Abstract The Cañones fault zone in north-central New Mexico is a boundary between the Colorado Plateau to the west and the Rio Grande rift to the east. It consists of a major fault, the Cañones fault, and a series of synthetic and antithetic normal faults within the Abiquiu embayment in the northwestern Española basin. The Cañones fault is a southeast-dipping high-angle normal fault, striking ~N20°E in the south, N40°E in the middle, and east-west at its northern end. The synthetic and antithetic faults are sub-parallel to the major fault. Detailed fault kinematic studies from the master fault reveal that the trends of slickenlines range S85°E - S70°E, and average approximately S76°E. Slickenlines on antithetic faults trend S20°W – N30°W, clustering at ~ N70°W. The attitude of fault surfaces and slickenlines indicate east-southeast/west-northwest extension within the Cañones Fault Zone. The sense of motion on the major fault is normal dominantly with left-slip. Fault throw is at least 225 m, based on Mesozoic units as hanging wall and footwall cutoffs. Thus, the heave is as ~143 m and the left-lateral displacement is ~60 m, given the averaged fault attitudes. In contrast to sub-horizontal Permian-Triassic units in its footwall, hanging wall strata of the Cañones fault zone dips in two directions: west-dipping Jurassic Entrada, Todilto, and Morrison formations; and south-east-dipping Eocene El Rito, Oligocene Ritito, and Oligocene-Miocene Abiquiu formations. Tilted Jurassic strata suggest that the overall structure is monoclinal, probably resulting from Laramide orogeny shortening. The Eocene-Miocene basin fill sediments, surprisingly, dip 10° – 30° away from the Cañones Fault, instead of dipping northwest towards the fault. This phenomenon, in contrast to the prediction of the rollover structure, suggests a different mechanism on this fault zone. Field observation provides direct evidence that basinward tilting is accommodated by multiple antithetic normal faults that cut through Permian to Miocene units. We propose that extensional fault-propagation folding model is a possible mechanism to result in the regional tilting of the basin fill. During upward propagation of the fault tip, horizontal-axis rotation and antithetic and synthetic faulting occur within a triangle zone above the fault tip. Alternatively, a buried large-scale low-angle normal fault can also generate such basinward tilting. In this scenario, the Cañones fault and other southeast-dipping normal faults are antithetic faults that grow on the detachment. These hypothetical mechanisms take into account the antithetic faulting within a rift-bounding fault zone and can be indicative of the evolution of other rift basins in which basin fills dip to the axis, such as the eastern Española basin and San Luis basin in northern New Mexico and southern Colorado.

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.

New 40 Ar/ 39 Ar results from drill-hole cuttings of basaltic and basaltic andesite flows from the Guaje well field of the Pajarito Plateau along the western part of the Española Basin in north-central New Mexico yielded Middle Miocene ages (11.5–13.2 Ma). The volcanic eruptions were closely associated with intense faulting, subsidence, and sedimentation, and the results provide age constraints for the volcanic and tectonic processes along the western margin of the Española Basin. The Middle Miocene volcanic rocks are interbedded within the Santa Fe Group, which is divided into the Hernandez and Vallito Members of the Chamita Formation and the Chama–El Rito Member of the Tesuque Formation, in descending stratigraphic order. New and published geochemical results from the Guaje well field and from other surface and subsurface mafic and intermediate lava flows within the Pajarito Plateau suggest that the volcanic rocks erupted from different magmatic sources and centers close to the Pajarito fault zone. Multiple pulses of volcanic eruptions mostly confined to the hanging wall of the Pajarito fault zone, which represents the current western boundary fault of the Española Basin, suggest that the Pajarito fault system has been sporadically reactivated several times, beginning at least in the Middle Miocene and continuing to the Plio-Pleistocene. Moreover, the volcanic, tectonic, and sedimentary records in the Pajarito Plateau suggest that there is no evidence for eastward migration of tectonic and volcanic activities from the Cañada de Cochiti fault zone in the southern part of the Jemez Mountains to the Pajarito fault zone during the early Pliocene (4–5 Ma).

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.

Two- and three-dimensional electrical resistivity models derived from the magnetotelluric method were interpreted to provide more accurate hydrogeologic parameters for the Albuquerque and Española Basins. Analysis and interpretation of the resistivity models are aided by regional borehole resistivity data. Examination of the magnetotelluric response of hypothetical stratigraphic cases using resistivity characterizations from the borehole data elucidates two scenarios where the magnetotelluric method provides the strongest constraints. In the first scenario, the magnetotelluric method constrains the thickness of extensive volcanic cover, the underlying thickness of coarser-grained facies of buried Santa Fe Group sediments, and the depth to Precambrian basement or overlying Pennsylvanian limestones. In the second scenario, in the absence of volcanic cover, the magnetotelluric method constrains the thickness of coarser-grained facies of buried Santa Fe Group sediments and the depth to Precambrian basement or overlying Pennsylvanian limestones. Magnetotelluric surveys provide additional constraints on the relative positions of basement rocks and the thicknesses of Paleozoic, Mesozoic, and Tertiary sedimentary rocks in the region of the Albuquerque and Española Basins. The northern extent of a basement high beneath the Cerros del Rio volcanic field is delineated. Our results also reveal that the largest offset of the Hubbell Spring fault zone is located 5 km west of the exposed scarp. By correlating our resistivity models with surface geology and the deeper stratigraphic horizons using deep well log data, we are able to identify which of the resistivity variations in the upper 2 km belong to the upper Santa Fe Group sediments

The structural geometry of transfer and accommodation zones that relay strain between extensional domains in rifted crust has been addressed in many studies over the past 30 years. However, details of the kinematics of deformation and related stress changes within these zones have received relatively little attention. In this study we conduct the first-ever systematic, multi-basin fault-slip measurement campaign within the late Cenozoic Rio Grande rift of northern New Mexico to address the mechanisms and causes of extensional strain transfer associated with a broad accommodation zone. Numerous (562) kinematic measurements were collected at fault exposures within and adjacent to the NE-trending Santo Domingo Basin accommodation zone, or relay, which structurally links the N-trending, right-stepping en echelon Albuquerque and Española rift basins. The following observations are made based on these fault measurements and paleostresses computed from them. (1) Compared to the typical northerly striking normal to normal-oblique faults in the rift basins to the north and south, normal-oblique faults are broadly distributed within two merging, NE-trending zones on the northwest and southeast sides of the Santo Domingo Basin. (2) Faults in these zones have greater dispersion of rake values and fault strikes, greater dextral strike-slip components over a wide northerly strike range, and small to moderate clockwise deflections of their tips. (3) Relative-age relations among fault surfaces and slickenlines used to compute reduced stress tensors suggest that far-field, ~E-W–trending σ 3 stress trajectories were perturbed 45° to 90° clockwise into NW to N trends within the Santo Domingo zones. (4) Fault-stratigraphic age relations constrain the stress perturbations to the later stages of rifting, possibly as late as 2.7–1.1 Ma. Our fault observations and previous paleomagnetic evidence of post–2.7 Ma counterclockwise vertical-axis rotations are consistent with increased bulk sinistral-normal oblique shear along the Santo Domingo rift segment in Pliocene and later time. Regional geologic evidence suggests that the width of active rift faulting became increasingly confined to the Santo Domingo Basin and axial parts of the adjoining basins beginning in the late Miocene. We infer that the Santo Domingo clockwise stress perturbations developed coevally with the oblique rift segment mainly due to mechanical interactions of large faults propagating toward each other from the adjoining basins as the rift narrowed. Our results suggest that negligible bulk strike-slip displacement has been accommodated along the north-trending rift during much of its development, but uncertainties in the maximum ages of fault slip do not allow us to fully evaluate and discriminate between earlier models that invoked northward or southward rotation and translation of the Colorado Plateau during early (Miocene) rifting.

Previous paleomagnetic work in the north-central Rio Grande rift (RGR) of northern New Mexico has demonstrated the presence of counterclockwise paleomagnetic rotations, possibly due to left-lateral shearing across the rift. To improve the spatial coverage and resolution of the intrarift rotation, we analyzed the late Tertiary sediments within the exposed Española Basin for paleomagnetic rotations. From five sites broadly distributed across the rift, the amount of rotation varies from little on the eastern edge to over 20° counterclockwise in the central and western rift. If interpreted as tectonic net rotation axes, the amount of rotation varies from 10 to 24°. Gently northeast plunging net rotation axis orientations in the eastern part of the rift indicate dominantly extension-related deformation. Steeper axis inclinations near the center and western part of the rift and Embudo accommodation zone indicate the presence of increased horizontal shearing in these regions. The paleomagnetic data show that the north-central Rio Grande rift is not rotating as a unit but rather consists of a number of smaller independently, counterclockwise-rotating blocks.