Large vertical displacements of a crystalline massif recorded by Raman thermometry

We present a novel approach for the restoration of cross sections in collisional mountain belts, including the reconstruction of orientation and depth of key horizons prior to deformation. The method presented is based on an automated and quantitative assessment of metamorphic peak temperature (T-p) by Raman spectroscopy of carbonaceous material along the basement-cover contact, a marker horizon available in many orogens. The approach is tested in the Aar Massif (AM), Swiss Alps, an area with a well-developed metamorphic gradient and structural relief. We demonstrate that T-p, combined with structural observations, can be used to (1) establish the relative timing of deformation and metamorphism, and (2) quantify horizontal and vertical crustal movements. We identify intense postmetamorphic deformation since ca. 20 Ma with a ratio of uplift to shortening >0.7 (20 km uplift versus 27 km shortening, estimated for the southern AM). This large vertical uplift component points to the role of continental slab dynamics and/or erosional unloading as driving forces for late-stage orogenic deformation.