Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010geoji.180..999h&link_type=abstract
Geophysical Journal International, Volume 180, Issue 8, pp. 999-1012.
Astronomy and Astrophysics
Astronomy
4
Composition Of The Mantle, Seismic Tomography, Cratons, Heat Generation And Transport
Scientific paper
Cratons are the long-term tectonically stable cores of the continents. Despite their thermal stability they display substantial seismic complexity with lateral and vertical lithospheric anomalies of up to several percent in both VS and VP. Although some of these anomalies have been correlated with compositional variations, others are too large to be explained with any common mantle lithosphere compositions ranging from fertile peridotites to highly melt-depleted dunites, under the assumption that thermal perturbations are negligible. To test whether temperature anomalies could contribute to seismic complexity, we performed a set of 2-D thermal calculations for a range of cratonic tectonic models and converted them into seismic structure, accounting for variations in phase and elastic and anelastic response to pressure and temperature. With the long thermal equilibration time in cratonic settings, even relatively mild variations in concentrations of radioactive elements can leave long-lasting lithospheric thermal anomalies of 100-300°C. Concentrations of radioactive elements decrease with increasing melt depletion (or decreasing metasomatic refertilization), resulting in lower temperatures and increased seismic velocities. This thermal seismic effect enhances the intrinsic velocity-increasing compositional seismic signature of melt depletion. The joint thermochemical effects can leave cratonic seismic anomalies of up to 3-4.5 per cent in VS and up to 2.5-4 per cent in VP, with gradients sometimes as sharp as a few kilometre in width. Thus the variations in major and minor element mantle lithosphere composition commonly seen in mantle samples can account for much of the variability in imaged seismic structure of cratonic lithosphere.
Goes Saskia
Hieronymus Christoph F.
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