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HPP-01 General contributions to Precambrian geology
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IR-spectroscopy and C isotope results of Palaeoproterozoic graphitic schists at outokumpu, Finland
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Ludmila Taran, Institute of Geochemistry and Geophysics, NAS of Belarus (Belarus)
Kirsti Loukola-Ruskeeniemi, Helsinki University of Technology (Finland)
Elena Kozlovskaya, Sodankylä Geophysical Observatory/Oulu Unit, University of Oulu (Finland)
Maria Onoshko, Institute of Geochemistry and Geophysics, NAS of Belarus (Belarus)
Nikolai Michailov, Institute of Geochemistry and Geophysics, NAS of Belarus (Belarus)
Igor Kolosov, Institute of Geochemistry and Geophysics, NAS of Belarus (Belarus)
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Samples of graphite-bearing rocks were collected from three intervals of the Outokumpu Deep Drill Hole drill core representing different stratigraphic levels. Corganic of the samples varies from 1.42 to 16.1 %. The lower values of Corganic (1.42 - 8.35 %, average 4.78 %) were from the upper part of the section representing mostly metasedimentary sequence. The middle (1332.25 - 1514.30 m) and the lower (1514.30 - 2516.0 m) parts where graphitic schists are associated with serpentinites, are characterized with higher values of Corganic (8.68 - 16.1 %, average 11.24 %).
Organic matter of the graphitic rocks composes of insoluble and bitumoid parts. Insoluble part significantly predominate (93.9 - 97.0 %) while values of bitumoids vary from 0.52 to 2.17 %. Concentration of bitumoid C (alcohol-bensole type) is 2 - 14 times higher bitumoid A (chloroform type), a characteristic feature for graphitic rocks in the Fennoscandian Shield. The highest concentrations of bitumoid C were measured from the middle and lower parts of the section. In contrast to bitumoid A, content of bitumoid C is positively correlated with Corganic.
Infra red spectra of bitumoids demonstrate aliphatic character of the structure. Aliphatic compounds are mostly represented by CH2- and CH3-groups (2925 - 2855 cm-1) as well C = O acids, ethers, ketones and aldegites (1740 - 1700 cm-1). Absorb lines at 1300 - 1000 cm-1, 1680 - 1600 cm-1 and 3400 cm-1 display different oxygen-bearing groups. Predominance of aliphatic and oxygen-bearing groups in bitumen structure suggests sapropel origin. Particularities of distribution of Corganic and chemical changes in bitumen composition along the core section might evidence for different sources of organic matter and possibly re-deposition.
Carbon isotope σ13C values of graphitic C vary from -18.4 to -27.4 ‰. The values are within the range of those measured earlier in the Kainuu-Outokumpu region. Graphitic schists from the middle part of the core in association with serpentinite show more elevated σ13C values up to -18.4 and -22 ‰. The higher values may suggest the incorporation of isotopically heavy carbon species during metamorphism, probably resulted from reaction of decarbonation in Ca-bearing rocks.
This study was supported by the Academy of Finland (exchange visitors grant No. 121490) and Belarussian Fond for Fundamental Investigations, grant X07MC - 014
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