Geology of metasedimentary rocks and Late Cretaceous deformation history in the northern Valhalla complex, British Columbia

The Valhalla complex, a Cordilleran metamorphic core complex, is a domal cu lmination made up of gently dipping interlayered sheets of igneous and supr acrustal rocks that were deformed and metamorphosed in the Middle Jurassic and Late Cretaceous, and exhumed by extensional faults in the Eocene. Mappi ng, fabric, and metamorphic studies of predominantly metasedimentary rocks in Valhalla and Passmore domes in the northern part of the complex, togethe r with published geochronological data, reveal a significant Late Cretaceou s tectonic history. This includes extensive magmatism, the culmination of u pper amphibolite facies metamorphism (approx. 800 degrees C and 8 GPa), mig matization, development of a dominant penetrative transposition foliation, and localization of strain on ductile thrust faults termed the Gwillim Cree k shear zones. The Valhalla assemblage, a package of metasedimentary rocks in Valhalla and Passmore domes, comprises a heterogeneous sequence of pelit ic schist, marble, calc-silicate gneiss, psammitic gneiss, metaconglomerate , quartzite, amphibolite gneiss, and ultramafic rocks. Based on the presenc e of distinct laterally continuous marker units and similar lithologic orde ring, we propose that the Valhalla assemblage is correlative with part of t he Palaeozoic North American stratigraphic succession. If this is correct, then the Valhalla assemblage represents an inverted sequence of strata that has been thinned by as much as 60%; thinning may have occurred during Late Cretaceous transposition foliation development. The Gwillim Creek shear zo nes, originally mapped in a restricted locality in Gwillim Creek, were foun d to merge into one broad, ductile shear zone beneath Valhalla dome and ext end throughout the entire Valhalla complex. The general style and timing of Late Cretaceous deformation in the Valhalla complex is characteristic of t hat found throughout the Shuswap complex in a belt of rocks that were at mi d-crustal levels during the Cretaceous. This zone is thought to have accomm odated Cretaceous - Early Tertiary shortening in the eastern Cordillera, an d is the ductile equivalent of the higher level Rocky Mountain thrust belt to the east.