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Luigi Beccaluva, University of Ferrara (Italy)
Gianluca Bianchini, University of Ferrara (Italy)
Ali Charroud, Abdelmalek Essaâdi University of Tétouan (Morocco)
Nachite Driss, Abdelmalek Essaâdi University of Tétouan (Morocco)
Mohamed Ouazzani Touhami, Abdelmalek Essaâdi University of Tétouan (Morocco)
Alessandro Santato, University of Ferrara (Italy)
Franca Siena, University of Ferrara (Italy)
Ottavia Zeda, University of Parma (Italy)
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Mantle xenoliths from Pliocene-Quaternary volcanic diatremes in the Azrou-Timhadite area (Mid Atlas, Morocco) include spinel lherzolite xenoliths characterized by protogranular to porphyroclastic textures with superimposed metasomatic textures involving clinopyroxene, ortopyroxene and spinel as the main reacting phases.
Primary olivine consists of large kink-banded crystals (up to 1 mm) with Fo ranging between 88.7 and 91.8. br>
Orthopyroxene composition varies with the following ranges: Wo 0.7 - 1.9, En 88.2 - 90,0, Fs 9.2 - 10.7, and Cr/# [Cr/(Cr+Al)] 0.02 - 0.08. Clinopyroxene shows wide compositional variations in relation to textural position: Wo 41.5 - 49.0, En 45.6 - 53.4, Fs 4.4 - 8.7, Cr# 0.03 - 0.2, Na2O wt% 0.61 - 1.67 and TiO2 wt% 0.05 - 0.72.
Spinel is generally characterized by brown cores (Mg# 0.77 - 0.80 and Cr# 0.08 - 0.11), and secondary black rims (Mg# 0.72 - 0.80 and Cr# 0.14 - 0.32). Similar compositional variations, related to primary spinel crystals progressively destabilized toward the rims have been generally attributed to metasomatic reactions.
Bulk rocks have flat heavy rare earth element (HREE) patterns (0.6-2.0 times chondrite) and are variably enriched in light REE (LREE; LaN/YbN between 1.1 and 15.6).
The constituent clinopyroxenes are characterized by flat HREE distributions (3-12 times chondrite) and variable LREE enrichment with LaN/YbN from 0,4 to 23.7, which generally conform to the bulk rock chemistry. Trace elements characteristics of the metasomatized clinopyroxenes suggest that the metasomatasing agents where highly alkaline carbonate-rich melts such as nephelinites/mellilities or, as extreme silico-carbonatites. Comparison with mantle xenoliths from the north African lithosphere reveals that the studied xenoliths bear close analogies with those of the Hoggar district (Beccaluva et al. 2007).
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