Geotectonic motions of the Yukon-Tanana terrane, northern Cordillera: Paleomagnetism and geobarometry of mesozoic and cenozoic intrusions

Five intrusions of Early Jurassic to Paleocene age from the Yukon Tanana terrane (YTT) have undergone paleomagnetic study to assess the past Geotectonic motion history of the YTT with respect to other terranes of the northern Cordillera and North America. These five studies, comprising data from 1280 specimens in 103 sites, represent a substantial addition of primary paleomagnetic results to the small data base for the YTT, and to the study of the assembly of the northern Cordillera. For two intrusions, Al-in-hornblende geobarometry provided constraint on paleohorizontal, which is the reference frame for the paleomagnetic directions. Paleomagnetic results from the YTT are mostly counterclockwise-rotated with respect to North America, unlike those from the Intermontane Belt terranes which are typically clockwise-rotated. YTT paleomagnetic estimates of latitudinal translation relative to North America agree with those of the Intermontane Belt for Early Jurassic and mid-Cretaceous time, indicating that these northern Cordilleran terranes were together and southwards-moving through that time, consistent with models of the relative motion between the Farallon oceanic plate and North America. Mid- and Late Cretaceous paleomagnetic results from the YTT and Intermontane terranes are most consistent with their moderate northwards translation, and do not support proposed mid- to Late Cretaceous paleogeography which places the YTT ∼3000 km to the south of its present position. Late Cretaceous to Eocene paleomagnetic data are consistent with moderate northwards translation having ended by mid-Eocene time. The new paleomagnetic database from the YTT complements the substantial body of Intermontane Belt paleomagnetic results, and permits a broader assessment of northern Cordillera tectonic history.