The causes and effect of temporal changes in magma generation processes in space and time along the Central Andes (13°S – 25°S) Dissertation zur Erlangung des mathematisch-naturwissenschaftlichen Doktorgrades "Doctor rerum naturalium" der Georg-August-Universität Göttingen im Promotionsprogramm Geowissenschaften / Geographie der Georg-August University School of Science (GAUSS) vorgelegt von Rosanne Marjoleine Heistek aus Nederland/Niederlande Göttingen 2015 Betreuungsausschuss: Prof. Dr. Gerhard Wörner, Abteilung Geochemie, GZG Prof. Dr. Andreas Pack, Abteilung Isotopengeologie, GZG Referent: Prof. Dr. Gerhard Wörner Prof. Dr. Andreas Pack Weitere Mitglieder der Prüfungskommission: Prof. Dr. Sharon Webb Prof. Dr. Hilmar von Eynatten Prof. Dr. Jonas Kley Dr. John Hora Tag der mündlichen Prüfung: 25.06.2015 TABLE OF CONTENTS Acknowledgements .................................................................................................................................1 Abstracts .................................................................................................................................................2 Chapter 1: Introduction .........................................................................................................................7 1.1.The Andean volcanic belt .............................................................................................................................. 7 1.2. The Central volcanic zone ............................................................................................................................ 9 1.2.1. The basement....................................................................................................................................... 10 1.2.2. The onset of magmatic systems ........................................................................................................... 10 1.2.3. Subduction of the Nazca plate ............................................................................................................. 11 1.2.4. Movements of the Nazca and Juan Fernández Ridge ......................................................................... 12 1.2.5. Uplift ................................................................................................................................................... 14 1.3. Hypotheses and open questions .................................................................................................................. 15 References.......................................................................................................................................................... 17 Chapter 2: Constraints on P-T conditions of crystallization and rates of magma formation before and after crustal thickening in the Central Andes ................................................................24 Abstract .............................................................................................................................................................. 24 2.1. Introduction ................................................................................................................................................. 25 2.2. Methods ...................................................................................................................................................... 31 2.2.1. Sample selection .................................................................................................................................. 31 2.2.2. Single lava flow volume calculation ................................................................................................... 32 2.2.3. Major and trace elements .................................................................................................................... 33 2.2.4. Thermometry ...................................................................................................................................... 33 2.2.5. MELTS ............................................................................................................................................... 36 2.2.6. ABS .................................................................................................................................................... 37 2.2.7. Barometry ............................................................................................................................................ 38 2.2.8. Crystal Size Distribution (CSD) .......................................................................................................... 38 2.3. Results......................................................................................................................................................... 39 2.3.1. Petrography ......................................................................................................................................... 39 2.3.2. Geochemistry ...................................................................................................................................... 40 2.3.3. Volume estimates through time ........................................................................................................... 46 2.3.4. Conditions of the final stage of magmatic evolution .......................................................................... 50 2.3.4.1. Thermometry .................................................................................................................................... 50 2.3.4.2. Hygrometry and barometry .............................................................................................................. 53 2.3.4.3. APT-11 ............................................................................................................................................. 55 2.3.5. Plagioclase CSD and compositions .................................................................................................... 57 2.4. Discussion ................................................................................................................................................... 61 2.4.1 Formation of homogeneous intermediate magmas ............................................................................... 61 2.4.2. Magma bodies ..................................................................................................................................... 63 2.4.3. A change in effusion rate..................................................................................................................... 66 2.4.4. Erosion patterns ................................................................................................................................... 67 2.5. Conclusions ................................................................................................................................................. 69 References.......................................................................................................................................................... 71 Chapter 3: Temporal changes in mantle wedge geometry and magma generation processes in the Central Andes: towards linking petrological data to thermomechanical models ....................................79 Abstract .............................................................................................................................................................. 79 3.1. Introduction ................................................................................................................................................. 80 3.2. Methods ...................................................................................................................................................... 83 3.2.1. Volume calculations ............................................................................................................................ 83 3.2.2. Magma differentiation and assimilation): MELTS.............................................................................. 84 3.2.3. Energy constrained model: EC-RAXFC ............................................................................................. 85 3.3. Areal extent, volumes and eruption rates: comparison of Miocene shields and Pliocene/Quaternary stratovolcanoes .................................................................................................................................................. 88 3.3.1. Quality of data ..................................................................................................................................... 88 3.3.2. Volumes and eruption rates for Miocene lava shields and Pliocene/Quaternary stratovolcanoes trough time............................................................................................................................................................... 90 3.3.3. Fractionation and/or assimilation ........................................................................................................ 91 3.4. EC-RAXFC ................................................................................................................................................. 93 3.4.1 geochemical trends ............................................................................................................................... 93 3.4.2. Source contamination – HREE depletion ............................................................................................ 97 3.5. Evaluation of Andean