Geochemistry and tectonic setting of the Orvar Hill mafic volcanic rocks of the Tiveden area, south‐central Sweden

Abstract

The Orvar Hill formation in Tiveden, south‐central Sweden, constitutes a unique low‐strain window of well preserved Svecofennian mafic volcanic rocks on the southwestern border of the Svecokarelian orogen. The area can be considered as the southwestern border of the Bergslagen region of the Svecokarelian orogen. The Orvar Hill formation consists of coherent pillowed and non‐pillowed basalts alternating with mafic volcaniclastic rocks in the lower part of the Lindberga supracrustal succession. Only minor felsic volcanic rocks occur in the upper part. Quartz‐bearing metagreywackes comprise the top part of the Lindberga supracrustal succession. Geochemistry of lavas and volcaniclastic rocks suggests that the Orvar Hill mafic volcanic rocks were emplaced in a volcanic‐arc setting. This demonstrates that the Tiveden supracrustal units probably formed in response to volcanism related to subduction. The Tiveden area may thus represent a 1.89 Ga primitive, sediment‐starved volcanic arc at the margin of the continental volcanic arc of the Bergslagen district. The relationship between Tiveden and Bergslagen at the time of formation is not clear and Tiveden may represent a remnant of an arc that accreted to a continent at c. 1.88–1.86 Ga. Björklund, L. & Weihed, P., 1997: Geochemistry and tectonic setting of the Orvar Hill mafic volcanic rocks of the Tiveden area, south‐central Sweden. GFF, Vol. 119 (Pt. 2, June), pp. 127–134. Stockholm. ISSN 1103–5897.