Transpressional structures on a Late Palaeozoic intracontinental transform fault, Canadian Appalachians
Published:January 01, 2007
J. W. F. Waldron, C. Roselli, S. K. Johnston, 2007. "Transpressional structures on a Late Palaeozoic intracontinental transform fault, Canadian Appalachians", Tectonics of Strike-Slip Restraining and Releasing Bends, W. D. Cunningham, P. Mann
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The east–west Minas fault zone, separating the Early Palaeozoic Meguma and Avalon terranes of the Appalachians, experienced dextral strike-slip motion during the Carboniferous. Abundant oblique contractional structures indicate localized dextral transpression, immediately south of the zone, probably associated with a restraining bend. Subsurface data indicate that the deformed Horton Group clastic rocks are thrust above younger Windsor Group evaporites.
Excellent exposures on wave-cut platforms of the Bay of Fundy show structures developed in transpression, including NE-trending upright and inclined folds; south-verging thrust and reverse faults; and NW-striking normal faults. Northwest-trending boudins, which are perpendicular and slightly rotated in a clockwise sense relative to fold hinges, provide a field indicator for dextral transpression. The earliest folds (F1) are curvilinear and may have formed by deformation of wet sediment. F2 tectonic folds show weak axial-planar cleavage. Locally, these have been rotated into reclined orientations; spectacular downward-facing folds are probably due to refolding by more east–west F3 folds. The structures observed are consistent with pure-shear-dominated transpression, with the local angle of convergence α increasing over time. This strain history is compatible with progressive strain partitioning, probably associated with the spreading of topography developed at the restraining bend.
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Tectonics of Strike-Slip Restraining and Releasing Bends
Restraining and releasing bends are common, but enigmatic features of strike-slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation. Regional-scale restraining bends are sites of mountain building, transpressional deformation and basement exhumation, whereas releasing bends are sites of topographic subsidence, transtensional deformation, basin sedimentation and possible volcanism and economic mineralization. Because restraining and releasing bends often occur as singular self-contained domains of complex deformation, they are appealing natural laboratories for Earth scientists to study fault processes, earthquake seismology, active faulting and sedimentation, fault and fluid-flow relationships, links between tectonics and topography, tectonic and erosional controls on exhumation, and tectonic geomorphology.
This volume addresses the tectonic complexity and diversity of strike-slip restraining and releasing bends with 18 contributions divided into four thematic sections: (1) a topical review of fault bends and their global distribution; (2) bends, sedimentary basins and earthquake hazards; (3) restraining bends, transpressional deformation and basement controls on development; (4) releasing bends, transtensional deformation and fluid flow.