Shoemaker Impact Structure Western Australia

Impact cratering and distal ejecta: the Australian record

“…It was renamed 'Shoemaker impact structure' in honour of the late Gene Shoemaker, and as a tribute to his and Carolyn Shoemaker's work on Australian impact structures (Pirajno & Glikson 1998). Further detailed mapping and other studies by the Geological Survey of Western Australia are reported in Pirajno (2002) and Pirajno et al (2003).…”

“…The Yelma Formation, which is low in the target stratigraphy has a maximum depositional age of 2027 + 23 Ma based on the ages of detrital zircons (Pirajno et al 2003); this provides a maximum possible age for the impact event. Bunting et al (1980) reported two whole-rock Rb -Sr isochrons of ca 1630 Ma and ca 1260 Ma from moderately fresh and altered/weathered granite from the central uplift, respectively.…”

“…The circular nature is defined by arcuate salt lakes and by a broken double ring of Palaeoproterozoic sedimentary rocks, cored by a poorly exposed central uplift of Archaean Teague Granite. The 12 km-diameter central uplift is surrounded by a ring syncline and ring anticline, with an outer limit of structural disturbance at 29 -31 km diameter (Pirajno et al 2003). Considering the depth of erosion the original crater rim was potentially somewhat greater.…”

“…The unusual alkali-rich syenitic composition of the Teague Granite may be the produce of alkali metasomatism related to impact-induced hydrothermal activity (Pirajno et al 2003;Pirajno 2005). The structure is clearly visible on aeromagnetic images with magnetic response mainly reflecting the different target lithologies in the structure, particularly the distribution of banded iron-formation, although arcuate highs on the southeastern flank may reflect impactinduced hydrothermal activity (Hawke 2003a;Pirajno et al 2003). A gravity survey by Plescia (1999a) revealed a central negative Bouguer anomaly coinciding with the central uplift.…”

“…The significance of these dates is unclear. The granite itself is pre-impact and dated at 2648 + 8 Ma (Pirajno et al 2003). Bunting et al (1980) and Shoemaker and Shoemaker (1996) argued that the ca 1630 Ma date may represent a thermal resetting of the isotopic system during the event which formed the structure; alternatively it could relate to other regional thermal events (Pirajno et al younger age may reflect impact-induced hydrothermal activity and thus it is possible that the impact event occurred during the Late Neoproterozoic.…”