A geophysical model of the Española Basin, Rio Grande rift, New Mexico

Abstract

A model of the subsurface structure of the eastern part of the Española Basin in the northern Rio Grande rift of New Mexico was constructed from geophysical data obtained since 1983 by the Summer of Applied Geophysical Experience (SAGE) field course. Approximately 742 new gravity observations, 1276 ground magnetic stations, 30 km of seismic refraction lines, 19 km of seismic reflection lines, 22 magnetotelluric stations, and several Schlumberger and dipole‐dipole resistivity lines were established. Our studies provide new information on one boundary of a major continental rift and on the depositional and structural style of an extensional basin within the rift. Integration of these data sets into a single transect indicates that the Española Basin is asymmetrical with approximately 2 to 3 km of sediments and sedimentary rocks near the center, thinning eastward to the Precambrian outcrop of the flanking Sangre de Cristo uplift. Several minor faults with throws of less than 200 m were found, but no major eastern bounding fault was observed. Thus, the Española Basin could be an asymmetrical, west‐dipping half‐graben. However, major fault offset, down toward the basin axis, may occur within Precambrian rocks of the Sangre de Cristo uplift. In either case, the geometry of the basin does not agree well with current models for the structural evolution of continental rifts, which emphasize low‐angle detachment faults which create asymmetrical, hinged half‐grabens. These models predict that major shoulder uplift should occur adjacent to the side of the graben bounded by a listric master fault rather than adjacent to the hinged side. In contrast, for the Española Basin major uplift occurred adjacent to the eastern side, which could be the hinged side of the basin. A thick wedge of older sedimentary rocks with high P‐wave velocity (4.4 km/s) and low electrical resistivity (5 Ω⋅m) was discovered under the younger Tertiary sediments and sedimentary rocks near the center of the basin. This wedge has maximum thickness of 1.2 km at the western end of the profile and thins eastward. The physical properties suggest this layer could be older Tertiary, or possibly a Mesozoic‐Paleozoic, section of rocks. If the latter, it has potential economic importance because of the possible presence of a Cretaceous section which is known to produce oil and gas in the Albuquerque Basin to the south and the San Luis Basin to the north. However, based on data from the Yates La Mesa no. 2 well, 10 km south of the transect, this wedge is likely middle Tertiary lacustrine deposits (NMOCD, 1986). The great thickness of lake deposits may represent a major lacustrine facies of the Eocene Galisteo and El Rito formations, exposed around the southern, southwestern, and northwestern margins of the basin. Magnetotelluric data suggest the crystalline basement underlying the central Española Basin may be more conductive than near the eastern margin. The entire Española Basin is also underlain by a highly conductive layer of about 1 Ω⋅m at a depth of 15 km. Both the shallow and deep low‐resistivity zones may result from hot, saline fluids. Such fluids deep within the crust may reduce the shear strength of the crust significantly and concentrate crustal extension on the west side of the rift.

Stratigraphic consequences of episodic extension in the Lemitar Mountains, central Rio Grande rift

“…on July 23, 2015 specialpapers.gsapubs.org Downloaded from tions within the San Luis Basin (Brister and Gries, this volume; Kluth and Schaftenaar, this volume), Española Basin (Biehler et al, 1991;Cather, 1992), and Albuquerque Basin (Lozinsky, 1988;Russell and Snelson, 1990, and this volume) suggest that such faults did not play a major role in the early tectonic development of these basins. Instead, many of the presently active, moderate to steeply dipping faults appear to have also controlled early deposition within these basins.…”

Geologic Framework of a Groundwater System on the Margin of a Rift Basin, Pajarito Plateau, North‐Central New Mexico

“…The Española basin is a west‐tilted, half graben (Kelley, 1952, 1978; Biehler et al, 1991; Ferguson et al, 1995; Smith, 2004) filled by Santa Fe Group sediments derived from Precambrian‐cored highlands located primarily to the east and north (Galusha and Blick, 1971; Cavazza, 1989; Ingersoll et al, 1990) and by volcaniclastic sediments derived from the Jemez volcanic field (Smith et al, 1970; Ingersoll et al, 1990; Smith, 2004). The western front of the Sangre de Cristo Range marks the eastern‐hinged margin of the Española basin (Kelley, 1978; Biehler et al, 1991; Ferguson et al, 1995). The western structural margin of the Española basin is partly covered by rocks of the Jemez volcanic field, but probably includes a broad zone of north‐trending faults such as the Cañada de Cochiti fault zone (Fig.…”

“…The Yates La Mesa #2 exploration well penetrated 1200 m (3966 ft) of Tesuque Formation in the south‐central part of the basin (Myer and Smith, 2004). However, the thickest Santa Fe Group deposits are believed to occur in the western Española basin beneath the Pajarito Plateau (Kelley, 1978; Biehler et al, 1991; Ferguson et al, 1995; Smith, 2004). The thickness of these deposits is poorly known because the deepest wells on the plateau (e.g., PM‐5 depth 950 m; 3110 ft) do not fully penetrate the basin‐fill sediments.…”

Viability report for the ByWater Lakes project

“…The ByWater Lakes project site is geologically located in the east-central area of the Espanola Basin [Biehler, et al 1991] (Figure 3). The Espanola Basin is a set of complex, asymmetric grabens about 70 km long by 60 km wide (a graben is a depressed geologic block bordered by faults).…”

“…The basin is mainly filled with Tertiary and younger rift fill sediments [Carter and Winter 1995] that comprise the Santa Fe Group rocks, which are characterized as poorly consolidated basin-fill sediments that range in thickness from 0 to 3000 m [Cordell 1979]. The Santa Fe Group is subdivided into two formations (Tesuque and Chamita formations), each with several sub-members that reflect the diverse geology of the alluvial deposits that comprise the Group [Biehler et al 1991;Smith 2004;Cevik 2009]. At the ByWater Lakes site, the Santa Fe Group is approximately 1500 m thick and consists of mainly river, floodplain, and alluvial deposits ranging in age from the Pliocene to the lower Pleistocene (5.3 to 1.8 million years ago).…”