The Letang Peninsula - Frye Island area (Charlotte County, New Brunswick) was mapped on a scale of 16 in/mi and in part on a smaller scale. The following Silurian rocks are found: slates, sandstones, limestones, shales, conglomerates, rhyolites, tuffs, basic and acidic volcanic rocks, intrusive dykes and granites. The greater part of the mapped area is underlain by moderately to steeply dipping volcanic rocks and limestones. Slates border the northern part of the area, and sandstones with interbedded shales underlie the southeastern part of Frye Island in the southern part of the area.

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The Silurian rocks have been subjected to at least three phases of folding. The first recognized phase (F1), accompanied by low grade metamorphism, produced a regional axial plane cleavage (S1) and tight to open folds on both major and minor scales. In the greater part of the area, the dominant cleavage (S1) is nearly vertical with a northeast strike. The plunge of F1 minor fold axes varies both through the vertical and horizontal. In the southeastern part of Frye Island, however, F1 isoclines are recumbent with shallow plunges mainly towards the northeast. The mechanism of F1 folding is a function of rock ductility and ductility contrast. Observed mechanisms range from flexural slip to passive flow.

F1 deformation is attributed to near horizontal shortening in a northwest-southeast direction normal to S1 and near horizontal extension in a northeast-southwest direction parallel to S1.

The second phase (F2) produced minor folds in the greater part of the region but major folds are restricted to the southeastern part of the area. F2 minor axial planes are steep to vertical with two mean strike directions: north-northeast and east-northeast. The plunges of these folds are generally steep to vertical. however, in southeastern Frye Island the plunge is at a shallow angle predominantly towards the northeast. F2 folds, which are moderately tight to open, are formed primarily by flexural slip.

The geometry of F2 folds indicates a kinematic model similar to that of F1 implying that similar stress conditions existed during F1 and F2. The maximum and minimum stress axes during F2, however, may have been rotating in the horizontal.

The third phase (F3) is marked by complex small kinks and conjugate folds resulting in extreme variation in geometry. These folds are considered to have formed by slip along cleavage surfaces (S1 and S2). This is consistent with the field observation that F3 folds are almost exclusively confined to rocks cleaved by previous deformation. The principal stress axes have been determined from the orientation of intersecting axial planes of conjugate folds and from fold shapes.

Regional geometry is attributed primarily to F1, the superposition of F2 and F3 having only local significance. Faulting is associated with each fold phase. Movements on northeasterly trending faults are thought to be associated mainly with F1 and F2 whereas the northwest and east-west faults are associated with F3.

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