TY - JOUR

T1 - Fluid Regime of Gneiss Formation in the Meyeri Thrust Zone of the Northern Ladoga Area (South–Eastern Fennoscandian Shield)

AU - Baltybaev, S. K.

AU - Vivdich, E. S.

AU - Galankina, O. L.

AU - Borisova, E. B.

N1 - Baltybaev, S.K., Vivdich, E.S., Galankina, O.L. et al. Fluid Regime of Gneiss Formation in the Meyeri Thrust Zone of the Northern Ladoga Area (South–Eastern Fennoscandian Shield). Petrology 30, 171–197 (2022). https://doi.org/10.1134/S0869591122020023

PY - 2022/3/12

Y1 - 2022/3/12

N2 - Overthrusting of the allochthonous Svecofennian block onto the autochthonous block of the Karelian Craton margin caused compression and decompression in the Meyeri thrust zone of the Northern Ladoga area, which are recorded by the thermobarometry of mineral paragenesis in para- and orthogneisses. The highest calcium garnets in paragenesis with medium-calcium plagioclase, as well as biotite and/or muscovite yielded the mineral formation pressures up to 8–9 kbar, which is 2–3 kbar higher than metamorphic pressures typical of rocks surrounding the thrust zone. This is related to the additional pressure caused by the tectonic load on the rocks in the thrust zone. The subsequent evolution of the PT parameters of gneiss metamorphism indicates a simultaneous decrease in temperature and pressure until reaching the minimum values of Т = 500–550°С and Р = 1.6–3 kbar. The water activity in a metamorphic fluid was determined from mineral reactions with hydrous minerals within the range of ~0.20–0.44. Despite the narrow range, aH2O shows some variations at the present-day erosion level of the thrust zone, with the lowest value found in pre-muscovite garnet–biotite parageneses. An increase of water fraction in the metamorphic fluid and the appearance of muscovite parageneses did not lead to an increase in aH2O due to a simultaneous increase in the content of salt components in the fluid. The salt composition of the metamorphic fluid is revealed from the replacement of early minerals by late ones, the formation of which requires the presence of Na+ and K+ in the fluid.

AB - Overthrusting of the allochthonous Svecofennian block onto the autochthonous block of the Karelian Craton margin caused compression and decompression in the Meyeri thrust zone of the Northern Ladoga area, which are recorded by the thermobarometry of mineral paragenesis in para- and orthogneisses. The highest calcium garnets in paragenesis with medium-calcium plagioclase, as well as biotite and/or muscovite yielded the mineral formation pressures up to 8–9 kbar, which is 2–3 kbar higher than metamorphic pressures typical of rocks surrounding the thrust zone. This is related to the additional pressure caused by the tectonic load on the rocks in the thrust zone. The subsequent evolution of the PT parameters of gneiss metamorphism indicates a simultaneous decrease in temperature and pressure until reaching the minimum values of Т = 500–550°С and Р = 1.6–3 kbar. The water activity in a metamorphic fluid was determined from mineral reactions with hydrous minerals within the range of ~0.20–0.44. Despite the narrow range, aH2O shows some variations at the present-day erosion level of the thrust zone, with the lowest value found in pre-muscovite garnet–biotite parageneses. An increase of water fraction in the metamorphic fluid and the appearance of muscovite parageneses did not lead to an increase in aH2O due to a simultaneous increase in the content of salt components in the fluid. The salt composition of the metamorphic fluid is revealed from the replacement of early minerals by late ones, the formation of which requires the presence of Na+ and K+ in the fluid.

KW - fluid

KW - metamorphism

KW - mineral paragenesis

KW - PT-parameters

KW - thrust zone

KW - water activity

KW - ROCK INTERACTION

KW - KHONDALITE BELT

KW - U-PB

KW - PELITIC ROCKS

KW - DUCTILE SHEAR ZONE

KW - EQUILIBRIUM

KW - CARBON-DIOXIDE

KW - VOLUME LOSS

KW - TECTONIC EVOLUTION

KW - HENGSHAN COMPLEX

UR - http://www.scopus.com/inward/record.url?scp=85126250680&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/f7ae66d8-ba8d-3b45-a6ae-b17654db4027/

U2 - 10.1134/s0869591122020023

DO - 10.1134/s0869591122020023

M3 - Article

AN - SCOPUS:85126250680

VL - 30

SP - 171

EP - 197

JO - Petrology

JF - Petrology

SN - 0869-5911

IS - 2

ER -