RECONCILING GEOLOGY BETWEEN ALASKA AND THE YUKON – POTENTIAL ROLE OF REGIONAL MAGNETIC ANOMALY DATA

The pericratonic Yukon-Tanana terrane (YTT) has been called the largest tectonostratigraphic terrane in the northern North American Cordillera, and it provides the most direct geologic tie between Alaska and cratonic North America. It is host to a diverse array of syngenetic, intrusion-related, and orogenic mineral deposits of Late Devonian to Paleogene age. The YTT extends from east-central Alaska through Yukon Territory and into northern British Columbia, and what had previously been mapped as a single entity is now understood to be made up of at least two main parts with a complex history of rifting, ocean basin formation, collision and accretion (or re-accretion), and subsequent dismemberment and translation along regional strike-slip fault systems. The highly deformed North American continental margin (parautochthonous assemblage) is primarily exposed in Alaska, and an allochthonous assemblage is exposed primarily to the east and southeast in Yukon and British Columbia. The allochthonous assemblage has the same pre-Late Devonian basement as the continental margin but substantially different post-Late Devonian rocks. Owing to a combination of this difference, generally poor exposure and difficult access, contrasting levels of exposure, and differences in vintage and scales of mapping, a “border fault” exists near the Alaska-Yukon international boundary for parts of the region between the Denali and Tintina fault.

The purpose of this presentation is to explore the utility of regional geophysical data, in particular aeromagnetic anomaly compilations, to unravel the complex relationship between the two broad assemblages of the former YTT. We examine magnetic domains and trends in a new cross-border geophysical data compilation, propose some testable hypotheses for more accurately mapping the extent of and transition between these assemblages, and present a proposal for additional geophysical data collection to improve our understanding.