Deep-crustal metasedimentary rocks support Late Cretaceous "Mojave-BC" translation

Metasedimentary rocks in the mid- to lower crust of exhumed continental arcs preserve information about both sedimentary provenance and metamorphic pressure-temperature paths, providing a unique perspective on the tectonic history of an arc, including margin-parallel translation and sediment-burial mechanisms. The Swakane Biotite Gneiss (Washington State, USA) and the Pelona, Orocopia, Rand, Sierra de Salinas, and related schists (PORS) (California and Arizona) represent metasedimentary rocks that were incorporated into the deep levels of North American Cordilleran arc systems. We evaluated the provenances for the sedimentary protoliths of these units by detrital zircon U-Pb and Hf-isotope analyses to assess paleogeographic reconstructions for western North America. All samples have similar Mesozoic peaks, and Proterozoic age populations (1.38 Ga and 1.6-1.8 Ga) are present in samples with maximum depositional ages younger than ca. 86 Ma. Zircon Hf-isotope results are similar for these Proterozoic populations, but the Swakane Mesozoic zircon samples reveal slight differences in comparison to PORS samples. Similar detrital zircon patterns, timing of emplacement, lithology, and structural setting suggest that these two distinct units formed at the same latitude and are consistent with recent interpretations of paleomagnetic data that indicate "moderate" (~1600 km) northward translation for the North Cascades arc. This study provides an example of how sediment provenance signatures combined with interpreted metamorphic histories can be used to track vertical displacement and horizontal translation within a complex, long-lived, convergent-margin system.