Supervisors info:
-Δρ. Δημήτριος Κωστόπουλος, Αναπληρωτής Καθηγητής, Εθνικόν και Καποδιστριακόν Πανεπιστήμιον Αθηνών
-Δρ. Παναγιώτη Πομώνης, Καθηγητής, Εθνικόν και Καποδιστριακόν Πανεπιστήμιον Αθηνών
-Δρ. Ευάγγελος Μουλάς, Επίκουρος Καθηγητής, Johannes Gutenberg-Universität Mainz
Summary:
Geothermometry is the extraction of temperature information from rocks via thermodynamics, using
equilibrium phases whose chemical composition/interaction is sensitive to temperature variations. Mineral
geothermometry is based on cation exchange between minerals and effectively reflects the closure temperature
to diffusion during cooling. Each geothermometer is designed for a specific purpose and has its own merits
(mineral-melt equilibria for magma thermometry, inter-mineral equilibria for magmatic crystallization
temperatures, metamorphic temperatures, subcontinental mantle geotherms, etc.). By combining
geothermometers with geobarometers, it is possible to decipher the P-T path a rock has followed, in order to
clarify the sequence of events that best describe its geological history.
The present thesis focuses on the Fe2+– Mg cation exchange between coexisting orthopyroxene–spinel and
olivine–spinel pairs with the aim to create robust geothermometers that can be applied primarily to mantle
peridotites but also to other rock types from different geotectonic environments (e.g., mafic/ultramafic
cumulates in layered intrusions and ophiolites, chromitites, granulites, etc.). Experimental petrology
measurements were culled from the existing literature resulting in a database consisting of 945 Opx–Spl and
930 Ol-Spl pairs. Experimental temperatures and pressures range from 700 to 1600°C and 0.001 to 80 kbar
respectively, covering a variety of chemical systems/starting compositions. Olivine was treated as a binary
symmetric solution comprising the endmembers Fo and Fa; orthopyroxene was treated as an octal symmetric
solution comprising the endmembers En, Fs, Wo, Hd, MgTs, FeTs, MgCrTs and FeCrTs while spinel was
treated as an octal symmetric solution comprising the endmembers and Spl, Hc, Chr, Mag, Mchr, Usp, Qnd and
Mfr. After mathematical manipulation through robust multilinear regression, new thermometric expressions
were derived for the Fe2+– Mg cation exchange among mantle minerals.
Keywords:
Mineralogy, Petrology, Thermodynamics, Geotectonic Settings, olivine, spinel, orthopyroxene, geothermometry
