2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 8
Presentation Time: 8:00 AM-12:00 PM


MCNEILL, Paul D., Dept. of Geology, Univ of New Brunswick, PO Box 4400, Fredericton, NB E3B 5A3, Canada and WILLIAMS, Paul F., Dept. of Geology, Univ of New Brunswick, PO Box 4400, Fredericton, E3B 5A3, Canada, i4lcz@unb.ca

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