Shocked quartzite clasts with transverse fractures from Araguainha impact structure, Brazil

The central uplift area of Araguainha impact structure (Brazil) includes a quartzite pebble- and cobble-bearing stratigraphic facies that have been profoundly affected by impact processes. These quartzite clasts have been studied previously for their planar deformation features (PDFs), but not with regard to their noteworthy transverse fractures. Petrographic study of transverse fractures within seven selected impact-affected cobbles from the conglomeratic fluvial facies of the target Devonian Furnas Formation (near the central uplift of Araguainha impact structure) has revealed that there is a micro-breccia within these transverse fractures, and this micro-breccia originated by comminution of the host cobble. Further, the transverse fractures in these cobbles have different styles (well-defined, poorly defined, complex, and diffuse) and are evidently post-shock, brittle deformation features. We suggest that a late compression-stage process, perhaps collapse of the central peak, may be responsible for the development of these transverse fractures.