Geochemical Classification of Thuringian Granites using Multi-Dimensional Scaling

Granitoid complexes have gained increasing importance and scientific interest. They play a significant role as a repository for highly radioactive waste and in the exploration of deep geothermal potential. Geochemical variations, grain size differences and age are well suited for classifying granites; however also influence their rheological and petro-physical properties. A detailed understanding of these properties is necessary to draw conclusions about the thermal and hydraulic behavior.

A number of granite intrusions characterizes the Mid-German Crystalline Zone (MGCZ) and the Saxo-Thuringian Zone (STZ). These syn- to post-variscan magmatites are part of a complex arrangement with low- to high-grade metamorphic rocks. With approximately 20 “different” intrusive bodies, the classification of the Thuringian granitic rocks suggests a broad variety. Zircon crystallization ages range between 340 Ma and 280 Ma (e.g. Zeh et al. 2005; Thieme et al. 2023). However, there is no correlation of these intrusion ages and the intrusion bodies recognizable.

Whole-rock geochemical classification of the granitoids of the MGCZ and the STZ includes the analysis of 80 samples. To visualize differences and to identify similar chemical signatures, multidimensional scaling and clustering of the Kolmogorov-Smirnov similarities was applied.

The optimal number of clusters resulted in six geochemical types for the MGCZ and five for the STZ. These correlate with the petrological-structural description of the samples. Almost all geochemical types occur in almost all "different" intrusive bodies. Considering the crystallization ages with regard to the petrological-structural-geochemical results, the granitic rocks of the MGCZ and STZ indicates successive intrusions.