This EArly-concept Grant for Exploratory Research (EAGER) represents an interdisciplinary effort to address the geochemical processes that could be responsible for recent observations of stable isotope variations for "non-traditional stable isotopes" in igneous rocks (NTSI). Significant fractionations in the isotopes of Mg and Si are difficult to explain in terms of equilibrium between minerals and their melts during common igneous differentiation processes. The exciting new discovery that large isotopic fractionations occur in melts held within a temperature gradient offers a possible explanation for the observed isotope variations. The fractionation by thermal diffusion is so large that it may provide the basis for a unique tool to discern the role of thermal-gradient-driven processes for magmatic differentiation.
This project represents a synergistic and novel collaboration that brings experimental, analytical, and theoretical approaches to the study of this NTSI fractionation phenomenon. Three complementary efforts will be undertaken that include: 1) Laboratory silicate Soret (fully molten) experiments using both natural compositions and selected simple systems; 2) Analysis of major and trace element behavior and NTSI fractionation in thermal migration (partially molten) experiments on basalt to rhyolite bulk compositions and determination of BetaT for Mg, Si and Fe; and 3) Molecular dynamics simulations of isotope fractionation within a temperature gradient in the MgO-SiO2 system to investigate the physical basis for the effects of thermal diffusion on NTSI fractionation. The proposed science plan brings together three groups of researchers with different expertises in petrology/geochemistry research from field petrology to experimental petrology to molecular dynamics simulation.
