19. Acquisition of a Thermal Ionization Mass Spectrometer for Studies in the Solid Earth and Planetary Sciences

EAR 0320589

2003-2004

$414,584

Richard W. Carlson, Erik H. Hauri, Steven B. Shirey, Conel M. O'D. Alexander

This grant provides support for acquisition of a state-of-the-art thermal ionization mass spectrometer (TIMS) to be used for isotopic research in the earth and planetary sciences at Carnegie's Department of Terrestrial Magnetism (DTM). The new instrument will supercede an 18-yr old VG-354 that is still functioning but lacks the capability for the highest precision measurement of a number of radiogenic isotopes of interest for geochemical research (e.g. Os, Nd, Sr). The new TIMS will complement two multi-collector ICP-MS instruments at DTM that are employed in a multitude of geochemical research projects requiring high precision trace element and isotopic data. The new TIMS will be used for isotopic research on the early evolution of the solid earth, timing of core formation, studies in mantle chemical dynamics and igneous petrogenesis. The instrument will also serve to train the next generation of instrument-savvy isotope geochemists through the CIW-DTM postdoc program.

18. Integrated Studies of Diamond Age and Composition: Constraints on Continental Lithospheric Evolution, Kaapvaal-Zimbabwe Craton, Southern Africa

EAR 0310059

2003-2005

$198,685

Steven B. Shirey, Mark D. Schmitz, Richard W. Carlson

The stable interiors of continents (cratons or shields) are composed of 35 to 40 km thick continental crust overlying up to 180 km of ancient lithospheric mantle root. In certain cratonic regions such as southern Africa, volcanic eruptions of kimberlite have sampled and brought to the surface, rocks (e.g. peridotites and eclogites) and minerals (e.g. diamonds) found in the mantle root. These samples provide an important direct record of some of Earth's earliest continent-building. Diamonds and the silicate and sulfide minerals that they sometimes include are especially unique as they are the most robust capsules of geochemical and geochronological information in the mantle. Seven mines in kimberlites (Bobbejaan/Bellsbank, Helam/Swartruggens, Palmietgat, Premier, Orapa, Star, and Venetia) from the Kaapvaal-Zimbabwe craton will provide sulfide-inclusion-bearing diamonds that will be used to expand our knowledge of the geological history of the mantle keel beneath this ancient southern African continent. The broad goals of the re-search are to determine the ages of diamonds at each kimberlite with the Re-Os method on sul-fide inclusions and to relate the ages and the compositions of both inclusions and their host diamonds to the geologic setting of the diamond source region in the lithospheric mantle. More than three episodes of diamond formation are currently seen to match major episodes of creation (3.2-3.3 billion years ago), amalgamation (2.9-3.1 billion years ago) and magmatic modification of the craton (1-2 billion years ago). The new data will test the extent of these episodes, especially in areas like the eastern craton that have the oldest crustal history (3.3-3.5 billion years) or the Limpopo mobile belt that has been subject to craton collision. Supporting xenolith age and geo-chemistry studies will yield new information on the emplacement of diamondiferous protoliths or the source of the carbon-rich diamond fluids.

The broader impacts of the research are in the training and scientific development of a postdoctoral associate and two students. The postdoctoral associate will join the academic teaching community and his training will contribute directly to his supervision of students. Both students reside in South Africa and would otherwise have little chance to train and learn at a high-level research facility in the United States. One student, a female African geochemist, is so underrepresented as to be unique at the current time in southern Africa. The development of new analytical protocols is proposed; these will improve infrastructure for diamond research in general. The research will strengthen partnerships with the academic community (Universities of Glasgow, Cape Town, Witwatersrand) and the mining community (DTC - De Beers, Helam Mining). Dissemination of the research will enhance our background understanding of how diamonds, economically important in stable countries and a problematic resource in areas of conflict, were created. The project is partially supported by NSF's Office of International Science and Engineering.

17. An REU Site for Undergraduate Research Training in Geoscience

EAR-0097569

2001-2004

$285,174

William G. Minarik, Steven B. Shirey

During a ten-week summer program, thirteen undergraduate students will be given the opportunity to actively participate in the research program of a staff member at the Broad Branch Campus of the Carnegie Institution of Washington. The Broad Branch Campus includes both the Geophysical Laboratory and the Department of Terrestrial Magnetism. Recruitment efforts will especially target groups historically under-represented in science and students from institutions that are unable to offer a research experience. Scholarship, possible influence on career objectives, and the ability to match the student's scientific interests with available research projects will all be considered in the selection process. While at the Geophysical Laboratory and the Department of Terrestrial Magnetism, each student will be assigned an advisor and a research project. Although varied, most of the student's projects will involve some aspect of earth or planetary geoscience research. The students will be instructed by their advisors in the use of the experimental, and/or analytical and computational apparatus that are utilized in the research programs. Each week the students will also meet in a group for a lunch seminar. During this time Carnegie staff members will describe their own research interests and laboratory facilities. Students will tour some of the government research laboratories in the area. The students will be expected to prepare a paper describing their summer research results and to participate in a special student symposium where they will present their work to their peers and the scientific staff.

16. Collaborative Research: The Role of Mafic Crust in Orogenic Magmatism – New Perspectives from Re-Os Isotopes

EAR-9980525

2000-2002

$76,287

Steven B. Shirey

Seventy-five to eighty percent of the new crust that is generated at the world's orogenic arcs in the Cenozoic can be considered to belong to "juvenile" island or continental arcs, and such settings likely represent the major environments where new material is added to the crustal inventory of the Earth. However, intracrustal recycling through re-melting of juvenile arc basement is virtually undetectable in such settings because there is virtually no isotopic contrast using traditional isotopic tracers such as O, Sr, Nd, and Pb isotopes. Assessment of the role of intracrustal recycling is critical for calculation of net crustal growth rates. This work will focus on the Re-Os isotope system, which offers an exceptional means to evaluate intracrustal processing in juvenile arcs. The motivation for the proposed research lies in the recognition that basaltic magmas develop extreme fractionations in Re/Os ratios, which will produce radiogenic 187Os/188Os ratios that far exceed those of the mantle, over periods of several to 10's of m.y. The initial target of the proposed research is the Cascade Arc, NW USA, which is an ideal place to test our this hypothesis because the Quaternary centers are constructed on voluminous Miocene to Pliocene mafic sequences, and interpretation of the Re-Os isotope data will not be confused by a) the presence of old subduction of old oceanic crust.

15. A Comparative Elemental and Isotopic Study of Seawater Component Assimilation on the East Pacific Rise (EPR) Using Volatiles, Halogens, Boron and Lithium

OCE-9907174

1999-2003

$198,235

Steven B. Shirey, Erik H. Hauri, Petrus J. le Roux

An ion microprobe (secondary ion mass spectrometer) study of the halogens (Cl, F), volatiles (CO2, H2O, S), light elements (B, Li) and their relevant isotopic compositions (7Li/6Li, 11B/10B, 34S/32S and 37Cl/35Cl) will be carried out on well-characterized East Pacific Rise (EPR) glasses from the 9 degrees N,12 degrees N, and 15-16degrees N regions. Assimilation of seawater components into basaltic magma along the global ocean ridge system may be more widespread than is commonly assumed. At fast-spreading ridges such as the EPR where axial magma chambers are well-defined, this process may be ubiquitous. There is currently a poor understanding of the seawater-component assimilation process on the local spatial scale of volcanic features and petrologic segmentation. This work will use different geochemical tools, each with its own response to the assimilation process and look at segments of the ridge system where small differences in spreading rate, volcanic edifice, lithospheric structure and axial magma chamber morphology can be recognized. The purpose of this study is to determine how and where seawater component assimilation occurs in the oceanic lithosphere, to relate differences in the extent of this process to volcanic and morphologic features of the oceanic ridge system.

14. Collaborative Research: Anatomy of an Archean Craton: The Evolution of the South African Continental Lithosphere

EAR-9526840

1996-2003

$1,627,690

Richard W. Carlson, David R. Bell, David E. James, Paul G. Silver, Francis R. Boyd, Steven B. Shirey

This award is a component of an international, multi-institutional, interdisciplinary study of the Kaapvaal craton in southern Africa. This four-year project will determine the geological processes that led to the formation and stabilization of this and other ancient continental cratons. The Kaapvaal craton preserves Archean (2.6 to 3.6 Ga) continental crust and mantle. The crustal rocks are well exposed and the mantle and deep crust have been sampled by abundant kimberlites that provide information about the spatial distribution and temporal evolution of deep lithospheric structure. The Principal Investigators will use a number of geophysical and geochemical techniques to investigate the structure of the craton. The results of these diverse approaches will be integrated with research programs of several South African groups to provide a comprehensive understanding of the three-dimensional structure, chemical composition and tectonic evolution of the mantle and crust of the Kaapvaal craton. The data will be used to evaluate competing models of craton assembly and to provide constraints on the continental dynamics of the early earth. ***

13. REU: An Undergraduate Research Training Program in Geoscience

EAR-9876909

1999-2001

$162,337

Constance M. Bertka, Steven B. Shirey

During a ten-week summer program, 11 undergraduate students will be given the opportunity to actively participate in the research program of a staff member at the Broad Branch Campus of the Carnegie Institute of Washington. The Broad Branch Campus includes both the Geophysical Laboratory and the Department of Terrestrial Magnetism. Recruitment efforts will especially target groups historically underrepresented in science and students from institutions that are unable to offer a research experience. Scholarship, possible influence on career objectives, and the ability to match the student's scientific interests with available research projects will all be considered in the selection process. While at the Geophysical Laboratory and the Department of Terrestrial magnetism, each student will be assigned an advisor and a research project. Although varied, most of the students' projects will involve some aspect of earth or planetary geoscience research. The students will be instructed by their advisors in the use of the experimental, and/or analytical and computational apparatus that are utilized in our research programs. Each week the students will also meet in a group for a lunch seminar. During this time Carnegie staff members will describe their own research interests and laboratory facilities. The students will tour some of the government research laboratories in the area. The students will be expected to prepare a paper describing their summer research results and to participate in a special student symposium where they will present their work to their peers and our staff. If a student completes significant research during the summer, then they will also be encouraged to submit their work for presentation at a professional scientific meeting, or to use their summer research as the basis for a senior thesis at their home institution.

12. Os Isotopic Studies of Solid Earth Evolution

EAR-9804875

1998-2001

$195,000

Richard W. Carlson, Steven B. Shirey

This proposal requests an Accomplishment Based Renewal for continued support of our application of the Re-Os isotope system to problems concerning the geochemical evolution of the solid Earth. We will focus on: 1) Delineation of the importance of mafic components (pyroxenites, eclogites) in the mantle sources of mid-ocean ridge basalts and mafic-potassic volcanism from Italy, the Colorado Plateau and southwestern Africa. 2) Re-Os age dating of sulfide inclusions in diamonds from the Slave craton and N.W. Australia. 3) Extend our studies of the Re-Os systematics of cratonic mantle peridotite xenoliths to China and west Africa. 4) Examine the Re-Os systematics of lower crustal garnet granulite xenoliths from Minas Gerais, Brazil to define the chronology of crust formation in this area. 5) Study the Re-Os system of the eclogitic and peridotitic rocks of the Dabie and Su-Lu terranes in eastern China to date the igneous formation of these materials and to examine the behavior of Re and Os during high-grade metamorphism. 6) Improve the understanding of the behavior of the platinum group elements (PGE's) during igneous differentiation by measuring whole rock PGE patterns by isotope dilution ICP-MS in most of the samples studied for Re-Os isotopic variation.

11. Collaborative Research: Constraints on EPR Magmatism Through Studies of the North Orozco Region

OCE-9626934

1997-2000

$72,844

Steven B. Shirey

The East Pacific Rise (EPR) north of the Orozco transform fault off the coast of Mexico provides unique opportunities to further our understanding of the origin of the ocean crust and the nature of the upper mantle. This region is the shallowest, most-inflated portion of the northern EPR, and extends the range of axial morphology that has been examined in detail by a factor of two, which allows the test of a number of models relating axial morphology to magma chambers, volcanic behavior, and hydrothermal activity. Second, this region allows a clarification of the nature and origin of the chemical characteristics of the Pacific upper mantle. Basalts recovered from the EPR differ fundamentally in their distribution of chemical compositions from those recovered along the mid-Atlantic Ridge. There are two hypotheses for these differences: (1) that the mantle beneath the EPR is ubiquitously "veined" by small scale heterogeneities that are a natural consequence of plate recirculation in the upper mantle; (2) that hot spots under the EPR are smeared out and mixed in to the upper mantle more efficiently than along the MAR. The Orozco anomaly is a potential small hot spot track near the EPR. If we find that it is a hot spot, and that its chemical characteristics can explain the enriched MORB along the EPR, then the second model will be supported. If not, then model (1) is more likely.

10. Acquisiton of a Multiple Collector Inductively-Coupled Plasma Mass Spectrometer of Geochemical, Geochronological and Cosmochemical Applications

EAR-9724409

1997-1999

$574,172

Richard W. Carlson, Erik H. Hauri, Fouad Tera, Steven B. Shirey, Conel M. O'D. Alexander

This grant, made through the Major Research Instrumentation (MRI) Program, provides $574,172 as partial support of the costs of acquiring a multi-collector, high resolution inductively coupled plasma mass spectrometer (MC-HR-ICP-MS) with a laser ablation microprobe for high sensitivity, high precision and high spatial resolution studies in geochemistry, geochronology and cosmochemistry. The multi- collector HR-ICP-MS is considered a potentially revolutionary instrument for studies of the isotopic composition of elements with high ionization potentials which, prior to the advent of the MC-HR-ICP-MS, have alluded serious study. The Micromass Iso-PlasmaTrace ICP-MS that the PI's will acquire will enhance and/or make possible fundamental studies in the Earth sciences. Evidence for core-mantle exchange based on high precision analyses of platinum group elements (PGE) in mafic and ultramafic samples, determination of the degree of chemical heterogeneity in the early mantle using Lu-Hf isotope systematics and geochronologic investigations of time scales of magma transport through the mantle based on uranium disequilibria series isotope systematics are just a few of the examples of the research that can be addressed given the stated capabilities of this new generation instrument. This instrument will also provide training on state-of-the-art geochemical instrumentation for some of the top earth science scholars in the world through CIW-DTM's postdoctoral/guest scientist program.

9. Os Isotopic Studies of Solid Earth Evolution

EAR-9506713

1995-1997

$185,000

Steven B. Shirey, Richard W. Carlson

This proposal requests support to continue application of the Re-Os isotopic system to a wide range of problems concerning crust-mantle-core differentiation on the Earth. With the funding requested in this proposal we hope to address the following topics: 1) the mechanisms of formation of continental lithospheric mantle, focusing especially on across-craton variability, addition of lithospheric material at craton margins and the implications for Archean and Proterozoic tectonics; 2) secular changes in the Os isotopic composition of the convecting mantle that may reveal if the mantle records the effects of a) changing ratios of oceanic to continental crust production through time, b) decline in extraterrestrial input of PGE's to the mantle during early Earth history and c) mass exchange between core and mantle, and 3) Os isotopic characterization o lower crustal xenoliths to determine their initial mantle extraction ages in order to evaluate the significance of magmatic underplating as opposed to continental collision in thickening continental crust. These studies all make use of the unique characteristics of the Re-Os isotopic system that when used in conjunction with Sr, Nd, and Pb isotopic data offers the potential of new insights into the chronological, tectonic, and chemical evolution of the solid earth.

8. Rhenium-Osmium Isotope Systematics of Tektites and Impact Glasses

EAR-9218847

1993-1994

$18,000

Steven B. Shirey

Tektites are the product of melting and quenching of terrestrial rocks during hypervelocity impacts on the Earth. The advent of the highly-sensitive negative thermal ionization technique (NTIMS) for Re-Os isotopic analysis makes this system ideally suited to the problem of understanding the often elevated siderophile element content of tektites. The P.I.s propose to carry out Re-Os isotopic studies by NTIMS on tektites from the Australasian and Ivory Coast Strewn fields and on the Auoelloul glasses. With the Re-Os isotopic system there is the unique opportunity to determine if the Os found in tektites is really extraterrestrial, crustal or a mixture of both. This is necessary for showing whether the siderophile element signatures in tektites are a result of meteorite contamination or in-situ reduction of the target rocks.

7. Re-Os Investigations of Craton Development and Mantle Evolution

EAR-9204718

1992-1995

$179,900

Steven B. Shirey, Richard Carlson, Louis Brown

This project is to continue a series of Re-Os isotopic investigations designed to address the formation of Archean cratons; the composition and age of lithospheric mantle, the interaction between the lithosphere and asthenosphere and the chemical evolution of the mantle. Diverse samples of different ages will be analyzed: 1.8 - 3.3 Ga komatiites to basalts; 2.7-3.8 GA trondhjemites-tonalite-granodiorites; peridotitic mantle xenoliths; orogenic lherzolites; and continental mafic and alkalic lavas. Partitioning experiments for Re and Os between carbonatite-silicate liquids will be conducted to understand the behavior of Re and Os during mantle enrichment processes. The research will combine Re-Os isotopic data with data from one or more of these conventional isotopic systems (plus major and trace element data). Re and Os abundances and Os isotopic compositions will be analyzed at DTM by negative thermal ionization mass spectrometry (NTIMS). The results should not only shed new light on crust-mantle relationships, but also contribute significantly to the development of a new and exciting analytical technique.

6. Upgrade of DTM Mass Spectrometry Instrumentation

EAR-9204731

1992-1994

$39,666

Richard W. Carlson, Fouad Tera, Louis Brown, Julie D. Morris, Steven B. Shirey

This award provides one-half the funding necessary to modernize four older generation mass spectrometers at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington (DTM-CIW). DTM-CIW is committed to providing the remaining funds needed for the upgrade. The Department of Terrestrial Magnetism carries out research projects in isotope geochemistry of the Earth's crust and mantle regions. The research is carried out by in-house geochemists and through a program of visiting scientists and research students. The improved performance of the upgraded mass spectrometers will enhance the capabilities of this user group to explore new analytical techniques in solid earth geochemistry.

5. Development of a Mass Spectrometer for Re-Os Using Sputtering

EAR-9003549

1990-1992

$35,830

Louis Brown, Steven B. Shirey, Richard W. Carlson

This award is for the support of an instrument development project at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. A laser resonance ionization source mass spectrometer is being developed for the purpose of measuring Os isotopic ratios and Re and Os concentrations in natural samples via the isotope dilution method. Currently, the laser ionization of Re and Os takes place in an atom cloud above the sample that is produced by pulsed tantalum filament heating. The relatively slow thermal pulse of the filament compared to the short duration of the pulsed laser causes premature depletion of the atom cloud and limits the ultimate accuracy of the instrument. The goal of this project is to improve the ion source system by incorporating a pulsed sputtering gun to replace the thermal source.

4. Re-Os Isotopic Studies of Crust-Mantle Evolution on the Earth

EAR-9005412

1990-1992

$110,000

Steven B. Shirey, Louis Brown, Richard W. Carlson

The PIs will analyze the Re-Os isotopic systematics of Archean komatiites and tonalites-granodiorites; mafic layered intrusions; mantle xenoliths; and recent basalts from mid-ocean ridges, ocean islands and island arcs. The specific goals of these studies are to determine the Os isotopic mantle growth curve; to determine the source of cratonic core rocks; to understand the behavior of Re and Os in igneous systems; to study the formation of the subcontinental mantle and to investigate recycling of oceanic crust within the upper mantle and the role of oceanic crust in island arc volcanism. The Re-Os isotopic system has unique potential to contribute to geochemical studies of the Earth. This system provides new information complementary to that available from the Rb-Sr, SM-Nd and U-Th-Pb systems for several reasons: both Re and Os are siderophile elements, Os is compatible in the mantle while Re generally is incompatible, Os has a relatively high abundance in the mantle compared to the crust and the melting events that form basaltic rocks strongly fractionate Os from Re. The use of the Re-Os isotopic system will provide a greater understanding of the depleted and enriched reservoirs of the convecting mantle and the lithosphere, the creation of ancient continental crust with its lithospheric roots and the role of subducted slab components at convergent margins.

3. Re-Os Isotopic Studies of Crust-Mantle Evolution on the Earth

EAR-8720712

1988-1990

$91,800

Steven B. Shirey, Richard W. Carlson, Louis Brown

The Re-Os isotope system has unique potential to contribute to geochemical studies of the earth because information provided by this system will be complementary to that currently available from other isotope systems and should provide new insight on the geochemical evolution of the mantle, formation of the core and creation of continental crust. This project will determine an accurate Os isotope growth curve for the mantle, estimate the crustal residence time of the parents of 3.6 Ga craton core rocks, better understand the behavior of Re and Os in igneous systems and estimate the Os isotope heterogeneity of the present mantle. Techniques will be based on the ongoing work at the National Bureau of Standards (NBS) of J. Fassett and DTM Research Associate R. J. Walker. Funds will be used primarily to pay Walker's salary and to build a chemical facility at DTM for the separation of Re and Os. Initially, analyses will be performed by laser resonance ionization mass spectrometry (RIMS) on the Fassett-Walker 6" RIMS machine at NBS. Later, an improved 9" mass spectrometer, presently under construction at DTM, will be used.

2. Acquisition of a High Power Laser for Resonance Ionization Mass Spectrometry

EAR-8720836

1988-1989

$80,000

Louis Brown, Steven B. Shirey, Richard W. Carlson

This award provides partial funding to convert an existing 9.inch magnetic sector mass spectrometer into an instrument that uses resonance ionization and incorporates simultaneous multiple isotope detection with electron multipliers. The conversion will build on a laser resonance ionization system developed at the National Bureau of Standards. Development, installation and operation of the instrument will take place at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. The new system will allow measurements of the Re.Os isotope system at higher levels of precision and sensitivity than possible at present, and its successful development will provide important new research capabilities for the isotope geochemistry research community. Because of the geochemical behavior of the Re.Os system its study provides unique information on the evolution of the Earth's crust, mantle and core.

1. Acquisition of an Inductively-Coupled Plasma Emission Spectrometer (ICP) for the Chemical Analysis of Rock-FormingMaterials

EAR-8608339

1986-1987

$73,533

Steven B. Shirey, Bjorn O. Mysen, Gregory E. Muncill, Richard W. Carlson

This proposal requests matching funds for an inductively-coupled, plasma emission spectrometer to be shared between the Geophysical Laboratory (operating location) and the Department of Terrestrial Magnetism This instrument will provide state-of-the-art, high-quality elemental abundance analyses making potentially two-thirds of the elements of the periodic table accessible for scientific study in a wide range of geologic materials. The immediate use will be for major and trace elements of analyses of terrestrial rocks, experimental run products and hydrothermal solutions. These data will have specific applications in planned and ongoing projects in the following areas: supercritical fluids; mass transport; kinetic modeling, nucleation and crystal fractionation; high-P and high-T crystal-liquid-fluid equilibria; geochemical mapping of the subcontinental mantle and lower crust of the western U.S.; evolution of the Earth’s earliest crust and mantle in the Kaapvaal Craton and Superior Province; geochemical behavior of the high-field strength elements and the geochemical behavior of Be during subduction zone magmatism.