NEOACADIAN DEFORMATION WITHIN THE MEGUMA TERRANE

The Meguma Terrane comprises the Cambrian to Ordovician Meguma Group and disconformably overlying Silurian to Devonian metasedimentary and metavolcanic units, all are intruded by Devonian to Carboniferous plutons. Deformation related to the accretion of Meguma Terrane defines the Neoacadian Orogeny (Late Devonian-Early Carboniferous) within the Appalachian Orogen. Kilometre-scale and coeval larger folds are the dominant record of Neoacadian deformation within the Meguma Terrane. The folds have box and chevron geometries that show no systematic vergence, although map-scale variation in tightness and axial trend reflect proximity to the terrane boundary (Chedabucto Cobequid Fault System). Fold geometries reflect the layered character of the Meguma Group in which flexural folding was the dominant mechanism. Fold-related shortening is generally less than 35%. Variation of layer-parallel shortening recorded by cm-scale buckles is interpreted to reflect the time spent in the flat hinges of box folds during box fold to chevron evolution. Folding occurred mainly under regional low grade metamorphic conditions, however post-metamorphic flexural-slip folding deforms fold-related cleavage and is recorded by auriferous ‘saddle reef' vein arrays. The Early Devonian Torbrook Formation provides a minimum age on fold development and 40Ar/39Ar ages generally support a middle Devonian (ca 380-390 Ma) age. The Late Devonian (ca. 375 Ma) South Mountain Batholith (SMB) postdates the main folding event, it however records subtle internal strain consistent with folding accompanying transpression on the terrane-bounding fault. Flexural slip locally deforms porphyroblasts within the contact aureole of the SMB and 40Ar/39Ar ages for some auriferous saddle reef veins coincide with igneous ages. Shear zones parallel to the regional fold axial trend accompanied and may have played a role in granite emplacement. Rapid uplift following granite emplacement may explain the change to the late, brittle, flexural-slip folding.