. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography the Moon ca. 3700 mybp (T. Offield, personal communication). SHATTER CONES Although commonly only crudely developed, as is characteristic of their appearance in massive igneous and metamorphic rocks, shatter cones are widely present around the Sudbury Basin (Plate I). Since the original discovery (Dietz, 1964; Dietz and Butler, 1964) observations on their distribution and orientation have been greatly extended, especially by Bray (1968). There is no
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography the Moon ca. 3700 mybp (T. Offield, personal communication). SHATTER CONES Although commonly only crudely developed, as is characteristic of their appearance in massive igneous and metamorphic rocks, shatter cones are widely present around the Sudbury Basin (Plate I). Since the original discovery (Dietz, 1964; Dietz and Butler, 1964) observations on their distribution and orientation have been greatly extended, especially by Bray (1968). There is no doubt that the Sudbury shatter cones are bona fide examples of this mode of shock fracturing. More than a score of other shatter-coned, cryptoexplosive structures are now known around the world (Dietz, 1968). There is now good evidence that these are all astroblemes and that this style of fracturing in natural cryptoexplosion structures is uniquely formed by the shock waves emanating from a cosmic impact. They are not known from any structure which is clearly volcanic or otherwise 33 endogenic (Dietz, 1968). By the impact model there can be only one brief instant of shatter cone creation as the shock front interacts with the target rock. Clearly the imprint of shatter coning must affect pre-event strata but is prohibited from any post-event rocks. (It would be highly fortuitous for the effects of a second "cosmic cannonball" to overlap an earlier site, but apparently this has happened at Sudbury. Lake Wanapitei near Sudbury appears to be a Mesozoic or Paleozoic impact site (Dence and Popelar, this volume). However, the overlapping effects are minor and do not cause any important geologic confusion.) By the history proposed above, shatter cones should be present (and are) in the country rocks older than 1720 mybp, which make up the framework of the inferred Sudbury Basin crater. They also should be present in clasts in the Onaping microbreccia if it is a suevite, but
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