Heterogeneous deformation at triple junctions of exhumed crustal-scale deformation zones

Zones of localized brittle deformation can act as effective agents of fluid flow and mineralization. While brittle deformation is ubiquitous in the upper crust, where deformation is controlled by friction, it occurs more sporadically at deeper crustal levels, where deformation is temperature sensitive. Nonetheless, mineralization of precious metals is often spatially associated with ductile shear zones in exhumed high-grade metamorphic terranes. Hence, the question arises to what extent localized brittle and brittle-ductile deformation channels fluids during or following deformation under overall high-grade metamorphic conditions, which may have led to mineralization in ancient crustal terranes such as the Svecofennian in SW-Finland. The study area is located at the triple junction of the Paleoproterozoic crustal Kynsikangas Shear Zone, the Hämeenlinna Shear Zone and the Kolinummi Shear Zone and is characterized by strongly heterogeneous deformation. Therefore, we will elucidate the influence of heterogeneous deformation on the localization of brittle-ductile deformation structures, potentially having served as conduits of fluid flow. More specifically, our objective is to identify the scale, kinematics and geometric configuration of local strain fabrics and deformation zones in the context of regional deformation. The project builds on our work on the Kynsikangas Shear Zone and is complemented by physical modelling. The latter will also include the analysis of heterogeneous deformation at divergent plate boundary triple junctions.

Funding Agency: German Academic Exchange Service (DAAD)

Principal Investigator: Ulrich Riller

Ph.D. candidate: Tajuddeen Mustapha

Collaborators:
Dr. Jon Engström (Geological Survey of Finland, GTK)
Dr. Kaisa Nikkilä (Åbo Akademi University, Turku, Finland)