Paleomagnetism of the Weaubleau structure, southwestern Missouri
Shannon Dulin, R.D. Elmore, 2007. "Paleomagnetism of the Weaubleau structure, southwestern Missouri", The Sedimentary Record of Meteorite Impacts, Kevin R. Evans, J. Wright Horton, Jr., David T. King, Jr., Jared R. Morrow
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The Weaubleau structure consists of a 19-km circular feature that contains deformed Mississippian limestones. The age of the structure is stratigraphically constrained between deposition of the deformed Osagean limestones and the overlying undeformed Pennsylvanian (Desmoinesian) units. Paleomagnetic samples were collected from tilted Burlington-Keokuk Limestone (undivided), a polymict breccia inside the structure, and undeformed Burlington-Keokuk Limestone outside of the structure. Stepwise thermal and alternating-field demagnetization of tilted limestone samples reveals a characteristic remanent magnetization (ChRM) with southeasterly declinations and shallow positive inclinations with maximum unblocking temperatures of 475 °C. The ChRM is post-tilting and resides in magnetite. The pole is 30.2°N, 135.4°E (dp = 4.1°, dm = 7.9°), which lies on the Late Mississippian portion of the apparent polar wander path. The breccia samples only contain a present-day field component. Many of the samples from outside the structure contain a present-day field component residing in magnetite, although some contain a poorly defined component with southeasterly declinations and moderate positive inclinations. The ChRM is apparently localized within the deformation feature. Since the ChRM is post-tilting, the age of the deformation has been constrained better than the stratigraphic age. The post-deformational ChRM is not a shock magnetization and is interpreted as a chemical remanent magnetization (CRM). One hypothesis for the origin of the CRM is hydrothermal fluids that were activated as a result of the impact. This hypothesis is consistent with 87Sr/86Sr values in the deformed limestones, which suggest alteration by radiogenic fluids.