The signature of subducted continental crust in rift-related continental basalts
Continental intraplate basalts in most regions on Earth are inseparably linked to extensional tectonic regimes, i.e. to continental rifting. Rifting and lithosphere stretching and thinning might be controlled by larger scale plate tectonic movements or may occur more locally in response to asthenospheric upwelling within mantle plumes. In any case, lithospheric thinning frequently results in decompression melting of the underlying mantle. Most models assume melting within the deeper asthenosphere due to overall higher temperatures than in the overlying lithospheric part of the mantle. Several studies have shown, however, that despite thermal considerations many intraplate basalts bear geochemical signatures that are inherited from the metasomatised subcontinental lithospheric mantle rather than from asthenospheric sources. This rises the question to what extent the subcontinental lithospheric mantle contributes to the formation of continental basalts, and what its composition is. Understanding metasomatism, i.e. material flow within the deeper lithosphere is thus crucial in understanding the origin of intraplate basalts, but the nature and origin of metasomatising components remains mostly enigmatic. Subduction of oceanic and continental crust is the most fundamental mechanism to achieve downward material flow within the lithosphere and asthenosphere. This presentation outlines the effects of subduction related metasomatism, and its consequences on partial melting and melt composition. Melting may occur directly to form island arcs or active continental margins, or millions of years after subduction has ceased in response to extensional thinning of metasomatised lithosphere and thus contribute to the formation of continental basalts.
https://www.munich-geocenter.org/events/seminars/frontiers-in-earth-sciences-22/frontiers-in-earth-sciences-2018-12-21
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The signature of subducted continental crust in rift-related continental basalts
Abstract
Continental intraplate basalts in most regions on Earth are inseparably linked to extensional tectonic regimes, i.e. to continental rifting. Rifting and lithosphere stretching and thinning might be controlled by larger scale plate tectonic movements or may occur more locally in response to asthenospheric upwelling within mantle plumes. In any case, lithospheric thinning frequently results in decompression melting of the underlying mantle. Most models assume melting within the deeper asthenosphere due to overall higher temperatures than in the overlying lithospheric part of the mantle. Several studies have shown, however, that despite thermal considerations many intraplate basalts bear geochemical signatures that are inherited from the metasomatised subcontinental lithospheric mantle rather than from asthenospheric sources. This rises the question to what extent the subcontinental lithospheric mantle contributes to the formation of continental basalts, and what its composition is. Understanding metasomatism, i.e. material flow within the deeper lithosphere is thus crucial in understanding the origin of intraplate basalts, but the nature and origin of metasomatising components remains mostly enigmatic. Subduction of oceanic and continental crust is the most fundamental mechanism to achieve downward material flow within the lithosphere and asthenosphere. This presentation outlines the effects of subduction related metasomatism, and its consequences on partial melting and melt composition. Melting may occur directly to form island arcs or active continental margins, or millions of years after subduction has ceased in response to extensional thinning of metasomatised lithosphere and thus contribute to the formation of continental basalts.
