DATING OF A REGIONAL HYDROTHERMAL SYSTEM INDUCED BY THE 1850-MA SUDBURY IMPACT EVENT

New U-Pb geochronologic data from the Sudbury structure directly link extensive hydrothermal activity in crater-fill breccias with the 1850 Ma impact event, and constrain complex impact-induced processes to <4 m.y. Semiconformable alteration of breccias iri the Onaping Formation includes silicification, albitization, chloritization, calcitization, and complex feldspathization, which directly underlies Zn-Cu-Pb ore de posits. Geochronologic data demonstrate a middle to lower crustal sour ce for the crater-fill deposit that was subsequently affected by the h ydrothermal event at 1848.4 + 3.8/-1.8 Ma. These and other data confir m that the crater-fill breccia, hydrothermal system, Sudbury igneous c omplex, and its sublayer Ni-ore-bearing units were emplaced as a resul t of impact. The ages of events associated with the Sudbury structure are now more closely constrained than in any other meteorite impact st ructure.