Svecofennian intra-orogenic gabbroic magmatism: a case study from Turku, southwestern Finland
: Jenni Nevalainen, Markku Väisänen, Yann Lahaye, Esa Heilimo, Sören Fröjdö
Publisher: Geological Society of Finland
: 2014
: Bulletin of the Geological Society of Finland
: 86
: 2
: 93
: 112
: 20
: 0367-5211
DOI: https://doi.org/10.17741/bgsf/86.2.003
: http://www.geologinenseura.fi/bulletin/Volume86/Bulletin_vol86_2_2014_Nevalainen.pdf
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.