Geochemical and Petrographic Study of Melt Veins at the West Clearwater Lake Impact Structure, Canada

The formation of central uplifts in complex impact craters is poorly understood. It is generally accepted that a weakening mechanism is a necessary precursor to accommodate such a large movement of rock. It has been hypothesized that impact-generated melt may have a significant role in weakening the rock of a crater floor to allow for uplift, but it is uncertain if this melt rock is a product of in situ melting or injected melt. In this study, melt veins within surface and drill core samples of target rocks from the West Clearwater Impact Structure were analysed using optical microscopy,electron microprobe analysis, and bulk chemistry analysis to determine their formation process. Mixing model results suggest that melt vein structures within the very centre of the crater, collected from the surface and at depth exhibit in situ melting; whereas veins around the periphery of the central uplift are formed by the injection of impact melt.