ALASKA – YUKON GEOPHYSICAL BASEMENT DOMAINS FROM NEW MAGNETIC DATA COMPILATION

We map basement geophysical domains based on analysis of a new aeromagnetic data compilation across the Alaska-Yukon border. The geophysical domains reflect the relative amounts of magnetic minerals within the middle (5 to 10 km) and lower crust (10 to 25 km). Our data analysis involves: (1) conversion of total-field magnetic anomalies to pseudogravity (magnetic potential) anomalies; (2) matched-filtering to produce depth slicing of magnetic sources; and (3) separate identification of discrete (4 tiers from low to high amplitude) source domains for the mid (5 to 10 km) and lower (10 to 25 km) crust.

First-order observations related to the basement domains include: (1) strong correlation between mid and lower crustal domains; (2) primary association of geophysical domain boundaries with major transcurrent faults including the Denali, Tintina, and Shaw Creek faults; (3) secondary association of geophysical domain boundaries and trends with a number of NE-striking cross faults between the Denali and Tintina faults (e.g., the Black Mountain tectonic zone, the Mount Hayes fault, the Ketchumstuk fault zone, and the Sixtymile lineament); (4) significant correlation with mapped geologic elements including (a) the mid-Cretaceous Dawson Range–Gardiner Creek batholith, (b) the Late Triassic Taylor Mtn batholith, and (c) the parautochthonous North American rocks along the Denali fault (White River - Totatlanika continental margin assemblage).

Our primary geologic target is an improved understanding of metamorphic rock assemblages in eastern Alaska and their relation to the potentially correlative assemblages mapped and interpreted in Yukon, Canada. Our analysis of the new aeromagnetic compilation highlights the extent to which both the parautochthonous and allochthonous portions of the Yukon-Tanana terrane (YTT) have been disrupted by post-accretionary plutonism (and extension) and transcurrent faulting, the results of which affect the whole crust. Furthermore, the correlation of the surface and deeper geology in the region of the parautochthonous YTT outside the batholith complex contrasts with a general lack of correlation between surface and deeper geology in the region of the allochthonous YTT, supporting the thin-skinned interpretation of the allochthonous portion of the terrane.