Using single-grain zircon U-Pb dating by LA-MC-ICPMS and whole-rock geochemistry, we

have studied the Palaeoproterozoic gabbroic rocks from Moisio in southwest Finland.

Three ages were obtained. The interpreted intrusion age is ~1.86 Ga, which places it in

the 1.87–1.84 Ga intra-orogenic period of southern Svecofennia. The other ages, ~1.89

Ga and ~1.83 Ga, are inferred to be inherited and metamorphic ages, respectively.

The K, LREE, LILE, Fe-, P-, Ti- and F-concentrations reveal two compositionally distinct

groups: (i) an enriched monzogabbro group and (ii) a less enriched gabbro group. The

composition of the monzogabbro group resembles the other intra-orogenic intrusions

from southern Svecofennia, whereas the unrelated gabbro group is more comparable to

the synorogenic rocks in the region. The magma source the monzogabbro experienced a

subduction related carbonate metasomatism, induced by sediment subduction and

subduction erosion. Evidently, the Moisio monzogabbro represent enriched, mantle

derived magmatism in southern Svecofennia as a part of the intra-orogenic igneous

activity. The intra-orogenic magmatism is considered to have conveyed considerable

amounts of heat from the mantle into the crust contributing to subsequent lateorogenic

high-grade metamorphism.