13 research outputs found
Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa
Observation of Earth's free oscillation by dense GPS array: After the 2011 Tohoku megathrust earthquake
Wavelet filter analysis of splitting and coupling of seismic normal modes below 1.5 mHz with superconducting gravimeter records after the December 26, 2004 Sumatra earthquake
Comparison of the performances of different spring and superconducting gravimeters and STS-2 seismometer at the Gravimetric Observatory of Strasbourg, France
Composition, temperature, and thickness of the lithosphere of the Archean Kaapvaal craton
Integrated geophysical-petrological modeling of the lithosphere and sublithospheric upper mantle: Methodology and applications
A combined geophysical-petrological methodology to study the thermal, compositional, density, and
seismological structure of lithospheric/sublithospheric domains is presented. A new finite-element code
(LitMod) is used to produce 2-D forward models from the surface to the 410-km discontinuity. The code
combines data from petrology, mineral physics, and geophysical observables within a self-consistent
framework. The final result is a lithospheric/sublithospheric model that simultaneously fits all geophysical
observables and consequently reduces the uncertainties associated with the modeling of these observables
alone or in pairs, as is commonly done. The method is illustrated by applying it to both oceanic and
continental domains. We show that anelastic attenuation and uncertainties in seismic data make it
unfeasible to identify compositional variations in the lithospheric mantle from seismic studies only. In the
case of oceanic lithosphere, plates with thermal thicknesses of 105 ± 5 km satisfy geophysical and
petrological constraints. We find that Vp are more sensitive to phase transitions than Vs, particularly in the
case of the spinel-garnet transition. A low-velocity zone with absolute velocities and gradients comparable
to those observed below ocean basins is an invariable output of our oceanic models, even when no melt
effects are included. In the case of the Archean subcontinental lithospheric mantle, we show that ‘‘typical’’
depleted compositions (and their spatial distribution) previously thought to be representative of these
mantle sections are compatible neither with geophysical nor with petrological data. A cratonic keel model
consisting of (1) strongly depleted material (i.e., dunitic/harzburgitic) in the first 100–160 km depth and
(2) less depleted (approximately isopycnic) lower section extending down to 220–300 km depth is
necessary to satisfy elevation, geoid, SHF, seismic velocities, and petrological constraints. This highly
depleted (viscous) upper layer, and its chemical isolation, may play a key role in the longevity and stability
of cratons.This work
was supported by the Spanish research projects 01-LECEMA22F-
EUROMARGINS-ESF, CTM2005-08071-C03-03/
MAR, and Consolider TopoIberia CSD2006-00041 (J.C.A.
and M.F.), NSERC (Natural Sciences and Engineering Research
Council of Canada) grants (G.R.), and ARC and Macquarie
University grants (W.L.G.).Peer reviewe