Publication 138
Lithospheric structure in the Baikal-central Mongolia region from integrated geophysical-petrological inversion of
surface-wave data and topographic elevation
J. Fullea, S. Lebedev, M.R. Agius, A.G. Jones, and J.C. Afonso
Abstract
Recent advances in computational petrological modeling provide accurate methods for
computing seismic velocities and density within the lithospheric and sub-lithospheric
mantle, given the bulk composition, temperature, and pressure within them. Here, we
test an integrated geophysical-petrological inversion of phase-velocity curves of
Rayleigh and Love waves for fine-scale lithospheric structure. The main parameters of
the grid-search inversion are the lithospheric and crustal thicknesses, mantle
composition, and bulk density and seismic velocities within the crust. Conductive
lithospheric geotherms are computed using P-T-dependent thermal conductivity. Radial
anisotropy and seismic attenuation have a substantial effect on the results and are
modeled explicitly. Surface topography provides information on the integrated density
of the crust, poorly constrained by surface waves alone. Investigating parameter inter-dependencies,
we show that accurate surface-wave data and topography can constrain
robust lithospheric models. We apply the inversion to central Mongolia, south of the
Baikal Rift Zone, a key area of deformation in Asia with debated lithosphere
asthenosphere structure and rifting mechanism, and detect an 80-90 km thick
lithosphere with a dense, mafic lower crust and a relatively fertile mantle composition
(Mg# less than 90.2). Published measurements on crustal and mantle Miocene and Pleistocene
xenoliths are consistent with both the geotherms and the crustal and lithospheric mantle
composition derived from our inversion. Topography can be fully accounted for by
local isostasy, with no dynamic support required. The mantle structure constrained by
the inversion indicates no major thermal anomalies in the shallow sub-lithospheric
mantle, consistent with passive rifting in the Baikal Rift Zone.
Source
Geochemistry, Geophysics, Geosystems, , accepted, 15 June, 2012. [PDF preprint]
MTNet Home Page
Alan's Home Page
Alan G Jones / 15 June 2012 /
alan-at-cp.dias.ie