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Thermal nature and resolution of the lithosphere–asthenosphere boundary under the Pacific from surface waves
- Source :
- Geophysical Journal International, vol 216, iss 2, GEOPHYSICAL JOURNAL INTERNATIONAL, vol 216, iss 2
- Publication Year :
- 2018
- Publisher :
- Oxford University Press (OUP), 2018.
-
Abstract
- It is strongly debated whether the interface between the lithosphere and underlying asthenosphere is a temperature-dependent rheological transition, as expected in a thermal convection system, or additionally affected by the presence of melts and/or fluids. Previous surface wave studies of Pacific oceanic lithosphere have found that shear velocity and azimuthal anisotropy vary with seafloor crustal age as expected for a thermal control; however radial anisotropy does not. Various thermomechanical models have been proposed to explain this disparate behaviour. Nonetheless, it is unclear how robust the surface wave constraints are, and this is what we test in this study. We apply a Bayesian model space search approach to three published Pacific surface wave dispersion data sets, two phase-velocity and one combined phase- and group-velocity set, and determine various proxies for the depth of the lithosphere–asthenosphere boundary (LAB) and their uncertainties based on the velocity and radial anisotropy model distributions obtained. In their overall character and pattern with age, the velocity models from different data sets are consistent with each other, although they differ in their values of LAB depths. Uncertainties are substantial (as much as 20 km on LAB depths) and the addition of group-velocity data does not reduce them. Radial anisotropy structures differ even in pattern and display no obvious age dependence. However, given the uncertainties, we cannot exclude that radial anisotropy, azimuthal anisotropy and velocity models actually reflect compatible, age-dependent, LAB depth estimates. The velocity LAB trends are most like those expected for half-space cooling, because velocity differences persist at old ages, below the depth of common plate cooling models. Any direct signature of sub-ridge melt would be too small-scale to be resolved by these data. However, the velocity-increasing effects of dehydration and depletion due to melting below the ridge could explain why LAB proxy depths tend to a minimum of ∼60 km below young ocean floor.
- Subjects :
- Geochemistry & Geophysics
Seismic anisotropy
010504 meteorology & atmospheric sciences
FREE OSCILLATIONS
Statistical seismology
0404 Geophysics
GUTENBERG DISCONTINUITY
010502 geochemistry & geophysics
MELT EXTRACTION
01 natural sciences
Physics::Geophysics
NONLINEAR CRUSTAL CORRECTIONS
Geochemistry and Petrology
Core–mantle boundary
Thermal
AZIMUTHAL SEISMIC ANISOTROPY
0909 Geomatic Engineering
14. Life underwater
Inverse theory
Tomography
FORM TOMOGRAPHY
0105 earth and related environmental sciences
Lithosphere-Asthenosphere boundary
GEOPHYSICAL INVERSION
Science & Technology
UPPER-MANTLE
Resolution (electron density)
Geology
Geophysics
NEIGHBORHOOD ALGORITHM
Geomatic Engineering
Probability distributions
0403 Geology
13. Climate action
Surface wave
Physical Sciences
STRUCTURE BENEATH
Surface waves and free oscillations
Subjects
Details
- Language :
- English
- Database :
- OpenAIRE
- Journal :
- Geophysical Journal International, vol 216, iss 2, GEOPHYSICAL JOURNAL INTERNATIONAL, vol 216, iss 2
- Accession number :
- edsair.doi.dedup.....dc52e12e535079d6654a024d36a8f0b1