Sarahfreund Dissertation.Pdf

Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nurn¨ berg Tag der mundlic¨ hen Prufung:¨ 24.01.2014 Vorsitzender der Promotionsorgans: Prof. Dr. J. A. C. Barth Gutachter: Prof. Dr. K. M. Haase Prof. Dr. J. Koepke Contents List of Figures 6 List of Tables 8 Abstract 9 Kurzfassung 10 Statement of candidate 12 Full publication list 13 Acknowledgments 15 1 Introduction 16 2 Aims of the study 28 3 Oxygen isotope evidence for the formation of andesitic-dacitic magmas from the fast-spreading Pacific-Antarctic Rise by assimilation-fractional crystallisation 30 3.1 Abstract ..................................... 30 3.2 Introduction ................................... 31 3.3 Geological Background ............................. 32 3.4 Results ...................................... 32 3.4.1 Chemical and O isotopic compositions of the PAR glasses ..... 32 3.4.2 Petrography and mineral chemistry .................. 44 3.5 Discussion .................................... 45 3.5.1 Liquid lines of descent and fractional crystallisation processes ... 45 3.5.2 Constraints on assimilation processes in the generation of silicic PAR magmas .............................. 46 3.5.3 Evidence from mineral compositions for melt evolution and the link to oceanic ferrogabbros ........................ 47 3.5.4 Fractionation of the PAR magma: oxide crystallisation and its effects on the magma composition .................. 48 3.5.5 Thermobarometric constraints on the depth of the mafic magma reservoir ................................. 49 Contents 4 3.5.6 A quantitative AFC model for the PAR lavas ............ 50 3.5.7 The nature of the assimilant and the role of amphibole ....... 51 3.5.8 Potential relationship between occurrence of silicic magmas along spreading axes, tectonic and hydrothermal processes ........ 53 3.6 Conclusions ................................... 53 3.7 Acknowledgements ............................... 55 4 Constraints on the formation of geochemically variable plagiogranite intrusions in the Troodos Ophiolite, Cyprus 56 4.1 Abstract ..................................... 56 4.2 Introduction ................................... 57 4.3 Geological Background ............................. 57 4.4 Samples and analytical methods ....................... 59 4.5 Results ...................................... 61 4.5.1 Occurrence of the plagiogranites and field observations ....... 61 4.5.2 Petrology and mineral chemistry ................... 61 4.5.3 Major element composition of the rocks from plagiogranite intrusions 64 4.5.4 Trace element composition of the plagiogranitic intrusives and com- parison with the glassy lava ...................... 65 4.6 Discussion .................................... 68 4.6.1 Hydrothermal alteration of the samples and stratigraphic context of the plutonic section ......................... 68 4.6.2 Relations between evolved intrusive rocks and the lavas ...... 72 4.6.3 The relationship of the plagiogranitic intrusions to the mafic crustal plutonic rocks .............................. 73 4.6.4 Generation of the plagiogranite magmas: fractional crystallization versus partial melting ......................... 73 4.7 Conclusions ................................... 77 4.8 Acknowledgements ............................... 77 5 Constraints on the evolution of the crust of the Semail ophiolite (Oman) from the geochemical composition of plagiogranites 97 5.1 Abstract ..................................... 97 5.2 Introduction ................................... 98 5.3 Geological Background ............................. 99 5.3.1 Geographical and geological overview ................ 99 5.3.2 Geochemical overview ......................... 99 5.3.3 Ophiolite age .............................. 101 5.4 Samples and analytical methods ....................... 101 5.4.1 Sampling ................................ 101 5.4.2 Analytical methods ........................... 103 Contents 5 5.5 Results ...................................... 106 5.5.1 Petrology ................................ 106 5.5.2 Geochemistry .............................. 106 5.6 Discussion .................................... 114 5.6.1 Hydrothermal alteration of the plutonic rocks ............ 114 5.6.2 The geochemical relationship between the plutonic and volcanic rocks114 5.6.3 Formation of the felsic magmas .................... 116 5.6.4 Implications for the tectonic setting during formation of the Oman ophiolite ................................. 119 5.6.5 Evidence of source depletion, decoupling effects and the nature of the slab component .......................... 120 5.6.6 The influence of slab derived fluids on magma differentiation ... 121 5.6.7 Time interval between the two magmatic events .......... 122 5.7 Conclusions ................................... 123 5.8 Acknowledgements ............................... 123 6 Findings and Outlook 140 7 Supplementary materials 170 List of Figures 1.1 The Earth´s continental and oceanic crust. ................. 17 1.2 Composition of continental and oceanic crust ................ 18 1.3 Cross-section through the Oman ophiolite .................. 19 1.4 Processes that probably take place in an axial magma chamber. ...... 21 1.5 Five life-cycles of a SSZ ophiolite ....................... 24 1.6 Tonalite-trondhjemite-granodiorite discrimination diagram ......... 25 3.1 Bathymetric map of the Pacific-Antarctic ridge and the sample locations . 33 3.2 Neodymium isotopes and Nb/Zr ratio of the PAR glasses versus Latitude 36 3.3 Major elements of the PAR glasses ...................... 37 3.4 Trace element contents of the PAR ...................... 40 3.5 Sulphur and Cl contents of the PAR and EPR glasses ........... 41 3.6 Trace element ratios of the PAR and EPR glasses .............. 42 18 3.7 H2O/Ce, Li/Ce and δ O of the PAR, EPR and GSC glasses ....... 44 3.8 Oxygen isotopes versus Cl/K of the PAR and EPR and assimilation-fractional crystallisation trend .............................. 51 3.9 Formation of the basaltic, FeTi basaltic and silica rich lavas at the PAR . 54 4.1 Map of the Troodos Ophiolite in Cyprus with detailed geology of the Mount Olympos area and the distribution of plagiogranite intrusions ....... 60 4.2 Field photographs of plagiogranites in the Troodos Ophiolite ....... 62 4.3 Feldspar (anorthite-albite-orthoclas) composition diagram ......... 63 4.4 Tonalite-trondhjemite-granodiorite discrimination diagram ......... 64 4.5 Major element variations of the plagiogranites, lavas and mafic plutonics . 66 4.6 Incompatible elements and transition metals versus SiO2 from the plagiogranites, lavas and mafic plutonics ..................... 67 4.7 Rare earth element patterns of the plagiogranite groups .......... 69 4.8 Immobile-trace element ratios of the plagiogranite groups and lavas .... 70 4.9 Loss on ignition versus mobile and immobile elements ........... 71 4.10 Fractional crystallization and partial melting models in terms of incompatible elements .................................. 76 5.1 Maps of the Sumail ophiolite and sample locations ............. 100 5.2 Field photographs of plagiogranites in the Oman ophiolite ......... 102 List of Figures 7 5.3 Normative calculated plutonic rock classification .............. 107 5.4 Major element variations of the plagiogranites and wall-rocks, lavas, sheeted dyke rocks and plutonic rocks ......................... 108 5.5 Multi element diagrams of the plagiogranites and lavas ........... 109 5.6 Incompatible element compositions, ratios and Nd isotope ratios of the volcanic and plutonic rock groups ....................... 110 5.7 Major and trace elements versus loss on ignition .............. 111 5.8 Incompatible element ratios of the plagiogranite groups and lavas ..... 113 5.9 Isotope ratios and mother/daughter trace element ratios of the plagiogranites and lavas .................................. 115 5.10 Discrimination between fractional crystallization and partial melting processes ...................................... 117 5.11 Magmatic age of plagiogranite sample locations versus incompatible elements and isotope ratios ............................ 122 List of Tables 3.1 Representative major and trace elements and isotopic compositions of silicic and basaltic glasses from the Pacific-Antarctic Rise ............. 34 3.2 Details of the AFC calculations of the PAR glasses ............. 38 3.3 Thermobarometry on the basis of clinopyroxene–melt equilibrium calculations 50 4.1 Major and trace elements of Troodos plagiogranites and aphyric dykes .. 78 4.2 Parameters for modeling Troodos plagiogranitic melt evolution ...... 93 4.3 Least squares model and trace element modeling .............. 94 4.4 Melting of amphibolite ............................. 96 5.1 Correlation of plagiogranite sample locations with U/Pb age analyses of zircons from early respectively late stage plutonics ............. 103 5.2 Standard measurements ............................ 104 5.3 Major elements of the Oman plagiogranites.................. 125 5.4 Trace elements and isotope ratios of the Oman plagiogranites ....... 130 Abstract The magmatic oceanic crust mainly consists of mafic rock types like plutonic gabbros and volcanic basalts. Comparable small amounts of felsic rocks with >60 wt% SiO2 are known in the oceanic crust in forms of intrusive veins and plagiogranite bodies but only rarely in form of erupted lavas. Plagiogranitic rocks are well known from ophiolite complexes, which represent a typical sequence of rocks formed in an

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