Structural and stratigraphic study of the Keewatin-type and Shebandowan-type rocks west of Thunder Bay, Ontario / G. Heather Brown. --

Detailed mapping was carried out in the Shebandowan
\nLakes area and eastward to the Kaministiquia River to study
\nthe structural and stratigraphic relationships between the
\nKeewatin and Timiskaming rocks (herein referred to as
\nKeewatin-type and Shebandowan-type, respectively, to avoid
\nconnotations of time-stratigraphic equivalence with type
\nareas) of the region.
\nIt is believed that the Shebandowan-type rocks are
\nyounger than the Keewatin-type rocks. Although no actual
\ncontact between the two has been seen in outcrop in the
\nstudy area, the trend of their contact is discordant with the trend of cleavage in the Shebandowan-type rocks. This,
\nalong with the less recrystallized appearance of the
\nShebandowan-type rocks, and the presence of clasts of
\njasper in conglomerates of the Shebandowan-type sequence
\nsimilar in appearance to the jaspilitic iron formation
\ninterbedded with the Keewatin-type mafic volcanics, leads
\nto the conclusion that an unconformity separates the two
\ngroups of rocks. Recent geochronological work on some of
\nthe rocks in the region, carried out by the Ontario
\nGeological Survey, supports this theory.
\nThe macroscopic, microscopic and sub-microscopic
\nstructure of both groups of rocks was examined in detail.
\nThe minor structures seen in outcrop, the examination of
\nthin sections, scanning electron microscope work, and the
\ndetermination of the magnetic fabric of the rocks all show
\nthat the rocks in the present study area contain a single,
\npenetrative, primary cleavage, which has a consistent trend
\nacross the whole area. The regional structural picture
\nwhich emerges from the data is characterized by
\nclose-spaced, isoclinal folding with sub-vertical fold
\naxial traces trending roughly east-west. Local variations
\nexist in the eastern portion of the study area where more
\nwidely-spaced and open folding is more common. No evidence
\nof a second, significant period of deformation in the
\npresent study area has been found.

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