¹Gordon R. OSINSKI,¹Adam B. COULTER,¹Roberta L. FLEMMING,¹Alexandra OZARUK,¹Annemarie E. PICKERSGILL,¹Alaura C. SINGLETON
Meteoritics & Planetary Science (in Press) Open Sccess Link to Article [doi: 10.1111/maps.13986]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The~5 km diameter Gow Lake impact structure formed in the Canadian Shield ofnorthern Saskatchewan approximately 197 Myr ago. This structure has not been studied indetail since its discovery during a regional gravity survey in the early 1970s. We report hereon field observations from a 2011 expedition that, when combined with subsequentlaboratory studies, have revealed a wealth of new information about this poorly studiedCanadian impact structure. Initially considered to be a prototypical central peak (i.e., acomplex) impact structure, our observations demonstrate that Gow Lake is actually atransitional impact structure, making it one of only two identified on Earth. Despite its age,a well-preserved sequence of crater-fill impactites is preserved on Calder Island in themiddle of Gow Lake. From the base upward, this stratigraphy is parautochthonous targetrock, lithic impact breccia, clast-rich impact melt rock, red clast-poor impact melt rock, andgreen clast-poor impact melt rocks. Discontinuous lenses of impact melt-bearing brecciaalso occur near the top of the red impact melt rocks and in the uppermost green impactmelt rocks. The vitric particles in these breccias display irregular and contorted outlines.This, together with their setting within crater-fill melt rocks, is indicative of an origin asflows within the transient cavity and not an airborne mode of origin. Following impact, ahydrothermal system was initiated, which resulted in alteration of the crater-fill impactites.Major alteration phases are nontronite clay, K-feldspar, and quartz.