FIELD STUDY OF HIGH-STRAIN ZONES IN THE SOUTHEASTERN NEW ENGLAND APPALACHIANS TO CHARACTERIZE THE SOUTHERN TERMINATION OF THE NORUMBEGA FAULT SYSTEM

The NE-trending >300 km long, middle Paleozoic, crustal-scale right-lateral transpressive Norumbega Fault system (NFS) in Maine (ME) and New Brunswick, is a large strike-slip fault similar to the San Andreas fault system. However, while its southern extent and the nature of its termination are unknown. Since this fault has not been previously recognized in Massachusetts (MA), shear zones in SE New Hampshire (NH) and topographic lineaments in NH and MA were investigated to see if they could be related to its continuation.

NNE-trending lineaments along the Merrimack and Concord Rivers in MA did not show evidence for highly sheared rocks or dextral movement. Instead, weakly sheared granitic rocks, schist and migmatitic gneiss with local folds and shear structures exist. The sheared rocks exhibited foliation that generally dips steeply and strikes NNE. Local mineral lineations generally trend NE-SW and plunged at varying degrees. These structures are consistent with deformation related to the Acadian orogeny and are not thought to indicate the presence of Norumbega related structures.

However, previously mapped high strain zones in SE NH, including the Portsmouth, Calef, Nannie Island, Great Commons, and Campbell Hill shear zones are potentially better correlatives. The Rye Complex and the Portsmouth Fault contain mylonites and deformational structures similar to exposures of the NFS in ME, with dextral asymmetric mica fish and feldspar porphyroclasts. Foliations in both the Rye Complex and along the NFS in ME dip steeply to the NW with sub-horizontal lineations that trend north. These data suggest that while the NFS does not extend into MA that shear zones present along the southeastern coast of NH, in areas such as the Rye Complex, may be related to the NFS. To further investigate the extent of the NFS, in situ monazite U-(Th-)Pb laser ablation inductively coupled mass spectrometry geochronology will be conducted to determine if the ages of the dextral shearing along several high strain zones in southeast NH are consistent with those of the NFS in ME.