Moukadiri, A. and Pin, C. (1998) Major and rare earth element geochemistry of metasedimentary granulite xenoliths in Quaternary alkali basalts from the Middle Atlas (Morocco): Evidence for a partly restitic lower crust Geochimie (elements majeurs et terres rares) des granulites meta-sedimentaires en xenolithes dans les basaltes alcalins quaternaires du Moyen Atlas (Maroc): Arguments en faveur de la nature pour partie restitique de la croute inferieure. Comptes Rendus de l'Academie de Sciences - Serie IIa: Sciences de la Terre et des Planetes, 327 (9). pp. 589-595.

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Abstract

High-alumina granulite xenoliths equilibrated under lower crustal conditions (850-900°C; 9±1 kbar) have been found in the Tafraout maars and analysed for major and rare earth elements. Starting from a protolith of pelitic composition, a strong decrease of SiO2 and alkalis and a concomitant increase of Al2O3, Fe2O3 and MgO are observed. These variations are interpreted to reflect partial melting and extraction of granitic magmas. Lanthanide elements show a progressive depletion of LREE combined with a marked increase of HREE. These variations result, in the most restitic samples, in V-shaped chondrite-normalized patterns. These peculiar patterns are interpreted in terms of incomplete separation between a garnet-sillimanite-rich refractory residue, highly depleted in LREE and enriched in HREE, and a small amount of trapped partial melt, containing most of the LREE. Negative Eu anomalies, inherited from the pelitic protolith, occur throughout. They are not erased, but rather enhanced, by partial melting and granitic magma removal. A simple modeling, based on K2O and La concentrations, allows us to propose that most of the xenoliths represent refractory residues derived from high degrees (about 65) of partial melting of evolved sources similar to average post-Archean shales. In the most restitic samples, the amount of partial melt left behind in the source can be estimated to be only a few percent.

Item Type: Article
Uncontrolled Keywords: geochemistry; granulite; metamorphic rock; xenolith, Morocco
Subjects: Agricultural and Biological Sciences
Divisions: SCIENTIFIC PRODUCTION > Agricultural and Biological Sciences
Depositing User: Administrateur Eprints Administrateur Eprints
Last Modified: 31 Jan 2020 15:44
URI: http://eprints.umi.ac.ma/id/eprint/1473

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