Development of a folded thrust stack: Humber Arm Allochthon, Bay of Islands, Newfoundland Appalachians.

In the Humber Arm area of the western Newfoundland Appalachians, four distinct stratigraphic successions derived from the Laurentian continental margin are exposed. Each succession is believed to be characteristic of a separate thrust sheet. The platform sheet represents the ancient Laurentian shell and its foreland basin cover; the Watsons Brook sheet is characterized by a succession including shelf-margin carbonates overlying foreland basin clastics; the Corner Brook sheet comprises continental slope and rise clastic and carbonate sedimentary rocks of the Humber Arm Supergroup; and the Woods Island sheet includes clastics of the Blow Me Down Brook formation that overlie mafic volcanics. Sheets are subdivided by thrusts into tectonic slices. Disrupted units and mélange, with scaly S[sub1] foliation, are found along the boundaries of some slices. Thrust sheets and related structures have been deformed by F[sub2] folds with axial planar S[sub2] cleavage. S[sub1] scaly foliations are transposed into parallelism with S[sub2]. There is a transition in the style of F[sub2] folds across the area, from upright and subhorizontal in the west to overturned folds with west-dipping axial planes and steeply raking or reclined fold hinges in the cast. Strongly curved fold hinges may reflect later shearing along the S[sub2] surfaces, producing sheath-like fold geometries. Shear zones close to the cast edge of the outcrop of the Watsons Brook sheet display kinematic indicators indicating both D[sub2] reverse-sense and D[sub3] normal-sense dip-slip shears. Subsequent events produced L[sub4] and L[sub5] crenulation lineations on the S[sub2] surfaces. At minimum, several tens of kilometres of shortening affected the part of the margin preserved in the Humber Arm area; true shortening and... [ABSTRACT FROM AUTHOR]