This study will measure 226Ra-230Th disequilibria and oxygen isotope compositions in whole-rock samples, groundmass separates and plagioclase separates from recent lavas of Krafla volcano in Iceland. This approach will be applied both on the relatively broad scale of variations in whole-rock (226Ra)/(230Th) and d18O between different eruptions, and also in detail by separating and analyzing more than one size fraction of plagioclase separates from the same lava. Because the fractionation of oxygen isotopes between coexisting plagioclase and silicate liquid is relatively well-known, d18O measured in crystals can be related directly to variations in d18O of the liquids from which they crystallized. Thus, d18O of early-formed crystals can preserve a record of the compositions of liquids before magma mixing or crustal assimilation occurred. The diversity of oxygen-isotope composition of plagioclase in Krafla lavas, both between different eruptions and within a single lava, will provide information on the relative influence of mantle-derived and crustally-derived material and the process of producing intermediate lavas. By dating the same crystal populations, the timing of mixing/assimilation can be established, providing unprecedented information about the rates of these magmatic processes.
Intellectual Merit: The results of this project will enhance our understanding of the processes of magmatic differentiation and crustal assimilation by linking information about the timescales over which such processes occur to mass balance of crustally-derived and mantle-derived material. These results will have important implications in terms of the mass and heat balance of crustal reservoir systems, and will be compared to the extensive body of work in Iceland on geophysical observations of crustal structure, reservoir volume, and geothermal activity. These results will provide background and groundwork for future studies of magma mixing and crustal assimilation in other areas of Iceland and in other tectonic settings. Broader Impacts: This project will serve to broaden the participation of underrepresented groups in the geosciences by supporting the early career development of a female PI. Furthermore, we anticipate that a graduate student will be extensively involved in this project as part or all of his or her thesis project, and that an undergraduate will be involved in the technical aspects of this project; funding for this project would therefore support the education and training of the next generation of scientists. Finally, an explicit goal of this collaboration is that the PI Cooper will travel to WHOI with the graduate student in order to gain experience in U-series analyses specifically by PIMMS. She will transfer this expertise to the new analytical facilities at UW, and these techniques will subsequently be applied to a variety of solid earth and oceanographic problems.
