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How Do Metamorphic Fluids Move Through Rocks? an Investigation of Timescales, Infiltration Mechanisms and Mineralogical Controls

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How Do Metamorphic Fluids Move Through Rocks? an Investigation of Timescales, Infiltration Mechanisms and Mineralogical Controls How do metamorphic fluids move through rocks? An investigation of timescales, infiltration mechanisms and mineralogical controls Barbara I. Kleine ©Barbara I. Kleine, Stockholm University 2015 ISBN 978-91-7649-120-1 Cover picture: A relict of glaucophane from Fabrika Beach. Printed in Sweden by Holmbergs, Malmö 2015 Distributor: Publit Abstract This thesis aims to provide a better understanding of the role of mountain building in the carbon cycle. The amount of CO2 released into the atmosphere due to metamorphic processes is largely unknown. To constrain the quantity of CO2 released, fluid-driven reactions in metamorphic rocks can be studied by tracking fluid-rock interactions along ancient fluid flow pathways. The thesis is divided into two parts: 1) modeling of fluid flow rates and durations within shear zones and fractures during greenschist- and blueschist-facies metamorphism and 2) the assessment of possible mechanisms of fluid infiltration into rocks during greenschist- to epidote-amphibolite-facies metamorphism and controlling chemical and mineralogical factors of reaction front propagation. On the island Syros, Greece, fluid-rock interaction was examined along a shear zone and within brittle fractures to calculate fluid flux rates, flow velocities and durations. Petrological, geochemical and thermodynamic evidence show that the flux of CO2-bearing fluids along the shear zone was 100-2000 times larger than the fluid flux in the surrounding rocks. The time- averaged fluid flow velocity and flow duration along brittle fractures was calculated by using a governing equation for one-dimensional transport (advection and diffusion) and field-based parameterization. This study shows that fluid flow along fractures on Syros was rapid and short lived. Mechanisms and controlling factors of fluid infiltration were studied in greenschist- to epidote-amphibolite-facies metabasalts in SW Scotland. Fluid infiltration into metabasaltic sills was unassisted by deformation and occurred along grain boundaries of hydrous minerals (e.g. amphibole) while other minerals (e.g. quartz) prevent fluid infiltration. Petrological, mineralogical and chemical studies of the sills show that the availability of reactant minerals and mechanical factors, e.g. volume change in epidote, are primary controls of reaction front propagation. III Sammanfattning Denna avhandling syftar till att öka förståelsen för bergskedjebildningens roll i kolcykeln. Mängden CO2 som släpps ut i atmosfären till följd av metamorfa processer under orogens är i stort sett okända. För att bestämma den mängd CO2 som frigörs, kan fluiddrivna reaktioner i metamorfa bergarter studeras genom att spåra växelverkan mellan fluid och berggrund längs tidigare flödesvägar. Avhandlingen är uppdelad i två delar: 1) modellering av flödeshastigheter och deras varaktighet i skjuvzoner och sprickor under grönskiffer och blåskiffer facies-metamorfos och 2) undersökning av möjliga mekanismer för fluiders infiltrering i bergarter under grönskiffer till epidot-amfibolit facies-metamorfos, samt kemiska och mineralogiska kontrollfaktorer som påverkar reaktions frontens utbredning. På den grekiska ön Syros undersöktes fluid-berggrundsinteraktionen längs en skjuvzon och i sprickor för att beräkna flödeshastigheter och deras varaktighet. Bevis från petrologiska, geokemiska och termodynamiska studier visar att flödet av CO2-bärande fluider längs skjuvzonen var 100-2000 gånger större än flöden i det omgivande berget. Med hjälp av en styrande ekvation för endimensionell transport (advektion och diffusion) och parametrar framtagna i fält kunde den genomsnittliga tidsflödeshastigheten och varaktigheten av flöden längs sprikorna, vilka skär igenom kvarts-glimmer skiffrar, beräknas. Denna studie stödjer att fluidflöden längs sprickor på Syros var snabba och kortlivade. Mekanismer och kontrollerande faktorer för fluiders infiltrering studerades i grönskiffer till epidot-amfibolit facies-metabasalter i sydväst Skotland. Bevis som presenteras i denna studie visar att fluidinfiltreringen i metabasalter skedde längs korngränser av vattenhaltiga mineral (t.ex. amfibol) medan andra mineral (t.ex. kvarts) förhindrar infiltrering. Infiltreringen skedde utan påverkan från deformation. Stöd från mineralogiska och kemiska profiler genom dessa metabasalter, och de reaktions texturer som bevarats inom dem visar att tillgången på reagerande mineral och mekaniska faktorer, såsom volymförändringar i epidot kontrollerar fluiddrivna reaktionsfronters utbredning under metamorfos. IV List of papers/ manuscripts This thesis is comprised of a summary that outlines the main aims and implications of this doctoral dissertation and the key results. The following manuscripts are included in the thesis. Paper I is reprinted with the permission of the Oxford University Press Journals. Papers II and III are submitted and paper IV is a manuscript. Paper I Kleine, B.I., Skelton, A.D.L., Huet, B., Pitcairn, I.K. (2014). Preservation of blueschist-facies minerals along a shear zone by coupled metasomatism and fast-flowing CO2-bearing fluids. Journal of Petrology, 55, 1905-1939. Paper II Kleine, B.I., Zhao, Z., Skelton, A.D.L. (submitted to American Journal of Science). Rapid fluid flow along fractures at greenschist-facies conditions on Syros, Greece. Paper III Kleine, B.I., Pitcairn, I.K., Skelton, A.D.L. (submitted to American Mineralogist). The mechanism of infiltration of metamorphic fluids recorded by hydration and carbonation of epidote-amphibolite-facies metabasaltic sills in the SW Scottish Highlands. Paper IV Kleine, B.I., Pitcairn, I.K., Skelton, A.D.L. (manuscript). Pre-metamorphic controls on the propagation of fluid-driven reaction fronts at greenschist-facies metamorphic conditions. B. Kleine was the main contributor in terms of field work, analyses and the writing of all four manuscripts, with help from all of the co-authors. For paper II, Zhihong Zhao derived the transport equations for inverse modeling of fluid flow along fractures. The ideas for paper I were developed primarily by B. Kleine and A. Skelton. B. Kleine and Z. Zhao proposed the ideas for paper II. The ideas behind papers III and IV were developed by B. Kleine and I. Pitcairn. V Table of Contents Abstract .................................................................................................................................... III Sammanfattning ....................................................................................................................... IV List of papers/ manuscripts ....................................................................................................... V Introduction ................................................................................................................................ 1 Metamorphic fluids .................................................................................................................... 2 Formation and migration of metamorphic fluids .................................................................... 2 Fluid-rock interactions and reaction textures ......................................................................... 2 Isochemical reactions .......................................................................................................... 3 Metasomatic reactions ........................................................................................................ 3 Pseudomorphism ................................................................................................................. 4 T-XCO2 diagrams and pseudosections ..................................................................................... 5 Calculation of metamorphic fluid fluxes ................................................................................ 7 Time-integrated fluid fluxes................................................................................................ 8 Time-averaged fluid fluxes ................................................................................................. 8 Controls on metamorphic fluid flow ...................................................................................... 8 Study sites .................................................................................................................................. 9 The Cycladic archipelago in Southern Greece ....................................................................... 9 Geological background ....................................................................................................... 9 Metamorphic fluid flow in the Cyclades .......................................................................... 11 Fabrika Beach ................................................................................................................... 12 Delfini ............................................................................................................................... 12 The SW Scottish Highlands .................................................................................................. 12 Geological background ..................................................................................................... 12 Metamorphic fluid flow in the SW Scottish Highlands .................................................... 13 Loch Stornoway ................................................................................................................ 14 The Ard of Port Ellen .......................................................................................................
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