Formation Stages and Conditions of Carbonate–Silicate Veins and Their Wall-Rock Aureoles in the Early Proterozoic Complexes of the Belomorian Mobile Belt, Northern Karelia

• Published in: Petrology Vol. 31; no. 5; pp. 538 - 557
• Main Authors: Volkov, I. S., Kozlovskii, V. M.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-10-2023; Springer Nature B.V
• Subjects: Amphibolites; Biotite; Calcite; Carbonates; Chlorite; Copper; Dolomite; Dolostone; Earth and Environmental Science; Earth Sciences; Fluids; Gangue; Geochemistry; High temperature; Mineralogy; Plagioclase; Precambrian; Quartz; Rock; Rocks; Silicates; Sulfides; Sulphides; Temperature; Thermometers; Veins (geology); amphibolite aureoles; dolomite–ankerite; metabasites; carbonate–silicate veins; chlorite; calcite; Belomorian mobile belt
• ISSN: 0869-5911; 1556-2085
• DOI: 10.1134/S0869591123050077

Archean gneisses cropping out on islands in the White Sea and its coast in northern Karelia host widespread bodies of Early Proterozoic metamorphosed gabbroids. Carbonate–silicate veins hosted in these metabasite bodies and constrained to their contacts with the gneisses contain Fe–Cu sulfides, whose concentrations occasionally reach economic levels. The dominant gangue minerals are plagioclase, quartz, carbonates, and chlorite. The formation stages of the veins correspond to the transition from the early quartz–plagioclase to late quartz–carbonate associations with chlorite and sulfides. The early (high-temperature) stage is discernible in the wall-rock amphibolite aureoles, which were formed at temperature of about 550–650°C (estimates by the TWQ method). This stage corresponds to the quartz–plagioclase association in the marginal zones of the veins. The transition to the late stage and the formation of veined quartz–carbonate (±biotite) associations occurred at temperatures of 540°C and lower, judging by the calcite–dolomite associations. The further development of the quartz–chlorite–carbonate and sulfide associations in the veins and wall-rock amphibolites corresponded to a temperature decrease to 350°C and below, as evaluated with the application of chlorite thermometers. The veins and wall-rock amphibolitization may have been induced by metamorphic fluids during the latest retrograde metamorphic stage in the Early Proterozoic.