STRAIN PARTITIONING OF D1 ACADIAN DEFORMATION IN THE PRESIDENTIAL RANGE, NEW HAMPSHIRE
EUSDEN, J. Dykstra Jr, Geology, Bates College, Lewiston, ME 04240, deusden@bates.edu.

The multiply deformed metsedimentary Devonian Littleton Formation in the Presidential Range, N. H., shows dramatic partitioning of Acadian D1 strain at regional and outcrop scales. In the NW portion of the range with the highest elevations, D1 is characterized by F1 macroscopic folds and few mesoscopic folds. In the SE part of the range, at lower elevations, no macroscopic F1 folds exist and mesoscopic folds dominate. The boundary between the NW and SE structural domains is remarkably well delineated by both the termination of macroscopic F1 axial traces and the reorientation of F4 hinge lines that refold the D1 structures. This abrupt transition marking a change from lower (NW domain) to higher (SE domain) ductility is related to regional scale vertical crustal variations in deformation in the Acadian orogen.

L1 mineral lineations composed of pseudomorphed andalusites are common. L1 is sub-parallel to F1 hinge lines and never seen in the principal stretching direction, perpendicular to the hinge lines. Reverse refraction of S1 schistosity in andalusite bearing schists suggests that andalusite growth occurred prior to the main phase of D1 deformation. Outcrop scale stratigraphic/rheological variations control whether L1 develops. In thick (> 10 cm) massive schists, peudoandalusites are unaligned within the S1 schistosity, whereas lithologies where original sedimentary bedding, S0, is characterized by thin beds (< 10 cm) of alternating schist and quartzite, the L1 mineral lineation is well defined. L1 and F1 hinge lines vary in orientation along the length of the D1 macroscopic axial traces reflecting the non--cylindrical, sheath-like fold geometry for D1 nappes. As such, the concentration of L1 lineations, which trend shallowly to moderately WSW, record the ENE transport direction of the easterly facing nappes.

Northeastern Section - 37th Annual Meeting (March 25-27, 2002)
General Information for this Meeting
Session No. 34
Paleozoic Tectonics of the Northern Appalachian Mountains: New Insights and Persistent Problems: First Annual NETectonics Symposium (Posters)
Sheraton Springfield: Ballroom North
8:00 AM-12:00 PM, Wednesday, March 27, 2002
 

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