We describe the structure of the eastern Española Basin and use stratigraphic and stratal attitude data to interpret its tectonic development. This area consists of a west-dipping half graben in the northern Rio Grande rift that includes several intrabasinal grabens, faults, and folds. The Embudo–Santa Clara–Pajarito fault system, a collection of northeast- and north-striking faults in the center of the Española Basin, defines the western boundary of the half graben and was active throughout rifting. Throw rates near the middle of the fault system (i.e., the Santa Clara and north Pajarito faults) and associated hanging-wall tilt rates progressively increased during the middle Miocene. East of Española, hanging-wall tilt rates decreased after 10–12 Ma, coinciding with increased throw rates on the Cañada del Almagre fault. This fault may have temporarily shunted slip from the north Pajarito fault during ca. 8–11 Ma, resulting in lower strain rates on the Santa Clara fault. East of the Embudo–Santa Clara–Pajarito fault system, deformation of the southern Barrancos monocline and the Cañada Ancha graben peaked during the early–middle Miocene and effectively ceased by the late Pliocene. The north-striking Gabeldon faulted monocline lies at the base of the Sangre de Cristo Mountains, where stratal dip relations indicate late Oligocene and Miocene tilting. Shifting of strain toward the Embudo–Santa Clara–Pajarito fault system culminated during the late Pliocene–Quaternary. Collectively, our data suggest that extensional tectonism in the eastern Española Basin increased in the early Miocene and probably peaked between 14–15 Ma and 9–10 Ma, preceding and partly accompanying major volcanism, and decreased in the Plio-Pleistocene.

In the Galisteo drainage basin south of Santa Fe, a fold and several faults related to the Rio Grande rift deform late Eocene–Oligocene dikes, laccoliths, and the Espinaso Formation. The largest rift-related feature, a northerly plunging syncline, comprises the south end of the Santa Fe embayment of the Española Basin and the northern end of the Estancia Basin. The east limb of the syncline is cut by northerly trending, graben-forming, normal faults of the Agua Fria fault system in the Santa Fe embayment. East of the Tijeras-Cañoncito fault system, the east limb of the Estancia Basin is disrupted by down-to-the-west, normal faults of the Glorieta Mesa boundary fault and the Hub Mesa fault system. The fold is offset by down-to-the-northwest movement, and a small component of right slip, on the Tijeras-Cañoncito fault system, which separates the two basins. The above-mentioned rift-related fold and north-trending faults are superimposed across the southeastern margin of the San Luis uplift and the younger Galisteo Basin. Geologic maps and drill data reveal four, and possibly five, phases of Laramide deformation associated with recurrent movement along the Tijeras-Cañoncito fault system: (1) a possible Late Cretaceous, cryptic phase of strike slip associated with elevation of the highest portions of the Santa Fe Range uplift to the north-northeast; (2) the early Paleocene San Luis uplift that formed a southwest plunging, V-shaped anticlinal nose whose southeast limb is the Lamy monocline, which extends 25 km southwest from Precambrian basement at the margin of the Santa Fe Range at Cañoncito to the Cretaceous Menefee Formation; (3) following erosional beveling, the collapse of the southern shoulder of the San Luis uplift, forming a portion of the north-northeast–trending, latest Paleocene–Eocene Diamond Tail subbasin, the axial portion of which lies along the trend of the Tijeras-Cañoncito fault zone; (4) minor Eocene uplift which interrupted deposition in the basin; and (5) Eocene subsidence across the broader Galisteo subbasin and deposition of the Galisteo Formation and latest Eocene–Oligocene Espinaso Formation. Late Eocene–Oligocene intrusions in Los Cerrillos and the Ortiz Mountains deformed the Cretaceous and Tertiary host rocks. Across the Tijeras-Cañoncito fault system, the northwest-trending erosional edge of the Campanian Point Lookout Sandstone displays 400 m of pre–Diamond Tail Formation, right-lateral separation, and the Diamond Tail Formation shows no lateral offset between the overlapping San Lazarus and Los Angeles faults. Although the axis of the Galisteo Basin parallels the fault system, and the basin has been proposed to have formed in a releasing bend of a strike-slip fault along the Tijeras-Cañoncito fault system, any major Laramide strike-slip movement pre-dates the deposition of the Diamond Tail Formation and the formation of the Lamy monocline. The faulted core of the pre–Diamond Tail Lamy monocline, initially up ~800 m on the northwest, was reactivated during rift development and downdropped on the northwest by ~250 m of dip slip. An earlier period of movement (either early Laramide or older strike slip or down-to-the southeast Pennsylvanian movement) is suggested by contrasting thicknesses of Paleozoic formations across the fault zone.

We have developed a conceptual model for the Tesuque aquifer system in the southeastern Española Basin near Santa Fe, New Mexico, based on measurements of chemical, isotopic, and thermal properties of groundwater from 120 wells. This study concentrates on a single groundwater-flow unit (GFU) of the Tesuque aquifer associated with the Santa Fe River drainage, where groundwater flows east to west across north-trending rift structures. We examine links between groundwater flow, temperature, water chemistry, and major fault structures. Hydrologic and hydrochemical processes are assessed through spatial mapping of temperature and chemical composition (Ca:Na ratios, F, As, B, Li, δ 2 H, and δ 18 O), Piper and bivariate plots, Spearman rank-order correlations, and flow-line modeling of mineral saturation (PHREEQC software). Results help delineate recharge and discharge areas and demonstrate spatial correspondence of major rift structures with changes in chemical and thermal data. Thermal wells with anomalous discharge temperatures and regional thermal gradients exceeding 40 °C/km align with structural boundaries of the Cañada Ancha graben and Caja del Rio horst. Mg-Li geothermometry characterizes temperatures associated with deep circulating groundwater. Important features of the conceptual model are (1) a forced convection system in the Tesuque aquifer associated with the Caja del Rio horst drives upward flow and discharge of warm, Na-rich groundwater in the western half of the Cañada Ancha graben; and (2) major horst-graben structures concentrate upward flow of deep, NaSO 4 thermal waters from underlying bedrock. Both features likely contribute to chemical anomalies and thermal disturbances in the shallow Tesuque aquifer.

We used tephrochronology for upper Neogene deposits in the Española Basin and the adjoining Jemez Mountains volcanic field in the Rio Grande rift, northern New Mexico, to correlate key tephra strata in the study area, identify the sources for many of these tephra, and refine the maximum age of an important stratigraphic unit. Electron-microprobe analyses on volcanic glass separated from 146 pumice-fall, ash-fall, and ash-flow tephra units and layers show that they are mainly rhyolites and dacites. Jemez Mountains tephra units range in age from Miocene to Quaternary. From oldest to youngest these are: (1) the Canovas Canyon Rhyolite and the Paliza Canyon Formation of the lower Keres Group (ca. <12.4–7.4 Ma); (2) the Peralta Tuff Member of the Bearhead Rhyolite of the upper Keres Group (ca. 6.96–6.76 Ma); (3) Puye Formation tephra layers (ca. 5.3–1.75 Ma); (4) the informal San Diego Canyon ignimbrites (ca. 1.87–1.84 Ma); (5) the Otowi Member of the Bandelier Tuff, including the basal Guaje Pumice Bed (both ca. 1.68–1.61 Ma); (6) the Cerro Toledo Rhyolite (ca. 1.59–1.22 Ma); (7) the Tshirege Member of the Bandelier Tuff, including the basal Tsankawi Pumice Bed (both ca. 1.25–1.21 Ma); and (8) the El Cajete Member of the Valles Rhyolite (ca. 60–50 ka). The Paliza Canyon volcaniclastic rocks are chemically variable; they range in composition from dacite to dacitic andesite and differ in chemical composition from the younger units. The Bearhead Rhyolite is highly evolved and can be readily distinguished from the younger units. Tuffs in the Puye Formation are dacitic rather than rhyolitic in composition, and their glasses contain significantly higher Fe, Ca, Mg, and Ti, and lower contents of Si, Na, and K. We conclude that the Puye is entirely younger than the Bearhead Rhyolite and that its minimum age is ca. 1.75 Ma. The San Diego Canyon ignimbrites can be distinguished from all members of the overlying Bandelier Tuff on the basis of Fe and Ca. The Cerro Toledo tephra layers are readily distinguishable from the overlying and underlying units of the Bandelier Tuff primarily by lower Fe and Ca contents. The Tshirege and Otowi Members of the Bandelier Tuff are difficult to distinguish from each other on the basis of electron-microprobe analysis of the volcanic glass; the Tshirege Member contains on average more Fe than the Otowi Member. Tephra layers in the Española Basin that correlate to the Lava Creek B ash bed (ca. 640 ka) and the Nomlaki Tuff (Member of the Tuscan and Tehama Formations, ca. 3.3 Ma) indicate how far tephra from these eruptions traveled (the Yellowstone caldera of northwestern Wyoming and the southern Cascade Range of northern California, respectively). Tephra layers of Miocene age (16–10 Ma) sampled from the Tesuque Formation of the Santa Fe Group in the Española Basin correlate to sources associated with the southern Nevada volcanic field (Timber Mountain, Black Mountain, and Oasis Valley calderas) and the Snake River Plain–Yellowstone hot spot track in Idaho and northwestern Wyoming. Correlations of these tephra layers across the Santa Clara fault provide timelines through various stratigraphic sections despite differences in stratigraphy and lithology. We use tephra correlations to constrain the age of the base of the Ojo Caliente Sandstone Member of the Tesuque Formation to 13.5–13.3 Ma.