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Rapid fluid flow along fractures at greenschist-facies conditions on Syros, Greece
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Using an equation for one-dimensional transport by advection along a single fracture and transverse diffusion outwards from this fracture to model field, petrological and geochemical data we calculated time-averaged fluid velocities and constrain the duration of fluid flow along brittle fractures cutting through greenschist-facies metamorphosed quartz-mica schists at Delfini on Syros, Greece. These quartz and carbonate filled fractures are surrounded by symmetrical dark reaction halos. These reaction halos were formed by diffusion of CO2 outwards from the fracture in a hydrous fluid which caused carbonation of the country rock. Changes in concentration of relatively mobile elements (e.g. K, Na, Cs, Ba, Pb and Sr) occurred. However, little to no changes in most of the major elements and less mobile trace elements were observed. This implies that carbonation was largely isochemical with respect to most non-volatile components. The Sr/Ca ratio was used to model time-averaged fluid velocities and the duration of fluid flow along the fractures. Fluid flow along narrower fractures with discernibly tapering haloes was found to be rapid (10-6 to 10-5 ms-1) and short lived (0.1 to 400 years). These are time-averaged values and can therefore alternatively record a series of even shorter and faster pulses, perhaps associated with fracture propagation and associated seismicity. Within the widest fractures with constant halo widths (ca. 60 cm) fluid flow was slower (10-8 to 10-6 ms-1) and longer lived (100 to 15000 years). We suspect that the constant width of these haloes reflects a steady state having been reached at which halo width was controlled by the relative rates of fluid flow along the fracture and in the surrounding rock.

Keyword [en]
Fluid flow velocities, one-dimensional transport modeling, metamorphic fluid flow, carbonation, greenschist-facies metamorphism
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-115168OAI: oai:DiVA.org:su-115168DiVA: diva2:795873
Available from: 2015-03-17 Created: 2015-03-17 Last updated: 2016-01-29Bibliographically approved
In thesis
1. How do metamorphic fluids move through rocks?: An investigation of timescales, infiltration mechanisms and mineralogical controls
Open this publication in new window or tab >>How do metamorphic fluids move through rocks?: An investigation of timescales, infiltration mechanisms and mineralogical controls
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2015. 35 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 356
Keyword
Metamorphic fluid flow, fluid-rock interaction, fluid infiltration mechanisms, fluid flux rates, thermodynamic modeling, reaction front propagation, fluid flux calculation
National Category
Geology
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-115172 (URN)978-91-7649-120-1 (ISBN)
Public defence
2015-04-28, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

 

Available from: 2015-03-31 Created: 2015-03-17 Last updated: 2015-06-18Bibliographically approved

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