Nature and evolution of the Norumbega fault system in the Great Pond-Grand Lake stream area, eastern Maine

The early ductile shearing in the Norumbega fault system in eastern Maine occurred within an environment of oblique convergence as the result of adjustments following Acadian plate collision during middle to late Paleozoic times. Metasedimentary rocks were ductilely sheared into phyllonite and granite into mylonite. It took place at conditions of the lower greenschist facies, at confining pressures of 2–2.5 kbars and peak temperatures on the order of 300–350° based on comparison of quartz and feldspar microstructures and analysis of their different deformation mechanisms. Kinematical indicators at different scales confirm the dextral strike-slip movement. A regional ductile shear model is proposed based on the study of shear zone geometry and identification of three granite slivers (Amazon Mountain, Third Lake Ridge, and Morrison Ridge granites) and synthetic shear bands existing between the Kellyland and Waite zones. Shear strain was initially partitioned into the Kellyland, Waite, and Codyville zones. Extended dextral shearing and displacement between the Kellyland and Waite zones were concentrated in the synthetic shear bands representing megascopic c′-bands, displacing the Morrison Ridge and Third Lake Ridge slivers farther from their original positions. Restoration of the Morrison Ridge and Third Lake Ridge slivers to their presumed original positions yields approximately 25 km of dextral strike-slip offset along the Kellyland and synthetic ductile shear zones.; The Waite ductile fault zone was reactivated brittlely by three compressional tectonic events identified by studies of minor conjugate faults: an early WNW-ESE compression, followed by a NE-SW-directed compression, and by a drastic change in stress orientation to a N-S-oriented compression observed only in Pennsylvanian (?) redbeds. Brittle Episode 1 was a dextral-oblique-reverse faulting event that superimposed a wide and continuous cataclasite and breccia zone on the pre-existing Waite ductile shear zone. Episode 2 brittle faulting was dextral strike-slip and probably responsible for the formation of a series of narrow pull-apart redbed basins that apparently nucleated at releasing bends.; Post-Carboniferous sinistral-strike-slip brittle faulting (Episode 3) tilted the Carboniferous redbeds and juxtaposed them with older metamorphic rocks of the Fredericton belt. Episode 3 faulting is apparently the only product of Alleghanian deformation in the study area.