Moho temperature and mobility of lower crust in the western United States

Schutt, D.; Lowry, A. R.; Buehler, J. S.

doi:10.1130/g39507.1

Cited by 70 publications

(74 citation statements)

References 35 publications

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“…Other features of the density field estimates can be useful to interpret phase dynamics of the region. Along a profile through the thickest crust in the Illinois basin and the Granite‐Rhyolite province (the Line PP′ in Figure ), we estimate temperatures to be 510 ± 86 °C at 35 km depth and 622 ± 140 °C at 55 km, based on a conductive thermal model combining surface heat flow and mineral physics of Pn seismic velocity (Ma & Lowry, ; Schutt et al, ). Corresponding pressures would be 990 and 1,580 MPa, respectively, assuming 15 km of granitic upper crust (2,750 kg/m 3 ) underlain by gabbro (3,000 kg/m 3 ).…”

Section: Discussionmentioning

confidence: 99%

“…These parameters are significantly different for the western United States as shown in Figure , where , Δρ Moho ,

\frac{dρ}{d κ_{c}}

and

\frac{dρ}{d κ_{m}}

are estimated at 70, 1,180, and −100 kg/m 3 , respectively. The differences likely reflect warmer uppermost mantle (Schutt et al, ) and removal of western U.S. lower crustal garnet phases by hydrous melting (Ma & Lowry, ; Schmandt et al, ). The western U.S. relationships were discussed in the study of Lowry and Pérez‐Gussinyé (), whereas our present study is focused on the central and eastern United States.…”

Section: Estimation Of Density Parametersmentioning

confidence: 99%

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Crustal Composition and Moho Variations of the Central and Eastern United States: Improving Resolution and Geologic Interpretation of EarthScope USArray Seismic Images Using Gravity

2020

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EarthScope's USArray Transportable Array has shortcomings for the purpose of interpreting geologic features of wavelengths less than the Transportable Array station spacing, but these can be overcome by using higher spatial resolution gravity data. In this study, we exploit USArray receiver functions to reduce nonuniqueness in the interpretation of gravity anomalies. We model gravity anomalies from previously derived density variations of sedimentary basins, crustal Vp/Vs variation, Moho variation, and upper mantle density variation derived from body wave imaging informed by surface wave tomography to estimate Vp/Vs. Although average densities and density contrasts for these seismic variations can be derived, the gravity anomalies modeled from them do not explain the entire observed gravity anomaly field in the United States. We use the unmodeled gravity anomalies (residuals) to reconstruct local variations in densities of the crust associated with geologic sources. The approach uses velocity‐density relationships and differs from density computations that assume isostatic compensation. These intracrustal densities identify geologic sources not sampled by and, in some cases, aliased by the USArray station spacing. We show an example of this improvement in the vicinity of the Bloomfield Pluton, north of the bootheel of Missouri, in the central United States.

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Section: Discussionmentioning

confidence: 99%

“…These parameters are significantly different for the western United States as shown in Figure , where , Δρ Moho ,

\frac{dρ}{d κ_{c}}

and

\frac{dρ}{d κ_{m}}

Section: Estimation Of Density Parametersmentioning

confidence: 99%

Crustal Composition and Moho Variations of the Central and Eastern United States: Improving Resolution and Geologic Interpretation of EarthScope USArray Seismic Images Using Gravity

2020

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“…In the topmost portions of the Colorado Plateau's lower crust, our model can accommodate over 59 wt.% SiO

_{2}

(Table ). However, such intermediate‐felsic material cannot reach high enough velocities to match the seismic signal deeper in the crust, where temperatures increase above 700 °C (Schutt et al, ). Furthermore, our set of granulites can explain the seismic signal at the base of the crust more often than at the top, whereas we might expect equal probabilities at all depths if the lower crust were compositionally uniform (shown by the colors of Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…Temperature inputs at the top and base of the crust allowed us to calculate a geothermal gradient and therefore a temperature for each kilometer within the crust. We assumed that the top of the crust resides at 5

\pm 5

°C and temperature at the Moho follows Schutt et al ().…”

Section: Methodsmentioning

confidence: 99%

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Lower Crustal Composition in the Southwestern United States

2020

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The composition of the lower continental crust is well studied but poorly understood because of the difficulty of sampling large portions of it. Petrological and geochemical analyses of this deepest portion of the continental crust are limited to the study of high‐grade metamorphic lithologies, such as granulite. In situ lower crustal studies require geophysical experiments to determine regional‐scale phenomena. Since geophysical properties, such as shear wave velocity (Vs), are nonunique among different compositions and temperatures, the most informative lower crustal models combine both geochemical and geophysical knowledge. We explored a combined modeling technique by analyzing the Basin and Range and Colorado Plateau of the United States, a region for which plentiful geochemical and geophysical data are available. By comparing seismic velocity predictions based on composition and thermodynamic principles to ambient noise inversions, we identified three compositional trends in the southwestern United States that reflect three different geologic settings. The Colorado Plateau (thick crust), Northern Basin and Range (medium crust), and Southern Basin and Range (thin crust) have intermediate, intermediate‐mafic, and mafic deep crustal compositions. Identifying the composition of the lower crust depends heavily on its temperature because of the effect it has on rock mineralogy and physical properties. In this region, we see evidence for a lower crust that overall is intermediate‐mafic in composition (53.7 ± 7.2 wt.% SiO2) and notably displays a gradient of decreasing SiO2 with depth.

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USArray Imaging of Continental Crust in the Conterminous United States

Lowry

2017

Tectonics

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The thickness and bulk composition of continental crust provide important constraints on the evolution and dynamics of continents. Crustal mineralogy and thickness both may influence gravity anomalies, topographic elevation, and lithospheric strength, but prior to the inception of EarthScope's USArray, seismic measurements of crustal thickness and properties useful for inferring lithology are sparse. Here we improve upon a previously published methodology for joint inversion of Bouguer gravity anomalies and seismic receiver functions by using parameter space stacking of cross correlations of modeled synthetic and observed receiver functions instead of standard H‐κ amplitude stacking. The new method is applied to estimation of thickness and bulk seismic velocity ratio, vP/vS, of continental crust in the conterminous United States using USArray and other broadband network data. Crustal thickness variations are reasonably consistent with those found in other studies and show interesting relationships to the history of North American continental formation. Seismic velocity ratios derived in this study are more robust than in other analyses and hint at large‐scale variations in composition of continental crust. To interpret the results, we model the pressure‐/temperature‐dependent thermodynamics of mineral formation for various crustal chemistries, with and without volatile constituents. Our results suggest that hydration lowers bulk crustal vP/vS and density and releases heat in the shallow crust but absorbs heat in the lowermost crust (where plagioclase breaks down to pyroxene and garnet resulting in higher seismic velocity). Hence, vP/vS variations may provide a useful proxy for hydration state in the crust.

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Moho temperature and mobility of lower crust in the western United States

Cited by 70 publications

References 35 publications

Crustal Composition and Moho Variations of the Central and Eastern United States: Improving Resolution and Geologic Interpretation of EarthScope USArray Seismic Images Using Gravity

Crustal Composition and Moho Variations of the Central and Eastern United States: Improving Resolution and Geologic Interpretation of EarthScope USArray Seismic Images Using Gravity

Lower Crustal Composition in the Southwestern United States

USArray Imaging of Continental Crust in the Conterminous United States

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