Bachelor Thesis presentation by Diana Carlsson

Qualitative and quantitative petrography of meta-mafic rocks at Ölme, in the Eastern Segment of the Sveconorwegian orogen

Supervisors: Professor Alasdair Skelton and Jenny Andersson at the Swedish Geological Survey
Examiners: Iain Pitcairn and Christophe Dupraz

Time and date: Wednsday, November 11, 10.00–11.00
Place: Room U29, Geohuset (link to the house plan)

Meta-mafic intrusions with an intrusion age of 1.60.9 Ga are found along a north-south trend in the Transitional section of the Eastern Segment in Sweden. These intrusions are garnet-bearing and thus an exception to other meta-mafic intrusions found in Sweden. Meta-mafic intrusions that are garnet-bearing are usually found in the Caledonides to the northeast and in the south west of Sweden where the pressures have been naturally high due to orogenic events or subduction. 

The study was conducted on these intrusions around the community of Ölme, to understand the metamorphic and metasomatic history of the area. The focus lies on the transition from magmatic gabbroic intrusions to metamorphosed metagabbros and highly foliated garnet-amphibolites. Average PT estimates was calculated using THERMOCALC and classical geothermobarometry, so that a comparison between the qualitative and quantitative data could be made.
The study indicates metamorphism at amphibolite facies conditions for the metagabbros and the garnet-amphibolites.
Average PT-estimates for the garnet-amphibolites gives metamorphic peak temperatures of 680°730° C with pressures of 9.011.0 kbar at the Träfors locality, and metamorphic peak temperatures of 660°770° C with pressures of 9.511.0 kbar at the Skråkvik locality. These results are comparable to research done further to the south on similar intrusions, with temperatures of 600°630° C and pressures of 1012 kbar.
It is concluded that the meta-mafic intrusions at the Skråkvik locality have been metamorphosed in a dry system, in contrast to the Träfors locality which seems to have been affected by more pervasive retrograde metamorphism and fluid-rock interaction. It is also concluded that mafic intrusions can preserve their magmatic textures even under high pressure conditions.



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