PRELIMINARY TECTONIC FRAMEWORK INTERPRETATIONS OF AEROMAGNETIC DATA IN THE YUKON-TANANA UPLAND, ALASKA

The Yukon-Tanana upland (YTU) in eastern Alaska is thought to host undiscovered deposits of critical minerals. The geologic framework and mineral systems of the YTU have been mapped using geologic and geochemical methods with mixed success due to poor bedrock exposure. Airborne geophysical data are effective at mapping poorly exposed areas like the YTU, but existing data were too coarse for mapping mineral systems components. We present a modern aeromagnetic merge of the YTU with the addition of new data. Leveraging higher-resolution data than previously available allows us to better establish terrane boundaries and identify characteristics of mineral systems unique to each terrane.

The YTU consists primarily of the allochthonous Yukon-Tanana Terrane (YTT) and the parautochthonous North American basement (NAb). The YTT is a crustal fragment that rifted from North America in the Late Devonian, forming an ocean basin now represented by the Seventymile – Slide Mountain Terrane (SSMT). The YTT was subsequently accreted to, and eventually thrust over the NAb in the Jurassic. Cretaceous extension then exhumed underlying NAb rocks, emplacing granitoids thereafter. Mineral deposits are thought to be related to Mesozoic tectonomagmatic events where differences in crustal composition and structure likely contributed to variations in mineral deposits within each terrane.

The YTT-NAb boundary is interpreted to be a low-angle extensional detachment and the juxtaposed rocks have similar lithologies that are difficult to distinguish aeromagnetically. However, plutonic suites unique to each terrane can help define their boundaries and better understand their associated mineral systems. Our initial interpretations suggest that Triassic and Jurassic intrusive bodies are generally strongly magnetized compared to the weakly magnetized metamorphic rocks of the YTT. The metamorphic rocks within the NAb are invariably weakly magnetized, and highly magnetized rocks within the NAb appear to consist of Cretaceous plutonic and younger volcanic rocks. Magnetic lineaments are consistent with high-angle, post-detachment faults associated with movement between the Tintina and Denali faults that bound the YTU. By refining our understanding of the geologic framework, our work paves the way for more targeted exploration efforts of undiscovered critical mineral deposits in the YTU.