Isotope Geochemistry Laboratory

Professor Richard J. Walker, Director  (rjwalker AT geol.umd.edu)
Dr. Igor S. Puchtel, Laboratory Manager (ipuchtel AT geol.umd.edu )

(top) Peridotite xenolith from quarry near Yangyuan, China was erupted onto the surface approximately 38 million years ago. Materials like this are examined in order to study the evolution of the lithospheric mantle underlying the North China Craton. Evidence suggests that the ancient lithospheric mantle that underlay China as late as the Ordovician has been replace by younger mantle represented by the rock shown.

(bottom) Lunar impact melt rock 14321. This approximately 3.85 billion year old rock and other lunar breccias formed by the massive impacts that generated the large lunar basins are studied in order to better constrain the chemical characteristics of planetesimals that impacted the Moon and Earth at that time.

Isotope Geochemistry Laboratory

There are a variety of opportunities for undergraduate geology students to participate in research with members of the IGL . These include the possibility of work on samples from Earth's mantle and crust, and extraterrestrial materials. Interested students are encouraged to contact Professor Richard J. Walker for further information.

Overview

Facilities

Current Research in the IGL

Staff

Former IGL Postdocs

Students

Opportunities for Undergraduates

IGL Publications 1992-2007

OVERVIEW

The Isotope Geochemistry Laboratory (IGL) is part of the Geochemistry Laboratories of the Department of Geology, University of Maryland. The IGL comprises a set of laboratories for the preparation and isotopic analysis of a wide range of geological materials. These laboratories include separate Mass Spectrometry (2), Chemistry (3), Mineral Separation and Rock Preparation facilities. The IGL began operations in 1991 with the acquisition of a NBS-design single-collector solid source mass spectrometer. In 1992 a VG Sector 54 mass spectrometer with 7 faraday collectors, was added to the complement of analytical tools. A third thermal ionization mass spectrometer, a Thermo Electron Triton was installed in 2007. A second mass spectrometry laboratory, shared with the Plasma Laboratory, houses a Nu Plasma multi-collector inductively coupled plasma mass spectrometer.

The mission of the IGL is to produce the highest quality isotope data, to innovate in techniques development and applications, to train students and visitors the techniques involved in gathering such data, and to maintain itself as a world-class isotope measurement facility.


FACILITIES


The Thermal Ionization Mass Spectrometry Laboratory of the IGL currently houses three solid source mass spectrometers, two filament degassing apparatuses, and laminar flow benches for sample loading. Each mass spectrometer has dedicated positive and negative ion optics sources.

Our first thermal ionization mass spectrometer is an NBS-designed and built 68 degree sector, 12 inch radius of curvature instrument (originally built in Washington D.C. in the mid-1960’s) that was modernized in 1991. This instrument has one movable faraday cup. Behind it lies an ETP discrete dynode electron multiplier that allows measurement of small ion beams. This instrument is now largely used for the measurement of small quantities of Os (in negative polarity). A total of more than 9,500 analyses had been logged on this instrument by July 2007.

(right) Photo shows source end of the NBS 68° sector thermal ionization mass spectrometer. This instrument is currently used primarily for low level Os isotope measurements.

 

 

 

 

 

 

 


Our second thermal ionization mass spectrometer is a 1992 vintage VG Sector 54 with 7 faraday collectors and a 20-sample turret. It was the first Sector 54 shipped with negative ion capability. With the axial Faraday cup moved out of place, small positive ion beams may be measured using a Daly knob-photomultiplier tandem. This instrument is used for Nd and Sr isotope analyses, as well as for U, Pb, S, Sm and Li samples. In negative polarity, high abundance Os, W, Mo and Ru samples are commonly analyzed using multiple faraday cups. This instrument also has an electron multiplier that is used to measure small negative ion beams. A total of more than 11,900 analyses had been logged on this instrument by July 2007.

(left) Photo shows the Sector 54 mass spectrometer that was installed at Maryland in 1992.

 

 

 

 

 

 

 

 

A Thermo Electron Triton was installed in the spring of 2007. We have just begun to apply this instrument to geological/cosmochemical projects. We are particularly eager to apply the instrument for high precision measurement of Os, Ru, W and Mo isotopes.

 

The Nu Plasma multi-collector ICP-MS uses high temperature plasma to ionize elements that have been either chemically separated and purified from a material, or liberated from a solid matrix via laser ablation. The relative intensities of the different isotopes of a given element are quantified using either the multiple faraday cups or multiple electron multipliers. This instrument is commonly used to measure the isotopic compositions of Mo, Li, W, Pt, Ru, Ir, Pd and Re.

 

 

(left) Photo of Nu Plasma multi-collector ICP-MS, installed at Maryland in 2001.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Most samples for isotopic analysis are purified in the Chemistry Clean Laboratories. Two 500 sq. ft. laboratories are supplied with HEPA filtered air. Each contains class-100 vented laminar flow hoods, chemical fume hoods and multiple work stations (with fume extraction). The facility also utilizes a Milli-Q water purification system, and currently operates eight sub-boiling stills (quartz and teflon).

Upper photo shows air-lock entrance foyer to clean room facility (CHEM0216). Lower photo shows vented work stations (foreground) and 2 of 4 class 100 laminar flow hoods (background) present in chemical clean laboratory.

Photo of a first stage rhenium elution accomplished using disposable anion exchange columns.

The Mineral Separation (CHEM0221) and Rock Preparation (CHEM0219) laboratories were most recently renovated in 2002-2003. The Rock Preparation lab houses, short-term sample storage, a ceramic jaw crusher and disk mill, alloy mortar and pestle, rock splitter, SPEX Industries Shatterbox and Mixer Mill (both with agate and alumina grinding chambers), and a Leco diamond slow-speed saw for cutting iron meteorites. The Mineral Separation lab has high density liquids for mineral density separations (Tl-mallonate, methylene iodide, bromoform, Na and alkali polytungstate; these are used in a chemical fume hood), a Frantz Co. L-1 isodynamic magnetic separator, as well as binocular microscopes for hand-picking separates. The lab also houses two ovens (one can achieve temperatures as high as 380°C), one muffle furnace and both oxy-propane and oxy-hydrogen torches (for sealing Pyrex and quartz Carius tubes).

 

 

 

(left) Photo of the mineral separation laboratory. This lab is used for separating and purifying mineral fractions removed from bulk rock samples. The room is also used for fusions, oven digestions and torch work associated with the closure of Carius tubes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Torchbox for sealing Carius tubes. An oxygen-propane torch is used for sealing Pyrex tubes, and an oxygen-hydrogen torch is used to seal quartz tubes.

 

 

 

 

 

 

 

 

 

Nickel-sulfide fire assays are used for concentrating highly siderophile elements from large quantities of matrix.

 

 

 

 

 

 

 

 

 

Rock crushing/short-term storage room.


CURRENT RESEARCH IN THE IGL

Some of the main thrusts of research in the IGL include studies of the mantle and crust, the isotopic evolution of the oceans, and the evolution of the early solar system. Applications also target tectonic and environmental problems. The range of specific research topics currently active in the IGL include:

  • Use of coupled 187Re-187Os and 190Pt-186Os isotope systems to examine possible interaction between the Earth's core and lowermost mantle.
  • The evolution of highly siderophile elements in Earth’s mantle and crust through time. Recent targets of interest include mafic-ultramafic rocks (including komatiites and ophiolites) from Finland, Canada, North Carolina, Chile, Switzerland and Russia, and oceanic rocks including abyssal peridotites.
  • The chronology and chemical evolution of solar system materials. Specific targets include iron meteorites, pallasites, chondrites, lunar volcanic glasses and basalts, lunar highland breccias, Martian meteorites and presolar grains. These studies include the application of short- and long-lived chronometers based on radioactive decay, and research on isotopic heterogeneities in meteorites and their implications for solar system formation and stellar nucleosynthesis
  • Study of peridotite xenoliths plucked from the subcontinental lithospheric mantle as a means of constraining the age of lithospheric mantle creation, assemblage and possible destruction (in some regions, such as underlying the North China Craton). Work is currently centered mostly on samples from China and Korea.
  • Determinations of variations in the stable (Mo) and radiogenic (Os and Sr) isotope compositions of the world oceans through time as a means of monitoring the chemical conditions of the oceans and weathering history of the continents.

STAFF

The faculty/staff presently engaged in research in the IGL are currently: James Day, Sarah Penniston-Dorland, Jay Kaufman, Aaron Martin, Igor Puchtel, Roberta Rudnick, Tetsuya Saito, Richard Walker, Tetsuya Yokoyama.

Past members of the IGL have included (with present affiliation):

Harry Becker (Freie University, Berlin), Eirik Krogstad (Georgia State University), Christina Gallup (Univ. Minnesota Duluth), Mary Horan (Carnegie Institution), Bill Minarik (McGill University), Tim Mock (Carnegie Institution), Sonia Esperança (NSF), John Morgan (retired), and Paul Tomascak (SUNY Oswego).

FORMER IGL POSTDOCS (and current affiliation)

  • Thomas Meisel (1995-1996) (University of Leoben, Austria)
  • Alan Brandon (1997-1999) (NASA, Johnson Space Center)
  • Tod Waight (1998-1999) (University of Copenhagen, Denmark)
  • Harry Becker (1998-2001) (Freie University, Berlin)
  • Diane McDaniel (2000-2003) (Montgomery College)
  • Aaron Pietruszka (2002-2003) (San Diego State University)

STUDENTS

Theses/dissertations completed:

  • Jerry L. Burgess (M.S., 1994—with LCP) Pressure-temperature-time-deformation (P-T-t-D) history of high-grade gneisses of the Port aux Basques area, southwest Newfoundland, Canada.
  • Jeffrey D. Jarriel (M.S., 1994) Use of Sr isotopic, hydrophysical, and other Geochemical data to delineate catchment flow paths during baseflow and storm events.
  • Paul B. Tomascak (Ph.D., 1995) The petrogenesis of granitic rocks in southwestern Maine.
  • Alison B. Schwab (M.S., 1995) Li isotope variability in ground and surface water in a first order agricultural catchment, eastern Maryland.
  • Michael I. Smoliar (Ph.D., 1996) Re-Os isotopic studies of magmatic iron meteorites.
  • Asuka Tsuru (M.S., 1997) The Os isotopic evolution of the upper mantle: the Jormua ophiolite complex, Finland.
  • Sarah E. Libeau (M.S., 1997) Pb isotope tracers in oyster shells from historic native American middens around the Chesapeake Bay.
  • Rachel A. Pressley (M.S.—with LCP, 1997) Petrogenesis of the Phillips pluton, Maine.
  • Gary S. Solar (Ph.D.—with LCP, 1999) Tracing melt migration and dating deformation, west-central Maine.
  • Donna Gunderson (M.S., 1999) Paleorecords of climate change.
  • Jinmei Tian (M.S.—with LCP, 2000) Petrogenesis of the Moose-lookmeguntic plutonic complex, Maine.
  • Ji Li (M.S., 2001) Use of the Re-Os isotope system to trace the origin of gold mineralizing fluids in the Allegheny District, California.
  • David Cook (M.S., 2001) Re-Os and Pt-Os isotopic systematics of evolved iron meteorites.
  • Stephen Lynton (Ph.D.—with LMDR, 2003) An experimental study of the isotopic fractionation and partitioning of lithium among quartz, muscovite, and fluids.
  • Amitava Gangopadhyay (Ph.D., 2004) Petrologic, geochemical and Os isotope studies of selected Precambrian komatiites.
  • Feng-Zhen Teng, (Ph.D., 2005) Quantifying the Li isotope composition of the upper continental crust.
  • Jacqueline L. Mann (Ph.D., 2005) Determination of sulfur isotope composition in sulfate from two high elevation snowpits by multi-collector thermal ionization mass spectrometry using a double spike.
  • Nick Geboy (M.S., 2006) Re-Os geochronology of organic-rich sediments.
  • Ruth Thompson Schulte (M.S., 2007) Isotopic systematics of mafic-ultramafic rocks of the Taitao ophiolite, Chile.

Theses/dissertations in progress:

  • Tracey Centorbi (M.S.) Age structure of lithospheric mantle underlying northeastern North America.
  • Tom Ireland (Ph.D.) Isotopic and highly siderophile element study of plume-derived lavas.
  • Katherine Scheiderich (Ph.D.) Stable Mo isotopes as a tracer of paleo-redox conditions.
  • Jingao Liu (Ph.D.) Investigations of the history of the lithospheric mantle underlying the North China Craton.

As of 2007, the IGL has hosted research for a total of 18 senior undergraduate student theses.

Guest Users of the IGL have included (with affiliation at the time of visit):

Lukas Ackerman (University of Prague), Peter Ashley (Johns Hopkins University), Julie Bartley (West Georgia College), Lars Borg (Johnson Space Center), Chris Fedo (Virginia Tech), Robert Frei (Geologisk Institut Kobenhavns Universitet, Denmark), Shan Gao (Key Laboratory of Continental Dynamics, Department of Geology, Northwestern University, Xi’an, 710096, China), Jenny Hall (Yale University), Eero Hanski (Geological Survey of Finland), Debra Hassler (Harvard University), Melissa Hicks (University of Nevada, Las Vegas), Steve Lev (Towson University), Gabriela Mora-Klepeis (University of Vermont), Brent Owens (College of William and Mary), Marcio Pimentel (Universidade de Brasilia, Brazil), John Rakovan (Miami University of Ohio), Manuel Schilling (University of Chile), Paula Shafer (Indiana University), Department of Geology, Northwestern University, Xi’an, 710096, China), Susanna Sichel (Universidade Federal Fluminense, Brazil), Michael Smoliar (Carnegie Institution of Washington), Ilona Suominen (University of Helsinki), Yasutaka Terakado (Kobe University), Malissa Washburn (University of Maine), Elizabeth Widom (Miami University of Ohio), Fu-yuan Wu, (Changchun Univ. of Science and Tech., China), Hong-Lin Yuan (Key Laboratory of Continental Dynamics, Department of Geology, Northwestern University, Xi’an, China), David van Acken (Frei University, Berlin).

OPPORTUNITY FOR UNDERGRADUATES

There are a variety of research opportunities for undergraduate geology to pursue with members of the IGL. These include the possibility of work on samples from Earth’s mantle and crust, and extraterrestrial materials. Interested students are encouraged to contact Professor Richard J. Walker (rjwalker AT geol.umd.edu) for further information.

IGL PUBLICATIONS 1992-2007

Peer-reviewed publications produced as a consequence of work partially or wholly conducted in the IGL since its creation in 1991.

1992

Horan M.F., Morgan J.W., Walker R.J. and Grossman J.N.(1992) Re-Os isotope constraints on the age of iron meteorites. Science 255 , 1118-1121.

Morgan J.W., Walker R.J. and Grossman J.N. (1992) Rhenium-osmium isotope systematics in meteorites I: Magmatic iron meteorite groups IIAB and IIIAB. Earth Planet. Sci. Lett. 108 , 191-202.

1993

Krogstad E.J., Walker R.J., Nabelek P.I. and Russ-Nabelek C. (1993) Pb isotopic constraints on the origin of Archean and Proterozoic granites, Black Hills, South Dakota. Geochim. Cosmochim. Acta 57 , 4677-4685.

1994

Walker , R.J., Morgan, J.W., Hanski, E.J. and Smolkin, V.F. (1994) The role of the Re-Os system in the study of magmatic sulfide ores: A tale of three ores. Proceedings of Sudbury-Norilsk Symposium, Ontario Geological Survey Spec. Pub. 5 , 343-355.

Horan M.F, Morgan J.W., Grauch R.I., Coveney R., Murowchick J., Hulbert L. (1994) Re-Os isotopes in black shales and Ni-Mo-PGE-rich sulfide layers, Yukon Territory, Canada and Guizhou and Hunan, China. Geochim. Cosmochim. Acta. 58 , 257-265.

Krogstad E.J. and R.J. Walker (1994) High closure temperatures of the U-Pb system in large apatites from the Tin Mountain pegmatite, Black Hills, South Dakota. Geochim. Cosmochim. Acta 58 , 3845-3853.

Walker, R.J., Morgan J.W., Horan M.F., Czamanske G.F., Krogstad E.J., Fedorenko V. and Kunilov V.E. (1994) Re-Os isotopic evidence for an enriched-mantle source for the Noril'sk-type ore-bearing intrusions, Siberia. Geochim. Cosmochim. Acta 58 , 4179-4197.

Lambert D.D., Walker R.J., Morgan J.W., Shirey S.B., Carlson R.W., Zientek M.L., Lipin B.R., Koski M.S. and Cooper R.L. (1994) Re-Os and Sm-Nd isotope geochemistry of the Stillwater Complex, Montana: Implications for the petrogenesis of the J-M Reef. Journ. Petrol. 35 , 1717-1753.

1995

Morgan J.W., Horan M.F., Walker R.J. and Grossman J.N. (1995) Rhenium-osmium concentration and isotope systematics in group IIAB iron meteorites. Geochim. Cosmochim. Acta 59 , 2331-2344.

Shirey S.B. and Walker R.J. (1995) Carius tube digestion for low-blank rhenium-osmium analysis. Anal. Chem . 34 , 2136-2141.

Krogstad E.J., Hanson G.N. and Rajamani V. (1995) Sources of continental magmatism adjacent to the later Archean Kolar Suture Zone, south India :distinct isotopic and elemental signatures of two late Archean magmatic series. Contrib. Mineral. Petrol . 122 , 159-173.

Walker R.J., Morgan J.W. and Horan M.F. (1995) 187Os enrichment in some mantle plume sources: Evidence for core-mantle interaction? Science 269 , 819-822.

Horan M.F., Walker R.J., Fedorenko V.A. and Czamanske G.K. (1995) Os and Nd isotopic constraints on the temporal and spatial evolution of Siberian flood basalt sources. Geochim. Cosmochim. Acta 59 , 5159-5168.

Burgess, J.L., Brown, M., Dallmeyer, R.D. and van Staal, C.R. (1995) Microstructure, metamorphism, thermochronology and P-T-t -deformation history of the Port aux Basques Gneisses, Southwest Newfoundland, Canada. Journal of Metamorphic Geology , 13 , 751-776.

1996

Smoliar M.I., Walker R.J. and Morgan J.W. (1996) Re-Os ages of group IIA, IIIA, IVA and IVB iron meteorites. Science 271 , 1099-1102.

Meisel T., Biino G.G. and Nagler T. (1996) Re-Os, Sm-Nd and rare earth element evidence for Proterozoic subcontinental and oceanic lithosphere in tectonized ultramafic lenses from the Swiss Alps. Geochim. Cosmochim. Acta 60 , 2583-2593.

Tomascak P.B., Krogstad E.J. and Walker R.J. (1996) U-Pb monazite geochronolgy of granitic rocks from Maine :implications for late Paleozoic tectonics in the northern Appalachians . J. of Geol . 104 , 185-195.

Koide M., Goldberg E.D. and Walker R. (1996) The analysis of seawater osmium. Deep-Sea Res . 43 , 53-55.

Walker R.J., Hanski E.J., Vuollo J. and Liipo J. (1996) The Os isotopic composition of Proterozoic upper mantle:evidence for chondritic upper mantle from the Outokumpu ophiolite, Finland . Earth Planet. Sci. Lett . 141 , 161-173.

Krogstad E.J. and Walker R.J. (1996) Evidence of heterogeneous crustal sources: the Harney Peak Granite , South Dakota , U.S.A. Trans. Roy. Soc. Edinburgh; Earth Sciences 87 , 331-337.

Meisel T., Walker R.J. and Morgan J.W. (1996) The osmium isotopic composition of the Earth's primitive upper mantle. Nature 383 , 517-520.

Fedo C.M., Eriksson K.A. and Krogstad E.J. (1996) Geochemistry of shales from the Archean (~3.0 Ga) Buhwa Greenstone Belt, Zimbabwe : implications for provenance and source-area weathering. Geochim. Cosmochim. Acta 60 , 1751-1764.

Tomascak P.B., Krogstad E.J. and Walker R.J. (1996) Nature of the crust in Maine , USA : evidence from the Sebago batholith. Contrib. Mineral. Pet. 125 , 45-59.

Carlson R.W., Esperan ç a S. and Svisero D.P. (1996) Chemical and Os isotopic study of Cretaceous potassic rocks from southern Brazil . Contrib. Mineral. Pet. 125 , 393-405.

1997

Terakado Y., Fujitani T. and Walker R.J. (1997) Nd and Sr isotopic constraints on the origin of igneous rocks resulting from the opening of the Japan Sea , southwestern Japan . Contrib. Mineral. Pet. 129 , 75-86.

Walker R. J., Morgan J.W., Hanski E.J. and Smolkin V. (1997) Re-Os systematics of Early Proterozoic ferropicrites, Pechenga Complex, NW Russia:evidence for ancient 187 Os-enriched plumes. Geochim. Cosmochim. Acta 61 , 3145-3160.

Meisel T., Lange J.-M. and Krähenbühl U. (1997) The chemical variation of moldavite tektites: simple mixing of terrestrial sediments. Meteoritics & Planetary Science 32 , 493-502.

Walker R.J., Morgan J.W., Smoliar M.I., Beary E., Czamanske G.K. and Horan M.F. Application of the 190Pt- 186Os isotope system to geochemistry and cosmochemistry (1997) Geochim. Cosmochim. Acta 61 , 4799-4807.

Meisel T., Melcher F., Tomascak P., Dingeldey C. and Koller F. (1997) Re-Os isotopes in orogenic peridotite massifs in the eastern Alps, Austria. Chemical Geology 143 , 217-229.

Esperança S, Carlson R.W., Shirey S.B. and Smith D. (1997) Dating crust-mantle separation: Re-Os isotopic study of mafic xenoliths from central Arizona. Geology 25 , 651-654.

Ashley, P., Krogstad, E., Lees, P., Silbergeld, E., and Smith, D. (1997) The use of stable lead isotopes to identify and apportion sources of lead in urban house dust. in: Hazardous Waste: Impacts on Human and Ecological Health , (B. Johnson, C. Xintaras, and J. Andrews, eds.), Princeton Science Publications, p. 139-150.

1998

Horan M.F., Smoliar M. and Walker R.J. (1998) 182W and 187Re- 187Os systematics of iron meteorites: chronology for melting, differentiation and crystallization of asteroids. Geochim. Cosmochim. Acta 62 , 545-554.

Shirey S.B. and Walker R.J. (1988) Re-Os isotopes in cosmochemistry and high-temperature geochemistry . Annual Reviews of the Earth and Planetary Sciences 26 , 423-500.

Asmerom Y. and Walker R.J. (1998) Pb and Os isotopic constraints on the composition and rheology of the lower crust. Geology 26 , 359-362.

Brandon A., Walker R.J., Morgan J.W., Norman M.D. and Prichard H. (1998) Coupled 186Os and 187Os evidence for core-mantle interaction. Science 280 , 1570-1573.

Tomascak P.B., Krogstad E.J. and Walker R.J. (1998) Nd isotope systematics and the derivation of granitic pegmatites in southwestern Maine , USA . Can. Min . 36 , 327-337.

1999

Tomascak P.B., Krogstad E.J. and Walker R.J. (1999) Clues to the significance of the Norumbega Fault Zone in southwestern Maine from the geochemistry of granitic rocks. In, The Norumbega Fault Zone , eds. A. Ludman and D.P. West, G.S.A. Special Paper 331. 105-119.

Pressley, R.A. and Brown, M. (1999) The Phillips Pluton, Maine , USA : Evidence of heterogeneous crustal sources, and implications for granite ascent and emplacement mechanisms in convergent orogens. Lithos 46 , 335-366.

Brown, M. and Pressley, R.A. (1999) Crustal melting in nature: Prosecuting source processes. Physics and Chemistry of the Earth 24 , 305-316.

Walker R.J., Storey M., Kerr A. and Tarney J. (1999) Implications of 187Os heterogeneities in mantle plumes: evidence from Gorgona Island and Curaçao. Geochim. Cosmochim . Acta 63 , 713-728.

Tomascak P.B., Tera F., Helz R. and Walker R.J. (1999) The absence of lithium isotope fractionation during basalt differentiation: New measurments by multicollector sector ICP-MS. Geochim. Cosmochim. Acta 63 , 907-910.

Brandon A.D., Norman M.D., Walker R.J. and Morgan J.W. (1999) 186Os- 187Os systematics of Hawaiian picrites. Earth Planet. Sci. Lett. , 172 , 25-42.

2000

Tsuru A., Walker R.J., Kontinen A., Peltonen P. and Hanski E. (2000) Re-Os isotopic systematics of the Jormua Ophiolite Complex, NW Finland. Chemical Geology 164 , 123-141.

Böhlke J.K. and Horan M. (2000) Strontium isotope geochemistry of groundwaters and streams affected by agriculture, Locust Grove , MD. Applied Geochemistry 15 , 599-609.

Righter K., Walker R.J. and Warren P.H. (2000) Significance of highly siderophile elements and Os isotopes in the lunar and terrestrial mantles. in Origin of the Earth and Moon , R. Canup and K. Righter eds., Univ. of Arizona Press, Tucson, 291-322.

Borisov A. and Walker R.J. (2000) Os solubility in silicate melts: new efforts and results. American Mineralogist 85 , 912-918.

Brandon A.D., Snow J.E., Walker R.J., Morgan J.W. and Mock T.D. (2000) 190Pt- 186Os and 187Re- 187Os systematics of abyssal peridotites. Earth Planet. Sci. Lett. 177 , 319-335.

Borg L.E., Brandon A.D., Clynne M.A. and Walker R.J. (2000) Re-Os isotopic systematics of primitive basalts from the Lassen region of the Cascade arc, California . Earth Planet. Sci. Lett. 177 , 301-317.

Helz G.R., Adelson J.M., Miller C.V., Cornwell J.C., Hill J.M., Horan M. and Walker R.J. (2000) Osmium isotopes demonstrate distal transport of contaminated sediments in Chesapeake Bay . Environmental Science and Technology 34 , 2528-2534.

Becker H. (2000) Re-Os isotopic systematics of eclogites: Implications for crustal recycling. Earth Planet. Sci. Lett. 177 , 287-300.

Walker R.J. (2000) News & Views: The extraterrestrial wedding ring. Nature 406 , 359-360.

Brandon A.D., Walker R.J., Morgan J.W. and Goles G.G. (2000) Re-Os isotopic evidence for early differentiation of the Martian mantle. Geochim. Cosmochim Acta . 64 , 4083-4095.

Czamanske G.K., Wooden J.L., Walker R.J., Fedorenko V.A., Simonov O.N., Budahn J.R. and Siems D.F. (2000) Geochemical, isotopic and SHRIMP age data for Precambrian basement rocks, Permian volcanic rocks, and sedimentary host rocks to the ore-bearing intrusions, Noril'sk-Talnakh District, Siberian Russia. International Geology Review , 42 , 895-927.

Böhlke J.K. and Horan M.F. (2000) Strontium isotope geochemistry of groundwaters and streams affected by agriculture, Locust Grove , MD. Applied Geochemistry 15 , 599-609.

2001

Begemann F., Ludwig K.R., Lugmair G.W., Min K.W., Nyquist L.E., Patchett P.J., Renne P.R., Shih C.-Y., Villa I.M. and Walker R.J. (2001) Towards and improved set of decay constants for geochronological use. Geochim. Cosmochim Acta 65 , 111-121.

Meisel T., Walker R.J., Irving A.J., and Lorand J.-P. (2001) Osmium isotopic compositions of mantle xenoliths: a global perspective. Geochim. Cosmochim Acta . 65 , 1311-1323.

Walker R.J. and Stone W.R. (2001) Os isotope constraints on the origin of the 2.7 Ga Boston Creek flow, Ontario , Canada . Chemical Geology 175 , 567-579.

Hanski E., Walker R.J., Huhma H. and Suominen I. (2001) The Os and Nd isotopic systematics of the 2.44 Ga Akanvaara and Koitelainen mafic layered intrusions in northern Finland. Precambrian Research 109 , 73-102.

Horan M.F., Morgan J.W., Walker R.J. and Cooper R. (2001) Re-Os isotopic constraints on magma mixing in the peridotite zone of the Stillwater Complex, Montana . Contrib. Mineral. Petrol . 141 , 446-457.

Becker H., Walker R.J., MacPherson G.J., Morgan J.W. and Grossman J.N. (2001) Rhenium-osmium systematics of calcium-aluminum-rich inclusions in carbonaceous chondrites. Geochim. Cosmochim. Acta 65 , 3379-3390.

Morgan J.W., Walker R.J., Brandon A.D. and Horan M.F. (2001) Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx. Meteoritics and Planetary Science 36 , 1257-1275.

Waight T.E., Wiebe R.A., Krogstad E.J. and Walker R.J. (2001) Isotopic responses to basaltic injections into silicic magma chambers: a whole rock and microsampling study of macrorhythmic units in the Pleasant Bay layered gabbro-diorite complex, Maine, USA . Contrib. Mineral. Petrol . 142 , 323-335.

Becker H., Shirey S.B. and Carlson R.W. (2001) Effects of melt percolation on the Re-Os systematics of peridotites from a Paleozoic convergent plate margin. Earth Planet. Sci. Lett . 188 , 107-121.

Meisel T., Moser J. and Wegscheider W. (2001) Recognizing heterogeneous distribution of platinum group elements (PGE) in geological materials by means of the Re-Os isotope system. Fresenius J. Anal. Chem. 370 , 566-572.

Dorais, M. J., Wintsch, R. P., Becker H. (2001) The Massabesic gneiss complex, New Hampshire: a study of a portion of the Avalon terrane. American Journal of Science 301 , 657-682.

2002

Morgan J.W., Walker R.J., Horan M.F. and Beary E.S. (2002) 190Pt- 186Os and 187Re- 187Os systematics of the Sudbury Igneous Complex, Ontario. Geochim. Cosmochim. Acta 66 , 273-290.

Walker R.J., Prichard H.M., Ishiwatari A. and Pimentel M. (2002) The osmium isotopic composition of convecting upper mantle deduced from ophiolite chromitites. Geochim. Cosmochim. Acta 66 , 329-345.

Tomascak P.B., Widom E., Benton L.D., Goldstein S.L. and Ryan J.G. (2002) The control of lithium budgets in island arcs. Earth Planet. Sci. Lett . 196, 227-238.

Owens B.E. and Tomascak P.B. (2002) Mesoproterozoic lamprophyres in the Labrieville Massif , Quebec : Clues to the origin of alkalic anothosites? Can. J. Earth Sci. 39 , 983-997.

Zack T., Tomascak P.B., Rudnick R.L., Dalpe C. and McDonough W.F. (2003) Extremely light Li in orogenic eclogites: The role of isotope fractionation during dehydration in subducted oceanic crust. Earth and Planetary Science Letters 208 , 279-290.

Walker R.J. and Nisbet E. (2002) 187Os isotopic constraints on Archean mantle dynamics. Geochim. Cosmochim. Acta 66 , 3317-3325.

Walker R.J., Horan M.F., Morgan J.W., Becker H., Grossman J.N. and Rubin A. (2002) Comparative 187Re- 187Os systematics of chondrites: Implications regarding early solar system processes. Geochim. Cosmochim. Acta 66 , 4187-4201.

Becker H., Dalpe C. and Walker R.J. (2002) High precision Ru isotopic measurements by multi-collector ICP-MS. The Analyst 127 , 775-780.

2003

Brandon A.D., Walker R.J., Puchtel I.S., Becker H, Humayun M. and Revillon S. (2003) 186Os- 187Os systematics of Gorgona Island komatiites: implications for early growth of the inner core. Earth Planet. Sci. Lett . 206, 411-426.

Horan M.F., Walker R.J., Morgan J.W., Grossman J.N. and Rubin A. (2003) Highly siderophile elements in chondrites. Chem. Geol. 196, 5-20 .

Becker H. and Walker R.J. (2003) The 98Tc- 98Ru and 99Tc- 99Ru chronometers: new results on iron meteorites and chondrites. Chem. Geol. 196 , 43-56.

Wu F., Walker R.J., Ren X-w, Sun D-y and Zhou X-h. (2003) Osmium isotopic constraints on the age of lithospheric mantle beneath northeastern China . Chem. Geol. 196 , 107-129.

Gangopadhyay A. and Walker R.J. (2003) Re-Os systematics of the ca. 2.7 Ga Alexo komatiites, Ontario , Canada . Chem. Geol . 196 , 147-162.

Tomascak P.B., Hemming N.G., and Hemming S.R. (2003) The lithium isotopic composition of waters of the Mono Basin, California. Geochim. Cosmochim. Acta 67 , 601-611.

Arndt N.T., Czamanske G.K., Walker R.J., Chauvel C. and Fedorenko V.A. (2003) Geochemistry and origin of the intrusive hosts of Noril'sk-Talnakh Cu-Ni-PGE deposits. Econ. Geol. 98 , 495-515 .

Becker H. and Walker R.J. (2003) Efficient mixing of the solar nebula from uniform Mo isotopic composition of meteorites. Nature 425 , 152-155.

2004

Lazar G.C., Walker D. and Walker R.J. (2004) Experimental partitioning of Tc, Mo, Ru and Re between solid and liquid during crystallization in Fe-Ni-S. Geochim. Cosmochim. Acta 68 , 643-651.

McDaniel D.K., Walker R.J., Hemming S.R., Horan M.F., Becker H. and R. I Grauch (2004) Sources of osmium to the modern oceans: New evidence from the 190 Pt- 186 Os system. Geochim. Cosmochim. Acta 68 , 1243-1252.

Cook D.L. Walker R.J., Horan M.F., Wasson J.T. and Morgan J.W. (2004) Pt-Re-Os systematics of group IIAB and IIIAB iron meteorites. Geochim. Cosmochim. Acta 68 , 1413-1431.

West, D.P., Jr., Coish, R.A., and Tomascak, P.B. (2004) Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine : Evidence from trace element and isotope geochemistry: Geol. Mag . 141 , 125-140.

Hanski E.J., Walker R.J. Huhma H., Polyakov, G.V., Glotov, A.I., Tran Trong Hoa, Ngo Thi Phuong (2004) Origin of Permo-Triassic komatiites, northwestern Vietnam. Contrib. Mineral. Petrol. 147 , 453-469.

Balykin, P.A., Polyakov, G.V., Hanski, E., Walker, R.J., Huhma, H., Glotov, A.I., Trang Trong Hoa, Ngo Thi Phuong, Hoang Huu Thanh, Tran Quoc Hung, Petrova, T.E. (2004) Late-Permian komatiite-basalt complex in the Song Da rift, northwestern Vietnam. Journal of Geology ( Vietnam ) , Series B, No. 23 , 52-64.

Gornostayev S.S., Walker R.J., Hanski E.J. and Popovchenko S.E. (2004) Evidence for the emplacement of ca. 3.0 Ga lithospheric mantle in the Ukrainian Shield. Precamb. Res . 132 , 349-362.

Gelinas A., Kring D.A., Zurcher L., Urrutia-Fucugauchi J., O. Morton and Walker R.J. (2004) Osmium isotope constraints on the proportion of bolide component in Chicxulub impact meltrocks. Meteoritics Planet. Sci. 39 , 1003-1008.

Teng F.Z., McDonough W.F., Rudnick R.L., Dalpé C., Tomascak P.B., Gao S., Chappell B.W. (2004) Lithium isotopic composition and concentration of the upper continental crust. Geochim. Cosmochim. Acta 68 , 4181-4192.

Tomascak P.B. (2004) Developments in the understanding and application of lithium isotopes in the Earth and planetary sciences. In: Johnson CM, Beard BA, and Albarede F (eds) Geochemistry of Non-Traditional Isotope Systems, Min. Soc. Amer. Reviews Mineralogy Geochemistry . 55 , 153-195.

Walker R. J., Horan M.F., Shearer C.K. and Papike J.J. (2004) Depletion of highly siderophile elements in the lunar mantle: evidence for prolonged late accretion. Earth Planet. Sci. Lett. 224 , 399-413.

2005

Hulbert L.J., Hamilton M.A., Horan M.F. and Scoates R.F.J. (2005) U-Pb zircon and Re-Os isotope geochronology of mineralized ultramafic intrusions and associated nickel ores from the Thompson nickel belt, Manitoba, Canada. Econ. Geol. 100, 29-41.

Tomascak P.B., Brown M., Solar G.S., Becker H., Centorbi T.L., and Tian J. (2005) Source contributions to Devonian granite magmatism near the Laurentian border, New Hampshire and Western Maine, USA. Lithos 80, 75-99.

Walker R. J., Brandon A.D., Bird J.M., Piccoli P.M., McDonough W.F. and Ash R.D. (2005) 186Os-187Os systematics of Os-Ir-Ru alloy grains, southwestern Oregon. Earth Planet. Sci. Lett 230, 211-226.

Brandon A. D. and Walker R.J. (2005) The debate over core-mantle interaction. Earth Planet. Sci. Lett. Frontiers 232, 211-225.

Terakado Y. and Walker R.J. (2005) Nd, Sr and Pb isotopic and REE geochemical study of Miocene submarine hydrothermal deposits (Kuroko deposits), Japan, Contrib. Mineral. Petrol. 149, 388-399.

Walker R.J. and Walker D. (2005) Does the core leak? EOS 86, 237-242.

Lynton S.J., Walker R.J. and Candela P.A. (2005) Lithium isotopes in the system Qz-Ms-fluid. Geochim. Cosmochim. Acta 69, 3337-3347.

Puchtel I.S., Brandon A.D., Humayun M., and Walker, R.J. (2005) Evidence for the early differentiation of the core from Pt-Re-Os isotope systematics of 2.8-Ga komatiites. Earth Planet. Sci. Lett. 237, 118-134.

Gangopadhyay A., Sproule R.A., Walker R.J. and Lesher M. (2005) Re-Os systematics of komatiites and komatiitic basalts at Dundonald Beach, Ontario, Canada: Evidence for a complex alteration history and implications of a late-Archean chondritic mantle source. Geochim. Cosmochim. Acta 69, 5087-5098.

2006

Pietruszka A.J., Walker R.J. and Candela P.A. (2006) Determination of mass dependent molybdenum isotopic variations by MC-ICP-MS: an evaluation of matrix effects. Chem. Geol. 225, 121-136.

Gangopadhyay A., Walker R.J., E. Hanski, and P. Solheid (2006) Origin of Paleoproterozoic Ti-enriched komatiitic rocks from Jeesiörova, Kittilä Greenstone Complex, Finnish Lapland. Journal of Petrology 47, 773-789.

Teng F.-Z., McDonough W.F., Rudnick R.L. and Walker R.J. (2006) Diffusion-driven extreme lithium isotopic fractionation in country rocks of the Tin Mountain pegmatite. Earth Planet. Sci. Lett. 243, 701-710.

Brandon A.D., Walker R.J. and Puchtel I.S. (2006) Platinum-Os isotope evolution of the Earth’s mantle: constraints from chondrites and Os-rich alloys. Geochim. Cosmochim. Acta 70, 2093-2103.

Lee S. R., Horton J.W. and Walker R.J. (2006) Osmium-isotope and platinum-group element systematics of impact melt rocks, Chesapeake Bay Impact Structure, Virginia, USA. Meteoritics Planet. Sci. 41, 819-833.

Teng F.-Z., McDonough W.F., Rudnick R.L. and Walker R.J. (2006) Lithium isotopic systematics of granites and pegmatites from the Black Hills, South Dakota. Am. Min. 91, 1488-1498.

Lee S. R. and Walker R. J. (2006) Re-Os isotope systematics of mantle xenoliths from South Korea: evidence for complex growth and loss of lithospheric mantle beneath East Asia. Chem. Geol. 231, 90-101.

Becker H., Horan M.F., Walker R.J., Gao S., Lorand J.-P. and Rudnick R.L. (2006) Highly siderophile element composition of the Earth’s primitive upper mantle: Constraints from new data on peridotite massifs and xenoliths. Geochim. Cosmochim. Acta 70, 4528-4550.

Wu F-Y., Walker R.J., Yang Y-H., Yuan H-L., and Yand J-H. (2006) The chemical-temporal evolution of lithospheric mantle underlying the North China Craton. Geochim. Cosmochim. Acta 70, 5013-5034.

2007

Yuan H., Gao S., Rudnick R.L., Jin Z., Liu Y., Puchtel I., Walker R.J. and Yu R. (2007) Re-Os evidence for age and origin of peridotites from the Dabie-Sulu ultrahigh pressure metamorphic belt, China. Chem. Geol. 236, 323-338.

West Jr D.P., Tomascak P.B., Coish R.A., Yates M.G. and Reilly M.J. (2007) Petrogenesis of the ultrapotassic Lincoln syenite, Maine: late Silurian-early Devonian melting of a source region modified by subduction-driven metasomatism. Amer. J. Sci. 307, 265-310.

Yokoyama T., Rai V.K., Alexander C.M.O’D., Lewis R.S., Carlson R.W., Shirey S.B., Thiemens M.H. and Walker R.J. (2007) Osmium isotope evidence for uniform distribution of s- and r-process components in the early solar system. Earth and Planet. Sci. Lett. 259, 567-580.

Puchtel I., Humayun M. and Walker R.J. Os-Nd-Pb isotope and lithophile and siderophile trace element systematics of komatiitic rocks from the Volotsk suite, SE Baltic Shield. Precambrian Res., in press.

Walker R.J., Böhlke J.-K., McDonough W.F. and Li J. Combined Re-Os isotope, gold and platinum-group element study of epigenetic gold ores, Alleghany District, California. Economic Geology, in revision.

Walker R.J., McDonough W.F., Honesto J., Chabot N.L., McCoy T.J., Ash R.D. and Bellucci J.J. Origin and chemical evolution of group IVB iron meteorites. Geochim. Cosmochim. Acta, in revision.

Last updated: July 2007