T243 New Insights on the Tectonic, Magmatic, Paleobiogeographic, and Metallogenic Evolution of Terranes in the North American Cordillera from Alaska to California I

Wednesday, 3 November 2010
8:00 AM - 12:00 PM
Room 406

GEOLOGIC RELATIONSHIPS OF WRANGELLIA IN YUKON: IMPLICATIONS FOR INSULAR TERRANE TECTONICS

Paper number: T243-13
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Abstract

Details of Wrangellian internal stratigraphy and of its relationships with adjacent terranes are limited. Recent bedrock mapping combined with new geochemical and isotopic age information from southwest Yukon has improved the knowledge of Wrangellian geology and allows for possible correlation with other parts of the terrane in Alaska and British Columbia.

The majority of Wrangellia in Yukon occurs in a southeast-tapering wedge between the Denali and Duke River faults, where it comprises late Paleozoic volcanic and associated sedimentary rocks, overlain by Triassic flood basalt, carbonate and marine siliciclastic rocks. New U-Pb zircon ages suggest Wrangellian rocks, in Yukon, are at least as old as early Mississippian (352 Ma). Locally, Permian sedimentary rocks of Wrangellia lay unconformably on top of newly dated 364 Ma gabbro complexes. Similar gabbro complexes are known to intrude Ordovician to Devonian sedimentary rocks of the Alexander terrane.

The new U-Pb ages from Wrangellia in Yukon are similar to new ages from Vancouver Island. These ages and other stratigraphic similarities between southwest Yukon and Vancouver Island suggest that Wrangellia was likely one coherent terrane in the Paleozoic and does not represent an amalgamation of a number of smaller terranes.

New detrital zircon analyses from Permian Wrangellian rocks supports ideas that Wrangellia and the Alexander terrane were stitched together by Pennsylvanian. The data also suggests some similarities to the Taku terrane, and possible influence from Stikinia igneous rocks. Published paleomagnetic and fossil data indicate that all of these terranes were likely in close proximity to one another during the late Paleozoic.

An unconformity between Permian rocks of Wrangellia and Devonian gabbro complexes suggests a pre-Permian deformation event affected Wrangellia. This event likely records initial interaction between Wrangellia and the Alexander terrane. If this is the case it suggests that Wrangellia, at least in part, was built upon the Alexander terrane.