Fluid regime and the behavior of ore, trace, and rare-earth elements during granitization of metagabbro-norites of the Belomorian Group (Gorelyi Island, Kandalaksha Bay)

Abstract

The study of metagabbro-norites of the Belomorian Group metamorphosed under the amphibolite-lower granulite facies conditions (Gorelyi Island, Kandalaksha Bay) showed that at contact with Bt-Hbl-Kfs-Pl-Qtz gneiss-granites they were affected by silicic-alkaline H2O-Cl-CO2 brines, which caused the enrichment in alkalis, silica, Rb, Ba, Pb, Zr, LREE and redistribution of Cu, Zn, Cr, Co, V, and Ni along the filtration pathway. The granitization of metagabbro-norite proceeded simultaneously with increase in fluid oxygen fugacity from one log unit below to four log units above QFM. The microprobe determinations of Cl content in biotites and apatites made it possible to calculate variations in the \( f_{H_2 O} \)-fHCl relations in fluid during its percolation through the rock. It was shown that biotite was formed at metamorphic peak in the presence of highly aggressive high-fHCl fluids (log \( f_{H_2 O} \)/fHCl ≈ 0.8–1.2). Apatite was formed in the presence of less acid and more aqueous residual solutions (log \( f_{H_2 O} \)/fHCl ≈ 2.98−3.91), which presumably lost their salt components at metamorphic peak. The calculations showed that the flux of fluid that percolated through the rock during granitization accounted for q ≈ 4 × 102 to 2 × 103 cm3/cm2. Due to insignificant volume of the fluid, the transformations spanned only marginal part of the metagabbro-norites on Gorelyi Island.