Magnetic fabrics and boundary structure at the Quetico - Shebandowan subprovince boundary, near Kashabowie, NW Ontario

Abstract

The Quetico metasedimentary subprovince and the volcanic-plutonic Shebandowan belt to the south meet along an east-west steeply dipping boundary that is believed to have been affected by dextral transpressional deformation. It is also parallel to a steep metamorphic gradient from greenschist facies rocks to the north. Macroscopic petrofabrlcs are difficult to observe along the belt to the west of Thunder Bay but magnetic susceptibility fabrics (low-field) are quite consistent. These define a gently plunging extenslonal fabric parallel to the belt boundary. Within the Kashabowle area, general field observations of subhorizontal stretching (and intersection) lineations, and cleavage directions are in agreement with magnetic susceptibility axis directions. Mineral separation reveals that all samples have multiple sources of magnetic susceptibility, dominated by metamorphic phyllosilicates. Consequently it is not possible to simply quantitatively relate the magnetic fabrics to strain magnitudes although the magnetic fabrics accurately monitor significant kinematic directions. Analyses of strain of low-grade detrital quartz grains, magnetic fabrics and general field observations recognize flattened oblate fabrics. Moreover oblique, subhorizontal lineations favour a transpresslve kinematic model with compression normal to the belt boundary. The obliquity between mineral and magnetic lineations seem to indicate dextral transpresslve deformation.