To: hank2010 who wrote (32264 ) 2/8/2007 2:08:34 PM From: E. Charters Respond to More light reading on Sudbury deformation and shearing, subsequent brecciation of rock types, and support for impact theory...uwsp.edu Some authors (Thomson, 1952; Speers, 1957) have held that the Sudbury breccia formed over an appreciable span of time or in several separate events, whereas the impact hypothesis requires a single, brief brecciation event. The relationship between brecciation and deformation in and near the Creighton pluton is anomalous; nowhere else within the Southern Province was brecciation preceded by penetrative deformation. With only local exceptions, foliation occurs throughout the Creighton pluton, and everywhere predates the breccia. Possible evidence of more than one brecciation event, such as intersecting breccia veins of different ages or blocks of early breccia within later breccia, has not been observed, and no breccia is present within the nickel irruptive immediately adjacent to the Creighton pluton. It will be shown later that the pre-brecciation deformation was the result of forceful intrusion of the Creighton pluton prior to the intrusion of the nickel irruptive. Therefore, the field evidence is consistent with the idea that a single brecciation event preceded the intrusion of the nickel irruptive. Vein breccia, the so-called Sudbury breccia (Speers, 1957; Plates 1-3), intrudes the Creighton and Murray plutons, the Nipissing diabase, and all older rocks within about 50 kilometers of the Sudbury Basin, but not the nickel irruptive or the rocks of the Whitewater Group. The nickel irruptive postdates both brecciation (Speers, 1957) and the deposition of at least part of the Whitewater Group and may be a product of impact-triggered magmatic activity (French, 1970, 1972). The relationships between the breccia, the Nipissing diabase, and the irruptive bracket the time of brecciation between 1800 and 2150 m.y. ago (Table I). The Sudbury breccia consists of veins or irregular patches in which disoriented blocks of country rock are enclosed in a matrix of comminuted rock fragments. The composition of the matrix is essentially the same as that of the enclosing host rock (Speers, 1957). Breccia veins range from thin seams to bodies hundreds of meters wide and several kilometers long, and the blocks within the breccia range in size from millimeters to tens of meters. Some breccia veins were emplaced along lithologic contacts. The breccia has been considered as volcanic or diatreme breccia (Fairbairn and Robson, 1942; Speers, 1957) and meteorimpact breccia (Dietz, springerlink.com
