Pj. Umhoefer et Kl. Kleinspehn, MESOSCALE AND REGIONAL KINEMATICS OF THE NORTHWESTERN YALAKOM FAULT SYSTEM - MAJOR PALEOGENE DEXTRAL FAULTING IN BRITISH-COLUMBIA, CANADA, Tectonics, 14(1), 1995, pp. 78-94
The northwestern Yalakom fault system (YFS) lies on the eastern margin
of the Coast Belt in southwestern British Columbia. The Yalakom fault
is the most significant structure in the fault system, with at least
115 km of dextral slip, mostly of early Tertiary age. The NW YFS is up
to 25 km wide and is bounded on the southwest by the Tchaikazan fault
zone, which had 5 km or more of dextral slip. Kinematic and paleostre
ss analysis of mesofaults and map-scale structures shows that secondar
y faults within the NW YFS had both dextral and sinistral oblique slip
. Three large synclines had increasing amounts of clockwise, vertical
axis rotation from southeast to northwest. Block rotation between two
synthetic strike-slip faults with large offset (Yalakom) and moderate
offset (Tchaikazan) is similar to current kinematics between the San A
ndreas and San Jacinto faults in southern California. The NW YFS was a
ctive from latest Cretaceous(?) to (mainly) Eocene time and postdates
early Late Cretaceous thrust faulting to the southwest. Early stage me
sofaults are compatible with the thrust belt and suggest that open fol
ds developed in the foreland of the thrust belt before strike-slip fau
lting commenced. The abrupt northwest termination of the YFS may be re
lated to extension within the adjacent Tatla Lake metamorphic complex.
Some dextral slip may have been transferred farther northwest through
the Coast Belt, but these structures have not been documented in west
central British Columbia. Most of the 120 km of dextral slip on the Y
FS was transferred to the north via a mosaic of normal and strike-slip
faults in central British Columbia. Thus the YFS forms the southweste
rn margin of a broad zone of transtensional structures that extends to
the Tintina-Rocky Mountain Trench fault zone; these structures accomm
odated northwestward displacement of the northwestern Cordillera in Pa
leogene time.