Phengite composition and high- pressure metamorphism of the Rheinische Schiefergebirge in the Rhenohercynian belt: implication of phengite in S2-cleavage

The white K-micas as a phengite (Si3.2-3.5) grow an alignment parallel to S-cleavage and high angles to the pre-existing structures, e.g., S1-cleavage and bedding (S0). To confirm phengite, the electron microprobe analysis is carried out in three samples from different localities in the Lahn-Dill areas. The white K-micas are common in the Rheinische Schiefergebirge, the Rhenohercynian belt, known as anaccretionary prism. In the world example of an accretionary setting, phengite micas are transformed at the high anchizone and epizone, which is different from the syn-tectonic S1-cleavage and late-tectonic S2-cleavage of Variscan in the Rhenohercynian belt. Phengite geothermobarometry analysis shows the pressure in 4.5-6.5 kbars and the temperature in 300°C. The P-T path through lower greenschist to blueschist is manifested in this study. The S2-cleavage formed as an S1-cleavage kinking due to shear in the S1-cleavage, which is deduced from the S1-cleavage rotations: one anticlockwise due to thecollision with the London-Brabant Massif and one clockwise due to the dextral shear movement of the Rhenohercynian belt during the late Variscan orogeny.