Rethinking “Yellowstone in Yukon” and Baja British Columbia: Paleomagnetism of the Late Cretaceous Swede Dome stock, northern Canadian Cordillera

Abstract

Paleomagnetic results obtained from the 69.8 Ma Swede Dome stock, emplaced into the pericratonic Yukon Tanana Terrane (YTT) west of Dawson, Yukon, indicate a minimal northward translation of 360 ± 575 km and a clockwise rotation of 20° ± 23° with respect to North America, in accord with the displacement of 425 km along the nearby Tintina Fault. Coeval Carmacks Group volcanics in contrast have previously indicated ∼1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed Yellowstone hot spot, thus providing an independent estimate of the Late Cretaceous paleoposition of the “Baja British Columbia” terranes of western North America. A compilation of recent mid and Late Cretaceous paleomagnetic results from the YTT and Intermontane Belt (IMB) terranes reveals that the Carmacks Group paleomagnetic result is anomalous. The YTT and IMB terranes, which form the bulk of Baja British Columbia, appear instead to have experienced <1000 km northward translation with respect to North America since 70 Ma, consistent with geological estimates of motion along plausible accommodating faults. In addition, past mobility of the Hawaii‐Emperor hot spot implies that the Pacific hot spots may have experienced ∼1200 km of southward motion from 81 to 47 Ma. If so, then the paleoposition of the Yellowstone hot spot if it existed at 70 Ma would likely have produced the Carmacks magmatism ∼1000 km north of Yellowstone's current latitude, consistent with a “moderate” (<1000 km) post‐70 Ma northward translation of the YTT and IMB terranes to their present position in North America.

Post-Triassic para-autochthoneity of the Yukon-Tanana Terrane: paleomagnetism of the Early Cretaceous Quiet Lake batholith

“…The second model of Enkin et al (2006) in its most recent re-incarnation (see also Marquis & Globerman 1988;Butler 1990;Marquis et al 1990;Johnston et al 1996;Wynne et al 1998) infers a northward translation of 1950 ± 600 km since 70 Ma relative to cratonic North America. In making the estimate, Enkin et al (2006) rejected using the approximately co-eval paleolatitudes determined for the widely separated Seymour Creek (McCausland et al 2001) and Swede Dome stocks (McCausland et al 2005) in the YTT, suggesting that both stocks were tilted on uplift in such a way as to unfortuitously steepen both ChRM directions substantially (Fig. 1).…”

“…We agree that the mean ChRM direction of the Seymour Creek stock may have been tilted slightly by post-intrusion rotation on the crosscutting Big Creek fault . However, the Swede Dome stock is emplaced into essentially flatlying comagmatic Carmacks andesitic flows and tuffs (Mortensen 1988;McCausland et al 2005). Thus, it is highly unlikely that these two plutons, separated by >300 km, have unrecognized geologic tilts to similarly steepen their ChRM directions.…”