Current Topics in Geosciences: PD Dr. Susanne Theodora Schmidt, Petrology and Volcanology, University of Geneva
Dating low-temperature/hydrothermal alteration of sedimentary and basaltic rocks using the K/Ar method is not a straightforward task. In basaltic rocks, the rare low-temperature K-mineral celadonite can be dated. Its age is considered to reflect the crystallization of the mineral phase and therefore the age of a low-temperature metamorphic event. In metapelites and quartzites the K-bearing micas muscovite/illite are common constituents and occur as detrital and authigenic phases reflecting different growth events. The careful characterization of different grain size fractions (2-6 mm, <2 mm and <0.2 mm) using traditional imaging methods, the determination of the illlite crystallinity (Kübler Index), the determination of illite polytypes, the determination of the maturation of organic matter and the dating of the three illite size fractions by K/Ar allow to reconstruct the geological and thermal history. This seminar will show that the various illite growth events can be dated and are related to early thrusting, diagenesis and burial, thrust driven exhumation as well as contact metamorphic events in the Patagonian fold-and-thrust-belt. The synthesis of these low-grade metamorphic events allows for a better understanding of fold-and-thrust-belt formation in the Chilean Patagonian Andes.