[1] Volcanic activity focuses along plate boundaries. However, large volcanoes are also found in intraplate settings. For these volcanoes, geodynamic processes responsible for magma generation and structural controls on magma rise and extrusion need to be evaluated. We merge original (field and remote sensing) and available (geodetic, geophysical, and petrological) data to consider the tectono-magmatic relationships of three large intraplate volcanoes in the E-Anatolian-Iranian plateau; Sar'akhor (NE Iran), Damavand (Central Alborz) and Ararat (E Anatolia). In NE Iran, a Miocene-Pliocene NW-trending compression activated E-W dextral faults to the NW of Sar'akhor and N-S sinistral faults to the SE, creating an extruding wedge to the west of this volcano. Since Quaternary, NE-trending compression inverted fault movement, hindering further block extrusion and volcanism terminated. The adakitic composition of the Sar'akhor rocks suggests post-collisional melting of oceanic slab and/or mafic lower crust, possibly triggered by an asthenospheric rise after slab break-off or intramantle delamination. For the active Damavand and Ararat volcanoes, available data suggest magma generation due to rising hot asthenosphere, following lithospheric delamination or slab break-off in a transtensional environment. The features common to Sar'akhor, Damavand and Ararat allow proposing a model, where transtension focuses the rise of magma in intraplate settings overlying hot asthenosphere produced by delamination or slab break-off.

The mafic-ultramafic complex of Sikhoran presents a long geological history, marked out by various magmatic, metamorphic and tectonic events. This history is much more complex than a simple ophiolite obduction over a continental margin. As early as the Upper Permian, following a mantle uprise in a Tethysian supra-subduction zone, the opening of a (back-arc?) basin in extensional/transtensional conditions provoked the intrusion of multiple gabbroic dykes, veins and plutons charged with fluids, through a mafic/ultramafic complex and its metamorphic cover. Several basins, characterised by abundant submarine basaltic volcanism developed during Jurassic, whose feeding dykes may be represented by the diabase dyke swarms intruding the whole Sikhoran complex and its metamorphic cover. To cite this article: H. Ghasemi et al., C. R. Geoscience 334 (2002) 431-438.  2002 Académie des sciences / Éditions scientifiques et médicales Elsevier SAS Central Iran / ophiolites / 40 K-40 Ar ages / Triassic-Jurassic-Cretaceous Résumé -Le massif basique-ultrabasique de Sikhoran (Iran central) : un complexe ophiolitique polygénétique. Nous présentons de nouvelles données cartographiques, pétrographiques et géochronologiques ( 40 K-40 Ar), qui montrent que le complexe basique-ultrabasique de Sikhoran, en Iran central, (1) représente un ancien fragment de lithosphère océanique (ophiolite), d'âge Paléozoïque, et ( 2) présente une longue histoire géologique, jalonnée par de multiples événements magmatiques, métamorphiques et tectoniques. Cette histoire va bien au-delà de la simple obduction d'un complexe ophiolitique sur une marge continentale. Dès le Permien supérieur, à la suite d'une remontée de manteau en arrière d'une zone de subduction téthysienne, l'ouverture d'un bassin (arrière-arc ?) en extension/décrochement a provoqué l'intrusion de multiples filons et plutons de magma basique chargé de fluides, à travers un complexe basique-ultrabasique et sa couverture métamorphique. Plusieurs bassins à volcanisme sous-marin abondant se sont développés au Jurassique, dont les dykes d'alimentation sont probablement représentés par les essaims de dykes de diabase recoupant tout le massif de Sikhoran et sa couverture métamorphique.

Soltan Maidan Basaltic Complex with thickness up to about 1300 m is located in the eastern Alborz zone, north of Iran. This complex is dominantly composed of transitional to mildly alkaline basaltic lava flows, agglomerates and tuffs, together with a few thin sedimentary interlayers. Field geological evidence and study of palynomorph assemblages in the shale interlayer show Late Ordovician to Early Late Silurian ages. Chondrite-and primitive-mantle normalized multi-element patterns of Soltan Maidan basalts demonstrate enrichment in highly incompatible elements relative to less incompatible ones and their patterns are most similar to

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Abstract. Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclasemelt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ∼ 350 (130 to 468) MPa, while amphiboles record both low pressures (∼ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.