Variations in magma composition in time and space along the Central Andes (13°S-28°S) Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultäten der Georg-August-Universität zu Göttingen vorgelegt von Mirian-Irene Mamani-Huisa aus Cuyocuyo (Peru) Göttingen 2006 D 7 Referent: Prof. Dr. G. Wörner Koreferent: Prof. Dr. B.T. Hansen Tag der mündlichen Prüfung: 24, Oktober 2006 1 Contents Abstract.......................................................................................................................................3 Zusammmenfassung...................................................................................................................5 Resumen .....................................................................................................................................7 Acknowledgements ....................................................................................................................9 Preamble...................................................................................................................................10 1 Introduction ...........................................................................................................................11 1.1 Variations in magma composition in time and space along the Central Andes (13°S- 28°S): Facts and open questions...........................................................................................11 1.2 Working Hypothesis.......................................................................................................11 1.3 Previous work.................................................................................................................12 1.3.1 The Andes................................................................................................................12 1.3.2 Pre-Andean history..................................................................................................15 1.3.3 The Andean Cycle ...................................................................................................17 1.3.4 Uplift of the Central Andes and subducting Nazca plate ........................................18 1.3.5 Andean volcanism ...................................................................................................20 1.3.6 Magma genesis ........................................................................................................21 2 Geochemical variations in south Peruvian volcanic rocks (13°S-18°S): The role of crustal composition and thickening through time and space ...............................................................25 2.1 Introduction ....................................................................................................................25 2.2 Tectonic Setting..............................................................................................................26 2.3 Description of Cenozoic units and sampled volcanic centers ........................................27 2.3.1 Middle Eocene - Lower Oligocene, ~ 45 to ~30 Ma (Lower Moquegua Formation, Anta Group)......................................................................................................................27 2.3.2 Upper Oligocene - Middle Miocene, ~30 to ~15 Ma (Upper Moquegua Formation, Tacaza Group) ..................................................................................................................28 2.3.3 Upper Miocene – Lower Pliocene, ~10 to ~3 Ma (Lower Barroso Formation)......29 2.3.4 Pliocene, ~3 to ~2 Ma (Sencca Formation).............................................................29 2.3.5 Upper Pliocene to Pleistocene, 3 to 0.8 Ma (Upper Barroso Formation)................29 2.3.6 Holocene Volcanoes < 0.01 Ma ..............................................................................29 2.4 Results ............................................................................................................................30 2.4.1 Geochemistry...........................................................................................................30 2.4.1.1 Temporal variations of element ratios..............................................................39 2.4.1.2 Isotopes.............................................................................................................40 2.5 Discussion.......................................................................................................................45 2.5.1 Chemical isotopic composition of magmatic rocks in southern Peru and northern Chile .................................................................................................................................46 2.5.2 Lithopheric Cross Sections and the Tectonic and Magmatic History in southern Peru...................................................................................................................................52 2.6 Conclusions ....................................................................................................................56 3 Regional and temporal patterns in Meso-Cenozoic magmatic evolution in the Central Andes (13°S to 28°S)...........................................................................................................................57 3.1 Introduction ....................................................................................................................57 3.2 Database .........................................................................................................................58 2 3.3 Geochemistry of Meso-Cenozoic magmatic rocks in the CA ........................................60 3.3.1 Major and trace elements.........................................................................................60 3.3.2 Isotopes....................................................................................................................66 3.4 Summary and Discussion: Implications for a tectonic model ........................................71 3.4.1 Source or Processes? ...............................................................................................72 3.4.2 Geochemical constraint in a Tectonic model ..........................................................80 4 Geochemical variations in time and space of lead isotopic domains in the Central Andes (13°S -28°S): Implications of the crustal structure and metal sources.....................................82 4.1 Introduction ....................................................................................................................82 4.2 Information systems and Pb isotope data .......................................................................83 4.2.1 Lead isotope data.....................................................................................................83 4.3 Results ............................................................................................................................84 4.3.1 Mapping of Pb isotopes and geochemical variations in Pb-domains ......................84 4.4 Discussion.......................................................................................................................87 4.4.1 Pb isotope mapping crustal domains .......................................................................87 4.4.1.2 Isotopic framework of basement in the Central Andes ....................................88 4.4.2 Crustal Contamination in the Pb domains ...............................................................92 4.4.3 Isotopic domains constrained by 3D density model................................................94 4.4.4 The Nature of the Transition Zones.........................................................................95 4.4.5 Segmentation of the Central Andes plateau related to the Pb-isotope domains......96 4.4.6 Rheological and structural identity of the Pb domains during Andean Orogeny....97 4.4.7 Pb-isotopes of gold, silver copper and tin deposits, their relationship with the Pb- domains.............................................................................................................................98 4.5 Conclusions ..................................................................................................................103 5 Appendix .............................................................................................................................104 5.1 Sample locations...........................................................................................................104 5.2 Analytical Methods ......................................................................................................105 5.2.1 Sample Preparation................................................................................................105 5.2.2 XRF (X-Ray Fluorescence Spectroscopy) analysis ..............................................106 5.2.3 ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis...................106 5.2.4 TIMS (Thermal Ionization Mass Spectrometer) analysis .....................................107 6 References ...........................................................................................................................108 3 Abstract This dissertation investigates the diversity of magma chemistry along and across the arc with time in the Central Andes, with emphasis in the Neogene magmatism. The main body of this thesis is formed by three independent chapters. The specific regions, results and conclusions of these individual