Stable isotopes (i.e., isotopes that do not undergo radioactive decay) of different elements comprising rocks are used as tracers of redistribution of mass in Earth. The present study plans to exploit a new methodology for measuring accurately the stable isotope ratios of many important rock-forming elements to improve our knowledge of several geological processes. As part of the research plan, it is to establish the fundamental parameters necessary to use the isotopes of iron and magnesium as tracers of the movement of these important elements between different geological reservoirs.
Whereas in past decades investigations of stable isotope fractionation in geological materials meant mainly studies of the isotopes of the lighter elements carbon, hydrogen, oxygen, nitrogen, and sulfur (of these, only oxygen is a major rock-forming element), the advent of multiple-collector inductively-coupled plasma-source mass spectrometry (MC-ICPMS) has allowed geoscientists to examine the distribution of isotopes of major rock-forming elements such as iron, magnesium, and silicon. At the same time, advances in computational chemistry have afforded the capacity to make quantitative predictions for the partitioning of isotopes between materials of geological interest. In this work, the investigators outline a research program that takes advantage of both of these advances. The ultimate goal is to determine equilibrium distribution of the isotopes of iron and magnesium in mineral materials of geological significance, and to compare these distributions in the laboratory to the distributions of the stable isotopes of these major rock-forming elements in natural systems.
The investigators intend to test theoretical predictions of iron (Fe) and magnesium (Mg) isotope fractionation among mineral phases experimentally. Iron and Mg were selected as the focus of the study because of the importance of these rock-forming elements in many geochemical and biogeochemical cycles. The research is composed of three related facets: 1) prediction of the ways that Fe and Mg isotopes partition themselves between different minerals; 2) implementation of so-called three-isotope experiments designed to determine equilibrium isotope partitioning of isotopes among minerals of interest; and 3) high-precision measurement of stable isotope ratios in the experimental products. The experiments involve subjecting minerals of interest to high temperatures and pressures in a heated "piston cylinder" until isotopic equilibrium is achieved. The three isotope technique, by which samples are artificially enriched ("spiked") with a particular isotope, permits quantitative assessment of the degree to which the experimental products achieved equilibrium.
This project will take advantage of several sub-disciplines in the geological sciences to further our understanding of how elements move deep within Earth. A benefit is the highly unusual interdisciplinary training afforded a Ph.D. student associated with the project. Communication between members of the disparate groups of geoscientists is expected to have a lasting positive impact on the field. The project promotes participation of underrepresented groups in the sciences by including members of such groups (women, African American) on the research team.
