Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p22b0404l&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P22B-0404
Physics
0905 Continental Structures (8109, 8110), 0925 Magnetic And Electrical Methods, 0935 Seismic Methods (3025), 5420 Impact Phenomena (Includes Cratering)
Scientific paper
It has been proposed that a 7 km diameter meteor impact crater is located entirely within the 9 km Wanapitei Lake, Ontario (Canada). The lake is immediately bounded on its west side by the deformed East rim of the larger Sudbury impact structure. Evidence for the Wanapitei impact include a circular gravity low centered over the northern area of the lake, a concentric pattern of rivers and lakes in the region and features of shock metamorphism in samples of glacial drift found on the southern shores. These samples include boulders of suevite, coesite and glassy breccia. Two of these glassy samples were dated at 37 m.y. based on K/Ar methods, thus the possibly of any relation to the 1.8 billion year Sudbury structure was rejected. The purpose of the present marine seismic and magnetic study is to further constrain the crater's exact location and size. Prominent diabase dikes trending North-West through the region were used as markers indicative of an impact event, as brecciation of the crater floor will attenuate their magnetic anomaly. A ground survey was done to constrain the position and magnetic signature of the dikes passing through the central area of the lake where the crater is suggested to be located. Over 100 km of high frequency seismic data have been acquired over the lake in order to determine the thickness of unconsolidated sediments and map basement structures to better constrain inversion/depth estimates obtained from magnetic field data. Marine magnetics were able to map the late Precambrian dikes from the western shore to a distance of approximately 4-5 km inward. The marine trace resumes on the East side after a small gap over the >100 m depth portion of the lake. It is not known if this discontinuity is due to the fact that the dike's magnetic signature could not be detected with the shallow methods used here. Preliminary results of the survey therefore suggest that the crater is smaller than originally proposed (3-4 km?).
Boyce J. I.
Eyles Nick
L'Heureux Elizabeth
Milkereit Bernd
Morris William A.
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