Kinematic interpretation of mylonitic rocks in part of the Columbia River fault zone, Shuswap terrane, British Columbia

Mylonitic rocks of the Columbia River fault zone have been examined in a 600 m thick section, 20 km north of Revelstoke, British Columbia. At this locality coarse-grained granite with well-preserved igneous texture lies in the hanging wall of the fault zone. Adjacent to the boundary of the mylonite zone the granite is foliated and mineral segregation gives rise to well-defined compositional layering. The foliation (Sf) is defined by oriented mineral grains and flattened porphyroclasts. In areas of intense strain compositional layering (Sc) is parallel to Sf. At the boundary of the mylonite zone and in weakly deformed areas within the mylonite zone Sc and Sf are inclined at angles up to 30°. Sf is taken to be a plane of flattening, and Sc appears to parallel a plane of shear. After correction for effects of late-stage flexural slip folding the angular relationship of Sc to Sf may be used to determine sense of shear in the mylonitc zone; the hanging-wall rocks have been displaced toward the east relative to the footwall. Formation of mylonitic fabrics and associated displacement of the Selkirk allochthon eastward relative to the underlying Monashee Complex occurred after the Middle Jurassic peak of regional metamorphism and before brittle reactivation and uplift in the Tertiary.

A primary igneous texture from the Lizard Peridotite, Cornwall

SummaryDetailed studies by Flett and Green have shown the Lizard complex to be a deformed body of considerable complexity. One of the principal results of the deformation has been the recrystallization of the primary peridotite. New evidence is presented concerning the original features of this high temperature peridotite. It is concluded that in some of the primary rocks there is preserved the structure and texture of the crystallization of an interstitial pore liquid trapped within a primary framework of olivine crystals.