same patients from a more reliable, but more elaborate and expensive procedure (“gold standard” in epidemiological context). A relatively undeveloped, 65 km2 focus area where we have aerial photographs that are effectively contemporaneous with the ALSM flights serves as the “clinical trial”. The xy-locations in the focus area are the “patients” in the trial. The “diagnostic test” for having “sinkhole disease” is inclusion in a database of sinkhole polygons delimited by ALSM contours (“ALSM-alone”), as detailed in Part 1. The standard of comparison (“gold standard” would be an overstatement in the absence of geophysical testing) is inclusion in a database of sinkhole outlines derived by best judgment of conjunctive interpretation of ALSM and aerial photography. GIS intersections that indicate the sensitivity and specificity of the test (ALSM-alone) are 43 and 98.3%, respectively, and, in the focus area where the prevalence of “sinkhole disease” is 4.7%, the positive and negative predictive values are 55.5 and 97.2%, respectively. Over much of the rest of the county, where only the test can be applied, the prevalence of sinkholes is sufficiently small that it cannot be determined to be any different from zero given the paucity of interpreted sinkholes (positive diagnoses) and the low specificity of the test method. The conclusion, therefore, is that contemporaneous aerial photography is essential to compile an ALSM-derived database that aims to state that the given xy-points lay inside or outside of topographic depressions in the covered karst of west-central Florida.  相似文献   

20.
We use an analytical model for the post-injection spreading of a plume of CO2 in a saline aquifer under the action of buoyancy and capillary trapping to show that the spreading behavior is at all times strongly influenced by the shape of the plume at the end of the injection period. We solve the spreading equation numerically and confirm that, at late times, the volume of mobile CO2 is given by existing asymptotic analytical solutions. The key parameters governing plume spreading are the mobility ratio, M, and the capillary trapping number, Γ—the former sets the shape of the plume at the end of the injection period, and the latter sets the amount of trapping. As a quantitative measure of the dependence of the spreading behavior on the initial shape, we use a volume ratio. That is, we evolve the plume from a true end-of-injection initial shape and also from an idealized “step” initial shape, and we take the ratio of these mobile plume volumes in the asymptotic regime. We find that this volume ratio is a power-law in M, where the exponent is governed exclusively by Γ. For conditions that are representative of geologic CO2 sequestration, the ratio of mobile volumes between “true” and “step” initial plume shapes can be 50% or higher.  相似文献   

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