A sequence of three phases of recumbent folding has been established within some western-most exposures of gneiss of the Shuswap Complex, near Vaseaux Lake, in the southern Okanagan Valley of British Columbia. These three structural events comprise large northerly trending recumbent folds (Phase 1) that have been refolded, first about northeasterly dipping axial surfaces (Phase 2) and secondly about southerly dipping axial surfaces (Phase 3).Much of the ductile strain visible in these rocks appears associated with Phase 2. Strain analysis of plastically deformed garnets, originally synkinematically developed during early stages of Phase 2, indicates that the growth of Phase 2 recumbent folds was associated with extreme flattening strain across their axial surfaces, accompanied by intense constriction subparallel with their hinge lines. A similar but less intense mode of strain appears associated with Phase 3 folds. No useful strain markers are associated with Phase 1 and perhaps this was a translational phase of strain.The Phase 3 event probably is an early part of the Columbian Orogeny, with Phases 1 and 2 being formed either during or earlier than the Permo-Triassic.Early Tertiary events have gently warped and fractured these three early main structures.
The western margin of the Omineca Belt near Crooked Lake, British Columbia, consists of metasedimentary rocks (Snowshoe Group) and orthogneisses of the Barkerville terrane, structurally overlain by a mafic volcanic – sedimentary package of rocks belonging to the allochthonous Slide Mountain (Crooked Amphibolite) and Quesnel terranes (Triassic phyllite and Nicola Group). At least two episodes of regional deformational (phases 2 and 3) affected this composite package. Deformation and metamorphism (phase 1) in the Snowshow Group predate the formation of this package and are nowhere evident within the allochthonous terranes.Middle Jurassic metamorphism ranging from chlorite zone through sillimanite zone affected all units. Isograds are folded, together with the junction between the terranes, indicating that the metamorphic assemblages developed prior to folding of this boundary. Granitic orthogneiss (Boss Mountain, Quesnel Lake, and Perseus gneisses), having a minimum age of Late Devonian to Early Pennsylvanian, was intruded into and deformed with the Snowshoe Group during the earliest recognizable phase of deformation in the Barkerville terrane (phase 1). Slide Mountain terrane rocks occupy a narrow zone where large eastward displacement occurred during overthrusting of the Intermontane superterrane upon the western margin of North America in Middle Jurassic time.
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