TY - JOUR

T1 - Sr- and C-Chemostratigraphy Potential of the Paleoproterozoic Sedimentary Carbonates under Medium-Temperature Metamorphism

T2 - the Ruskeala Marble, Karelia

AU - Kuznetsov, A. B.

AU - Gorokhov, I. M.

AU - Azimov, P. Ya

AU - Dubinina, E. O.

N1 - Publisher Copyright: © 2021, Pleiades Publishing, Ltd. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/4/2

Y1 - 2021/4/2

N2 - Comprehensive petrological and isotope-geochemical study of marble was carried out in the upper part of the Sortavala Group of the northeastern lense at the Ruskeala deposit in the Northern Ladoga area. The petrological study showed that the carbonate rocks of the Sortavala Group underwent medium-temperature low-pressure amphibolite-facies metamorphism. The mineral assemblages of Ruskeala marbles were formed at temperature of 550–600°C and pressure of ~3–5 kbar in equilibrium with a mixed water-carbon dioxide fluid with $${{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ ~ 0.5–0.8. Dolomite marbles contain admixture (up to 2%) of finely disseminated carbonaceous matter and about 8–15% of calcite. Dolomites contain small amounts of Mn (70–110 ppm) and Fe (1600–3600 ppm) and high content of Sr (122–256 ppm). The initial 87Sr/86Sr ratio in the dolomites is within 0.70465–0.70522, δ13C values vary between +0.6…+1.9 ‰, and δ18О within –13.2 … –10.2‰ (V-PDB). Calcite marbles are free of carbonaceous matter, have very low contents of Mg (0.2–0.8%), Mn (10–90 ppm) and Fe (160–640 ppm) and very high Sr concentration (850–2750 ppm). The initial 87Sr/86Sr ratios in the calcite marbles range from 0.70482 to 0.70489, δ13С from 1.5 to 2.1‰, and δ18О from –10.9 to ‒8.1 ‰ (V-PDB). Tremolite-bearing marbles have higher 87Sr/86Sr ratio (up to 0.70522), while their δ13С and δ18О values decrease to 0.1‰ and –12.2‰, respectively. The metamorphism of Ruskeala carbonate even under medium-temperature amphibolite-facies conditions was essentially isochemical process, which retained the unique Sr and C chemostratigraphic potential of calcite and dolomite marbles for the reconstruction of 87Sr/86Sr and δ13C in the Paleoproterozoic seawater. The 87Sr/86Sr ratio in the 1.9–2.0 Ga Svecofennian ocean was 0.70463–0.70492, and δ13С value +1.5 ± 1‰. New Sr-isotope data record an increase in radiogenic Sr input in the ocean about 2 billion years ago, which was probably related to the growth of continental crust and more intense weathering. The δ13С in Ludicovian carbonates mark the beginning of C-isotope stasis in ocean after the Lomagundi-Jatulian anomaly of 13Ccarb.

AB - Comprehensive petrological and isotope-geochemical study of marble was carried out in the upper part of the Sortavala Group of the northeastern lense at the Ruskeala deposit in the Northern Ladoga area. The petrological study showed that the carbonate rocks of the Sortavala Group underwent medium-temperature low-pressure amphibolite-facies metamorphism. The mineral assemblages of Ruskeala marbles were formed at temperature of 550–600°C and pressure of ~3–5 kbar in equilibrium with a mixed water-carbon dioxide fluid with $${{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ ~ 0.5–0.8. Dolomite marbles contain admixture (up to 2%) of finely disseminated carbonaceous matter and about 8–15% of calcite. Dolomites contain small amounts of Mn (70–110 ppm) and Fe (1600–3600 ppm) and high content of Sr (122–256 ppm). The initial 87Sr/86Sr ratio in the dolomites is within 0.70465–0.70522, δ13C values vary between +0.6…+1.9 ‰, and δ18О within –13.2 … –10.2‰ (V-PDB). Calcite marbles are free of carbonaceous matter, have very low contents of Mg (0.2–0.8%), Mn (10–90 ppm) and Fe (160–640 ppm) and very high Sr concentration (850–2750 ppm). The initial 87Sr/86Sr ratios in the calcite marbles range from 0.70482 to 0.70489, δ13С from 1.5 to 2.1‰, and δ18О from –10.9 to ‒8.1 ‰ (V-PDB). Tremolite-bearing marbles have higher 87Sr/86Sr ratio (up to 0.70522), while their δ13С and δ18О values decrease to 0.1‰ and –12.2‰, respectively. The metamorphism of Ruskeala carbonate even under medium-temperature amphibolite-facies conditions was essentially isochemical process, which retained the unique Sr and C chemostratigraphic potential of calcite and dolomite marbles for the reconstruction of 87Sr/86Sr and δ13C in the Paleoproterozoic seawater. The 87Sr/86Sr ratio in the 1.9–2.0 Ga Svecofennian ocean was 0.70463–0.70492, and δ13С value +1.5 ± 1‰. New Sr-isotope data record an increase in radiogenic Sr input in the ocean about 2 billion years ago, which was probably related to the growth of continental crust and more intense weathering. The δ13С in Ludicovian carbonates mark the beginning of C-isotope stasis in ocean after the Lomagundi-Jatulian anomaly of 13Ccarb.

KW - carbon isotopes

KW - Ludicovi

KW - marble

KW - Northern Ladoga area

KW - Paleoproterozoic

KW - regional metamorphism

KW - strontium isotopes

UR - http://www.scopus.com/inward/record.url?scp=85103831278&partnerID=8YFLogxK

U2 - 10.1134/S0869591121010033

DO - 10.1134/S0869591121010033

M3 - Article

AN - SCOPUS:85103831278

VL - 29

SP - 175

EP - 194

JO - Petrology

JF - Petrology

SN - 0869-5911

IS - 2

ER -