Tectonometamorphic history of the Erzgebirge – open questions

We are in the process of making a tectonometamorphic map of the Erzgebirge and present our preliminary state of this work. We follow the scheme of previous studies and distinguish four major allochthonous units in the Erzgebirge: Basal Gneiss Unit, Gneiss-Eclogite Unit, Mica schist-Eclogite Unit, and Phyllite Unit.

In the course of this project we would like to address the following open questions:

1. Where are tectonic boundaries between these units? Which subunits can be distinguished?

2. Do high-pressure/ultrahigh-pressure (HP/UHP) conditions form different clusters? If so, what is the extent of these clusters and is the current scheme of two HP and one UHP cluster accurate?

3. Are high-pressure rocks solitary occurrences in a matrix with different pressure-temperature evolutions or did the units share a common evolution? If units behaved coherently – how do the HP clusters fit into this picture and where are the associated tectonic boundaries?

4. Does the main foliation in the HP units reflect exhumation from eclogite-facies conditions, exhumation from mid-crustal levels or even something else?

5. What explains the overall distribution of metamorphism in the Erzgebirge? While high-pressure and Barrovian conditions seem to fade out towards higher structural levels in the west, the eastern border of the Erzgebirge towards the Elbe Zone is metamorphically abrupt, represents a major structural jump and shows similarities to an extensional detachment fault.