This geothermobarometric investigation of St Persholmen, Utö, in the south central part of Sweden presents an attempt at determining the metamorphic conditions of this important part of the Svecofennian province. Belonging to the geology of the Bergslagen area, Utö historically represent part of Sweden’s vast ore resources with concentrations of iron, copper and sulfides. Rock types from this area are around 1.91-1.89 Ga old (Stephens et al. 2009) and as such Paleoproterozoic in age. The rocks on Utö are considered representative of Bergslagen and record the closing of an ocean starting with subduction followed by volcanic episodes and orogeny (Talbot 2008). The bedrock we observe at Persholmen is thought to represent the remains of the aforementioned orogeny where greywackes from the oceanic stage have been preserved at the base of the mountain range (Stålhös 1982). The two rock types of interest at Persholmen which have been evaluated in this study are 1) normal greywackes and 2) greywackes which have been migmatised either because of the influence of fluids, reworking in an accretionary prism or melted at the base of a mountain range. In this project the area of study has been mapped and samples have been retrieved in order to distinguish the mineralogy and metamorphic history of the bedrock. After petrographic analysis I have determined mineral chemistry by the use of a SEM (Scanning Electron Microscope). These chemical data have then been entered into the computer programs AX and THERMOCALC for determination of temperature and pressure. For the normal/migmatised greywackes a temperature of 538 ±36/756±133°C and a pressure of 3.1±1.3/3.8±3.2 kbars respectively have been estimated. Two generations of muscovite provide evidence of fluid-rock interactions and at the north coast of Persholmen the occurrence of sillimanite indicates a high grade of metamorphism.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-92298 |
| Date | January 2011 |
| Creators | Engström, Adam |
| Publisher | Stockholms universitet, Institutionen för geologiska vetenskaper |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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