Geologic map of the upper Arkansas River valley region, north-central Colorado

Kellogg, Karl S.; Shroba, Ralph R.; Ruleman, Chester A.; Bohannon, Robert G.; McIntosh, William C.; Premo, Wayne R.; Moscati, Richard J.; Brandt, Theodore R.

doi:10.3133/sim3382

Cited by 9 publications

(8 citation statements)

References 48 publications

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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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“…The Arkansas River valley is a topographic expression of the northernmost extent of the Rio Grande Rift that became tectonically active ca. 30-25 Ma (Kellogg et al, 2017). Many peaks exceed 4000 m and features typical of alpine glaciation and periglacial activity characterize landscapes at higher elevations.…”

Section: Study Areamentioning

confidence: 99%

“…Many peaks exceed 4000 m and features typical of alpine glaciation and periglacial activity characterize landscapes at higher elevations. Structurally the range is cored by Precambrian crystalline rocks unconformably overlain by complexly faulted and folded Paleozoic clastics and carbonates that were later intruded by a suite of Tertiary sills, dikes and small plutons (McCalpin et al, 2012a, b;Kellogg et al, 2017).…”

Section: Study Areamentioning

confidence: 99%

“…Although the elevations of catchment areas are comparable ($3600-3800 m), glaciers there terminated at lower elevations than did those on the western slopes. Wellpreserved terminal and lateral moraines of the last (Pinedale) and penultimate (Bull Lake) glaciations are common at the mouths of glaciated valleys, and in most are delineated on bedrock maps (Widmann et al, 2007;McCalpin et al, 2012a,b;Bohannon and Ruleman, 2013;Kellogg et al, 2017). The relative ages of these moraines can generally be distinguished by morphostratigraphic criteria (boulder abundance and freshness, sharpness of moraine crests, etc.).…”

Section: Study Areamentioning

confidence: 99%

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Late Pleistocene glaciation in the Mosquito Range, Colorado, USA: chronology and climate

Brugger

Laabs

Reimers

et al. 2019

J Quaternary Science

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New cosmogenic 10Be surface exposure ages from 17 moraine boulders in the Mosquito Range of Colorado suggest that glaciers were at their late Pleistocene (Pinedale) maximum extent at ∼21–20 ka, and that ice recession commenced before ∼17 ka. These age limits suggest that the Pinedale Glaciation was synchronous within the Colorado Rocky Mountain region. Locally, the previous (Bull Lake) glaciation appears to have occurred no later than 117 ka, possibly ∼130 ka allowing for reasonable rock weathering rates. Temperature‐index modeling is used to determine the magnitude of temperature depression required to maintain steady‐state mass balances of seven reconstructed glaciers at their maximum extent. Assuming no significant differences in precipitation compared to modern values, mean annual temperatures were ∼8.1 and 7.5 °C lower, respectively, on the eastern and western slopes of the range with quantifiable uncertainties of + 0.8/−0.9 °C. If an average temperature depression of 7.8 °C is assumed for the entire range, precipitation differences − that today are 15–30% greater on the eastern slope due to the influence of winter/early spring snowfall − might have been enhanced. The temperature depressions inferred here are consistent with similarly derived values elsewhere in the Colorado Rockies and those inferred from regional‐scale climate modeling.

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“…Topographically, the Sawatch Range is the highest in Colorado and within the study area several peaks exceed 4000 m, including Mount Elbert (4401 m) and Mount Massive (4398 m) that are respectively the highest and second highest summits in the Rocky Mountains. Late Quaternary glaciations were extensive and characterized by valley glacier systems that sculpted alpine landscapes at higher elevations and deposited prominent terminal and recessional moraines in valleys [36]. Individual glaciers were typically interconnected by thin, upland ice fields and/or pervasive ice divides.…”

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confidence: 99%

Climate during the Last Glacial Maximum in the Northern Sawatch Range, Colorado, USA

et al. 2019

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Temperature-index modeling is used to determine the magnitude of temperature depression in the northern Sawatch Range required to maintain steady-state mass balances of six reconstructed glaciers at their extent during the local Last Glacial Maximum (LLGM), dated at ~21 ka. Assuming no significant differences in precipitation compared to modern values, mean annual temperatures in the region were on average 8.8 + 0.5/– 0.8 °C cooler than they are today. Allowing for modest (± 10 cm) increases or decreases in precipitation, required temperature depressions only differ by ±0.2 °C. Temperature depression in the northern Sawatch Range is consistent, although slightly greater, with those determined in other ranges in Colorado using similar approaches. The estimates presented here are, however, substantially less than those suggested by several downscaled simulations of global Last Glacial Maximum (LGM) climate, that might be due to the need for improved calibration of such downscaled simulations, or the models from which they are derived. Our estimates of LGM temperature depression are considerably greater than that previously determined in the study area and those in two other ranges in Colorado derived using different methodologies, the latter being most likely responsible for the discrepancies.

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Geologic map of the upper Arkansas River valley region, north-central Colorado

Cited by 9 publications

References 48 publications

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

Late Pleistocene glaciation in the Mosquito Range, Colorado, USA: chronology and climate

Climate during the Last Glacial Maximum in the Northern Sawatch Range, Colorado, USA

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