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

University essay from Stockholms universitet/Institutionen för geologiska vetenskaper


Meta-mafic intrusions with an intrusion age of 1.6-0.9 Ga are found along a north-south trend in theTransitional section of the Eastern Segment in Sweden. These intrusions are garnet-bearing and thus anexception to other meta-mafic intrusions found in Sweden. Meta-mafic intrusions that are garnet-bearingare usually found in the Caledonides to the northeast and in the south west of Sweden where the pressureshave been naturally high due to orogenic events or subduction.The study was conducted on these intrusions around the community of Ölme, to understand themetamorphic and metasomatic history of the area. The focus lies on the transition from magmaticgabbroic intrusions to metamorphosed metagabbros and highly foliated garnet-amphibolites. AveragePT estimates was calculated using THERMOCALC and classical geothermobarometry, so that acomparison between the qualitative and quantitative data could be made.The study indicates metamorphism at amphibolite to upper amphibolite facies conditionsfor the metagabbros and the garnet-amphibolites.Average PT-estimates for the garnet-amphibolites gives metamorphic peak temperatures of 680°-730° Cwith pressures of 9.0-11.0 kbar at the Träfors locality, and metamorphic peak temperatures of 660°-770° Cwith pressures of 9.5-11.0 kbar at the Skråkvik locality. These results are comparable to research donefurther to the south on similar intrusions, with temperatures of 700° C and pressures of 10 kbar.It is concluded that the meta-mafic intrusions at the Skråkvik locality have been metamorphosed in adry system, in contrast to the Träfors locality which seems to have been affected by more pervasiveretrograde metamorphism and fluid-rock interaction. It is also concluded that mafic intrusionscan preserve their magmatic textures even under high pressure conditions.

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