Characterization of Shock-metamorphic Effects in Quartz from Sandstones at the Haughton

Introduction: The 23 km diameter and ~39 Ma Haughton impact structure, located on Devon Island, Canada, was formed in Cambrian to Silurian sedimentary rocks and Precambrian crystalline basement gneissic rocks [1]. Previous studies show that Haughton sandstones (" Hs ") have undergone melting at low pressures (<20 GPa; [2]). However, even though the presence of planar deformation features (PDFs) in quartz grains has been recognized in relatively less shocked samples [e.g., 2], the distribution and crystallographic orientations of the PDFs in quartz grains from Hs has not been studied in any detail. Here, we report on preliminary petrographic and universal-stage microscope investigations of planar fractures (PFs) and PDFs orientations in quartz grains from Hs samples from the central uplift. Results: Haughton sandstones are typically fine-grained, well sorted, grain-supported, sub-angular to rounded quartz arenites, generally with authigenic quartz overgrowths. A cement of calcite is visible in some Hs; rare detrital K-feldspar was also noted. Quartz grains show sharp to slightly undulatory extinction and contain abundant fracturing, such as concussion fractures and PFs. Poorly developed, non-decorated planar deformation features (PDFs), generally only 1 set per grain, are visible. Several quartz grains also display grain mosaicism. A few grains contain open PFs with c(0001) orientation and with incipient, possible PDF sets that branch off of the PFs. Very similar features have been described from the Rock Elm structure [3]. Our initial U-stage measurements show that ~35% and ~80% of the PFs and PDFs, respectively, have indexed Miller-Bravais crystallographic orientations equivalent to c(0001). Approximately 17% and 12% of the PFs are oriented parallel to ξ{