Cristallisation fractionnée et contamination crustale dans la série magmatique jurassique transitionnelle du Haut Atlas central (Maroc)Fractional crystallisation and crustal contamination in the transitional Jurassic magmatic series of Central High Atlas (Morocco)

The Middle Jurassic plutonism of the Central High Atlas (Morocco) was emplaced in N45° trending anticlinal ridges. It is characterised by various petrographic facies including mafic rocks (troctolites), intermediate rocks (diorites, monzodiorites), and evolved rocks (syenites), together with heterogeneous facies resulting from mixing between acidic and the intermediate magmas. Mineralogical and chemical data show (i) the transitional character of the Jurassic magmatic series of the Central High Atlas and (ii) the implication of continental crust as a contaminant during fractional crystallization. To cite this article: R. Zayane et al., C. R. Geoscience 334 (2002) 97–104.     

Métabasites de la cordillère occidentale d'Équateur,témoins du soubassement océanique des Andes d'Équateur

The building-up of the Andean Range is linked to the subduction of the Pacific lithosphere beneath the South American plate. However, the formation of the Central Andes is marked by continental crustal shortening, whereas accretion and underplating of exotic oceanic terranes occurred in the northern Andes. The study of various magmatic and metamorphic rocks exhumed in the Western Cordillera of Ecuador by Miocene transpressive faults enables us to constrain the nature and thermal evolution of the crustal root of this part of Ecuador. These rocks are geochemically similar to oceanic plateau basalts. The thermobarometric peak conditions of a granulite and an amphibolite indicate temperatures of 800–850?°C and pressures less than 6–9 kbar (lack of garnet). The abnormally high geothermal gradient (≈40?°C?km^?1) is probably due to the activity of the magmatic arc, which developed on the accreted oceanic terranes after Late Eocene times, and may have provoked the re-mobilisation of deeply underplated oceanic material during the genesis of the Neogene to Recent arc. To cite this article: É. Beaudon et al., C. R. Geoscience 337 (2005).     

Geochemical characteristics of an intracontinental shoshonitic association: the example of the Damavand volcano,IranCaractéristiques géochimiques d'une association shoshonitique intracontinentale : exemple du Damavand,Iran

Lavas of the Quaternary Damavand volcano (Central Alborz, Northern Iran) have been analysed for major and trace elements. The shoshonitic character of this magmatic series is definitively confirmed and most samples correspond to banakites. The Nb, Ta and Ti negative anomalies observed in all lavas suggest that they derive from of a sub-continental lithosphere metasomatised in a subduction setting. Their variable trace element enrichments are explained both by mineral fractionation and by crustal contamination in a shallow magmatic chamber. To cite this article: H. Mehdizadeh et al., C. R. Geoscience 334 (2002) 111–117.