Characterization and age determination of Quaternary volcanism in the southern Ankaratra region (central Madagascar) through novel approaches in luminescence dating Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Daniel Rufer von Ittigen / BE Leiter der Arbeit: PD Dr. G. Schreurs Institut für Geologie, Universität Bern PD Dr. A. Berger Department of Geography and Geology, University of Copenhagen PD Dr. E. Gnos Muséum d’Histoire naturelle de Genève PD Dr. F. Preusser Institut für Geologie, Universität Bern Characterization and age determination of Quaternary volcanism in the southern Ankaratra region (central Madagascar) through novel approaches in luminescence dating Inauguraldissertation der Philosophisch-naturwissenschaftlichen Fakultät der Universität Bern vorgelegt von Daniel Rufer von Ittigen / BE Leiter der Arbeit: PD Dr. G. Schreurs Institut für Geologie, Universität Bern PD Dr. A. Berger Department of Geography and Geology, University of Copenhagen PD Dr. E. Gnos Muséum d’Histoire naturelle de Genève PD Dr. F. Preusser Institut für Geologie, Universität Bern Von der Philosophisch-naturwissenschaftlichen Fakultät angenommen. Der Dekan: Bern, 23. Oktober 2009 Prof. Dr. Urs Feller Characterization and age determination of Quaternary volcanism in the southern Ankaratra region (central Madagascar) through novel approaches in luminescence dating Dissertation submitted to the Faculty of Science of the University of Bern for the degree of Doctor of Science (Dr. phil. nat.) by Daniel Rufer from Ittigen / BE Supervisors: PD Dr. G. Schreurs Institute of Geological Sciences, University of Bern PD Dr. A. Berger Department of Geography and Geology, University of Copenhagen PD Dr. E. Gnos Museum of Natural History, Geneva PD Dr. F. Preusser Institute of Geological Sciences, University of Bern No man should escape our universities without knowing how little he knows. J. Robert Oppenheimer (1904 – 1967), Physicist CONTENTS ABSTRACT V MISAOTRA BETSAKA!-THANKS! VII 1INTRODUCTION AND OUTLINE OF THESIS 1 1.1 INTRODUCTION . 3 1.2 OUTLINE OF THESIS . 4 1.3 REFERENCES . 7 2 NEW APPROACHES FOR DATING YOUNG VOLCANIC ERUPTIONS BY LUMINESCENCE METHODS 11 2.1 ABSTRACT . 13 2.2 INTRODUCTION . 13 2.3 DATING OF PHREATIC EXPLOSION DEPOSITS . 15 2.3.1 OCCURRENCE AND FORMATION PROCESSES OF PHREATIC EXPLOSION DEPOSITS . 15 2.3.2 THE PROBLEM OF SIGNAL RESETTING IN ABSENCE OF THERMAL OR OPTICAL BLEACHING . 16 2.3.3 SAMPLING AND SAMPLE PREPARATION . 17 2.4 DATING OF THERMALLY BLEACHED XENOLITHS FROM LAVA FLOWS . 18 2.4.1 SAMPLING AND SAMPLE PREPARATION . 19 2.4.2 THERMAL BLEACHING OF SAMPLES DURING EMPLACEMENT . 20 2.4.3 VOLUME HEATING MODEL AND CALEFACTION EXPERIMENTS . 20 2.4.4 MICRODOSIMETRIC CONSIDERATIONS WHEN MEASURING COARSE GRAINED, SOLID MATERIALS . 23 2.5 SUMMARY AND OUTLOOK . 23 ACKNOWLEDGEMENTS . 23 2.6 REFERENCES . 24 3 POTENTIAL OF AUTORADIOGRAPHY TO DETECT SPATIALLY RESOLVED RADIATION PATTERNS IN THE CONTEXT OF TRAPPED CHARGE DATING 29 3.1 ABSTRACT . 31 3.2 INTRODUCTION . 31 3.3 THE PROBLEM OF DETERMINING NON-UNIFORM RADIATION FIELDS IN THE DOMAIN OF TRAPPED CHARGE DATING . 33 I 3.4 COMPUTED AUTORADIOGRAPHY SYSTEMS . 34 3.4.1 THE SAMPLE MATERIAL . 34 3.4.2 THE IMAGE SENSOR. 34 3.4.3 THE IMAGE READER AND IMAGE PROCESSOR . 35 3.5 METHODOLOGY . 36 3.5.1 SAMPLES AND SAMPLE PREPARATION . 36 3.5.2 EXPOSURE, READOUT AND IMAGE TREATMENT . 37 3.5.3 PSL SIGNAL PRODUCTION FROM DIFFERENT TYPES OF RADIATION . 39 3.6 QUALITATIVE DETERMINATION OF RADIATION INHOMOGENEITY. 41 3.7 FIRST INVESTIGATIONS INTO THE POTENTIAL TO QUANTIFY PSL SIGNALS . 44 3.7.1 THEORETICAL BACKGROUND . 44 3.7.2 ESTABLISHING A CALIBRATION CURVE . 45 3.7.3 APPLICATION TO GEOLOGICAL SAMPLES . 47 3.7.4 THE PROBLEM OF LINKING SPECIFIC ACTIVITY AND DOSE RATES BASED ON PSL VALUES . 49 3.8 CONCLUSIONS . 49 ACKNOWLEDGEMENTS . 50 3.9 REFERENCES . 50 4 VARIABLE FADING RATES IN K-FELDSPAR CAUSED BY DIFFERENT IRSL COMPONENTS AND IMPLICATIONS FOR G-VALUE DETERMINATION 55 4.1 ABSTRACT . 57 4.2 INTRODUCTION . 57 4.3 MATERIALS AND METHODS . 57 4.4 RESULTS AND DISCUSSION . 59 4.5 CONCLUSIONS . 63 ACKNOWLEDGEMENTS . 63 4.6 REFERENCES . 63 5 LATE QUATERNARY VOLCANIC HISTORY OF THE VAKINANKARATRA VOLCANIC FIELD (CENTRAL MADAGASCAR): INSIGHTS FROM LUMINESCENCE DATING OF PHREATIC ERUPTIONS 65 5.1 ABSTRACT . 67 5.2 INTRODUCTION . 67 5.3 GEOLOGICAL SETTING . 69 5.3.1 PHREATIC ERUPTIONS IN THE VAKINANKARATRA VOLCANIC FIELD . 70 II 5.4 EXISTING CHRONOSTRATIGRAPHY . 72 5.5 METHODOLOGY . 74 5.5.1 INTRODUCTION TO LUMINESCENCE DATING . 74 5.5.2 LUMINESCENCE DATING OF PHREATIC EXPLOSION DEPOSITS . 75 5.5.3 SAMPLE PREPARATION AND EXPERIMENTAL PARAMETERS . 75 5.5.4 DETERMINATION OF SAMPLE MOISTURE CONTENTS . 77 5.5.5 DETERMINATION OF INTERNAL K CONTENT OF THE FELDSPAR SEPARATE . 78 5.5.6 CORRECTIONS FOR ANOMALOUS FADING . 80 5.6 SITES AND DATING RESULTS . 80 5.6.1 LAC ANDRAIKIBA AREA . 80 5.6.2 LAC TRITRIVAKELY . 84 5.6.3 FIZINANA AND AMPASIMIKAIKI AREAS . 85 5.6 CONCLUSIONS . 88 ACKNOWLEDGEMENTS . 88 5.8 REFERENCES . 89 6 CONCLUSIONS 93 A CONFERENCE CONTRIBUTIONS 99 B GEOLOGICAL MAP:WEST OF ANTSIRABE 111 C SAMPLE LOCATIONS 113 D MAJOR AND TRACE ELEMENTS (XRF) 119 E BERNESE LOW ARGON BLANK LINE ASSEMBLY (BLA-BLA) - MACHINE INTERFACE AND DATA ACQUISITION SYSTEM (M.I.D.A.S.) 123 DECLARATION 129 CURRICULUM VITAE 131 III ABSTRACT This work introduces two novel approaches for the application of luminescence dating techniques to Quaternary volcanic eruptions: crystalline xenoliths from lava flows are demonstrated to be basically suitable for luminescence dating, and a set of phreatic explosion deposits from the Late Quaternary Vakinankaratra volcanic field in central Madagascar is successfully dated with infrared stimulated luminescence (IRSL). Using a numerical model approach and experimental verification, the potential for thermal resetting of luminescence signals of xenoliths in lava flows is demonstrated. As microdosimetry is an important aspect when using sample material extracted from crystalline whole rocks, autoradiography using image plates is introduced to the field of luminescence dating as a method for detection and assessment of spatially resolved radiation inhomogeneities. Determinations of fading rates of feldspar samples have been observed to result in aberrant g-values if the pause between preheat and measurement in the delayed measurements was kept short. A systematic investigation reveals that the phenomenon is caused by the presence of three signal components with differing individual fading behaviour. As this is restricted to short pauses, it is possible to determine a minimal required delay between preheating and measurement after which the aberrant behaviour disappears. This is applied in the measuring of 12 samples from phreatic explosion deposits from the Antsirabe – Betafo region in the Late Quaternary Vakinankaratra volcanic field. The samples were taken from stratigraphically correlatable sections and appear to represent at least three phreatic events, one of which created the Lac Andraikiba maar near Antsirabe. The obtained ages indicate that the eruptive activity in the region started in the Late Pleistocene between 113.9 and 99.6 ka. A second layer in the Betafo area is dated at approximately 73 ka and the Lac Andraikiba deposits give an age between 63.9 and 50.7 ka. The youngest phreatic layer is dated between 33.7 and 20.7 ka. These ages are the first recorded direct ages of such volcanic deposits, as well as the first and only direct ages for the Late Quaternary volcanism in the Vakinankaratra volcanic field. This illustrates the huge potential of this new method for volcanology and geochronology, as it enables direct numerical dating of a type of volcanic deposit which has not been successfully directly dated by any other method so far. V MISAOTRA BETSAKA!-THANKS! “Aza mandalo tana-misy havana.” – “Don’t pass by the house of a friend without paying him a visit.” (Malagasy proverb) Over the past years, these ‘houses’ have become more and more numerous, and I would not like to simply pass them by on my way to submit this thesis… Thank you, Guido, for giving me the opportunity to work on this project and for introducing me to (not only the geology of) Madagascar. I enjoyed the time in the field, the discussions and the THB. Even though the project turned out to be similar to driving along the back ways of the Hauts Plateaux, you kept your confidence in me. Thank you! Alfons, thank you for all the discussions in the field, your efforts in the final drawing of the geologic map and your help with the microprobe. Edwin, your enthusiasm in getting samples from the top of all those volcanoes made for arduous fieldwork, but this was more than balanced by the wealth of keen observations, fruitful discussions and generally the good time we spent in the field or over dinner “Chez Jacky”. Thanks a lot! I want to express a particularly big ‘Thank you!’ to Frank, who very kindly agreed to scientifically ‘adopt’ me when the entire project was on the verge of going south. Thank you for introducing me into the ‘circle of bright grains’ and to venture on an undertaking in which the sentence “Hey, nobody has done this before, but lets try it!” became something like a mission statement for a series of very interesting projects. I am grateful for your boundless optimism and enthusiasm, thank you - it was sorely needed. I am also very grateful to Markus Fiebig, who kindly agreed to evaluate this thesis as an external referee. I would also like to thank all other people who were, in one way or another, involved in this project: Michel Rakotondrazafy for helping with the exportation of rock samples from Madagascar, Lydia Zehnder for the XRF measurements, Marco Herweg for the introduction to the SEM and Igor Villa for providing me with the opportunity to learn so much about “Zen and the Art of Noble Gas Mass Spectrometer Maintenance”.