Deformation and Fluid Interactions in the Mineral Fork Diamictites, Antelope Island, Utah

Deformed diamictite from the Mineral Fork formation on Antelope Island, Utah contains pinkish- and greenish- gneissic clasts that have similar compositions. Separate strain analyses were conducted for each clast type demonstrating that 1) there is a strain gradient within the diamictite unit and, 2) the two clast types exhibit different strain magnitudes. For this study, we explore the factors that controlled the different strain responses in the two clast types. Composition may not be the only factor controlling the differences in finite strain because both clast types have similar composition and mineralogy. Grain size, water content, connectivity of weaker minerals, and fluid enhanced reaction softening may also partially control finite strain differences. Within the clasts, water content in quartz grains was determined using Fourier Transform Infrared (FTIR) spectroscopy and the infrared beamline on a synchrotron. The results from these techniques reveal that 1) water content increases with strain, and 2) there is a distinct difference in the type of water contained within the two clast types. We used X-Ray Fluorescence (XRF) to measure chemistry (major, minor, and trace elements). Concentrations of Al₂O₃, TiO₂, and Zr, which are relatively immobile, remained approximately the same from medium to high strain. SiO₂ decreased slightly from the medium to high strain samples for both the pink and green clasts, possibly indicating minor volume loss and the presence of fluid during deformation. The trace elements cerium and barium increased significantly with increasing strain, which may reflect unusual fluid compositions. From the FTIR and XRF results, it seems likely that deformation in the diamictites was aided by fluid movement, and the two clast types strained differently based on their individual fluid interactions.