PhD defence: Frederik E. Brandt

Frederik E. Brandt defends his thesis,

Mantle enrichment by volatiles as the Nazca plate subducts beneath the Payenia backarc of the Southern Volcanic Zone, Argentina
- A geochemical study of melt inclusions, minerals and tephra.

Supervisors:
Associate Professor Paul martin Holm, IGN
Senior Scientist Thor Hansteen, Geomar, Kiel - Germany

Assessment Committee:
Professor Valentin Troll, Uppsala University - Sweden
Lecturer Ralf Halama, Keele University - UK
Professor Tod Waight (chair), IGN

Summary:
The thesis is a contribution towards the understanding of the generation of the source mantle for magmas related to the subduction of the Nazca plate under South America with an emphasis on the geochemistry of the volatiles Cl, F, S, H2O and CO2. The study presents analytical data for tephra, minerals, fluid and melt inclusions from the Payenia backarc province of the Andean Southern Volcanic Zone. Major emphasis has been on olivine hosted melt inclusions. The study gives evidence for the role of fluids in the metasomatism of the backarc mantle, and outlines the trend of the variation of the metasomatism in Payenia, which is also characterized by a variation in oxidation state and other geochemical parameters of the melt inclusions, and is moreover related to mantle lithological variations. The mantle metasomatism by melts of subducted crust and fluid-borne enrichment is quantitatively modelled, the origin of Chlorine is explained via slab-derived fluids, and the contrast between backarc and frontal arc magmas is discussed. These results add to the understanding of the origin of the complexities in the mantle wedge under arc-backarc in a subduction zone which has transition to flat slab conditions to the north and has input of OIB type mantle to the south.

The thesis is available for inspection at the administration office, 04.1.417