The acadian fold belt in the Meguma Terrane, Nova Scotia: Cross sections, fold mechanisms, and tectonic implications

[ 1] Structural data and cross sections from the eastern part of the Devonian-Carboniferous fold belt of the Meguma Terrane give insight into its structural development and crustal tectonics. The sandy Goldenville Formation, the active competent member during buckling, formed a multilayer several kilometers thick that lay beneath the denser, softer muds and silts of the Halifax Formation. Cross sections reveal 2 orders of folds: 11 - 18 km wavelength folds are interpreted as resulting from buckling under the influence of gravity; 4 - 6 km wavelength folds reflect the thickness of the multilayer with buckle shortening in the range 32 - 44%. Depth to detachment derived from the sections ( 11 - 13.5 km below present erosion surface) is such that given the depth of the detachment below the paleosurface during the main phase (pre-Devonian granite) of folding, it would likely have been a relatively soft and thick shear zone that would have influenced profile geometry of the main phase folds at this stage of fold belt development. Granite production that may have been triggered by mantle delamination during continuing convergence accompanying terminal Pangean assembly and ocean basin closure was followed by rapid exhumation. Later localized deformation ( Late Devonian - Carboniferous) in the fold belt took place as the Meguma Terrane was displaced along the terrane-bounding Cobequid-Chedabucto fault system. The characteristic asymmetric cross sections of structures of this phase are attributed to cooling and strengthening of the detachment that was a consequence of the postgranite uplift and exhumation.