TIMING OF HIGH-PRESSURE METAMORPHISM IN THE YUKON-TANANA TERRANE, CANADIAN CORDILLERA - CONSTRAINTS FROM U-PB ZIRCON DATING OF ECLOGITE FROM THE TESLIN TECTONIC ZONE

Zircon from eclogite near Last Peak in the Teslin tectonic zone yielde d a U-Pb isotopic age of 269 +/- 2 Ma (2 sigma), the first precise age for such a rock in the Yukon-Tanana terrane of the Canadian Cordiller a. Both the morphology and geochemistry of the eclogitic zircons indic ate a metamorphic origin, and the U-Pb age therefore constrains the ti ming of peak high-pressure metamorphism in this rock. The U-Pb age dem onstrates for the first time that an Early Permian high-pressure metam orphic event occurred in rocks now making up the Teslin tectonic zone, and possibly elsewhere in the Yukon-Tanana terrane. This U-Pb age pro vides a new geochronologic ''pin'' in the evolution of the Yukon-Tanan a terrane prior to its Mesozoic accretion to the North American contin ental margin and, combined with recent Ar-40/Ar-39 muscovite data, ind icates that high-pressure metamorphism at this time was a relatively s hort-lived event.