Browsing ELibrary by Author "Walker R.J."
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Browsing ELibrary by Author "Walker R.J."
Now showing items 1-19 of 19
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Horan M.F.; Smoliar M.I.; Walker R.J. (1998)W isotopic compositions (measured by N-TIMS) in five iron meteorite groups are used in conjunction with 187Re-187Os isotopic data to constrain the timing of metal segregation and crystallization, respectively, in the iron ...
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Walker R.J.; Morgan J.W.; Smoliar M.I.; Horan M.F.; Beary E.S.; Czamanske G.K. (1997)New analytical techniques are utilized that permit the precise and accurate measurement of Pt-190-Os-186 isotope systematics. These techniques are applied to three different systems: sulfide ores associated with the 251.2 ...
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Begemann F.; Ludwig K.R.; Lugmair G.W.; Min K.; Nyquist L.E.; Patchett P.J.; Renne P.R.; Shih C.Y.; Villa I.M.; Walker R.J. (2001)The accuracy of radioisotopic ages is, at present, limited by the accuracy of radioactive decay constants. A literature survey reveals that decay constants used in geo- and cosmochronology usually are assigned uncertainties ...
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Walker R.J.; Morgan J.W.; Becker H.; Horan M.F.; Grossman J.N.; Rubin A.E. (2002)A suite of 47 carbonaceous, enstatite, and ordinary chondrites are examined for Re-Os isotopic systematics. There are significant differences in the 187Re/188Os and 187Os/188Os ratios of carbonaceous chondrites compared ...
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Puchtel I.S.; Humayun M.; Walker R.J.; Brandon A.D. (2005)Komatiite samples from the 2.8-Ga Kostomuksha greenstone belt in the Baltic Shield define Pt–Os and Re–Os isochrons with ages of 2816 ± 190 and 2880 ± 83 Ma, respectively. The mean initial 186Os / 188Os and 187Os / 188Os ...
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Gornostayev S.S.; Walker R.J.; Hanski E.J.; Popovchenko S.E. (2004)The Archean bedrock of the Ukrainian Shield is divided into western and central blocks by a N–W trending tectonic zone known as the Golovanevsk suture zone. Within this zone, there are numerous mafic-ultramafic bodies ...
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Lazar C.; Walker D.; Walker R.J. (2004)Technetium isotopes 97Tc, 98Tc and 99Tc decay to 97Mo, 98Ru and 99Ru, with half-lives of 2.6 My, 4.1 My, and 0.21 My respectively. If there were early solar system processes that resulted in significant fractionation of ...
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Horan M.F.; Walker R.J.; Morgan J.W.; Grossman J.N.; Rubin A.E. (2003)The abundances of the highly siderophile elements (HSE), Re, Os, Ir, Ru, Pt and Pd, were determined by isotope dilution mass spectrometry for bulk samples of 13 carbonaceous chondrites, 13 ordinary chondrites and 9 enstatite ...
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Becker H.; Walker R.J. (2003)The short-lived 98Tc-98Ru (Half-life between 4 and ~10 Ma) and 99Tc-99Ru (Half-life 0.21 Ma) decay systems have the potential to provide important information on the relative chronology of processes that affected metal ...
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Lynton S.J.; Walker R.J.; Candela P.A. (2005)The fractionation of lithium isotopes among quartz, muscovite, and a chloride-bearing aqueous fluid has been investigated experimentally at 400°–500°C and 50–100 MPa. Experiments were performed for 15–60 days in cold seal ...
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Borisov A.; Walker R.J. (2000)New experimental results are reported on the partitioning of Os between Ni94Os6 (at) alloys and silicate melt at 1400 °C at one atmosphere total pressure and oxygen fugacities ranging from 10−6 to 10−8 atm. Specially ...
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Horan M.F.; Walker R.J.; Fedorenko V.A.; Czamanske G.K. (1995)High-Mg volcanic rocks from the ca. 250 Ma old Siberian Flood Basalt Province (SFBP) were analyzed for their osmium and neodymium isotopic compositions in order to help to constrain source characteristics as the system ...
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Meisel T.; Walker R.J.; Irving A.J.; Lorand J.P. (2001)The Re-Os isotopic systematics of spinel- and garnet-bearing mantle xenoliths from North and Central America, Europe, southern Africa, Asia, and the Pacific region were determined to define more precisely the isotopic ...
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Cook D.L.; Walker R.J.; Horan M.F.; Wasson J.T.; Morgan J.W. (2004)The Pt-Re-Os isotopic and elemental systematics of 13 group IIAB and 23 group IIIAB iron meteorites are examined. As has been noted previously for iron meteorite groups and experimental systems, solid metal-liquid metal ...
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Walker R.J.; Krogstad E.J.; Morgan J.W.; Horan M.F.; Czamanske G.K.; Fedorenko V.A.; Kunilov V.E. (1994)Magmatic Cu-Ni sulfide ores and spatially associated ultramafic and mafic rocks from the Noril'sk I, Talnakh, and Kharaelakh intrusions are examined for Re-Os isotopic systematics. Neodymium and lead isotopic data also are ...
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Walker R.J.; Morgan J.W.; Hanski E.J.; Smolkin V.F. (1997)The Re-Os isotopic systematics of various ferropicritic flows and sills of the Pechenga Complex, Russia, have been examined. During crystallization about 1.98 Ga ago, many of these bodies became highly differentiated. In ...
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Becker H.; Morgan J.W.; Walker R.J.; MacPherson G.J.; Grossman J.N. (2001)The Re-Os isotopic systematics of calcium-aluminium-rich inclusions (CAIs) in chondrites were investigated in order to shed light on the behavior of the Re-Os system in bulk chondrites, and to constrain the timing of ...
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McDaniel D.K.; Walker R.J.; Hemming S.R.; Horan M.F.; Becker H.; Grauch R.I. (2004)High precision Os isotope analysis of young marine manganese nodules indicate that whereas the composition of modern seawater is radiogenic with respect to 187Os/188Os, it has 186Os/188Os that is within uncertainty of the ...
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Shirey S.B.; Walker R.J. (1998)The Re-Os isotope sytem, based on the long-lived β − transition of 187 Re to 187 Os, has matured to wide use in cosmochemistry and high-temperature geochemistry. The siderophilic/chalcophilic behavior of Re and Os is ...
Now showing items 1-19 of 19
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