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Microstructures in mylonites: examples from the Caledonian and Svecofennian orogens
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2012 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

The thesis is focussed on defining deformation mechanisms for different minerals to get an estimate of the temperature during deformation in a mylonite zone separating two nappes in the central Scandinavian Caledonides, the Blåhammarfjället Nappe and the Snasahögarna Nappe. In addition, kinematic indicators and relative timing of mineral growth and deformation are studied in Paleoproterozoic Svecofennian rocks in the Hamrånge area, east Central Sweden.

The work is carried out by microstructural analysis and identification of mineral assemblages in petrographic thin sections by applying optical microscopy. Composition and chemical zoning in some minerals is revealed by microprobe analysis. The latter method is also applied to identify some accessory minerals formed during or after deformation.

A temperature range of 450–600 ºC is indicated during peak deformation in the Caledonian samples and approximately 500 ºC during post-tectonic, static recrystallization. Restricted post-tectonic recrystallization and the recognition of garnet and biotite, but not e.g. chlorite, in the syn- to post-tectonic, retrograde mineral assemblage indicates that cooling was relatively fast after mylonitization.

In the Paleoproterozoic samples from the Hamrånge area, which was affected by regional metamorphism of LP-HT type, kinematic indicators are still partly visible although they are obscured by comprehensive, static recrystallization. In another sample, the sequence of mineral growth in relation to folding is established in a metagreywacke.

Place, publisher, year, edition, pages
2012. , p. 55
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-355207OAI: oai:DiVA.org:uu-355207DiVA, id: diva2:1227891
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Available from: 2018-06-27 Created: 2018-06-27 Last updated: 2018-06-27Bibliographically approved

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