LATE ACADIAN D4 STRAIN PARTITIONING AND SHORTENING, CHANDLER RIDGE, MT. WASHINGTON, NEW HAMPSHIRE

Late Acadian D4 deformation is ubiquitous in the alpine zone of Mt. Washington and other peaks of the Presidential Range, New Hampshire. D4 is characterized by outcrop-scale, asymmetric, moderately inclined, flexural slip folds that deform bedding (S0) and S1 schistosity. A weakly to strongly developed S4 crenulation is also typical of D4 deformation. F4 fold strain partitioning was evaluated within the context of the lithologic setting and the structural setting of macroscopic D4 folding and earlier D1 nappes. D4 fold wavelength, amplitude and stratigraphic viscosity (based upon schist to quartzite ratios) was measured on 350 mesoscopic F4 folds along a transect from Mt. Washington down the Chandler Ridge. This transect has near continuous exposures of the folded Devonian Littleton Formation. An accurate cross-section has been constructed and used to determine mesoscopic and macroscopic shortening during D4. Combining the shortening and strain estimates of the D4 Late Acadian with calculated D1 Early Acadian strain allows the amount of overall Acadian deformation to be described and may be used to refine models of Acadian plate tectonics. The Chandler Ridge transect was divided into five structural domains based on S4 axial plane orientations and F4 hinge lines. From the Mt. Washington eastward down the transect, the domains and their average S4 strike and dip and F4 trend and plunge are: Washington Domain, 41.7, 66.4E, 202.3, 33.6; Ball Crag Domain, 151.5, 63.7W, 275.8, 24.7; Cow Crag Domain, two S4 sub-domains 28.4, 77.1 W, 217.5, 18.6, and 129.6, 31.3 S, 211.5, 18.6; Nelson Crag Domain, two S4 sub-domains 183.7, 65.4E, 184.1, 13.9, and 171.7 49.3W, 203.0, 26.0; and Cragway Spring 178.3, 64.8W, 165.1, 12.2. The D4 domains appear to change rapidly in the vicinity of the Chandler Ridge Dome, which is likely a D4 macroscopic structure. At the crest of the dome the two most complex domains, Cow Crag and Nelson Crag, are found.