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Eocene structural development of the Valhalla Complex, southeastern British Columbia
Author(s) -
Carr Sharon D.,
Parrish Randall R.,
Brown Richard L.
Publication year - 1987
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc006i002p00175
Subject(s) - geology , shear zone , pluton , metamorphic core complex , metamorphic rock , extensional definition , metamorphic facies , shear (geology) , fault (geology) , geochemistry , geomorphology , seismology , facies , petrology , tectonics , structural basin
The Valhalla complex, a Cordilleran metamorphic core complex, is a 100 km by 30 km structural culmination within the Omineca belt of southeastern British Columbia. It comprises sheets of granitic orthogneiss ranging in age from 100 to 59 Ma with intervening paragneiss of uncertain age and stratigraphic correlation. The complex is roofed by the ductile Valkyr shear zone and the ductile/brittle Slocan Lake fault zone; the upper plate comprises lower grade metasedimentary rocks intruded by middle Jurassic plutons. The Valkyr shear zone and the Slocan Lake fault zone deform 62 and 59 Ma granitic sheets in their footwalls. The easterly directed Valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern, western, and southern margins. The shear zone was active between 59 and 54 Ma under amphibolite facies conditions. The juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the Valkyr shear zone is a significant structure with large displacement. There is evidence to support an easterly rooting direction consistent with an extensional origin; its surface breakaway is suggested to be west of the Valhalla complex. The Slocan Lake fault zone on the eastern side of the complex is a gently (30°), easterly dipping ductile/brittle normal fault which roots to the east. It was active between 54 and approximately 45 Ma and truncates the Valkyr shear zone. Timing and structural relationships indicate that the Valkyr shear zone and the Slocan Lake fault zone are genetically related. Movement on the ductile Valkyr shear zone, arching of the complex, and displacement on the Slocan Lake fault zone occurred as a continuum in Early to Middle Eocene time. This paper documents the presence of significant Eocene ductile strain in the Valhalla complex and suggests that the role of extension in this region is more profound than had been previously recognized.