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Deformation history of, and a study of strain applied to, the Michipicoten Greenstone Belt near Wawa, Ontario
Abstract
A detailed structural study of a well-exposed portion of the Archean Michipicoten Greenstone Belt near Wawa, Ontario revealed multiple phases of Archean deformation. The earliest deformation (D$\sb{0-1}$) occurred prior to complete lithification and is characterized by a bedding-parallel cleavage which is axial planar to tight to isoclinal folds. Also associated with early deformation are moderately strained conglomerate clasts and bedding-parallel faults believed to be early thrust faults. A reversal in younging direction occurs across the Magpie River Fault. A second phase of deformation (D$\sb2$) is characterized by a northwest-trending cleavage. Northeast-trending cleavages and their associated folds represent D$\sb3$ and D$\sb4$. Late deformation including transposition of bedding is associated with reactivation of the early faults. Northwest- and northeast-trending faults, commonly occupied by diabase dikes cross cut all other structures. Lithostratigraphic units defined within the study area appear to be fault-bound packages which may be correlated to the east. Correlation is enhanced by "unfaulting" the late northwest-trending faults. It is proposed that similar unfaulting and correlation may be carried out Belt-wide suggesting large-scale folding and thrusting. This model can explain the reversal in younging direction along the Magpie River Fault as well as some of the structural complexity within the area studied. The proposed model and the observed structure are consistent with evolution of the Michipicoten Greenstone Belt in a compressional tectonic regime, possibly in an accretionary prism. An analysis of strain demonstrated that the Ramsay and Huber technique of strain analysis ignores a serious inherent problem as do all methods which attempt to define the strain ellipsoid using data from two non-principal plane sections. A method which recognizes this problem and attempts to find a best-fit ellipsoid by selective weighting of the data was developed and applied to the Wawa data.
Subject Area
Geology
Recommended Citation
Shrady, Catherine Harrie, "Deformation history of, and a study of strain applied to, the Michipicoten Greenstone Belt near Wawa, Ontario" (1991). Doctoral Dissertations Available from Proquest. AAI9132914.
https://scholarworks.umass.edu/dissertations/AAI9132914