U-PB GEOCHRONOLOGY OF THE OPATICA TONALITE-GNEISS BELT AND ITS RELATIONSHIP TO THE ABITIBI GREENSTONE-BELT, SUPERIOR PROVINCE, QUEBEC

U-Pb ages for zircon, monazite, and titanite from samples collected from two transects across the Opatica tonalite-gneiss belt in the Superior Province of Quebec indicate that the belt contains rocks that are significantly older than those in the adjacent low-grade northern Abitibi belt. Tonalite and tonalite gneiss, which make up most of the belt, formed over an interval of 100 Ma, from pre-2800 to 2702 Ma. Five samples have ages of ca. 2807 +/- 13, 2773 +/- 23, 2762(-15)(+42), 2740(-3)(+5) and 2702 +/- 3 Ma. Zircon growth at 2718-2721 Ma in the two oldest samples may record an early period of high-grade metamorphism in the belt. Hornblende diorite, monzodiorite, and tonalite plutons were intruded at 2693-2696 Ma, particularly along the southern boundary with the Abitibi belt. These include the Canet pluton at 2693(-2)(+3) Ma, the Lac Ouescapis pluton at 2693 +/- 2 Ma, and the Barlow pluton at 2696 +/- 3 Ma. Pink granite plutons and dykes are the youngest intrusive rocks in the belt; three samples have yielded zircon ages of 2690 +/- 2 and 2686 +/- 4 Ma and a monazite age of 2678 +/- 2 Ma. The timing of D-1 deformation is bracketed by the age of the youngest gneiss sample containing the D-1 structures, at 2702 +/- 3 Ma, and the 2690 +/- 2 Ma age of a granite dyke that cuts D-1 structures. The south-vergent D-2 event is recorded in the 2693 -2696 Ma plutons and must have occurred synchronously with or after this plutonism. D-3 dextral strike-slip movement on the Nottoway River shear zone occurred after 2686 +/- 4 Ma, and may be associated with post-regional metamorphic titanite growth at 2672 and 2657 Ma. Titanite ages cluster at 2678 -2681 Ma along the Matagami transect and at 2665 Ma north of Chibougamau, and record the time of cooling of the belt below the titanite closure temperature.