DEPOSITIONAL AGE AND PROVENANCE OF SUPERMATURE PROTEROZOIC QUARTZITES, COLORADO AND NEW MEXICO: NEW INSIGHTS FROM DETRITAL ZIRCON GEOCHRONOLOGY

Compositionally mature Proterozoic quartzites occur throughout the southwestern U.S. as part of thick (>2 km), extensively exposed metasedimentary successions (e.g., Uncompahgre Formation) and in numerous localized exposures. Quartzite and interlayered schist and conglomerate are interpreted to represent important regional sedimentation events during Paleoproterozoic accretionary orogenesis along southern Laurentia, but the depositional age of the successions can be difficult to determine and correlations are tenuous. New detrital zircon ages from ten samples representing six separate quartzite exposures in the Yavapai Province of Colorado and northern New Mexico were determined using laser-ablation ICP-MS methods. Quartzite samples were dominated by a single population of Paleoproterozoic-aged detrital zircon with a well defined range of ages between ca. 1780 – 1700 Ma. Archean-aged grains were rare (<5%) and were not found in numerous samples. The peak detrital age for each sample varied but closely matched the average age of surrounding Proterozoic exposures, suggesting that quartzite successions were locally derived. Quartzite sampled from different stratigraphic horizons up to 2 km apart within the same succession had similar detrital zircon signatures, suggesting that sources remained local throughout the depositional history. The youngest detrital zircon grains analyzed were consistently ca. 1700 Ma, indicating that deposition occurred after the ca. 1.70 Ga Yavapai Orogeny. Deposition locally occurred on exhumed, heavily weathered granitoid basement that only slightly predates the age of the sediments themselves. Local and regional structural arguments suggest that these quartzite successions were deformed during the ca. 1.65 Ga Mazatzal Orogeny, thus requiring that sedimentation occurred during a ca. 50 m.y. lull in regional orogenesis. Detrital zircon ages from quartzite exposed in the Mazatzal Province, central New Mexico, suggest that a second episode of regional sedimentation occurred during a lull in Mazatzal-aged orogenesis. These new results help to refine tectonic models for the Proterozoic southward growth of Laurentia and represent an important new tool for correlating these successions at the local and regional (and perhaps global) scale.