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Complex cratonic seismic structure from thermal models of the lithosphere: effects of variations in deep radiogenic heating
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2010 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 180, no 3, 999-1012 p.Article in journal (Refereed) Published
Abstract [en]

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 V(S) and V(P). 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 degrees 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 V(S) and up to 2.5-4 per cent in V(P), 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.

Place, publisher, year, edition, pages
2010. Vol. 180, no 3, 999-1012 p.
Keyword [en]
Composition of the mantle, Seismic tomography, Cratons, Heat generation and transport
National Category
Research subject
Geophysics with specialization in Solid Earth Physics
URN: urn:nbn:se:uu:diva-162531DOI: 10.1111/j.1365-246X.2009.04478.xOAI: oai:DiVA.org:uu-162531DiVA: diva2:460659
Available from: 2011-11-30 Created: 2011-11-30 Last updated: 2011-12-07Bibliographically approved

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