ETH Library Metamorphic fluid history along a cross section through the central Alps: constraints from LA-ICPMS analysis of fluid inclusions and Ar- Ar geochronology Doctoral Thesis Author(s): Rauchenstein-Martinek, Klara Publication date: 2014 Permanent link: https://doi.org/10.3929/ethz-a-010342954 Rights / license: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information, please consult the Terms of use. DISS. ETH Nr. 22012 Metamorphic fluid history along a cross section through the Central Alps: Constraints from LA-ICPMS analysis of fluid inclusions and Ar-Ar geochronology KLARA RAUCHENSTEIN-MARTINEK Master in Earthsciences ETH Zurich accepted on the recommendation of Prof. Dr. Christoph A. Heinrich Prof. Dr. Thomas Wagner Prof. Dr. Sarah Gleeson 2014 DISS. ETH Nr. 22012 Metamorphic fluid history along a cross section through the Central Alps: Constraints from LA- ICPMS analysis of fluid inclusions and Ar-Ar geochronology A dissertation submitted to ETH ZURICH For the degree of Doctor of sciences (Dr. Sc. ETH ZURICH) Presented by KLARA RAUCHENSTEIN-MARTINEK Master in Earthsciences ETH Zurich 25/12/1984 Citizen of Switzerland accepted on the recommendation of Prof. Dr. Christoph A. Heinrich Prof. Dr. Thomas Wagner Prof. Dr. Sarah Gleeson 2014 CONTENTS CONTENTS LIST OF FIGURES…………………………………………………………………………………...iv LIST OF TABLES…………………………………………………………………………………….vi ABSTRACT…………………………………………………………………………………………….1 ZUSAMMENFASSUNG………………………………………………………………………………4 ACKNOWLEDGEMENTS…………………………………………………………………………...7 1. INTRODUCTION…………………………………………………………………………...….…..9 1.1 METAMORPHIC FLUID FLOW…………………………………………….……………9 1.2 STUDY AREA: CENTRAL ALPS…………………………………………………...…..12 1.3 AIMS OF RESEARCH……………………………………………………………...…….13 1.4 LAYOUT OF THESIS……………………………………………………………..……..14 2. CHEMICAL EVOLUTION OF METAMORPHIC FLUIDS ALONG A CROSS SECTION THROUGH THE CENTRAL ALPS, SWITZERLAND…………………………………………..15 2.1 ABSTRACT……………………………………………………………………………….15 2.2 INTRODUCTION…………………………………………………………………….…..16 2.3 REGIONAL GEOLOGICAL SETTING……………………………………….…………19 2.4 GEOLOGY AND MINERALOGY OF SAMPLING LOCATIONS………………...…..23 2.5 ANALYTICAL METHODS……………………………………………………………...29 2.5.1 Whole-rock geochemistry………………………………………………………...……29 2.5.2 Fluid inclusion microthermometry………………………………………………...…30 2.5.3 LA-ICPMS microanalysis of fluid inclusions………………………………...……..31 2.5.4 Phase equilibria computation……………………………………………………..….33 2.6 FLUID INCLUSION RESULTS………………………………………………………….36 2.6.1 Inclusion petrography………………………………………………………………….36 2.6.2 Microthermometry……………………………………………………………..……….40 2.6.3 Element composition of fluid inclusions……………………………………….…….41 2.7 FLUID-ROCK EQUILIBRATION MODELING AND P-T EVOLUTION……………..48 2.8 DISCUSSION AND CONCLUSIONS……………………………………………….…..53 2.8.1 Fluid sources……………………………………………………………………….……53 2.8.2 Controls on elemental concentrations in fluid inclusions……………………..…..55 2.8.3 Big-scale geodynamics…………………………………………………………………59 i CONTENTS 3. GOLD CONCENTRATIONS IN METAMORPHIC FLUIDS: A LA-ICPMS FLUID INCLUSION STUDY FROM THE ALPINE OROGENIC BELT………………………………..61 3.1 ABSTRACT…………………………………………………………………………….…61 3.2 INTRODUCTION……………………………………………………….………………..62 3.3 REGIONAL GEOLOGY AND VEIN-WALL ROCK RELATIONSHIPS…………..…..65 3.4 ANALYTICAL TECHNIQUES AND QUANTIFICATION APPROACH………….…..67 3.4.1 Sources of uncertainty in LA-ICPMS microanalysis of fluid inclusions…….…..68 3.4.2 Bias for elements close to the limit of detection…………………………………....70 3.4.3 New quantification method for trace metals in fluid inclusions………………….72 3.5 CONCENTRATIONS OF GOLD AND OTHER ORE METALS IN METAMORPHIC FLUIDS……………………………………………………………………………………..…73 3.6 FLUID-MINERAL EQUILIBRIA MODELING…………………………………...…….76 3.6.1 Sources for thermodynamic data………………………………………..……………76 3.6.2 Input data and model conditions…………………………………………….………..79 3.6.3 Modeling results………………………………………………………………………...85 3.7 DISCUSSION AND CONCLUSIONS……………………………………………..…….86 4. 40AR/39AR GEOCHRONOLOGY DETERMINES MINERALIZATION AGES AND FORMATION TIME OF ALPINE FISSURE VEINS ON A CROSS SECTION THROUGH THE CENTRAL ALPS…………………………………………………….…………………...……89 4.1 ABSTRACT………………………………………………………………………....…….89 4.2 INTRODUCTION……………………………………………………………………..….90 4.3 GEOLOGICAL SETTING…………………………………………………………….….92 4.4 SAMPLE DESCRIPTION……………………………………………………………..….93 4.5 40AR/39AR ANALYTICAL PROCEDURE………………………………………….……97 4.6 RESULTS……………………………………………………………………………..…..99 4.7 DISCUSSION…………………………………………………………………………....108 4.7.1 Age spectrum characteristics……………………………………………………..…108 4.7.2 Crystallization versus cooling ages and closure temperature of the minerals110 4.7.3 Velocity of crystal growth…………………………………………………….111 4.7.4 Comparison with recent geochronological studies……………………………112 4.8 CONCLUSIONS……………………………………………………………..………..113 ii CONTENTS 5. THESIS CONCLUSIONS AND OUTLOOK…………………………………………..…….115 5.1 CONCLUSIONS…………………………………………..…………………………..115 5.2 OUTLOOK………………………………………………………………………….….117 REFERENCES………………………………………………………………………………….…119 CURRICULUM VITAE…………………………………………………………………….……135 APPENDIX A..………………………………………………………………………………………136     iii LIST OF FIGURES LIST OF FIGURES 2.1 Map of the Central Alps showing important geological features (major tectono- stratigraphic units, metamorphic isograds) and the location of the sampled Alpine fissure veins 17 2.2 Key field relationships of Alpine fissure veins 24 2.3 Thin sections of Faido samples 25 2.4 Representative LA-ICPMS signals for aqueous-carbonic (A, B) and aqueous (C, D) fluid inclusions 32 2.5 A,B,C-G Illustration of typical fluid inclusion assemblages (FIAs) from Alpine fissure veins and their relative time relationships 37 2.6 Variation plot of the final ice melting temperatures (Tm ) and total homogenization ice temperatures (Th ) 41 tot 2.7 Summary plot of the average composition of the fluid inclusion assemblages analyzed by LA-ICPMS from all investigated Alpine fissure veins 42 2.8 Summary diagram of the molar Cl/Br ratios obtained from FIA from Gauli, Gerstenegg, Tiefengletscher, Bedretto, Cavagnoli and Faido 44 2.9 Diagrams that illustrate the variation of (A) lithium, (B) rubidium, (C) boron, (D) potassium, (E) barium and (F) copper as function of bulk fluid salinity 45 2.10 Variation diagrams for fluid inclusion compositions 46 2.11 Comparison between modeled fluid composition and wall-rock mineral abundance and measured data. Lines show modeling results 50 2.12 Modeled host rock composition vs. observed alteration minerals 51 2.13 Diagram illustrating the estimated pressure-temperature conditions of fissure veins, compared to the peak-metamorphic conditions of their host rocks 52 2.14 Comparison between measured and calculated S, Al, Mg and Fe concentrations in vein-hosted fluids from five localities, plotted as function of temperature 56 2.15 Geological sketch map of the Central Alps, with superposed diagrams that illustrate the pressure-temperature evolution of the fissure veins and their respective host rocks 60 3.1 Map of the Central Alps showing the major tectono-stratigraphic units and sample locations 64 3.2 Photographs of typical fluid inclusion assemblages of Alpine metamorphic quartz veins 68 iv LIST OF FIGURES 3.3 Representative LA-ICPMS elemental signals (Si, Na, S, As and Au) of single aqueous (A) and aqueous-carbonic fluid inclusions (B) 70 3.4 Frequency distribution diagrams of results from 102 individual inclusions at Tiefen- gletscher, comparing all measured LOD’s with results from those analyses where a significant trace-element peak above LOD was measured 71 3.5 Example of a composite fluid inclusion signal (Tiefengletscher) 73 3.6 Summary diagram of fluid inclusion compositions 76 3.7 Variation diagrams of the average S, Ag, Au and As concentrations for each vein, obtained by summing the elemental peaks of all individual fluid inclusion signals from each locality 77 3.8 Comparison between measured (symbols) and calculated (lines) Au and S concentrations in vein-hosted fluids from five vein localities across the metamorphic profile 88 4.1 Geological map of the Central Alps with the investigated localities and the major tectonic units  91 4.2 Key features of the investigated samples 95 4.3 Inverse isochron diagrams with the results from first test singe fusion experiments 98 4.4 Summary plots for the Gauli samples KG8 and KG12 101 4.5 Summary plots for the Fibbia sample KFI4 and the Gerstenegg sample KGE1 102 4.6 Summary plots for the Fibbia samples KFI1 and KFI2 103 4.7 Summary plots for the Bedretto samples KB1 and KB2 105 4.8 Summary plots for the Cavagnoli samples KC1 and KC2 106 4.9 Summary plots for the Faido samples KF1, KF2 and KF3 107 4.10 Age plateau plots for the adularia core and rim samples (A, B and D) and the muscovite core-rim comparison (C) 109 4.11 Summary plot for all measured stepwise heating ages on top of the geological map of the Central Alps  112     v