Tectonized actinolite-albite rocks from the Outokumpu district, Finland: Field and geochemical evidence for mafic extrusive origin

Abstract

Field observations and the geochemistry of major and trace elements, including REE, suggest a mafic extrusive origin for the strongly tectonized, actinolite‒albite rocks in the Miihkali arch, in the NE part of the Outokumpu district, eastern Finland. These metabasalts occur in close association with massive serpentinites. Compared with the average composition of representative basalts from modern tectonic environments their MgO, Ni and Cr contents are somewhat elevated, and their TiO2 somewhat low. The REE contents are 5x to 10x chondrites. Their pattern is flat and slightly depleted in LREE. A Proterozoic ocean floor is postulated as the depositional environment.

Keywords

• actinolite-albite rocks
• metabasalts
• geochemistry
• Proterozoic
• Outokumpu-district