Journal of Geosciences Insights

ABSTRACT

The white K-micas as a phengite (Si_3.2-3.5) grow an alignment parallel to S₂-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 dierent localities in the Lahn-Dill areas. The white K-micas are common in the Rheinische Schiefergebirge, the Rhenohercynian belt, known as an accretionary prism. In the world example of accretionary setting phengite micas are transformed at the high anchizone and epizone, which is dierent from 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 the collision with London-Brabant Massif and one clockwise due to the dextral shear movement of the Rhenohercynian belt during the late Variscan orogeny.

KEYWORDS

1. Rheinische schiefergebirge
2. Rhenohercynian belt
3. Phengite
4. S₂-cleavage
5. Dextral shear
6. Variscan