STRUCTURAL EVOLUTION OF MIGMATITES OF THE THOR-ODIN AREA OF THE MONASHEE COMPLEX, SOUTHERN BRITISH COLUMBIA, CANADA

The rocks of the Monashee Mountains of southern British Columbia record a complex geological evolution that began in the Palaeoproterozoic and ended in the Tertiary. At a minimum, the tectonic history of the area appears consistent with three basic events: The development of basement gneiss through an unknown tectonic event, a period of convergence presumably related to the early development of the Cordilleran orogen and a period of extension resulting in the development of a core complex. Recent studies have demonstrated at least six generations of structures which are regional in extent as well as associated classic migmatite structures.

A complete range of metatextite to diatextite can be demonstrated within the area of Thor-Odin and divided into a minimum of three structurally distinct migmatite generations. The first generation predates all recognizable generations of structures, both regional and local and is unrelated to Cordilleran orogenesis; it is recognized only within the basement gneiss. The second generation of migmatite postdates a Proterozoic to Paleozoic (?) regional unconformity and either predates or is synchronous with the early structural development of the orogen; it is recognized within both the basement and the cover gneiss. The third generation of migmatite is broadly coeval with the late structural development of the orogen (core complex formation); it is recognized in both the basement and cover gneiss.

Current published interpretations of Thor-Odin recognize it as a core complex and claim migmatisation occurred at the time of extensional deformation. However, no attempt to differentiate between migmatite generations have been made; all the migmatites are grouped together as approximately coeval and this requires that the deformation all take place in the Tertiary. This is clearly incorrect, and a true understanding of the deformational history of the orogen requires a better understanding of these complexities