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«IZVESTIYA IRKUTSKOGO GOSUDARSTVENNOGO UNIVERSITETA». SERIYA «NAUKI O ZEMLE»
«THE BULLETIN OF IRKUTSK STATE UNIVERSITY». SERIES «EARTH SCIENCES»
ISSN 2073-3402 (Print)

List of issues > Series «Earth Sciences». 2026. Vol 55

The Parameters of Formation and Crystallization of Early Proterozoic I-type Granitoids of the Mogdinsk Borehole (Nepа-Botuobiya Anteclise, Central Part of the Siberian Platform)

Author(s)

M. O. Sukneva1,2, T. V. Donskaya1

1Institute of the Earth’s Crust SB RAS, Irkutsk, Russian Federation

2Vinogradov Institute of Geochemistry SB RAS, Irkutsk, Russian Federation

Abstract
In this paper we present the results of detailed petrographic, mineralogical, geochemical studies, as well as estimation of P-T parameter of formation and crystallization for the Early Proterozoic granitoids of one the borehole of the Mogdinsk group (Mogdinsk-11) located in the central part of the Nepa-Botuobiya anteclise of the Siberian platform. The representative sample of these granitoids corresponds to I-type amphibole granosyenite in its mineralogical and geochemical properties. The main rock-forming minerals of the granosyenite are quartz, amphibole, plagioclase, and potassium feldspar. Amphiboles are similar in composition to magnesian hornblende, and plagioclases correspond to oligoclase. Accessory minerals are titanite, apatite, zircon and magnetite. The granosyenite are charactirized by SiO2 = 64 wt.% and (Na2O+K2O) = 9 wt.%.The rock have magnesian, metaluminous (ASI = 1,0), and I-type granite-like compositions with Sr = 1152 ppm, Ba = 2629 ppm, Nb = 12 ppm, Th = 2 ppm. The REE spectra is fractionated, with (La/Yb)n = 14, and without Eu anomaly, Eu/Eu* = 1,06. We have defined the parameters of formation and crystallization of the parental melt for granosyenite using a series of geothermometers and geobarometers. The apatite saturation temperature obtained for the amphibole granosyenite is 901 °C. The zircon saturation temperatures are 752–774 °C. The amphibole-plagioclase and amphibole geothermometers gave the temperatures of 730–744 °C. The Al-in-hornblende, and amphibole–plagioclase geobarometers allowed to calculate pressures as 2,6–2,8 kbar. The studied granosyenite belong to magnetite series, contains the mineral association titanite–magnetite–quartz and are characterized by low Fe/(Fe+Mg) ratios in amphiboles. This indicates that they could form under high oxygen fugacity conditions. We tested about twenty geothermometers and geobarometers, but the most correct parameters of formation and crystallization of the I-type amphibole granosyenite of the Mogdinsk borehole were obtained using apatite and zircon saturation temperature expressions, amphiboleplagioclase and amphibole geothermometers, as well as amphibole geobarometers. The results obtained using these geothermometers and geobarometers are correct mainly due to the mineral composition of the granosyenite and chemical composition of both granosyenite and the amphibole and plagioclase maximally satisfy the conditions under which these geothermometers and geobarometers allow giving correct results for I-type amphibole granitoids.
About the Authors

Sukneva Maria Olegovna, laboratory Assistant Institute of the Earth's Crust SB RAS 128, Lermontov st., Irkutsk, 664033, Russian Federation Engineer Vinogradov Institute of Geochemistry SB RAS 1a, Favorsky st., Irkutsk, 664033, Russian Federation e-mail: masha.sukneva@mail.ru

Donskaya Tatiana Vladimirovna, Corresponding Member of RAS Doctor of Sciences (Geology and Mineralogy), Chief Research Scientist Institute of the Earth's Crust SB RAS 128, Lermontov st., Irkutsk, 664033, Russian Federation e-mail: tanlen@crust.irk.ru

For citation
Sukneva M.O., Donskaya T.V. The Parameters of Formation and Crystallization of Early Proterozoic I-type Granitoids of the Mogdinsk Borehole (Nepа-Botuobiya Anteclise, Central Part of the Siberian Platform). The Bulletin of Irkutsk State University. Series Earth Sciences, 2026, vol. 55, pp. 94-115. https://doi.org/10.26516/2073-3402.2026.55.94 (in Russian)
Keywords
I-type granitoids, amphibole, geothermobarometry, Siberian platform.
UDC
552.32:552.11:551.72(571.53/.55)
DOI
https://doi.org/10.26516/2073-3402.2026.55.94
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