A comparison of sandstone modal composition trends from Early Permian (Wolfcampian) strata of the Abo Formation in the Zuni and Manzano mountains with age-equivalent strata throughout New Mexico
— Alicia L. Bonar, Brian A. Hampton, and Greg H. Mack

—Early Permian (Wolfcampian) nonmarine siliciclastic strata of the Abo Formation and age-equivalent units record exhumation, erosion, and sedimentation associated with the final orogenic phase of the Ancestral Rocky Mountains throughout New Mexico. Sandstone modal composition data and documentation of secondary feldspar alteration (albitization) from these strata are presented here to provide first-order constraint on the provenance and diagenetic changes that occurred during and after these strata were deposited. Overall, compositional trends from this study exhibit elevated occurrences of quartz and feldspar grains with minor lithic fragments (Q–56%, F–42%, L–2%) and are interpreted to have been derived from Precambrian continental-block/basement sources that consisted of the Yavapai, Mazatzal, and Granite-Rhyolite provinces and recycled strata of the Grenville foreland basin (i.e., DeBaca Group of southeastern New Mexico). Strata contain elevated occurrences of plagioclase and K-feldspar grains (Qm–52%, P–35%, K–13%) with isolated sedimentary, volcanic, and metamorphic fragments (Ls–41%, Lv–32%, Lm–27%). There is a noticeable change in the relative abundance of plagioclase and K-feldspar as well as lithic fragments when comparing data from the Zuni and Manzano mountains with samples collected further north with field localities in southern part of the state. Strata in the northernmost field locality exhibit the highest overall percentages of K-feldspar (Qm–48%, P–29%, K–23%) compared with strata in the Zuni and Manzano Mountains (Qm–47%, P–44%, K–9%) and southernmost New Mexico (Qm–63%, P–36%, K–1%). The relative decrease in K-feldspar occurrences from north to south accompanies an increase in the amount and degree of observed K-feldspar albitization. Nearly all K-feldspar grains are partially to completely albitized in all field localities south of the Zuni and Manzano Mountains. Although secondary feldspar alteration trends presented here warrant a more detailed and comprehensive study, K-feldspar replacement and albitization appears to be most pervasive in localities that have the thickest successions of evaporite-rich overburden (i.e., regions south of the Zuni and Manzano Mountains). Evaporative concentrations of salts in these basins could have provided sodium-rich brines that reacted with K-feldspar to produce albite. Albitization may have also occurred due to high heat flow associated with regional-scale tectonic subsidence events (e.g., Sevier and Laramide foreland subsidence, and/or Rio Grande rift subsidence) that buried strata to depths and temperatures that initiated K-feldspar albitization (i.e., ~2000–2500 m and ~60–70°C), or high heat flow associated with igneous activity related to the Rio Grande rift.