SPATIAL ANALYSIS OF MODIFIED F2 FOLD STRUCTURES ON SEGUIN ISLAND, MAINE

Seguin Island, ~12 km SSW of Georgetown, ME, outcrops on the E limb of the S plunging Robinhood Cove syncline, SE of the Norumbega fault/shear zone system. The Ordovician Cape Elizabeth amphibolite (Hussey 1978) of Seguin generally conforms to the Devonian F2 upright folds formed by regional transpression. Orientations of foliations, fold axes and axial planes were positioned using GeoXT GPS. Folded foliation lines were traced using RTK GPS. Full island, high density coverage of orientation data, including outcrops within the vegetated interior, was achieved to characterize the complex geometry of folding. Folds on the NE tip/E lobe of the island exhibit the regional upright F2 structure with fold axes and axial planes at 35S9W and N18E74SE. Towards the W side of the W lobe, the folds are slightly rotated from the F2 pattern, exhibiting fold axes and axial planes at 53S43W, N45E75NW. At the S end, foliation trace lines indicate a parasitic fold complex on the limb of an island localized synform. To the E, there is a concentration of overturned to recumbent folds exhibiting fold axes and axial planes at 14S15W and N55W12NE. To spatially isolate variation in structural data, IDW and Kriging interpolation analyses were used in GIS. These analyses yield 1) significant variation in structural measurements within the W lobe contrasting with the relative homogeneity in the E lobe, suggesting the presence of a lobe-dividing fault; 2) consistent SW plunge direction, with significant variation in plunge angle with a clear discontinuity across the presumed fault trace; 3) average clockwise rotation of ~37° in fold axis trend from the E-W lobe border to the W shore; 4) localized overturned to recumbent folds in the SW end. Variability in axial plane orientations with consistent SW plunge can be attributed to polyclinal folding due to a room problem within the fold nose of the island-localized structure. Some of the variation and rotation in fold axis measurements may be related to deformation along the hypothesized lobe-dividing fault. Compiled topographic/bathymetric data and observed minor striated surfaces (strike-slip and dip-slip) in the N cove provide additional support. A reconstructed fold trace map incorporates regional structure and the spatially interpolated structural data to delineate the parasitic fold complex on Seguin.