Northeastern Section - 42nd Annual Meeting (12–14 March 2007)

Paper No. 1
Presentation Time: 8:20 AM


EUSDEN Jr., J. Dykstra, Geology, Bates College, 44 Campus Avenue, Lewiston, ME 04240, KUGEL, Kelley L., Geology, Bates College, Lewiston, ME 04240 and RODDA, Charles, Earth Sciences, University of Maine, Orono, ME 04469,

Shortening calculations of well-exposed D4 fold trains in the Presidential Range of New Hampshire were done at the micro-, meso-, and macro-scales to quantify the strain and to evaluate the strain partitioning of this last widespread Acadian deformation (380-365 ma). D4 folds are parallel, open, flexural slip to flexural flow, east vergent, fold all previous fabrics (S0, S1 and L1) and have a variably developed S4 crenulation cleavage. Transects along Osgood and Chandler Ridges containing well-exposed D1 nappes refolded by D4 were examined. Shortening was calculated using the equation e = (lf-lo/ lo) * 100, where lf = the hinge to hinge straight length of the fold train and lo = the length of the folded layer. For Chandler Ridge the following shortening calculations were made: macro-scale = 10.3%; 49 meso-scale fold trains varied systematically by domain over a macro-scale D4 Dome, ranging from 1.1% on the flank to 47.8% on the apex with a mean value of 14.2%; micro-scale shortening on 6 thin sections, with triplicates, varied non–systematically from 3.0% - 11.6% with a mean of 7.0%. The total shortening at all scales was 28.7%. The results for Osgood Ridge were very similar: macro-scale = 10.2%; 32 meso-scale fold trains varied systematically by individual fold train over several macro-scale D4 anticlinal synforms and synformal anticlines, ranging from 5.9% on the limbs to 32.3% on the crests or troughs, with a mean value of 16.4%; micro-scale shortening on 13 thin sections, again with triplicates, varied non-systematically from 6.1% - 20.9% with a mean of 12.2%. The total shortening at all scales was 32.5%. Collectively, these results suggest that meso-scale strain is preferentially partitioned on the crests and troughs of macroscopic folds by parasitic meso-scale folding, that macro-scale and micro-scale strain is fairly uniformly distributed across this part of the orogen, and that the total D4 shortening is approximately 30%. Osgood and Chandler Ridges are both approximately 3 km in length and would have been about 1 km longer prior to D4. Depending on the duration of the D4 event (10 mya - 1 mya), shortening or convergence rates would range from .1cm/yr to .01 cm/yr during the Late Acadian.