CONSTRAINTS ON THE TIMING OF CRUSTAL IMBRICATION IN THE CENTRAL TRANS-HUDSON OROGEN FROM SINGLE ZIRCON PB-207 PB-206 AGES OF GRANITOID ROCKS FROM THE PELICAN THRUST ZONE, SASKATCHEWAN/

The Pelican thrust is a major ductile high-strain zone in the Reindeer Zone, Trans-Hudson Orogen, northern Saskatchewan. It is interpreted a s the main sole thrust separating stacked juvenile Paleoproterozoic al lochthons and underlying Archean microcontinental crust in this centra l part of the orogen. Exposed nonmylonitic rocks in the footwall of th e thrust consist of the Sahli monzocharnockite and the smaller, more h ighly retrograded MacMillan Point granite. Protomylonitic to ultramylo nitic gneisses in the thrust zone derive from a variety of prethrust p rotoliths. A footwall ''internal suite'' mainly comprises quartzofelds pathic orthogneisses (''Q'' gneisses) and high-grade migmatitic paragn eisses. Hanging-wall ''external suite'' mylonitic gneisses include fel dspar-porphyroclastic hornblendic grey gneisses probably derived from are plutons, and laminated amphibolites derived from volcanic rocks. T he overlying allochthon mainly comprises protoliths equivalent to thos e of the porphyroclastic orthogneisses and laminated amphibolites, tog ether with interfolded and overlying Paleoproterozoic paragneisses of the Kisseynew domain. The Sahli monzocharnockite yields Pb-207/Pb-206 zircon and whole-rock Rb-Sr ages of ca. 2500 Ma, and the ''Q'' gneisse s give Pb-207/Pb-206 zircon ages of up to ca. 2900 Ma, implying that m ost of the internal suite (footwall) mylonite protoliths are Archean. In contrast, external suite (hanging wall) porphyroclastic orthogneiss es yield ca. 1880-1840 Ma Pb-207/Pb-206 zircon ages. Main, peak-metamo rphic displacement on the Pelican thrust is interpreted to have occurr ed mainly between 1840 and 1820 Ma, as indicated by Pb-207/Pb-206 zirc on ages from small, highly deformed synthrusting granite-pegmatite neo somal bodies in the thrust zone. Undeformed postcollisional granites a nd pegmatites were emplaced similar to 1789 Ma. Total duration from ar e development to completion of are-continent collision was similar to 100 Ma. The Pelican thrust zone may be similar in significance and sty le to younger, major, ocean closure related thrusts such as the Fronta l Pennine thrust of the western Alps and the Main Mantle, Main Boundar y, and Main Central thrusts of the Himalayas. As for the Pelican thrus t, these displace oceanic rocks over older basement.