Supervisors info:
Δημήτριος Κωστόπουλος, Αναπληρωτής Καθηγητής, Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
Amphibole is a secondary phase commonly found in ultramafic lithologies (mantle xenoliths, Alpine-type and ophiolitic peridotites) occurring in diverse environments such as magmatic arcs, plate interiors, transform faults, rifts and collision zones. Its formation has mainly been attributed to fluid-melt/rock interaction or direct crystallisation from melts/fluids. For the purpose of the present thesis, an extensive bibliographical database has been compiled. It involves major-element compositional data of amphibole in ultramafic rocks from various geotectonic settings around the globe. Additionally, amphiboles related to a wide spectrum of melts spanning from felsic to mafic in composition, both natural (rock samples) and synthetic (laboratory experiments) have also been considered. Type-I amphiboles (enriched in Na and Ti but depleted in Cr) are the products of direct crystallisation from basaltic, basanitic, andesitic and dacitic melts and are mostly found in continental arcs (e.g. Kamchatka, Russia), within-plate settings (e.g. West Eifel, Germany) and oceanic transform faults (e.g. 15°20´N Fracture Zone, Mid-Atlantic Ridge). Type-II amphiboles are Cr-rich, contain variable amounts of Ti and alkalis, and form via reaction between the aforementioned melts and primary mantle phases (mostly clinopyroxene and spinel). They are usually found in within-plate magmatic centers (e.g. Massif Central, France) and several localities in continental arcs (e.g. Ichino-megata, Japan). Amphiboles belonging to type-III reflect hydrous fluid/melt-rock interactions above subduction zones. Type-III amphiboles are predominantly encountered in oceanic arcs (e.g. TUBAF seamount, PNG) and ophiolites (Lycian ophiolite, Turkey) but occasionally they also occur in continental-arc settings. We have furthermore calibrated a new Fe Mg exchange thermometer between amphibole and clinopyroxene based on existing experimental data on ultramafic compositions with an error of ±46°C in the pressure range 0.5–3.7 GPa. Peridotite xenoliths that display good evidence of textural and chemical equilibration among their constituent minerals (e.g. West Eifel, Germany; Eastern Transylvanian Basin, Romania) yield amphibole temperatures comparable to those predicted from two-pyroxene Fe Mg exchange thermometry.
Keywords:
amphibole, clinopyroxene, mantle, equilibrium, thermometer
