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Integrated microstructural observations, X-ray powder diffractometric (XRPD) modal composition, illite Kubler index and chlorite “crystallinity” determinations and vitrinite reflectance measurements were carried out on marly slates from selected profiles of the Helvetic zone of the Central Alps, Switzerland. The studied profiles were: Upper Jurassic from the Wildhorn nappe, Brienz, Upper Jurassic from the Parautochthonous of the Aar massif, Glarus Alps, Eocene from the Griesstock nappe of the Glarus Alps and Upper Jurassic from the Axen nappe, Rhine Valley. In some of the localities studied, illite Kubler index (“crystallinity”) values were anomalously high, yielding only diagenetic conditions, while chlorite “crystallinity” and vitrinite reflectance showed anchi- and epizonal metamorphic conditions. Detailed XRPD observations carried out on Ca-saturated and glycolated mounts indicated subordinate amounts of swelling (smectitic) interstratifications in white mica. In addition to the dominant K-white mica, traces of discrete paragonite and paragonitic phases and tobelitic impurities in the form of either regular interstratifications or micas with mixed (K≫Na>NH4) interlayer compositions could be detected from the XRPD (00,10) basal reflections. On the basis of the organic maturity assumed from vitrinite reflectance, probable partitioning of N and H between organic and inorganic phases, and the results of elemental (C, H, N, S) analyses carried out on the |
