Paper No. 65
Presentation Time: 9:00 AM-6:00 PM
STRUCTURAL ANALYSIS OF COMPLEX FOLDING ON SEGUIN ISLAND, MAINE: VISUALIZATION THROUGH DIGITAL MAPPING AND SPATIAL ANALYSIS
Seguin Island is located ~12 km SSW of Georgetown, Maine and SE of the Norumbega fault system. It possesses the highest elevation values of any island along the Maine coast with areas over 40 m above mean sea level, and is nearly 1 km in length and .4 km at its widest area. Outcrops of Ordovician Cape Elizabeth amphibolite present on the island are characterized by Devonian age upright F2 anticlines and synclines and are accompanied by syntectonic granite dikes, exposed primarily along the coast. Within the larger fold structures are complex parasitic folds. Structural data of these parasitic folds was collected in the NE zone of the western lobe of the island. Measurements of gneissic layering, axial plane, and fold axis were taken using a Brunton compass and recorded with a handheld GPS. Gneissic layer lines were traced 2-3 m apart using RTK GPS and Total Stations. These complex fold structures are SW plunging with a NNE strike. Folds in general had wavelengths of ~10m and amplitudes of ~5m but exhibited high variation. Data concentrated in the NE region of the western lobe revealed gneissic layering strike values with a mode of 10o NNE and an average dip of ~77o SE. Strike of the axial plane had a mode of 11o and 200o NNE, and an average dip of ~76o SE. The mode of fold axis dataset was 185o NNE, and the average plunge was ~56o SW. These results were displayed by kriging of each category in order to remove outliers and show differences in the dataset. Through kriging a strong correlation was revealed between the variation in strike of gneissic layering, strike of axial plane, and trend of fold axis. Dip of gneissic layering and plunge of fold axis also strongly correlated. In general, dip measurements became shallower from N to S, while strike values alternated between two normalized classes with a difference of ~20o. Analysis of this data works toward better understanding of 1) how the amphibolite host rock was deformed, and 2) its placement in the regional geology. Parasitic fold structures were mapped with the objective of correlating them to larger fold structures. After digitizing the gneissic layering, extensions of these lines could easily be interpreted, bringing together the picture of smaller and larger fold structures. This result provides better understanding of the nature of folding when placed in the greater geologic landscape.