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The initiation of strain localisation in plagioclase-rich rocks: Insights from detailed microstructural analyses
Stockholm University, Faculty of Science, Department of Geological Sciences. (Petrotectonics Group)
Stockholm University, Faculty of Science, Department of Geological Sciences. (Petrotectonics Group)
(English)Manuscript (preprint) (Other academic)
National Category
Geology
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-42818OAI: oai:DiVA.org:su-42818DiVA: diva2:351562
Available from: 2010-09-16 Created: 2010-09-15 Last updated: 2010-09-16Bibliographically approved
In thesis
1. Deformation behaviour and chemical signatures of anorthosites:: Examples from southern West Greenland and south-central Sweden
Open this publication in new window or tab >>Deformation behaviour and chemical signatures of anorthosites:: Examples from southern West Greenland and south-central Sweden
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plagioclase is the most abundant mineral in the lower crust and it is thus important to constrain the behaviour of plagioclase during deformation. Anorthosites, which are plagioclase-rich rocks, are common in Archaean cratons but their origin and rheological importance is still debated. The aims of this thesis are to 1) describe a newly discovered Archaean anorthosite complex (Naajat Kuuat, SW Greenland), investigate its origin and a possible genetic relationship between the anorthosite and associated mafic-ultramafic rocks and 2) to study the rheology and deformation mechanisms in plagioclase-rich rocks. The main focus of this thesis is on the deformation studies.

(1) Geochemical whole-rock analyses from the Naajat Kuuat complex are indicative for an origin near a subduction zone setting. A genetic link by crystal fractionation between the anorthosite and associated mafic-ultramafic units is inferred. (2) Deformation behaviour of plagioclase is assessed from analyses of three anorthosite units deformed during different conditions. Samples were analysed using the electron backscatter diffraction technique (EBSD) in combination with optical and chemical analyses. All three case studies show significant strain localisation related to grain size reduction. A wet anorthosite deformed at dry conditions (T ~675-700°C) was dynamically recrystallised. Continuous bands of recrystallised grains developed a texture yet display microstructures and grain relationships indicative for grain size sensitive creep, suggesting that the rheology followed a Newtonian flow law. In the other two studies, samples with initially dry and wet composition, respectively, have experienced deformation during fluid present conditions at T ~550-620°C. These two samples show that fluids effectively caused reactions, replacements and aided strain localisation during deformation at mid crustal conditions.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2010. 36 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 340
Keyword
anorthosite, plagioclase, deformation, strain localisation, fluid-rock interaction, electron backscatter diffraction (EBSD)
National Category
Geology
Research subject
Mineralogy, Petrology and Geochemistry
Identifiers
urn:nbn:se:su:diva-42854 (URN)978-91-7447-137-3 (ISBN)
Public defence
2010-10-18, De Geersalen, Geovetensskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 2 Manuscript; Paper 3 Manuscript.Available from: 2010-09-24 Created: 2010-09-16 Last updated: 2010-10-04Bibliographically approved

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