From diagenesis to anchimetamorphism, upper Austroalpine sedimentary cover in Bavaria and Tyrol

Publisher Website
Google Scholar
Abstract
Vitrinite reflectance and illite crystallinity of a great number of samples of fine-grained Mesozoic sediments from the Northern Calcareous Alpes between Allgäu and the Karwendel Mountains have been investigated. Coalification varies from 0,4 % Rr to 6,2 % Rmax and allows a significant description of the low diagenetic temperature distribution in the greatest part of this area. For most stratigraphiC units, reliable correlations between vitrinite reflectance and illite crystallinity can be established. By means of both methods the fields of diagenesis and anchimetamorphism are subdivided into five stages. A comprehensive coal rank map, based on outcrop specimen is published. It represents the amount and the distribution of the weak alpidic temperature effects within the uppermost Austroalpine nappes. From the northern to the southern rim of the Northern Calcareous Alps and in each tectonic unit, a general temperature increase is charateristic. Nevertheless, rank disconformities and anomalies are widespread, caused by tectonic structures. They depend on the pre-orogenetic increase in diagenesis with depth, preserved in every single nappe sheet. The anchimetamorphic stage appears at the southern rim of the Northern Calcareous Alps (Lechtal Unit) and was obviously developed during nappe-piling, i.e. synorogenctic (Eo-Alpidic). In the southwestern part of the Lechtal Alps a younger post-nappe distinctly minor overprint of maturity is found. It is attributed to the heating effect of the Tertiary (Meso- to Neo-Alpidic) metamorphism of the Penninic. A subsequent northward movement of the Ötzal-Stubai Complex, overriding the Northern Calcareous Alps, is proved by the absence of anchimetamorphic rocks along the Inn valley 25 km in length.