RE-EVALUATING FOLD MODELS AND BALANCED SECTIONS AT THE TOE OF THE VARISCAN OROGENIC WEDGE, ON/OFF SHORE COUNTY CLARE, IRELAND

Deformation at the toe of the Variscan orogenic wedge in western Ireland is generally characterized as large wavelength (100’s m) concentric monoclines and detachment folds developed in Carboniferous turbidites, with virtually no deformation partitioning into high-strain zones. We combine new structural data from coastal exposures in County Clare, as well as recently acquired INFOMAR seabed imagery along the adjacent platform to document periclinal folding over several orders of magnitude and strain localization within “monoclinal” limbs. Detailed structural analysis on the “Loop Head” from Bridges of Ross southwest to the Lighthouse yield the following results: (1) doubly-plunging “periclinal” folding from kilometric to m scale, with axial traces trending toward 080-260; 2) fold lambda >100 m have interlimb angles > 70-120°, whereas open to isoclinal folds have lambda <100 m; and, 3) folding was accommodated by numerous m-displacement out-of-fold faults, flexural slip, buckling, and flexural flow where thick mudstones act as the ductile layer. Interpretation of new INFOMAR bathymetry demonstrates km-scale doubly-plunging folds, domes and basins cut by NE-striking faults (> 1-2 km in length). These faults appear to shear limbs of mega periclines offshore with similar structural style to the smaller-scale structures described above. Together, these data and interpretations are consistent with larger magnitudes of deformation within the orogenic wedge at this latitude than previously thought. These new observations and data imply that published values for total strains at the toe of the orogen may be inaccurate and that crosssection restoration utilizing cylindrical fold models may be invalid for the toe of the Variscan orogenic wedge.