INVESTIGATING ARCHEAN DOME FORMATION VIA INTEGRATED ANISOTROPY OF MAGNETIC SUSCEPTIBILITY AND ELECTRON BACKSCATTER DIFFRACTION: A CASE STUDY FROM THE MT EDGAR DOME, WESTERN AUSTRALIA

Large multicomponent granitic domes represent the felsic portion within many of Earth’s earliest contents. Unraveling their deformation histories can provide a critical constraint on the development of early felsic crust. We present a case study from a structurally complex area within the Paleoarchean Mt Edgar dome which showcases a novel approach to studying structures and flow patterns within weakly deformed granitic rocks. Our approach integrates anisotropy of magnetic susceptibility (AMS) and electron backscatter diffraction (EBSD) to investigate the magmatic to solid state flow during dome formation. AMS provide a quantitative measure of fabric orientation and geometry that reflect both magmatic and solid state deformation throughout dome development. EBSD maps from oriented thin sections provide several types of kinematic information which enable AMS data to be interpreted in terms of flow directions. Chief among these EBSD-derived analyses are crystallographic preferred orientation (CPO) of quartz and crystallographic vorticity axis (CVA) analysis. In contrast to AMS, EBSD-derived analyses provide information only for the solid-state portion of dome formation, since CPO and CVA patterns develop during dislocation creep. Our case study in the Mt Edgar dome shows that the region of interest is an upright synformal structure with sub vertical vorticity at is margins and hinge-parallel, subhorizontal vorticity near the center of the structure. EBSD-derived analyses do not always fit within the AMS reference frame, which implies that a significant portion of the AMS signal formed under magmatic conditions. Ultimately, we demonstrate that our integrated approach has the potential to unlock the under-tapped structural record of Archean granitic domes and may be widely applicable to weakly deformed granitic rocks.