2010: Pristine slab melts crystallized at depth in the subduction environment: End-members of adakites (Eastern Cuba Mélanges)

Pristine slab melts crystallized at depth in the subduction environment: End-members of adakites (Eastern Cuba Mélanges)

Abstract

In the subduction zones, several conditions can be attached and instigate the melting of the slab or the overlying mantle wedge. Under normal subduction zones the geothermal conditions of the slab may not attain P–T conditions for melting at sub-arc depths, but dehydrates and release LILE-enriched hydrous fluids that metasomatize the overlying mantle wedge and instigate its melting (e.g. Tatsumi and Kogiso, 1997). Adakites are volcanic or intrusive igneous rocks interpreted to form in subduction zones from the mixing of mantle material with felsic partial melts of descending slabs of oceanic crust basalt. Distinctive geochemical features are SiO2>56 wt.%, high Na2O contents (4.5-9wt.%), (K2O/Na2O)≈0.42, Mg#≈50, LREE enrichment, HREE depletion, and high La/Yb and Sr/Y. Examples of pristine slab melts reaching the Earth's surface are scarce. In rare cases of subduction complexes, such as the Catalina Schist mélange (California), partial melting of metabasite and metasomatic mass-transfer processes in the slab have been described (Sorensen, 1988; Bebout and Barton, 1993). The melts produced in this mélange were considered as primary adakitic liquids (e.g., Martin, 1999) generated at intermediate pressures due to the onset of subduction. In the Sierra del Convento mélange (E Cuba) pristine primary slab melts generated under water-saturated partial melting conditions were recently described (García-Casco et al,. 2008; Lázaro & García-Casco, 2008). New rocks enriched in mobile elements (K, Ba, Rb…..) have been catalogued and studied in Eastern Cuba mélanges. These rocks resemble to the rocks considered pristine primary slab melts and their residues but present geochemical and petrological (presence of magmatic muscovite) differences that link them to adakites.

Keywords: Pristine Melts, slabs, adakites

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To Cite this article: Lázaro, C., Blanco-Quintero, I.F., García-Casco, A. (2010): Pristine slab melts crystallized at depth in the subduction environment: End-members of adakites (Eastern Cuba Mélanges).Macla, 13, 137-138. http://www.ehu.es/sem/macla_pdf/macla13/Macla13_137.pdf

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