Sudbury-type breccias in the Huronian Gowganda Formation near Whitefish Falls, Ontario: products of diabase intrusion into incompletely consolidated sediments?

Sudbury breccias are commonly attributed to meteoritic impact at about 1.85 Ga in the vicinity of the Sudbury Igneous Complex. In the Whitefish Falls area, about 75 km southwest of Sudbury, similar breccias are widely develop ed in argillites of the similar to 2.3 Ga Gowganda Formation. There is abun dant evidence of "soft sediment" deformation of the Huronian sediments in t he form of complex "fault" contacts, clastic dyke intrusions, and chaotic f olding. These movements appear to have been penecontemporaneous with intrus ion of highly irregular diabase bodies, which are interpreted as being olde r than the similar to 2.2 Ga Nipissing diabase. Complex shapes of diabase b odies and highly irregular contact relationships between diabase and argill ites, including intrusions of sediment veins into diabase, support intrusio n of the diabase into incompletely consolidated sediments. These data, toge ther with chemical evidence of mixing of diabase, argillite, and other mate rials in the breccia bodies, suggest that the breccias at Whitefish Falls m ay have formed as a result of interaction between hot mafic magma and semic onsolidated, water-rich mud, more than 350 Ma prior to formation of the Sud bury Igneous Complex and attendant phenomena that are presumed to be impact related.