LATE ACADIAN FOLD TRAIN SHORTENING, MT JEFFERSON, PRESIDENTIAL RANGE, NH

Shortening calculations of well-exposed D4 fold trains in the Mt Jefferson summit cone of Presidential Range, 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. Shortening was calculated using the equation e = (lf-lo/ lo) * 100, where lf = the hinge to hinge straight length of the fold train and l0 = the length of the folded layer. All around the Mt Jefferson summit cone in the alpine zone a total of 43 mesoscale fold trains were measured in the Devonian Littleton Formation. The Littleton Formation in this region is dominated by schist-rich couplets of schist and quartzite that often preserve reverse graded bedding. The axial plane fabric (S4), hinge line (F4), limbs (S0), interlimb angle, wavelength and double amplitude of every fold in each fold train were measured. Mesoscale folds have double amplitudes ranging from 10 cm up to several meters and wavelengths from 10 cm to 10 meters. Interim angles classify all mesoscale folds as open. Axial surfaces generally strike N and dip moderately to steeply W. Hinge lines trend N or S with shallow plunges. The overall macroscale shortening is 12.4% with a range from 4% to 34%. The highest shortening values are on the Ridge of the Caps trail up to the summit of Mt Jefferson. A cross section drawn from Castellated Ridge to Monticello Lawn shows the Mt Jefferson summit to be a macroscale F4 fold suggesting that meso-scale strain is preferentially partitioned on the crests and troughs of macroscopic folds by parasitic meso-scale folding. Six samples were taken from this transect and were made into thin sections and will be analyzed for microscale shortening. The average macroscale shortening is quite similar to two other regions in the Presidential Range where similar calculations have been made. This suggests a somewhat homogeneous distribution of Late Acadian strain throughout the Presidential Range.