New Mexico Geological Society Annual Spring Meeting
April 13, 2018

Abstract
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Sediment Dispersal Trends and Timing of Basement-Block Uplift During the Early Permian Phase of the Ancestral Rocky Mountains, New Mexico

Alicia L. Bonar1, Brian A. Hampton1, Greg H. Mack1 and Jeffrey M. Amato1

1New Mexico State University, Department of Geological Sciences, P.O. Box 30001, Las Cruces, NM, 88003, albonar@nmsu.edu

U-Pb detrital zircon geochronology and sandstone modal composition trends from the nonmarine, synorogenic Early Permian (Wolfcampian) Abo Formation (and equivalent strata) are presented here in the context of constraining sediment dispersal patterns as well as basement-block uplift and subsequent onlap histories during the final phase of Ancestral Rocky Mountain (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 (Grenville province/De Baca Group) and 1378 Ma (Granite-Rhyolite province/Mesoproterozoic granitoids), and minor occurrences of Paleozoic, Neoproterozoic, and Archean age zircon. However, despite the lithologic homogeneity of these strata throughout New Mexico, U-Pb age spectra from individual samples (N=7) vary considerably. Early Permian strata in north-central and central New Mexico exhibit primary peak ages of 1692–1694 Ma and are locally sourced from the southern Uncompahgre (San Luis uplift). Fine-grained strata that outcrop southeast of the Defiance-Zuni uplift in west-central New Mexico have a primary peak age of 1706 Ma and a secondary peak age of 1451 Ma suggesting a more distal sediment source from the northern Uncompahgre uplift in Colorado. In northeastern New Mexico, strata exhibit a primary peak age of 1376 Ma and a secondary peak age of 1686 Ma and were likely sourced from the Sierra Grande and Uncompahgre uplifts (and Cimarron Arch) with no evidence of detrital contributions from Frontrangia. Strata in southeastern New Mexico exhibit one primary peak age of 1251 Ma reflecting local derivation from the Pedernal uplift. In south-central New Mexico, strata have no primary peaks and instead show a wide range of ages from 270–3106 Ma. These strata were likely locally and distally sourced with possible eolian contributions.

Sandstone modal composition trends from Early Permian strata show elevated occurrences of quartz and feldspar grains with minor lithic fragments (Q=53%, F=45%, L=2%) and are interpreted to have been derived from continental-block/basement source areas. Feldspar consist of both plagioclase and potassium feldspar grains (Qm=49%, P=38%, K=13%). However, northern samples contain both plagioclase and potassium feldspar grains (Qm=47%, P=34%, K=19%) whereas southern samples are marked by a near absence of potassium feldspar (Qm=55%, P=45%, K<1%). North-south trends in feldspar abundance are interpreted to be the result of secondary albitization during diagenesis of the Orogrande basin along the southern shoreline margin of the Hueco Sea.

Provenance data provide a powerful approach for testing uplift history and detrital contributions from basement-block uplifts and allow for an Early Permian sediment dispersal model for the final phase of ARM orogenesis. 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.

pp. 19

2018 New Mexico Geological Society Annual Spring Meeting
April 13, 2018, Macey Center, New Mexico Tech campus, Socorro, NM