Mapping the Earth's thermochemical and anisotropic structure using global surface wave data

TY - JOUR

T1 - Mapping the Earth's thermochemical and anisotropic structure using global surface wave data

AU - Khan, Amir

AU - Boschi, L.

AU - Connolly, J.A.D.

PY - 2011/1/1

Y1 - 2011/1/1

N2 - We have inverted global fundamental mode and higher-order Love and Rayleigh wave dispersion data jointly, to find global maps of temperature, composition, and radial seismic anisotropy of the Earth's mantle as well as their uncertainties via a stochastic sampling-based approach. We apply a self-consistent thermodynamic method to systematically compute phase equilibria and physical properties (P and S wave velocity, density) that depend only on composition (in the Na2-CaO-FeO-MgO-Al2O 3-SiO2 model system), pressure, and temperature. Our 3-D maps are defined horizontally by 27 different tectonic regions and vertically by a number of layers. We find thermochemical differences between oceans and continents to extend down to ∼250 km depth, with continents and cratons appearing chemically depleted (high magnesium number (Mg #) and Mg/Si ratio) and colder (>100C) relative to oceans, while young oceanic lithosphere is hotter than its intermediate age and old counterparts. We find what appears to be strong radial S wave anisotropy in the upper mantle down to ∼200 km, while there seems to be little evidence for shear anisotropy at greater depths. At and beneath the transition zone, 3-D heterogeneity is likely uncorrelated with surface tectonics; as a result, our tectonics-based parameterization is tenuous. Despite this weakness, constraints on the gross average thermochemical and anisotropic structure to ∼1300 km depth can be inferred, which appear to indicate that the compositions of the upper (low Mg# and high Mg/Si ratio) and lower mantle (high Mg# and low Mg/Si ratio) might possibly be distinct.

AB - We have inverted global fundamental mode and higher-order Love and Rayleigh wave dispersion data jointly, to find global maps of temperature, composition, and radial seismic anisotropy of the Earth's mantle as well as their uncertainties via a stochastic sampling-based approach. We apply a self-consistent thermodynamic method to systematically compute phase equilibria and physical properties (P and S wave velocity, density) that depend only on composition (in the Na2-CaO-FeO-MgO-Al2O 3-SiO2 model system), pressure, and temperature. Our 3-D maps are defined horizontally by 27 different tectonic regions and vertically by a number of layers. We find thermochemical differences between oceans and continents to extend down to ∼250 km depth, with continents and cratons appearing chemically depleted (high magnesium number (Mg #) and Mg/Si ratio) and colder (>100C) relative to oceans, while young oceanic lithosphere is hotter than its intermediate age and old counterparts. We find what appears to be strong radial S wave anisotropy in the upper mantle down to ∼200 km, while there seems to be little evidence for shear anisotropy at greater depths. At and beneath the transition zone, 3-D heterogeneity is likely uncorrelated with surface tectonics; as a result, our tectonics-based parameterization is tenuous. Despite this weakness, constraints on the gross average thermochemical and anisotropic structure to ∼1300 km depth can be inferred, which appear to indicate that the compositions of the upper (low Mg# and high Mg/Si ratio) and lower mantle (high Mg# and low Mg/Si ratio) might possibly be distinct.

U2 - 10.1029/2010JB007828

DO - 10.1029/2010JB007828

M3 - Journal article

SN - 0148-0227

VL - 116

SP - B01301

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

ER -