Geochronology and Multi-Isotope Geochemistry of Three Quaternary Volcanoes: Nisyros-Yali (Greece), Monte Vico and Monte Vulture (Italy)
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Geochronology and multi-isotope geochemistry of three Quaternary volcanoes: Nisyros-Yali (Greece), Monte Vico and Monte Vulture (Italy) Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Annett Büttner aus Deutschland Leiter der Arbeit: Prof. Dr. Igor M. Villa Institut für Geologie, Gruppe Isotopengeologie, Universität Bern Geochronology and multi-isotope geochemistry of three Quaternary volcanoes: Nisyros-Yali (Greece), Monte Vico and Monte Vulture (Italy) Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Annett Büttner aus Deutschland Leiter der Arbeit: Prof. Dr. Igor M. Villa Institut für Geologie, Gruppe Isotopengeologie, Universität Bern Von der Philosophisch-naturwissenschaftlichen Fakultät angenommen. Bern, den 2. November 2004 Der Dekan Prof. Dr. P. Messerli Acknowledgments I particularly want to thank you, Igor, for offering me the opportunity to think and work with you and for opening my eyes for critical scrutinising pretended facts. I really enjoyed these years! Thank you very much, Jan for many fruitful discussions and critical comments, which were always helpful and improved my work. I am grateful to Johannes C. Hunziker for initiating the work on Nisyros and for guiding through the field. Thanks to Thomas for many scientific and non-scientific discussions. Gerhard Brey from the University of Frankfurt, Germany, is grateful acknowledged, who honoured the position as Koreferent. Yann Lahaye, University of Frankfurt, is thanked for the analyses of trace element data. Edwin Gnos, Marco Herwegh and Karl Ramseyer supported the petrological part of this work. I am grateful to Borgi, the good fairy of the laboratory. Jürg Megert, Vreni Jakob, thank you for prompt manufacturing of loads of thin sections. Claude Lavanchy and H.R. Pfeifer from the CAM, Université de Lausanne, Switzerland, is thanked for XRF-analyses. A special thank belongs to Doro. I enjoyed being your "officemate" and the many times you let me participate to your joyful character. Your warmth and openness encouraged me very often. Good luck to you! Ilka, thanks for the countless interesting discussions about science, life..., which contributed to the success of the following pages. Thank you for your friendship! A special thanks goes also to Bärbel. You always had a shoulder for me! My dear colleges from inside and outside the Institute. I thank you for the good time here in Switzerland, for the numerous intermezzi and evenings. Danke, merci, grazie, sbosibo to Dänu, Reto, Jüre, Ronny, Nicola, Martin, Katja, Franzi, Schorsch and Marek. Thank you, Elena, for taking care of me beyond science. My beloved flatmate Xe is greatful thanked here for many things. It was a pleasure to gossip and philosophise with you at the “Chuchitisch” and it was balm for my stressed soul to listen to your acoustic highlights. Liebe Mama, danke für Deine Geduld, Dein Interesse und die Unterstützung bei allem, was ich tue. Jens, I thank you very much for being always on my side! Preface and Summary This thesis was supported by the Swiss National Science Foundation (SNSF–grant-numbers 21-63866.00 and 200020-100230) at the Institute of Geological Sciences – Isotope Geology Group – of the University of Bern, Switzerland under supervision of Prof. Dr. Igor M. Villa and Prof. Dr. Jan D. Kramers. The work included several field excursions to the study areas, namely Nisyros island (Greece), Monte Vico and Monte Vulture (Italy) in collaboration with Dr. Claudia Principe from the Istituto di Geoscienze e Georisorse, CNR, via G. Moruzzi 1, 56124 Pisa, Italy. The thesis is separated into four chapters. Chapter one and two contain geochemical and geochronological investigations of the Nisyros-Yali volcanic system. In the 3rd chapter geochronological and petrological investigations of Monte Vulture are presented. The 4th chapter deals with U-Th systematics of paleosols of all investigated volcanoes (Monte Vico, Monte Vulture and Nisyros-Yali). All tables of samples and analytical results are summarised in the Appendix A. Chapter one presents a petrological and geochemical study of Nisyros-Yali volcanic units. Petrological investigations were combined with major and trace element data and Lu-Hf, Sm-Nd Sr-, Pb-isotope systematics. This comprehensive data-set allows a detailed reconstruction of the magma genesis of the volcanic system. The volcanic history, subdivided into a pre- and a post-caldera cycle, is mirrored by a change in petrological style. Geochemical data exhibit a compositional gap (lacking intermediate major element concentrations) between these two cycles resulting in distinct petrological and geochemical characteristics. Chapter two is a continuation of the first chapter and includes 39Ar-40Ar and U-Th investigations of the Nisyros-Yali volcanic system. All volcanic products are characterised by the absence of K-bearing mineral-phases. Potassium is hosted in the volcanic glasses that contain mantle-gas inclusions with excess Ar. U-Th disequilibrium analyses show that most rocks and minerals plot in a "forbidden zone" due to a two-stage evolution. Chapter three presents a refined geochronological database of Monte Vulture ejecta. New selected mineral phases and samples from previous works were analysed with 39Ar-40Ar step heating. The combination of petrological observations and 39Ar-40Ar systematics reveal mineralogical complications, which were unravelled. The resulting interpretation is based on isochemical steps and refines the volcanostratigraphy. Furthermore, "allochthonous" tephra deposits can now be ascribed to certain eruptions of the Vesuvius area. Chapter four includes U-Th systematics of paleosols sandwiched by unpedogenised volcanics of all three investigated volcanic systems (Monte Vico, Monte Vulture and Nisyros-Yali). Bulk and sequential extraction procedures were applied to leach distinct soil components (adsorbed cations, authigenic carbonates, metal oxides and hydroxides from the silicate residue). U-Th data of each leach step exhibit laboratory fractionation of U from Th, which is excluded when calculated bulk ratios (summarising steps). Hence, it is evidenced that even supposedly arrested paleosols are open systems. Table of contents Chapter 1 1. Magma generation at the easternmost section of the Hellenic Arc: Hf, Nd, Pb and Sr isotope geochemistry of Nisyros and Yali volcanoes (Greece) 1.1 Introduction....................................................................................................................2 1.2 Geological setting ..........................................................................................................2 1.3 Previous studies .............................................................................................................3 1.4 Analytical techniques.....................................................................................................4 1.5 Petrography....................................................................................................................5 1.6 Geochemistry.................................................................................................................6 1.6.1 Geochemical signatures of fluid addition and fractional crystallisation ..............7 1.6.1.1 Role of Th and U ....................................................................................10 1.6.2 Geochemical signatures of crustal assimilation..................................................11 1.7 The compositional gap.................................................................................................15 1.8 Summary and conclusions ...........................................................................................17 Chapter 2 2. Geochronolgy of Nisyros 2.1 Introduction..................................................................................................................23 2.2 Analytical techniques...................................................................................................24 2.3 Results and discussion .................................................................................................25 2.3.1 39Ar-40Ar..............................................................................................................25 2.3.2 U-Th data............................................................................................................27 2.4 Conclusion ...................................................................................................................28 Chapter 3 3. Chronostratigraphy of Monte Vulture Volcano (southern Italy): 39Ar-40Ar systematics and the role of secondary processes 3.1 Introduction..................................................................................................................32 3.2 Analytical techniques...................................................................................................34 3.3 Mineralogy...................................................................................................................34 3.3.1 Leucite ................................................................................................................36 3.3.2 Sanidine ..............................................................................................................36 3.3.3 Biotite .................................................................................................................36 3.3.4 Phlogopite...........................................................................................................36