DETERMINING THE EXTENT AND DEGREE OF DIAGENETIC ALBITIZATION OF DETRITAL FELDSPAR IN EARLY PERMIAN (WOLFCAMPIAN) ARKOSIC, SYNOROGENIC, NONMARINE, STRATA THROUGHOUT NEW MEXICO

Feldspar and other detrital fragments in sedimentary strata have been used for decades to constrain basin provenance and exhumation history of orogenic systems. However, few studies have investigated the origin of diagenetic feldspar (e.g., secondary albite) and its implications on subsidence history, timing, and extent of thermal events in a basin. Provenance work on Early Permian strata in New Mexico including both modal composition trends (with ImageJ determination of percent albitizaton) and microprobe analyses, reveal unexpected, elevated occurrences of diagenetic albite, and a highly variable pattern in the percentages of plagioclase compared to K-feldspar in northern (P=53%; K=47%), central (P=85%; K=15%), and southern New Mexico (P=97%; K=3%), as well as elevated occurrences of diagenetic albite in parts of southern and central New Mexico.

Secondary albitization is common during the diagenesis of felsic, arkosic strata and often involves the process of sodium metasomatism associated with deep basin brines. In locations and basin conditions where felsic sedimentary strata react with available saline fluids, silt- and sand-size K-feldspar and plagioclase are partially-to-completely replaced by albite at a range of depth and temperature. At the basin surface and shallower basin depths, evaporative concentration of salts in the groundwater of a closed basin yield Na-rich brines that can react with detrital silicates to develop authigenic albite. At depth, the onset of albitization of feldspar occurs at temperatures between 60–70°C (near depths of ~2500 m) when formation waters transition out of the stability field of feldspar and begin to approach the stability field of albite.

Here, data were collected from three field transects selected based on geologic and tectonic criteria that included both near and far from Laramide and Rio Grande rift structures, and both near and far from shallow rift igneous systems. At the largest scale, data will help constrain (1) whether albitization is normal or hydrothermal and related to subsidence and/or heating events since the Permian, respectively, and (2) whether albitization parallels regional structures in the area (e.g., Laramide and/or Rio Grande Rift faults) or occurs in proximity to known shallow igneous systems (e.g., Jemez Volcanic Lineament).