Subcontinental lithospheric mantle

<h2 id="archaean-continental-lithospheric-mantle">Archaean continental lithospheric mantle</h2>
<p>Archaean lithospheric mantle is strongly depleted in fertile melt indicators such as CaO and Al2O3. This depletion in major-elements should then be consequence of the Archaean lithosphere's formation.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> <a href="/facts/Trace_element/fcIekKdo">Trace-elements</a> are abundant in Archaean lithosphere relative to <a href="/facts/Mid-ocean_ridge/wYdgdSW3">MORB</a> (which samples modern upper mantle) and have been sampled by Re-Os isotope dating of <a href="/facts/Peridotite/4NRPpWxw">peridotites</a> and <a href="/facts/Ophiolite/vX9Kg940">ophiolites</a>.
</p><p>The trace element composition of these xenoliths suggest mixing between the two different layers of subcontinental mantle. Particularly, the theory for the removal of Archaean continental lithospheric mantle below Archaean continental crust via <a href="/facts/Delamination_(geology)/TIvaDoXF">delamination</a> helps to explain mantle-peridotite <a href="/facts/Xenolith/nP1MlHvG">xenoliths</a> found in the extinct <a href="/facts/Sierra_Nevada_(U.S.)/tKcI8PeH">Sierra Nevada</a> arc.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> Though there is evidence for the preservation of the Archaean lithosphere, there is controversy over the preservation of the Archaean mantle, for which the Archaean lithosphere would have been derived.
</p><p>The formation of the Archaean CLM is enigmatic. One early theory that <a href="/facts/Komatiite/haEtqNaG">komatiite</a> melts formed the Archaean CLM<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> does not explain how komatiites, which form in hot and deep environments, creates a reservoir that is shallow and cool. Another model of Archaean CLM formation suggests that the CLM formed in a subduction environment in which new Archaean crust was created through slab melting.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> 
</p><p>If the primitive mantle is the starting composition for this CLM formation event, subducting slab would be composed of <a href="/facts/Tonalite-Trondhjemite-Granodiorite/8SE2FjNJ">TTG</a> crust, then the removal of basaltic melt and the enrichment of the mantle wedge with felsic melts could explain the formation of the depleted Archaean subcontinental lithosphere. For more information, see Archaean subduction.
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<h2 id="phanerozoic-continental-lithospheric-mantle">Phanerozoic continental lithospheric mantle</h2>
<p>The mechanism of arc <a href="/facts/Subduction/rkasNdTo">subduction</a> is well understood to be the location where new continental crust is formed and is presumably also the site of continental lithospheric mantle genesis. Firstly, hydrated oceanic crust slabs begin subducting which releases fluids (<a href="/facts/Subduction_zone_metamorphism/cvSSorwB">subduction zone metamorphism</a>) to the mantle wedge above. Continued subduction of the slab leads to further hydration of the mantle which causes partial melting in the mantle wedge. It is expected then that the modern continental lithospheric mantle is a former, melt-depleted mantle wedge. If the connection between continental crust and the continental lithospheric mantle does not exist, and rather a different Earth process formed both reservoirs, then it further complicates the mechanisms for how the Archaean subcontinental mantle formed.
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<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Pearson, D. G.; Nowell, G. M. (16 September 2002). Davies, J. H.; Brodholt, J. P.; Wood, B. J. (eds.). "The Continental Lithospheric Mantle: Characteristics and Significance as a mantle Reservoir". Philosophical Transactions of the Royal Society. 360 (1800). The Royal Society: 2383–410. Bibcode:2002RSPTA.360.2383P. doi:10.1098/rsta.2002.1074. ISSN 1364-503X. JSTOR 3558903. PMID 12460473. <a href="/wiki/Philosophical_Transactions_of_the_Royal_Society" target="_blank">/wiki/Philosophical_Transactions_of_the_Royal_Society</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Lee, Cin-Ty; Yin, Qingzhu; Rudnick, Roberta L.; Chesley, John T.; Jacobsen, Stein B. (15 September 2000). "Osmium isotopic evidence for Mesozoic removal of lithopsheric mantle beneath the Sierra Nevada, California". Science Magazine. 289 (5486). American Association for the Advancement of Science: 1912–1916. Bibcode:2000Sci...289.1912L. doi:10.1126/science.289.5486.1912. ISSN 1095-9203. JSTOR 3077682. PMID 10988067. <a href="/wiki/Science_Magazine" target="_blank">/wiki/Science_Magazine</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Parman, Stephen W.; Grove, Timothy L.; Dann, Jesse C.; de Wit, Maarten J. (2004). "A subduction origin for komatiites and cratonic lithospheric mantle". South African Journal of Geology. 107 (1–2). Geological Society of South Africa: 107–118. Bibcode:2004SAJG..107..107P. CiteSeerX 10.1.1.208.4938. doi:10.2113/107.1-2.107. <a href="/wiki/South_African_Journal_of_Geology" target="_blank">/wiki/South_African_Journal_of_Geology</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Rollinson, Hugh (December 2010). "Coupled evolution of Archean continental crust and subcontinental lithospheric mantle". GeoScienceWorld. 38 (12). Geological Society of America: 1083–1086. Bibcode:2010Geo....38.1083R. doi:10.1130/G31159.1. ISSN 1943-2682. <a href="/wiki/Geological_Society_of_America" target="_blank">/wiki/Geological_Society_of_America</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
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Subcontinental lithospheric mantle open-in-new

Subcontinental lithospheric mantle