Results from the proposed research will generate novel isotope measurements from barite, a highly stable and widely-distributed mineral found in magmatic, metamorphic, and sedimentary rocks of all ages, as well as in soils, aerosol dust, and extraterrestrial material. Establishing the controlling parameters of stable Sr-isotopic fractionation in barite will open a new avenue for geological and environmental research including geochemical, hydrogeological, hydrothermal, and paleoenvironmental studies. This fundamental research will lay the groundwork for future studies in the earth sciences using measurements of mass dependent Sr isotopes in barite. Barite may be an ideal vehicle to address critical questions in the earth sciences, including early earth biogeochemistry, evidence of potential life in extraterrestrial samples, reconstruction of temperatures in formation fluids such as springs and seeps, water rock interactions, tracking provenances of atmospheric inputs into soils, and reconstructing global changes in Sr2+ budgets during earth?s past.
Very few laboratories in the world have developed methods to measure stable Sr-isotope ratios; and work on this new stable isotopic system proposed here will provide a unique opportunity to contribute to the development of this new isotope system in its beginning stages. Graduate and undergraduate students will have the opportunity to work and interact in multiple laboratories on this research project (at Kent State Univ., USC, Univ. of Akron, UCLA, Univ. of Oklahoma) thus developing and mentoring research and analytical skills. They will conduct careful experiments, collect samples in the field at an established field site in western Oklahoma and interact with students involved in this project as well as field sites in western Colorado and northern Utah. Outreach activities in local high schools will be established through a published hands-on learning module which investigates fundamental concepts of the ?greenhouse effect? and will employ our current geology students to visit their old high schools and relay their excitement for the geosciences as a future career.
Barite (BaSO4) is a widely distributed mineral that incorporates strontium (Sr) during formation. Mass dependent fractionation of Sr isotopes occurs during abiotic precipitation of barite and formation of barite associated with biological processes (e.g., bacterial sulfide oxidation). Sr isotopes in barite can provide provenance information as well as potentially reconstruct sample formation conditions (e.g., saturation state, temperature, biotic vs. abiotic). Incomplete separation of Ba from Sr has complicated measurements of Sr isotopes by mass spectrometry. One of the outcomes of this study was the recognition that an improvment in the separation of Sr from Ba is required to make accurate and precise isotope measurements of Sr isotopes from Ba rich matrices. This includes marine sediments, soils, and barite. A very intriguing outcome of this work was the recognition that the behavior of positively charged ions in a plasma source mass spectrometer appears to change in the presence of high concentrations of barium. This study provides raw data that can be used to model the reasons for this deviation from the theoretical behavior of ions in mass spectrometers. We produced an updated extraction chromatography method tested with barite and Ba-doped seawater produces Sr sample solutions containing 10 to 100 ppb levels of Ba. As a result of this outcome, we are able to make accurate and precise Sr isotope measurements on synthetic and natural barite crystals to ascertain the physio-chemical controls on Sr isotopes during barite crystal precipitation. Several experiments were designed to test the sensitivity of Sr in barite to temperature, satruation state, pH, and other conditions of sample formation.
