DETRITAL ZIRCON GEOCHRONOLOGY FROM EARLY PERMIAN SYNOROGENIC STRATA IN NEW MEXICO: INSIGHTS ON UPLIFT HISTORY AND SEDIMENT DISPERSAL DURING FINAL STAGE ANCESTRAL ROCKY MOUNTAIN OROGENESIS

The Early Permian (Wolfcampian) nonmarine, clastic strata of the Abo Formation (and equivalents) record the final stage of synorogenic sedimentation associated with the Ancestral Rocky Mountain (ARM) orogeny in New Mexico. During this time, ARM deformation was characterized by uplift of at least seven basement-block uplifts that exposed a number of Proterozoic basement provinces throughout southwestern Laurentia. New U-Pb detrital zircon ages from these strata provide a basis for constraining uplift history and detrital contributions from basement blocks to create a new sediment dispersal model for the Early Permian stage of ARM orogenesis in New Mexico.

Bulk U-Pb age trends (n=662) from Early Permian strata reveal a primary peak age of 1689 Ma (Mazatzal-Yavapai province), with secondary peaks at 1247 Ma (overlap with the Grenville province/De Baca Group) and 1378 Ma (Granite-Rhyolite province/Mesoproterozoic granitoids), with minor occurrences of Paleozoic, Neoproterozoic, and Archean ages. However, despite the lithologic homogeneity of these strata, U-Pb age spectra from individual samples (N=7) vary considerably throughout New Mexico. Strata in northeastern New Mexico exhibit a primary peak age of 1376 Ma (Sierra Grande uplift), while strata in southeastern New Mexico have a primary peak age of 1251 Ma (Pedernal uplift). Strata in north-central New Mexico have primary peak ages of 1692–1694 Ma (southern Uncompahgre uplift in New Mexico), while strata in west-central New Mexico have a primary peak age of 1706 Ma with a secondary peak age of 1451 Ma (northern Uncompahgre uplift in Colorado). Two samples in southern New Mexico exhibit no primary peaks, but have a wide range of ages from 270–3106 Ma, and are both locally and distally sourced (Pedernal, Uncompahgre uplifts).

Data support a model where the Pedernal, Uncompahgre, and Sierra Grande uplifts were the primary detrital contributors during the Early Permian, with the Pedernal acting as a topographic barrier between discrete north-south flowing fluvial systems to the east and west. The Defiance-Zuni and Peñasco uplifts were likely tectonically inactive and onlapped by this time. Provenance trends support the existence of a topographic high (Cimarron Arch) separating drainage networks in northeastern New Mexico from southeastern Colorado.