Abstract

On the north side of a major fault three generations of folds F1, F2, F3 affect pre-Carboniferous phyllites; south of the fault two generations, C1, C2, affect middle Carboniferous clastic rocks. The F1 folds are isoclinal and obscure. The main folds, F2 in the phyllites and C1 in the Carboniferous rocks, trend east-northeast parallel to the fault. F2 are overturned southward and C1 northward, both toward the fault. Cross-folds, F3 in the phyllites and C2 in the Carboniferous rocks, trend northnortheast. Steeply plunging F3 and C2 are asymmetric and Z-shaped in plan profile.The F2 folds in the phyllites, though similar in geometry to folds in the middle Carboniferous rocks, appear, like F1 and F2, to have formed prior to the middle Carboniferous. This is indicated by the occurrence of unfolded Devonian(?) granitic intrusions crossing F3 folds, and a few miles north of the major fault, by middle Carboniferous rocks lying unconformably- above similar intrusions.One possible explanation for the repeated trends, which also accounts for the sense of overturning and asymmetry of the folds, relates the folding to alternating vertical and horizontal movements along the major fault. The vertical movements were followed by gravity sliding toward the fault to produce the main folds, and the horizontal movements, repeatedly dextral in sense, resulted in the Z-shaped cross-folds.

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