The deep structure of North American lithosphere illuminated by complementary seismic data types
Abstract
The internal structure of continental lithosphere holds the key to our understanding of plate tectonic cycles and the long-term stability of cratons. Detailed imaging of the upper mantle has the potential to reveal chemical alteration, deformation fabric, thermal structure, and melt distribution, providing not only a contemporary snapshot but also an integrated history of the interactions between the Earth's surface and its deep interior. We apply a transdimensional, hierarchical Bayesian inversion parameterised using piecewise discontinuous splines to solve for 1-D radially anisotropic shear velocity models of crust and upper mantle beneath long-lived stations across North America. The advantages of a Bayesian approach include quantitative uncertainty estimation and the ability to modularly incorporate multiple data types; we use Rayleigh wave and Love wave phase velocities from earthquakes and ambient noise, Rayleigh wave ellipticity ratios, and both P-s and S-p converted phases. Taken jointly, this combination of data types provides excellent constraints on absolute velocities, crustal structure, and sharp gradients in velocity within or at the base of the lithosphere. We find that S-p phases are essential to capture accurately the characteristics of deep velocity gradients, such as those seen widely but discontinuously in the cratonic mid-lithosphere. Observed structures include shallow melt and adiabatic geotherms immediately beneath thin lithosphere in portions of the western US, as well as intra-lithospheric low-velocity zones beneath the cratons that have amplitude and depth consistent with new data on exotic lithologies associated with subduction-derived fluid reaction products.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMDI51B0027E
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRYDE: 8031 Rheology: crust and lithosphere;
- STRUCTURAL GEOLOGYDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8124 Earth's interior: composition and state;
- TECTONOPHYSICS