Magnetic investigations of the West Hawk, Deep Bay and Clearwater impact structures, Canada

Details Magnetic investigations of the West Hawk, Deep Bay and Clearwater impact structures, Canada Magnetic investigations of the West Hawk, Deep Bay and Clearwater impact structures, Canada

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997m%26ps...32..293s&link_type=abstract

Meteoritics, vol. 32, pages 293-308

Physics

10

Scientific paper

Due to the effects of erosion, tectonism and burial, impact structures are often obscured or destroyed. Geophysical methods are increasingly being used in detecting the signatures of impact structures. While gravity lows associated with impact structures are well understood, associated magnetic anomaly lows are not. In this study, drill cores from three Canadian impact structures were analyzed for rock magnetic properties and mineralogy, in order to explain the magnetic anomaly lows associated with these structures. Samples from the drill cores were cut and measured for anisotropy of magnetic susceptibility (AMS) and natural remanent magnetization (NRM) parameters. Drill cores from the twin impact craters of the Clearwater structure exhibited different NRM characteristics, and samples from their respective drill cores were subject to demagnetization by alternating field and thermal techniques. The difference noted in their NRM characteristics was attributed to the acquisition of a viscous remanent magnetization (VRM) at depth in Clearwater East. At all three structures both magnetic susceptibilities and remanent magnetizations are well below regional values in impact generated breccias, melt rocks, shocked crystalline rocks, and in post-impact sedimentary infill. The processes of brecciation, alteration, shock, and infill by non-magnetic sediments contribute to the development of the magnetic lows. However, a significant contribution to the observed magnetic anomalies was found by first-order forward modeling to arise from basement rocks beneath the impact structures. This zone of reduced magnetization may be caused by the partial demagnetization of magnetite by the impact-induced transient stress wave traveling away from the point of impact.

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