Tilt and northward offset of Cordilleran batholiths resolved using igneous barometry

Abstract

CONSIDERABLE controversy surrounds the suggestion, based on palaeomagnetic evidence, that large segments of the North American Cordillera travelled long distances parallel to the coast during the latest Cretaceous and early Tertiary periods, well after the amalgamation of exotic terranes. Discordant palaeomagnetic data from mid-Cretaceous plutonic rocks of the Peninsular Ranges batholith of coastal southern California and Baja and the Mount Stuart batholith of the Cascade Range in Washington play a pivotal role in the controversy. The discordant data were originally interpreted to reflect northward transport of ≥1,000 km relative to cratonal North America, after the batholiths cooled through their magnetic blocking temperatures^1–5. More recently it has been argued that the discordances arise from local tilting of batholiths, rather than northward offset^6,7. Here we present and implement new methods based on hornblende barometry⁸ for determining the palaeohorizontal in granitic batholiths and correcting palaeomagnetic data for tilting. Our results indicate that the Peninsular Ranges and Mount Stuart batholiths have undergone northward offsets of ∼1,000 ±450 and ∼2,900±700 km, respectively, and also significant tilting.