Multiple Deformation in Archean Rocks of the Vermilion District, Northeastern Minnesota
The structure of the Precambrian rocks of the Vermilion district is critically examined. It is demonstrated that two significant deformations (F1 and F2) have affected the area in addition to a later set of faults, joints, and kink-bands (F3). The F1 folds are tight to isoclinal with gently plunging axes and vertical axial planes trending west–northwest and containing iron formation and greenstones in anticlinal cores. The second deformation forms a series of open to close asymmetric folds (F2) with steep axes and vertical axial planes trending east–west. Of these, F1 has the more significant effect on the pattern of rock outcrop and it is suggested that it is directly related to the diapiric rise of the batholiths lying immediately to the north and south. The F2 folds may be accounted for by further compression between the two granite bodies.