Geologic map of the Poncha Pass area, Chaffee, Fremont, and Saguache Counties, Colorado

Minor, Scott A.; Caine, Jonathan Saul; Ruleman, Chester A.; Fridrich, Christopher J.; Chan, Christine F.; Brandt, Theodore R.; Holm-Denoma, Christopher S.; Morgan, Leah E.; Grauch, V.J.S.

doi:10.3133/sim3436

Cited by 2 publications

(1 citation statement)

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“…ACZs aid in strain transfer and basin integration in different ways throughout the RGR. For example, the Poncha Pass ACZ transfers strain between the San Luis Basin and the UAR Basin along a narrow region of northeast‐southwest striking faults which developed in the late Miocene (Hubbard et al, ; Kellogg et al, ; Minor et al, ). In the central and southern RGR, strain transfer is more commonly accommodated via magmatic injection (e.g., Casey et al, ; Keir et al, ) and across broad areas of overlapping faults that gradually transfer displacement (e.g., Lewis & Baldridge, ; Figure ).…”

Section: Discussionmentioning

confidence: 99%

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

Abbey

Niemi

2020

Tectonics

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Analysis of spatiotemporal patterns of faulting and magmatism in the Rio Grande rift (RGR) in New Mexico and Colorado, USA, yields insights into continental rift processes, extension accommodation mechanisms, and rift evolution models. We combine new apatite (U-Th-Sm)/He and zircon (U-Th)/He thermochronometric data with previously published thermochronometric data to assess the timing of fault initiation, magnitudes of fault exhumation, and growth and linkage patterns of rift faults. Thermal history modeling of these data reveals contemporaneous rift initiation at ca. 25 Ma in both the northern and southern RGR with continued fault initiation, growth, and linkage progressing from ca. 25 to ca. 15 Ma. The central RGR, however, shows no evidence of Cenozoic fault-related exhumation as observed with thermochronometry and instead reveals extension accommodated through Late Cenozoic magmatic injection. Furthermore, faulting in the northern and southern RGR occurs along an approximately north-south strike, whereas magmatism in the central RGR occurs along the northeast to southwest trending Jemez lineament. Differences in deformation orientation and rift accommodation along strike appear to be related to crustal and lithospheric properties, suggesting that rift structure and geometry are at least partly controlled by inherited lithospheric-scale architecture. We propose an evolutionary model for the RGR that involves initiation of fault-accommodated extension by oblique strain followed by block rotation of the Colorado Plateau, where extension in the RGR is accommodated by faulting (southern and northern RGR) and magmatism (central RGR). This study highlights different processes related to initiation, geometry, extension accommodation, and overall development of continental rifts. Plain Language SummaryWe identify patterns of faulting and volcanism in the Rio Grande rift (RGR) in the western United States to better understand how continental rifts evolve. Using methods for documenting rock cooling ages (thermochronology), we determined that rifting began around 25 million years ago (Ma) in both the northern and southern RGR. Rift faults continued to develop and grow for another 10 to 15 million years. The central RGR, however, shows that rift extension occurred through volcanic activity both as eruptions at the surface and as magma injection below the surface since~15 Ma. Interestingly, RGR faulting in the north and south parts of the rift occurs on a north-south line, while volcanism in the central RGR is along a northeast to southwest line. The differences in the location and orientation of faulting and volcanic activity may be related to the thickness of the lithosphere beneath different parts of the rift. Using these patterns of faulting and magmatism, we propose the RGR evolved through a combination of (1) oblique strain-extension diagonal to the rift and (2) block rotation-where the Colorado Plateau is the rotating block. This detailed study highlights different processes related to the accommodation of extension...

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Section: Discussionmentioning

confidence: 99%

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

Abbey

Niemi

2020

Tectonics

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From Crystals to Crustal‐Scale Seismic Anisotropy: Bridging the Gap Between Rocks and Seismic Studies With Digital Geologic Map Data in Colorado

et al. 2022

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Deep continental crustal structures are enigmatic due to lack of direct exposures and limited tools to investigate them remotely. Seismic waves can sample these rocks, but most seismic methods focus on coarse crustal structures while laboratory measurements concentrate on crystal‐scale rock properties, and little work has been conducted to bridge this interpretation gap. In some places, geologic maps of crystalline basement provide samples of the intermediate‐scale fabrics and structures that may represent in situ deep crust. However, previous research has not considered natural geometric variations from map data, nor is this heterogeneity typically included in map‐scale seismic property calculations. Here, we test how map‐scale fabrics influence crustal seismic anisotropy in Colorado by analyzing structural data from geologic maps, combining those data with bulk rock elastic tensors to calculate map‐scale seismic properties, and evaluating the resulting comparisons with observed receiver function A1 (360° periodic) arrivals. Crystalline fabrics, predicted seismic properties, and tectonic structures positively correlate with shallow and deep crustal A1 arrivals. Additionally, widespread correlations occur between mapped fault traces and regional foliations, implying that preexisting mechanical heterogeneity may have strongly influenced subsequent reactivation. We interpret that various mapped geologic contact types (e.g., lithologic and structural) generate A1 arrivals and that multiple parallel features (e.g., faults, foliations, and intrusions) contribute to a seismically visible tectonic grain. Therefore, Colorado's exhumed basement, as expressed in outcrops and maps, offers insight into modern deep crustal geological and geophysical structure.

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Geologic map of the Poncha Pass area, Chaffee, Fremont, and Saguache Counties, Colorado

Cited by 2 publications

References 1 publication

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

From Crystals to Crustal‐Scale Seismic Anisotropy: Bridging the Gap Between Rocks and Seismic Studies With Digital Geologic Map Data in Colorado

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