NATURE OF SHAWINIGAN DEFORMATION IN THE NORTHWEST ADIRONDACK LOWLANDS

The Grenville Province, found mostly in eastern Canada, was constructed by multiple phases of orogenic activity during ca. 1300 to 1000 Ma. The Adirondack Lowlands is one portion of the Grenville Province in northwestern New York State. Currently debated is the relative importance of the Shawinigan Orogeny (ca. 1200-1160 Ma) and Ottawan Orogeny (ca. 1090-1035 Ma) to the geology of the Adirondack Lowlands. Research to better understand the temporal-kinematics of Adirondack Lowlands deformation with respect to these orogenies has been undertaken in an area southwest of Black Lake in the northwestern part of the Adirondack Lowlands. Two generations of folding in the area can be defined and their character is typical of F₁ and F₂ fold generations found throughout the Lowlands. Axial planar features of F₁ and F₂ folds include gneissic layering (S₁) and schistosity (S₂), respectively. Additional field observations and re-dating of zircons by the SHRIMP II RG of samples previously reported on, removes any direct evidence of Ottawan plutonism or deformation in this area of the Lowlands, but instead places development of F₁ and S₁ to during the later part of the Shawinigan Orogeny at ca. 1169 Ma. Synthesis of structural data from the two folding events suggests that a kinematic model that has the development of F₁ and F₂ resulting from progressive deformation is reasonable. Further the association and geometry of the large-scale F₂ Alamgin antiform with the Black Lake Ductile Shear Zone suggests that the fold developed as a result of significant sinistral tranpression along the vertical to sub-vertical NE/SW trending Black Lake Ductile Shear Zone. This work emphasizes that the Adirondack Lowlands is dissected by multiple ductile shear zones with kinematics perhaps consistent with some models for the Carthage-Colton Mylonite Zone on the Lowlands' SE boundary.