GEOCHEMICAL AND SIDEROPHILE ELEMENT ANALYSIS TO DETERMINE IMPACTOR CLASSIFICATION OF THE VISTA CORES, WEAUBLEAU IMPACT STRUCTURE, ST. CLAIR COUNTY, MISSOURI

The Weaubleau impact structure of west-central Missouri was produced by a large oblique angle meteorite impact in a shallow epicontinental sea approximately 335 million years ago. Principal evidence of this impact includes features known as planar microstructures, shatter cones, breccias, styolites, and folds. The crater rim is 8 km in diameter and circular in shape. An outer tectonic rim spans 19 km and is situated to the northeast of the main impact area. The Weaubleau impactor is hypothesized to be an Iron-Nickel meteorite that vaporized upon contact. During vaporization trace elements of chromium, manganese, and iron were defused into the surrounding target lithology. Two cores from the impact site and within the crater rim were chosen for this study and includes the Vista 5 core located at the center of the crater rim and Vista 1 core located approximately 2300 meters to the northeast of Vista 5. The principal objective of this research is to use X-ray fluorescence (XRF) to determine elemental composition and distribution of trace siderophile elements within the cores for inductively coupled plasma mass spectrometry (ICP-MS). The cores were geochemically examined through XRF analysis to determine concentrations of iron, nickel, chromium, and manganese. Results from XRF analysis were then utilized to target specific regions within the cores for ICP-MS analysis to determine isotopic ratios of chromium, iridium, osmium, and rare earth elements. These distinct chemical and isotopic ratios provide evidence for classification of the impactor and meteorite impact event.