Seismicity recorded in hematite fault mirrors in the Rio Grande rift

Exhumed fault rocks provide a textural and chemical record of how fault zone composition and architecture control coseismic temperature rise and earthquake mechanics. We integrated field, microstructural, and hematite (U-Th)/He (He) thermochronometry analyses of exhumed minor (square-centimeter-scale surface area) hematite fault mirrors that crosscut the ca. 1400 Ma Sandia granite in two localities along the eastern flank of the central Rio Grande rift, New Mexico. We used these data to characterize fault slip textures; evaluate relationships among fault zone composition, thickness, and inferred magnitude of friction-generated heat; and document the timing of fault slip. Hematite fault mirrors are collocated with and crosscut specular hematite veins and hematite-cemented cataclasite. Observed fault mirror microstructures reflect fault reactivation and strain localization within the comparatively weaker hematite relative to the granite. The fault mirror volume of some slip surfaces exhibits polygonal, sintered hematite nanoparticles likely created during coseismic temperature rise. Individual fault mirror hematite He dates range from ca. 97 to 5 Ma, and ~80% of dates from fault mirror volume aliquots with high-temperature crystal morphologies are ca. 25–10 Ma. These aliquots have grain-size–dependent closure temperatures of ~75–108 °C. A new mean apatite He date of 13.6 ± 2.6 Ma from the Sandia granite is consistent with prior low-temperature thermochronometry data and reflects rapid, Miocene rift flank exhumation. Comparisons of thermal history models and hematite He data patterns, together with field and microstructural observations, indicate that seismicity along the fault mirrors at ~2–4 km depth was coeval with rift flank exhumation. The prevalence and distribution of high-temperature hematite grain morphologies on different slip surfaces correspond with thinner deforming zones and higher proportions of quartz and feldspar derived from the granite that impacted the bulk strength of the deforming zone. Thus, these exhumed fault mirrors illustrate how evolving fault material properties reflect but also govern coseismic temperature rise and associated dynamic weakening mechanisms on minor faults at the upper end of the seismogenic zone.

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Geology, structure, and tectonics of the Pajarito fault zone in the Española basin of the Rio Grande rift, New Mexico

Geological Society of America Bulletin ◽

10.1130/0016-7606(1983)94<192:gsatot>2.0.co;2 ◽

1983 ◽

Vol 94 (2) ◽

pp. 192 ◽

Cited By ~ 21

Author(s):

MATTHEW P. GOLOMBEK

Keyword(s):

New Mexico ◽

Fault Zone ◽

Rio Grande ◽

Rio Grande Rift

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Geometry and rate of extension across the Pajarito fault zone, Española basin, Rio Grande rift, northern New Mexico

Geology ◽

10.1130/0091-7613(1981)9<21:garoea>2.0.co;2 ◽

1981 ◽

Vol 9 (1) ◽

pp. 21 ◽

Cited By ~ 18

Author(s):

Matthew P. Golombek

Keyword(s):

New Mexico ◽

Fault Zone ◽

Rio Grande ◽

Rio Grande Rift

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Controls on fault-zone architecture in poorly lithified sediments, Rio Grande Rift, New Mexico: Implications for fault-zone permeability and fluid flow

Faults and Subsurface Fluid Flow in the Shallow Crust - Geophysical Monograph Series ◽

10.1029/gm113p0027 ◽

1999 ◽

pp. 27-49 ◽

Cited By ~ 40

Author(s):

Michiel R. Heynekamp ◽

Laurel B. Goodwin ◽

Peter S. Mozley ◽

William C. Haneberg

Keyword(s):

Fluid Flow ◽

New Mexico ◽

Fault Zone ◽

Rio Grande ◽

Rio Grande Rift ◽

Fault Zone Architecture

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MULTI-METHOD THERMOCHRONOMETRIC RECORD OF EXHUMATION AND FAULT SLIP IN THE CENTRAL RIO GRANDE RIFT, SANDIA MOUNTAINS

10.1130/abs/2020rm-346734 ◽

2020 ◽

Author(s):

Margaret Odlum ◽

◽

Alexis K. Ault ◽

Gabriele Calzolari ◽

Michael A. Channer

Keyword(s):

Rio Grande ◽

Fault Slip ◽

Rio Grande Rift

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Hematite (U-Th)/He thermochronometry detects asperity flash heating during laboratory earthquakes

Geology ◽

10.1130/g46965.1 ◽

2020 ◽

Vol 48 (5) ◽

pp. 514-518 ◽

Cited By ~ 1

Author(s):

Gabriele Calzolari ◽

Alexis K. Ault ◽

Greg Hirth ◽

Robert G. McDermott

Keyword(s):

High Temperatures ◽

Temperature Rise ◽

Thick Layer ◽

Seismogenic Zone ◽

Experimental Conditions ◽

Slip Rates ◽

Seismic Slip ◽

Slip Surfaces ◽

Before And After ◽

Dynamic Weakening

Abstract Evidence for coseismic temperature rise that induces dynamic weakening is challenging to directly observe and quantify in natural and experimental fault rocks. Hematite (U-Th)/He (hematite He) thermochronometry may serve as a fault-slip thermometer, sensitive to transient high temperatures associated with earthquakes. We test this hypothesis with hematite deformation experiments at seismic slip rates, using a rotary-shear geometry with an annular ring of silicon carbide (SiC) sliding against a specular hematite slab. Hematite is characterized before and after sliding via textural and hematite He analyses to quantify He loss over variable experimental conditions. Experiments yield slip surfaces localized in an ∼5–30-µm-thick layer of hematite gouge with <300-µm-diameter fault mirror (FM) zones made of sintered nanoparticles. Hematite He analyses of undeformed starting material are compared with those of FM and gouge run products from high-slip-velocity experiments, showing >71% ± 1% (1σ) and 18% ± 3% He loss, respectively. Documented He loss requires short-duration, high temperatures during slip. The spatial heterogeneity and enhanced He loss from FM zones are consistent with asperity flash heating (AFH). Asperities >200–300 µm in diameter, producing temperatures >900 °C for ∼1 ms, can explain observed He loss. Results provide new empirical evidence describing AFH and the role of coseismic temperature rise in FM formation. Hematite He thermochronometry can detect AFH and thus seismicity on natural FMs and other thin slip surfaces in the upper seismogenic zone of Earth’s crust.

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Detecting fault zone characteristics and paleovalley incision using electrical resistivity: Loma Blanca Fault, New Mexico

Geophysics ◽

10.1190/geo2020-0375.1 ◽

2021 ◽

Vol 86 (3) ◽

pp. B209-B221

Author(s):

Heather Barnes ◽

Johnny R. Hinojosa ◽

Glenn A. Spinelli ◽

Peter S. Mozley ◽

Daniel Koning ◽

...

Keyword(s):

Electrical Resistivity ◽

Fault Zone ◽

Water Table ◽

Unsaturated Zone ◽

Late Quaternary ◽

Rio Grande ◽

Rio Grande Rift ◽

High Resistivity ◽

Low Resistivity ◽

Sand And Gravel

We have combined electrical resistivity tomography (ERT), geologic information from boreholes and outcrops, and hydrogeologic data to investigate field-scale fault-zone cementation of the Loma Blanca Fault in the Rio Grande Rift. We have collected electrical resistivity data from 16 transects and geologic samples from 29 boreholes (completed as groundwater wells to 30 m depth) across and around the fault. The 2D ERT profiles, whose interpretations are constrained by geologic data, indicate (1) a high resistivity zone in cemented portions of the fault below the water table and (2) in the unsaturated zone, a low-resistivity feature along the cemented portions of the fault. The high-resistivity zone below the water table is consistent with a 10% reduction in porosity due to the fault zone cementation. With the same porosity in the unsaturated zone, the low-resistivity feature in the cemented fault zone is consistent with saturation >0.7, in contrast to saturation 0.2–0.7 for sediment outside of the cemented fault zone. In addition, subsurface samples and ERT profiles delineate a buttress unconformity (i.e., steeply dipping erosional contact) corresponding to a paleovalley margin. This unconformity truncates the cemented fault zone and separates Pliocene axial-fluvial sand (deposited by an ancestral Rio Grande) from late Quaternary sand and gravel (deposited by the Rio Salado, a Rio Grande tributary). The cemented fault zone in the southern portion of the study area is a hydrogeologic barrier; north of the buttress unconformity, where the cemented fault zone has been removed by erosion, the fault is not a hydrogeologic barrier. The integration of geologic, geophysical, and hydrogeologic observations is key to developing our understanding of this complex system, and it allows us to demonstrate the utility of ERT in detecting subsurface fault-zone cementation.

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Study of Characteristics of Fault Slip and Induced Seismicity during Hydraulic Fracturing in HDR Geothermal Exploitation in the Yishu Fault Zone in China

Geofluids ◽

10.1155/2021/5515665 ◽

2021 ◽

Vol 2021 ◽

pp. 1-19

Author(s):

Zhiyong Niu ◽

Shiquan Wang ◽

Hongrui Ma ◽

Hengjie Luan ◽

Zhouyuyan Ding

Keyword(s):

Hydraulic Fracturing ◽

Fault Zone ◽

Geothermal Energy ◽

Seismic Event ◽

Geothermal Field ◽

Fault Slip ◽

Fault Reactivation ◽

Geothermal System ◽

Artificial Fracture ◽

Yishu Fault Zone

Hot dry rock (HDR) geothermal energy has become promising resources for relieving the energy crisis and global warming. The exploitation of HDR geothermal energy usually needs an enhanced geothermal system (EGS) with artificial fracture networks by hydraulic fracturing. Fault reactivation and seismicity induced by hydraulic fracturing raise a great challenge. In this paper, we investigated the characteristics of fault slip and seismicity by numerical simulation. The study was based on a hydraulic fracturing project in the geothermal field of Yishu fault zone in China. It revealed that fluid injection during hydraulic fracturing can cause the faults that exist beyond the fluid-pressurized region to slip and can even induce large seismic event. It was easier to cause felt earthquakes when hydraulic fracturing was carried out in different layers simultaneously. We also examined the effects of the location, permeability, and area of the fracturing region on fault slip and magnitude of the resulting events. The results of the study can provide some useful references for establishing HDR EGS in Yishu fault zone.

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A shallow rift basin segmented in space and time: The southern San Luis Basin, Rio Grande rift, northern New Mexico, U.S.A.

Rocky Mountain Geology ◽

10.24872/rmgjournal.54.2.97 ◽

2019 ◽

Vol 54 (2) ◽

pp. 97-131

Author(s):

Benjamin J. Drenth ◽

V.J.S. Grauch ◽

Kenzie J. Turner ◽

Brian D. Rodriguez ◽

Ren A. Thompson ◽

...

Keyword(s):

Fault Zone ◽

Rio Grande ◽

Volcanic Field ◽

Tectonic Activity ◽

Rio Grande Rift ◽

Low Density ◽

Maximum Thickness ◽

San Luis ◽

Sangre De Cristo ◽

Basin Fill

ABSTRACT Interpretation of gravity, magnetotelluric, and aeromagnetic data in conjunction with geologic constraints reveals details of basin geometry, thickness, and spatiotemporal evolution of the southern San Luis Basin, one of the major basins of the northern Rio Grande rift. Spatial variations of low-density basin-fill thickness are estimated primarily using a 3D gravity inversion method that improves on previous modeling efforts by separating the effects of the low-density basin fill from the effects of pre-rift rocks. The basin is found to be significantly narrower—and more complex in the subsurface—than indicated or implied by previous modeling efforts. The basin is also estimated to be significantly shallower than previously estimated. Five distinct subbasins are recognized within the broader southern San Luis Basin. The oldest and shallowest subbasin is the Las Mesitas graben along the northwestern basin margin, formed during the Oligocene transition from Southern Rocky Mountain volcanic field magmatism to rifting. In this subbasin, sediments are estimated to reach a maximum thickness of ~400 m within a north–south elongated structural depression. Other subbasins that likely initially developed during the Miocene are the dominant tectonic features in the southern San Luis Basin. This includes the Tres Orejas subbasin, which formed in the southwestern portion of the basin by the Embudo fault zone and a hypothesized fault zone along its western margin. This subbasin reaches a maximum thickness of ~2 km, as indicated by magnetotelluric and gravity modeling. The Sunshine Valley, Questa, and Taos subbasins occupy the eastern part of the southern San Luis Basin. The southern Sangre de Cristo fault zone is the dominant tectonic feature that controlled their development after ~20 Ma. The east-down Gorge fault zone controlled the western margins of significant parts of these eastern subbasins, although much of the Taos subbasin may be superimposed on the Tres Orejas subbasin. Maximum low-density basin-fill thicknesses are estimated to be 1.2 km for the Sunshine Valley subbasin, 800 m for the Questa subbasin, and 1.8 km for the Taos subbasin. Subbasin-forming tectonic activity along the Gorge fault zone and within the Tres Orejas subbasin ceased by the end of the development of the largely Pliocene Taos Plateau volcanic field. After that, rift-related subsidence became more narrowly centered on the eastern margin of the basin, controlled mainly by the linked Embudo and southern Sangre de Cristo fault zones.

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