Deciphering cryptic P-T-d-t histories in the western Thor-Odin dome, Monashee Mountains, Canadian Cordillera : a key to unravelling pre-Cordilleran tectonic signatures

A detailed structural and metamorphic study along a transect from the core of the Thor-Odin dome to its western margin (South-eastern Canadian Cordillera) has allowed the reconstruction of the P-T-d-t history estimating PT changes, during successive fabric development. The dome comprises a recumbently-folded and transposed Proterozoic high-grade basement and Late Proterozoic-Palaeozoic metasedimentary cover, characterised by a regional foliation (ST). An inferred, nearly-isothermal decompressional path, from a maximum depth of ca. 40 km, transgresses the " maximum relaxed geotherm", consistent with exhumation during lithospheric extension. Contrasting pre-ST PT conditions indicate that different units followed different PT paths before ST development. Traces of these early and variable structural and metamorphic re-equilibration steps are preserved in meter-scale boudins and granular-scale domains poorly affected by transposition. The various paths represent events, from Palaeoproterozoic to Proterozoic Rodinia break up, to Jurassic-Cretaceous convergence and final exhumation in the Eocene. Much of the deformational and metamorphic history may have been accumulated before onset of ST. However, the early structural history is overprinted, and mineral assemblages and their relative ages are mostly obscured by ST development. A glimpse of the earlier geologic history is possible only by combining micro-structural analysis and PT estimates.