TECTONIC INSIGHTS FROM DETRITAL ZIRCON STUDIES OF PROTEROZOIC METASEDIMENTARY SUCCESSIONS EXPOSED THROUGHOUT SOUTHWESTERN LAURENTIA

Detrital zircon studies of Proterozoic metasedimentary successions exposed throughout the southwestern United States provide unique and important insights into the evolution of continental lithosphere in southern Laurentia. Data from more than 40 quartzites and metaconglomerates from Colorado, New Mexico, and Arizona reveal relatively simple age distributions dominated by Paleoproterozoic grains. Dominant peak ages range from ca. 1775 to 1610 Ma, consistent with the juvenile character of the Yavapai and Mazatzal crustal provinces. Peak ages decrease from north to south and closely match the age of local, underlying basement. Archean and >1800 Ma grains typically make up <10% of the population and are entirely absent in 20% of the samples. Unimodal detrital zircon populations suggest a first-cycle origin and consistent local sources for successions that range in thickness from a few hundred meters to >2 km. Depositional age constraints suggest that protoliths of quartzite and interlayered schist were deposited in short-lived basins at two times during crustal assembly. Ca. 1700 Ma basin development followed the culmination of the Yavapai orogeny and was contemporaneous with voluminous rhyolitic magmatism to the south and post-orogenic granitic magmatism at deeper crustal levels to the north. Basin closure, deformation, and metamorphism of these older successions occurred ca. 1680–1660 Ma during early stages of the Mazatzal orogeny, with deformation extending into the very northern Yavapai province. Subsequent basin development began ca. 1660 Ma within the Mazatzal province, accommodating up to 2 km of rhyolite, quartzite, and schist. Closure of these basins occurred ca. 1630–1600 Ma, with substantial deformation in central New Mexico occurring after 1600 Ma. Our model for syntectonic deposition involves extensional basin development followed by thrust closure, possibly due to opening and closing of transient slab rollback basins within a long-lived convergent system. The close temporal association between basin development, sedimentation, magmatism, and orogenesis and the recurrence of sedimentation following the peak of regional deformation and metamorphism suggests that these processes might have been essential to the stabilization of the newly accreted lithosphere of southern Laurentia.