Zr-in-rutile thermometry in blueschists from Sifnos, Greece   总被引：1，自引：0，他引：1  

Frank S. Spear  David A. Wark  John T. Cheney  John C. Schumacher  E. Bruce Watson 《Contributions to Mineralogy and Petrology》2006,152(3):375-385

Zr-in-rutile thermometry on samples of blueschist from Sifnos, Greece, yields temperatures that reflect progressive crystallization of rutile from ca. 445 to 505°C with an analytical precision of + 18/−27 and ± 10°C using the electron microprobe and ± 1.5–3.5°C using the ion microprobe. Individual grains are generally homogeneous within analytical uncertainty. Different grains within a single sample record temperature differences as large 55°, although in most samples the range of temperatures is on the order of 25°. In several samples, Zr-in-rutile temperatures from grains within garnet are lower than temperatures from matrix grains, reflecting growth of rutile with increasing temperature of metamorphism. Although the specific rutile-producing reactions have not been identified, it is inferred that rutile grows from either continuous reaction involving the breakdown of lower grade phases (possibly ilmenite), or from pseudomorph reactions involving the breakdown of relic igneous precursors at blueschist-facies conditions. No systematic variation in rutile temperatures was observed across the blueschist belt of northern Sifnos, consistent with the belt having behaved as a coherent block during subduction.  相似文献   

Compositions and phase relations of calcic amphiboles in epidote- and clinopyroxene-bearing rocks of the amphibolite and lower granulite facies,central Massachusetts,USA     

Renate Schumacher 《Contributions to Mineralogy and Petrology》1991,108(1-2):196-211

Calcic amphiboles coexisting with epidotegroup minerals (zoisite, clinozoisite, epidote) and/or clinopyroxene±plagioclase±quartz±garnet occur in amphibolites and calc-silicate rocks that underwent amphibolite to lower granulite-facies metamorphism in the Acadian metamorphic high of central Massachusetts, USA. Across the region, peak metamorphic conditions range from about 580° C and 6.2 kbar to 730° C and 6.3 kbar. The coexistence of most Ca-amphiboles with Fe³⁺-rich epidote-group minerals suggests the presence of Fe³⁺ in most of these amphiboles. An empirical Fe³⁺ estimation for the microprobe analyses is based on two constraints: the Na?Ca content of the M4 sites of Ca-saturated, gravimetrically analyzed hornblendes gives the relation: Ca(M4) ^c =-1.479 Na(M4) ^c +2 (c=corrected). The second constraint is the stoichiometric equation Ca(M4)+Na(M4)+FM=15, where FM is the sum of all cations exclusive of Ca, Na, and K. Solving the two equations simultaneously gives: 20.185=0.479 Ca(M4)+1.479 ΣFM. Starting with the uncorrected values of Ca(M4) ^u and ΣFM(M4) ^u (u = uncorrected) of the all ferrous formula, the normalization factor NF for calculating the corrected cations of the ferric formulas is: 20.185/(0.478 Ca(M4) ^u +1.479 ΣFM ^u ). From the deficient oxygen the Fe³⁺ content which is equal to 2(23-ΣOX) can be calculated. Determinations of Fe³⁺ contents of four hornblende separates by Mössbauer spectroscopy are in agreement with the calculated values. The Ca-amphiboles show systematic changes in composition with increasing grade of metamorphism within the amphibolite and lower granulite-facies zones: increasing edenite and tschermakite substitution, increasing Ti content, and increasing Fe²⁺/(Fe²⁺+Mg) ratio. In addition, the coexisting clinopyroxenes are also characterized by an increase in Fe²⁺/(Fe²⁺+Mg) ratio. In quartz-free rocks with coexisting Ca-amphibole and plagioclase there is an increase in the ratio X _Ab/X _Ed, where X _Ab=Na/(Na+Ca) in plagioclase and X _Ed=Na in the amphibole A-site. These chemical changes in mineral composition together with the disappearance of epidote at the transition to granulite-facies metamorphic conditions are attributed to the continuous reaction: albite+epidote+Fe-Mg hornblende→Fe?Mg clinopyroxene+anorthite+(NaAlSi_-1)^Hbl+H₂O.  相似文献   

Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes   总被引：1，自引：0，他引：1  

Ben Buse  John C. Schumacher  R. Stephen J. Sparks  Matthew Field 《Contributions to Mineralogy and Petrology》2010,160(4):533-550

Metamorphic assemblages within Karoo basalt xenoliths, found within volcaniclastic kimberlite of the B/K9 pipe, Damtshaa, Botswana, constrain conditions of kimberlite alteration. Bultfonteinite and chlorite partially replace the original augite-plagioclase assemblage, driven by the serpentinisation of the kimberlite creating strong chemical potential gradients for Si and Mg. Hydrogarnet and serpentine replace these earlier metamorphic assemblages as the deposits cool. The bultfonteinite (ideally Ca₂SiO₂[OH,F]₄) and hydrogarnet assemblages require a water-rich fluid containing F⁻, and imply hydrothermal alteration dominated by external fluids rather than autometamorphism from deuteric fluids. Bultfonteinite and hydrogarnet are estimated to form at temperatures of ca. 350–250°C, which are similar to those for serpentinisation. Alteration within the B/K9 kimberlite predominantly occurs between 250 and 400°C. We attribute these conditions to increased efficiency of mass transfer and chemical reactions below the critical point of water and a consequence of volume-increasing serpentinisation and metasomatic reactions that take place over this temperature range. A comparison of the B/K9 kimberlite with kimberlites from Venetia, South Africa suggests that the composition and mineralogy of included xenoliths affects the alteration assemblages within kimberlite deposits.  相似文献   

Bio-electricity and land use in the Future Agricultural Resources Model (FARM)     

Ronald D. Sands  Hannah Förster  Carol A. Jones  Katja Schumacher 《Climatic change》2014,123(3-4):719-730

Bio-electricity is an important technology for Energy Modeling Forum (EMF-27) mitigation scenarios, especially with the possibility of negative carbon dioxide emissions when combined with carbon dioxide capture and storage (CCS). With a strong economic foundation, and broad coverage of economic activity, computable general equilibrium models have proven useful for analysis of alternative climate change policies. However, embedding energy technologies in a general equilibrium model is a challenge, especially for a negative emissions technology with joint products of electricity and carbon dioxide storage. We provide a careful implementation of bio-electricity with CCS in a general equilibrium context, and apply it to selected EMF-27 mitigation scenarios through 2100. Representing bio-electricity and its land requirements requires consideration of competing land uses, including crops, pasture, and forests. Land requirements for bio-electricity start at 200 kilohectares per terawatt-hour declining to approximately 70 kilohectares per terwatt-hour by year 2100 in scenarios with high bioenergy potential.  相似文献   

Phasing segmented mirrors using defocused images at visible wavelengths     

A. Schumacher  N. Devaney 《Monthly notices of the Royal Astronomical Society》2006,366(2):537-546

Plans for future optical telescopes of diameter more than 10 m are based on segmented mirrors, made up of hundreds or even thousands of segments. A challenge for these telescopes is the alignment in piston (cophasing) where phase differences between individual segments have to be reduced to a small fraction of the observing wavelength in order to avoid degradation of image quality.
Based on the phase discontinuity sensing method used at the Keck telescopes to measure small piston errors using infrared wavelengths, we develop a new method that allows fast high-precision measurements of large piston errors even at visible wavelengths.  相似文献   

Neuere Veröffentlichungen     

Arnold Schumacher  K. Kalle 《Ocean Dynamics》1949,2(1-3):111-116

  相似文献   

Neuere Veröffentlichungen     

Günter Dietrich  Walter Hansen  A. Schumacher  F. Errulat 《Ocean Dynamics》1952,5(2-3):153-156

Ohne Zusammenfassung  相似文献   

In memoriam     

H. C. Freiesleben  Arnold Schumacher  Otto Steppes 《Ocean Dynamics》1948,1(1):41-44

Ohne Zusammenfassung  相似文献   

    

A. Schumacher  G. Böhnecke und C. Simpson 《Ocean Dynamics》1948,1(1):1

Ohne Zusammenfassung

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Preface

  相似文献   

Correction of Discretization Errors Simulated at Supply Wells          下载免费PDF全文

Gordon J. MacMillan  Jens Schumacher 《Ground water》2015,53(4):651-657

Many hydrogeology problems require predictions of hydraulic heads in a supply well. In most cases, the regional hydraulic response to groundwater withdrawal is best approximated using a numerical model; however, simulated hydraulic heads at supply wells are subject to errors associated with model discretization and well loss. An approach for correcting the simulated head at a pumping node is described here. The approach corrects for errors associated with model discretization and can incorporate the user's knowledge of well loss. The approach is model independent, can be applied to finite difference or finite element models, and allows the numerical model to remain somewhat coarsely discretized and therefore numerically efficient. Because the correction is implemented external to the numerical model, one important benefit of this approach is that a response matrix, reduced model approach can be supported even when nonlinear well loss is considered.  相似文献