The long‐wavelength admittance and effective elastic thickness of the Canadian Shield

Kirby, Jonathan; Swain, Christopher J.

doi:10.1002/2013jb010578

Cited by 18 publications

(10 citation statements)

References 51 publications

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“…These deviations from the overall stress pattern can be possibly explained by post-glacial isostatic rebound (Adams and Basham, 1989;Adams and Bell, 1991). However, elastic thickness in the centre of the Canadian Shield is 80 km (Kirby and Swain, 2014), but the inner part of the Canadian Shield has V S velocities constantly lower than in the outer rim (Kao et al, 2013). Perhaps these structures explain even better that several of the S Hmax data are oriented towards the centre of the Canadian Shield, even for northward oriented data in the south of the Hudson Bay.…”

Section: Qualitymentioning

confidence: 97%

A revised crustal stress orientation database for Canada

et al. 2014

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Section: Qualitymentioning

confidence: 97%

A revised crustal stress orientation database for Canada

et al. 2014

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“…We further notice that in both NA07 and SL2013sv T e estimates vary sharply at the boundaries of the cratons due to the corresponding abrupt change of the thickness of the MSML layer (Figures a and b). Such a feature has been also observed in previous studies based on a rheological approach [ Hyndman et al ., ; Hardebol et al ., ] and on the free‐air gravity/topography (i.e., admittance), calculated using wavelet transforms [ Kirby and Swain , ]. In contrast, the studies based on other methods [ Wang and Mareschal , ; Flück et al ., ; Kirby and Swain , ; Audet and Mareschal , 2004; Audet and Bürgmann , ; Mouthereau et al ., ] show a much smoother transition in the peripheral parts of the cratons (Proterozoic regions), which are generally characterized by larger and lower values of T e (∼50 km) in comparison with those predicted by the NA07 and SL2013sv model, respectively.…”

Section: Effective Elastic Thickness Of the Na Lithospherementioning

confidence: 99%

“…T e has traditionally been inferred from the response of the lithosphere to tectonic stresses and vertical loads, e.g., through cross‐spectral analyses of the gravity field and topography [e.g., Bechtel et al ., ; Pilkington , ; Wang and Mareschal , ; Armstrong and Watts , ; Flück et al ., ; Kirby and Swain , ; Audet and Mareschal , , 2007; Poudjom Djomani et al ., ; Audet and Bürgmann , ; Kirby and Swain , ]. This method employs measures of the relationship between the observed gravity and topography in the spectral domain, namely the admittance and coherence.…”

Section: Introductionmentioning

confidence: 99%

“…In both models, intraplate earthquakes occur in weak lithosphere ($0.5 3 10 13 Pa s, T e $ 15 km) or near the edges of strong cratonic blocks, characterized by pronounced contrasts of strength and T e . and Mareschal, 2004aand Mareschal, ,b, 2007Poudjom Djomani et al, 2005;Audet and B€ urgmann, 2011;Kirby and Swain, 2014]. This method employs measures of the relationship between the observed gravity and topography in the spectral domain, namely the admittance and coherence.…”

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confidence: 99%

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Variations of the lithospheric strength and elastic thickness in North America

Tesauro

Kaban

Mooney

2015

Geochem Geophys Geosyst

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We evaluate the effect of temperature variations on strength and effective elastic thickness (T e ) of the lithosphere of the North American (NA) continent. To this purpose, we use two thermal models that are corrected for compositional variations and anelasticity effects in the upper mantle. These thermal models are obtained from a joint inversion of gravity data and two recent seismic tomography models (NA07 and SL2013sv). The crustal rheology was defined using NACr14, the most recent NA crustal model. This model specifies seismic velocities and thickness for a three-layer model of the crystalline crust. Strength in the lithosphere and in the crust has similar distributions, indicating that local geotherms play a dominant role in determining strength rather than crustal composition. A pronounced contrast is present in strength between cratonic and off-cratonic regions. Lithospheric strength in the off-cratonic regions is prevalently localized within the crust and T e shows low values (<20 km), while the inner part of the cratons is characterized by a strong lithosphere with large T e (>150 km). In contrast to previous results, our models indicate that Phanerozoic regions located close to the edge of the cratons, as the Appalachians, are characterized by low strength. We also find that locally weak zones exist within the cratons (e.g., beneath the intracratonic Illinois Basin and Midcontinent rift). Seismic tomography models NA07 and SL2013sv differ mainly in some peripheral parts of the cratons, as the Proterozoic Canadian Platform, the Grenville, and the western part of the Yavapai-Mazatzal province, where the integrated strength for the model NA07 is 10 times larger than in model SL2013sv due to a temperature difference (>2008C) in the uppermost mantle. The differences in T e between the two models are less pronounced. In both models, Proterozoic regions reactivated by MesoCenozoic tectonics (e.g., Rocky Mountains and the Mississippi Embayment) are characterized by a weak lithosphere due to the absence of the mechanically strong part of the mantle lithospheric layer. Intraplate earthquakes are distributed along the edges of the cratons, demonstrating that tectonic stress accumulates there, while the cores of the cratons remain undeformed. In both models, intraplate earthquakes occur in weak lithosphere ($0.5 3 10 13 Pa s, T e $ 15 km) or near the edges of strong cratonic blocks, characterized by pronounced contrasts of strength and T e .

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“…Here we use a 2‐D wavelet transform, where wavelets at different azimuths and scales are convolved with the entire magnetic anomaly grid, avoiding the segmentation of the signal into finite‐size windows. The wavelet transform offers a better compromise between spatial and wavenumber resolution than moving windows since the wavelet transform uses a combination of multiple wavelet scales to construct a power spectrum at each grid point (e.g., Audet et al, ; Kirby & Swain, ; Pérez‐Gussinyé et al, ; Swain & Kirby, ).…”

Section: Introduction and Tectonic Settingmentioning

confidence: 99%

Mapping Curie Depth Across Western Canada From a Wavelet Analysis of Magnetic Anomaly Data

2019

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In western Canada, geophysical studies infer an abrupt change in crustal temperatures between the Canadian Cordillera and the adjacent North American craton, with important implications for the tectonics and geodynamics of the area. We use a wavelet analysis of magnetic anomaly data in western Canada to map the depth to the bottom of the magnetic source, or Curie depth. This depth corresponds to the point at which crustal rocks reach their Curie temperature, thus providing an estimate of geothermal gradient. Our model is defined by a fractal distribution of magnetization characterized by the parameter β, as well as the depths to the top (z t ) and bottom (z b ) of the magnetized layer. Synthetic tests reveal the increased accuracy of the estimated z b when values for z t and β are fixed prior to the inversion. We set z t to the thickness of sedimentary rocks overlying the magnetic bedrock and use various values of β to estimate z b . We determine β a posteriori by comparing Monte Carlo simulations of predicted heat flow values (assuming a Curie temperature of 580°C) with observed heat flow in various regions. Our results suggest a β value of 2.5 for the Canadian Cordillera and Slave craton, and 2 for the remaining North American craton. The Curie depths resolve geological domains and important structural features, with estimates for z b averaging 15 ± 1 km in the Cordillera, 32 ± 3 km in the Slave craton, and 34 ± 3 km in the North American craton to the south.Plain Language Summary Despite a relatively high elevation, geophysical imaging of the Earth beneath Canada's western mountains reveals a distinct 150 km thinning of the tectonic plates. The plates define the rigid outer shell of the Earth, and the thickness change is coincident with a topographic difference (higher) at the surface and a temperature difference (hotter) at depth. The relationship between the high topography with the thinner tectonic plate and hotter material at depth is not well understood. The objective of this research is to estimate temperatures of the Earth's crust below the surface in western Canada using the magnetic properties of rocks. At a certain temperature, rocks lose their magnetization and therefore do not produce magnetic anomalies. By analyzing magnetic anomaly data, we can infer the depth at which this temperature is achieved, which provides estimates of the thermal gradient in the crust. Combining these estimates with heat flow measurements provides more accurate constraints on the physical properties of the tectonic plate and will allow different tectonic models to be evaluated, allowing for a better understanding of the mechanical behavior of the Canadian Cordillera.

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The long‐wavelength admittance and effective elastic thickness of the Canadian Shield

Cited by 18 publications

References 51 publications

A revised crustal stress orientation database for Canada

A revised crustal stress orientation database for Canada

Variations of the lithospheric strength and elastic thickness in North America

Mapping Curie Depth Across Western Canada From a Wavelet Analysis of Magnetic Anomaly Data

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