ABSTRACT
Talc represents a product of metamorphic reactions that can be enriched to pure talc lenses by subsequent deformation due to the high strength contrast between talc and other rock-forming minerals. This model is deduced from structural data collected within the Lassing talc deposit where talc constitutes fault cores within the Palten fault zone. Here, the talc is likely formed by the metamorphic reaction quartz + dolomite + H2O ↔ talc + calcite + H2O within greenschist facies conditions. Talc is subsequently enriched to pure talc lenses by a succession of regionally controlled deformation events as talc behaved ductilely in contrast to brittle-deformed country rocks. Consequently, talc lenses display all features of ductile shear zones including grain size reduction, S-C fabrics, and shear bands. Enrichment of talc is controlled by viscosity contrast between talc and other rock-forming minerals as talc bodies progressively formed along continuous C-surfaces along which slip occurred. Consequently, talc bodies are confined by an array of fault planes, and mainly occur along distensive oversteps along fault/shear zones.
