METEORITE OR METEOR-WRONG: THE USE OF PLANAR DEFORMATION FEATURES (PDFS) IN FELDSPAR GRAINS TO IDENTIFY A NEW HOLOCENE AGED IMPACT CRATER, WASHINGTON COUNTY, IDAHO

Currently there are ca. 175 known impact craters on earth, most being larger than one kilometer in diameter. Of these confirmed craters, 19 are known to have formed during the Holocene. Our student research team at the College of Western Idaho has a unique opportunity to investigate a potential new Holocene-age impact crater. We were notified of an anomalous circular bowl-shaped depression with an intact “rim” raised above the surrounding alluvial plain in Washington County, Idaho. Our initial field work showed the feature to be approximately 20 meters in diameter with a “rim” composed of basaltic sands and gravels elevated about one meter above the surrounding surface, with an interior approximately 0.5 meters below the alluvial surface. Additional examination of the soil revealed that nearly 20% percent of the largest soil separate was magnetically susceptible. These observations alone, while interesting, are not considered to be conclusive of an impact. In this paper, I will carry out thin-section analysis of potential impact breccias with focus on identifying planar deformation features (PDFs) in feldspar grains and/or the presence of impact derived pseudotachylite. Shock features such as PDFs in various minerals as well as the presence of pseudotachylite are generally seen as diagnostic for meteorite impact and identification of such features could confirm this feature as a new Holocene-age impact crater.