U-PB ZIRCON AGES FOR THE MISSANABIE RENABIE AREA AND THEIR RELATION TO THE REST OF THE MICHIPICOTEN GREENSTONE-BELT, SUPERIOR-PROVINCE, ONTARIO, CANADA

The Missanabie-Renabie area is the eastern portion of the Michipicoten greenstone belt. Ten new U-Pb zircon ages confirm and extend the chro nostratigraphy established previously for the Michipicoten and the adj oining Mishibishu and Gamitagama greenstone belts in northern Ontario. The Michipicoten belt evolved between 2661 and 2889 Ma, The igneous a ctivity was episodic. The bimodal cyclic volcanism occurred at similar to 2700, 2750, 2900 Ma. Extensive plutonic activity occurred at 2670 Ma and synchronously with the three volcanic cycles. The pattern of ag es in the Michipicoten belt is significantly different from that in th e Abitibi belt. The felsic volcanism in this area is dated by the Rena bie crystal tuff at 2740 Ma and by the Cradle Lakes porphyry at 2736 M a. These ages are typical of cycle 2 volcanism in the Michipicoten bel t. A deformed quartz-feldspar porphyry at Conboy Lake has an age of 26 75 Ma, which correlates with a well-documented regional plutonic event . It is possible that this rock unit is synvolcanic with a hitherto un recognized volcanic episode in this belt. The Conboy Lake tonalite, a pluton in the Wabatongushi Lake granitoid complex which lies to the no rth of the supracrustal rocks, has an age of 2688 Ma. The Nudulama ton alite of the Missanaibi Lake batholith to the east of the supracrustal rocks has an age of 2741 Ma. The southern flank of the greenstone bel t is bordered by the Ogasiwi Lake granitoid complex; the Hand Lake ton alite in this complex has an age of 2723 Ma. Four plutons internal to the belt are dated as follows: Ruby Lake stock, 2661 Ma; Lochalsh Bay stock, 2670 Ma; Ash Lake pluton, 2679 Ma; and Rennie Lake stock, simil ar to 2668 Ma. The four internal plutons dated here together with prev iously dated eight similar post-tectonic to syntectonic plutons were e mplaced between 2661 and 2679 Ma along the northern margin of the gree nstone belt. Most of the deformation in the supracrustal rocks develop ed between 2661 and 2741 Ma, but a period of late deformation related to the gold mineralization can be bracketed more precisely between 266 1 and 2679 Ma.