Reflectance of dispersed vitrinite in Palaeozoic rocks with and without cleavage: Implications for burial and thermal history modeling in the Devonian of Rursee area, northern Rhenish Massif, Germany

Vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks. In high grade diagenetic rocks, i.e. rocks at the boundary between diagenesis and metamorphism, vitrinites become increasingly anisotropic. Therefore, it has been suggested to study maximum/minimum reflectance instead of mean reflectance for rocks which reached this stage.In the present study, vitrinite reflectance data from a folded sequence of the northern Rhenish Massif (Germany) are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present. We show that vitrinites in different microtectonic domains (cleavage domains and microlithons) show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy. This behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons, so that vitrinite reflectance is controlled by the thermal and deformation history. Accordingly, estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial.Based on this finding, burial and temperature history of the Rursee area in the eastern Rhenish Massif is reconstructed. Numerical simulations indicate a maximum burial at the Siegen/Ems boundary of about 5000 m and a maximum burial temperature of about 220 °C.