Thermal classification of lithospheric discontinuities beneath USArray

Hansen, S. M.; Dueker, K. G.; Schmandt, Brandon

doi:10.1016/j.epsl.2015.09.009

Cited by 86 publications

(169 citation statements)

References 109 publications

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“…Overall, our NPR map agrees most closely with the negative velocity gradient (NVG) map of Hansen et al (; see their Figure ), particularly in the southwest, although there are also notable differences in some areas. Many of these are related to the fact that Hansen et al () include features below 100‐km depth in their NVG map. Although we sometimes see deep NPRs (see Figure ), they are generally weaker than the shallower NPR, and they do not appear as a continuous reflector, or one that deepens clearly from the shallower NPR.…”

Section: Resultssupporting

confidence: 88%

Imaging Upper‐Mantle Structure Under USArray Using Long‐Period Reflection Seismology

Shearer

Buehler

2019

JGR Solid Earth

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Topside reverberations off mantle discontinuities are commonly observed at long periods, but their interpretation is complicated because they include both near‐source and near‐receiver reflections. We have developed a method to isolate the stationside reflectors in large data sets with many sources and receivers. Analysis of USArray transverse‐component data from 3,200 earthquakes, using direct S as a reference phase, shows clear reflections off the 410‐ and 660‐km discontinuities, which can be used to map the depth and brightness of these features. Because our results are sensitive to the impedance contrast (velocity and density), they provide a useful complement to receiver‐function studies, which are primarily sensitive to the S velocity jump alone. In addition, reflectors in our images are more spread out in time than in receiver functions, providing good depth resolution. Our images show strong discontinuities near 410 and 660 km across the entire USArray footprint, with intriguing reflectors at shallower depths in many regions. Overall, the discontinuities in the east appear simpler and more monotonous with a uniform transition zone thickness of 250 km compared to the western United States. In the west, we observe more complex discontinuity topography and small‐scale changes below the Great Basin and the Rocky Mountains, and a decrease in transition‐zone thickness along the western coast. We also observe a dipping reflector in the west that aligns with the top of the high‐velocity Farallon slab anomaly seen in some tomography models, but which also may be an artifact caused by near‐surface scattering of incoming S waves.

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Section: Resultssupporting

confidence: 88%

Imaging Upper‐Mantle Structure Under USArray Using Long‐Period Reflection Seismology

Shearer

Buehler

2019

JGR Solid Earth

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“…Ample evidence supports the existence of this petrologic model at work in the southern Rocky Mountains in the very recent past. As stated previously, seismic tomography reveals the upper mantle directly beneath the Rocky Mountains to be anomalously warm (Hansen et al, ) and may contain melt that could be supplied to the lower crust (e.g., Humphreys et al, ). The presence of melt in the crust would increase seismic attenuation, and Phillips et al () observe that seismic attenuation of Lg surface waves at frequencies corresponding to crustal depths (0.75–1.5 Hz) is high for most of Colorado west of the Rocky Mountain Front.…”

Section: Discussionmentioning

confidence: 72%

“…In the high‐temperature extreme we assume that the melt has recently been extracted from the upper mantle. Hansen et al () map surface‐wave shear velocities to lithospheric temperature for most of the U.S. and find a maximum temperature of ~1,300°C beneath central Colorado at a depth of 82 km. Leat et al () performed major element geochemistry for 14 rock samples collected from four Quaternary basalt flows in central Colorado, including the Dotsero flow.…”

Section: Discussionmentioning

confidence: 99%

Magnetotelluric Imaging of Lower Crustal Melt and Lithospheric Hydration in the Rocky Mountain Front Transition Zone, Colorado, USA

2017

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We present an electrical resistivity model of the crust and upper mantle from two‐dimensional (2‐D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern‐day lithosphere beneath the Rocky Mountain Front to depths in excess of 150 km. Two key features of the 2‐D resistivity model are (1) a broad zone (~200 km wide) of enhanced electrical conductivity (<20 Ωm) in the midcrust to lower crust that is centered beneath the highest elevations of the southern Rocky Mountains and (2) hydrated lithospheric mantle beneath the Great Plains with water content in excess of 100 ppm. We interpret the high conductivity region of the lower crust as a zone of partially molten basalt and associated deep‐crustal fluids that is the result of recent (less than 10 Ma) tectonic activity in the region. The recent supply of volatiles and/or heat to the base of the crust in the late Cenozoic implies that modern‐day tectonic activity in the western United States extends to at least the western margin of the Great Plains. The transition from conductive to resistive upper mantle is caused by a gradient in lithospheric modification, likely including hydration of nominally anhydrous minerals, with maximum hydration occurring beneath the Rocky Mountain Front. This lithospheric “hydration front” has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere.

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“…The crustal thickness measurements obtained using 4045 RFs from 22 stations on the Ozark Uplift range from 37.6 to 50.3 km with a mean value of 42.5 ± 3.0 km, and the V p / V s results range from 1.75 to 1.84 with a mean value of 1.80 ± 0.02 (Figures and ). The crustal thickness values are in general agreement with previous studies for this area [ Chulick and Mooney , ; Ramírez‐Guzmán et al , ; Hansen et al , ; McGlannan and Gilbert , ]. Both the crustal thickness and V p / V s results are typical for the North American cratonic areas [ Keller , ].…”

Section: Resultsmentioning

confidence: 99%

“…The average crustal thickness is 44.0 ± 1.9 km, and the mean V p / V s value is 1.80 ± 0.02, which is comparable to those observed on the Ozark Uplift but is smaller than those obtained in the UME. The measured crustal thicknesses of Ramírez‐Guzmán et al [], Chen et al [], Pollitz and Mooney [], and McGlannan and Gilbert [] are approximately 40 km beneath the southernmost part of the Illinois Basin, while those of Hansen et al [] are greater than 45 km. Therefore, results from this study are in general agreement with those from previous studies.…”

Section: Resultsmentioning

confidence: 99%

Receiver function and gravity constraints on crustal structure and vertical movements of the Upper Mississippi Embayment and Ozark Uplift

et al. 2017

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The Upper Mississippi Embayment (UME), where the seismically active New Madrid Seismic Zone resides, experienced two phases of subsidence commencing in the Late Precambrian and Cretaceous, respectively. To provide new constraints on models proposed for the mechanisms responsible for the subsidence, we computed and stacked P‐to‐S receiver functions recorded by 49 USArray and other seismic stations located in the UME and the adjacent Ozark Uplift and modeled Bouguer gravity anomaly data. The inferred thickness, density, and Vp/Vs of the upper and lower crustal layers suggest that the UME is characterized by a mafic and high‐density upper crustal layer of ∼30 km thickness, which is underlain by a higher‐density lower crustal layer of up to ∼15 km. Those measurements, in the background of previously published geological observations on the subsidence and uplift history of the UME, are in agreement with the model that the Cretaceous subsidence, which was suggested to be preceded by an approximately 2 km uplift, was the consequence of the passage of a previously proposed thermal plume. The thermoelastic effects of the plume would have induced wide‐spread intrusion of mafic mantle material into the weak UME crust fractured by Precambrian rifting and increased its density, resulting in renewed subsidence after the thermal source was removed. In contrast, the Ozark Uplift has crustal density, thickness, and Vp/Vs measurements that are comparable to those observed on cratonic areas, suggesting an overall normal crust without significant modification by the proposed plume, probably owing to the relatively strong and thick lithosphere.

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Thermal classification of lithospheric discontinuities beneath USArray

Cited by 86 publications

References 109 publications

Imaging Upper‐Mantle Structure Under USArray Using Long‐Period Reflection Seismology

Imaging Upper‐Mantle Structure Under USArray Using Long‐Period Reflection Seismology

Magnetotelluric Imaging of Lower Crustal Melt and Lithospheric Hydration in the Rocky Mountain Front Transition Zone, Colorado, USA

Receiver function and gravity constraints on crustal structure and vertical movements of the Upper Mississippi Embayment and Ozark Uplift

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