The pioneer work of Bernard Kübler and Martin Frey in very low-grade metamorphic terranes: paleo-geothermal potential of variation in Kübler-Index/organic matter reflectance correlations. A review - Archive ouverte HAL
N°Spécial De Revue/Special Issue Swiss Journal of Geosciences Année : 2012

The pioneer work of Bernard Kübler and Martin Frey in very low-grade metamorphic terranes: paleo-geothermal potential of variation in Kübler-Index/organic matter reflectance correlations. A review

Résumé

Low-temperature metamorphic petrology occupies the P–T field between sedimentary and metamorphic petrology. Two important pillars of low-temperature metamorphism are coal petrology and claymineralogy. When low temperature petrology was established bridging a hiatus between the two classical geological disciplines of sedimentary geology and metamorphic petrology, geologists faced a need for the usage of different terminology tenets.Martin Frey and Bernard Ku¨bler were two pioneers in low-grade metamorphic petrology. They focused their research on clarifying the relationships of clay mineralogy and organic petrology to metamorphic pressure (P) and temperature (T) conditions. The ultimate aim of M. Frey and B. Ku¨bler was to establish a correlation between clay indices and organic parameters for different geodynamic setting and therefore for various pressure– temperature (P–T) conditions occurring in low grade metamorphic terranes. For this purpose, a special attention was addressed to the correlation between the Ku¨bler-Index (KI) and vitrinite reflectance (VR). All these efforts are dedicated to estimate the P–T conditions and thus to gain insight into the geodynamic evolution of low-grade metamorphic terranes. B. Ku¨bler and M. Frey honored here concentrated their studies to the Helvetic Central Alps area. The very lowgrade Helvetic domain is therefore of basic interest of this paper. Ensuing the extensive compilation of data from the Helvetic domain, a reinterpretation of Ku¨bler and Frey’s research is presented in the light of last decade’s scientific progress. A comprehensive dataset available enables to discriminate many factors influencing the Ku¨bler-Index and organic-matter reflectance alongside to time, temperature and pressure. The correlation is restricted to the KI and organic matter reflectance (mostly VR) because most of the studies used both methods. Organic matter reflectance (OMR) includes data from vitrinite reflectance and bituminite reflectance measurements. Geodynamics has important control on the KI/VR (OMR) correlation. Tectonic units having a similar geodynamic evolution are featured by the comparable KI/OMR trends, related to the particular paleo-geothermal conditions. Obviously the KI/OMR correlations provide a mean to characterise geothermal gradients and metamorphic very-low-grade pressure–temperature conditions. In terranes where high deformations rates are reported, exceeding the high anchizone conditions, strain promotes the kinetic effects of temperature and pressure on the KI versus OMR ratio.

Dates et versions

hal-04130026 , version 1 (15-06-2023)

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Rafael Ferreiro Mählmann, Ömer Bozkaya, Sébastien Potel, Ronan Le Bayon, Branimir Šegvić, et al.. The pioneer work of Bernard Kübler and Martin Frey in very low-grade metamorphic terranes: paleo-geothermal potential of variation in Kübler-Index/organic matter reflectance correlations. A review. Swiss Journal of Geosciences, 105 (2), pp.121-152, 2012, ⟨10.1007/s00015-012-0115-3⟩. ⟨hal-04130026⟩
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