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

摘要

Zircon from eclogite near Last Peak in the Teslin tectonic zone yielded 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 Cordillera. Both the morphology and geochemistry of the eclogitic zircons indicate a metamorphic origin, and the U-Pb age therefore constrains the timing of peak high-pressure metamorphism in this rock. The U-Pb age demonstrates for the first time that an Early Permian high-pressure metamorphic event occurred in rocks now making up the Teslin tectonic zone, and possibly elsewhere in the Yukon-Tanana terrane. This U-Pb age provides a new geochronologic ''pin'' in the evolution of the Yukon-Tanana terrane prior to its Mesozoic accretion to the North American continental margin and, combined with recent Ar-40/Ar-39 muscovite data, indicates that high-pressure metamorphism at this time was a relatively short-lived event.