Supervisors info:
Ιωάννης Μήτσης, Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Σχολή Θετικών Επιστημών, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
Sulfate minerals make up for a large part of the authigenic species that form in volcanic and fumarolic environments and such is the case for Soussaki area as well, where volcanic activity at the westernmost centre of the South Aegean arc is manifested by the existence of Pliocene rhyodacitic rocks and present-day fumarolic degassing, geothermal activity, circulation of hydrothermal fluids and consequent mineralization phenomena. Field work and sampling at Theiohoma site showed that Soussaki authigenic minerals form crusts and efflorescences both on the surface of the Plio-Pleistocene marlstones and ophiolites from which most samples were retrieved. The samples were analyzed by means of powder X-ray diffraction and SEM-EDS techniques. As shown in this study, sulfate minerals along with minor quantities of quartz, dolomite and clay minerals comprise the bulk composition of those aggregates and were further recognized as belonging to four main groups, namely Mg-, Ca-, Fe2+- and Fe2+, 3+/Al(of unidentified valence state)-rich, though the fourth was only microscopically visible and of unidentifiable characterization. The sulphate minerals detected are: Hexahydrite, epsomite, pentahydrite, starkeyite, melanterite, magnesiocopiapite, coquimbite, gypsum and anhydrite. The fact that all sulphates with the sole exception of anhydrite, are highly soluble indicates the influence of the atmospheric conditions to which the source material was exposed. The new findings of the present study include the metastable starkeyite and pentahydrite as pseudomorph mineral, that showcase the sensitivity of the Mg-group members to humidity and temperature changes, and the appearance of Fe3+coquimbite. The variety of cations in which the samples were enriched (Mg, Fe, Al, Mn, Cr and others) , the predominance of Mg+2 both in the number and variety of main mineral group members and as main substitute cation confirm that the altered ultramafic rocks of the area as well as some dolomitic marls observed at Theiohoma serve as the main source of chemical components, a fact that is established by previous studies. Furthermore, this study makes an attempt at interpreting aspects of microscopic analysis towards suggesting possible trends for the formation of observed mineral sequences, especially concerning the variety of hydrous Mg-rich combinations and the role of advancing oxidation in the creation of Fe-rich parageneses.
Keywords:
Sousaki, sulfate minerals, authigenesis, ultramafics, volcanic emanations
