Evolution of a transcurrent fault system in shallow crustal metasedimentary rocks: the Norumbega fault zone, eastern Maine

Differential exhumation in Maine exposes nearly half of the crustal profile of the Norumbega fault zone (NFZ), a major transcurrent fault zone of the Northern Appalachians. A large exposure of turbidites in eastern Maine records a multi-stage deformation history that provides insight into the epizonal evolution of the NFZ. Early deformation (Stage 1) involved episodic bed-parallel faulting with fluids playing a progressively smaller role. Strain was broadly distributed at the exposure but was localized by lithic anisotropy in pelitic layers. Little Stage 1 deformation occurred in the dominant wacke beds (by diffusive mass transfer); most took place in subordinate pelitic horizons by combined diffusive mass transfer and crystal plastic mechanisms. Later (Stage 2) activity was almost entirely brittle, producing isolated NE-trending faults and two deformation zones filled with cataclasite. The latter comprise complexly anastomosing fault strands with multiple slickenline generations indicating episodic faulting. al-scale NFZ structures and history mirror those at outcrop scale. Late brittle faulting was superimposed on a broad region that had experienced largely ductile shearing, and the regional-scale brittle deformation was concentrated in three deformation zones characterized by anastomosing fault strands. It is the Stage 2 features that are mapped elsewhere in the Northern Appalachians as the Norumbega fault zone.