EARLY AND LATE ACADIAN STRAIN PARTITIONING: D1 LINEATION AND D4 FOLDING ALONG AN ALPINE TRANSECT; MOUNT MADISON, NEW HAMPSHIRE

The alpine zone of the Presidential Range in New Hampshire affords excellent exposure of Silurian and Devonian metasedimentary rocks from the Acadian hinterland. Of the many phases of deformation recognized in the region, D1, characterized by isoclinal, east vergent nappes with a hinge-parallel pseudoandaulsite mineral lineation (L1) and D4, defined by moderately inclined to overturned, gently to moderately plunging, asymmetric folds, are the most ubiquitous deformations seen. Rapid transitions in the intensity of L1 development have been quantified by measuring trend/plunge at forty-two localities along a 2.1 km long transect. The data were plotted on rose plots to determine the longest petal using a running bin average method and then contoured to produce an L1 strain map. Maximum petal lengths measured by this technique range from 8% - 26%. In conjunction with schist/quartzite ratios reflecting bulk rock rheology it appears that L1 strain is highest in certain combination of thin (cm scale) schist and quartzite couplets. D4 shortening calculations were done by comparing folded line lengths to straight line lengths through the folds trains. Fold trains for thirty-one 2 –10 m long outcrops, one 2.1 km long cross section, and thirteen thin sections at the microscale were done. Preliminary results indicate that outcrop scale shortening is circa 14% and microscale shortening is circa 15%. An overall shortening estimate will be presented for the Mount Madison field area. This study represents an ongoing effort to quantify early and late Acadian strain in the Presidential Mountain Range.