Late Proterozoic (ca. 930 Ma) extension in eastern Laurentia
The northwest-dipping Carthage-Colton shear zone, located near the eastern margin of the Grenville province in northern New York, separates the Adirondack Lowlands of the Metasedimentary Belt from the Adirondack Highlands of the Granulite Terrane. Published U/Pb sphene ages are 1156‐1103 Ma in the Lowlands and 1050‐ 982 Ma in the Highlands, indicating an ;100 m.y. offset in metamorphic ages across the boundary. Our reported hornblende 40 Ar39 Ar ages are ;1060 Ma in the Lowlands and ;950 Ma in the Highlands. This confirms the offsets in sphene ages across the Carthage-Colton shear zone and indicates an average cooling rate in both the Lowlands and the Highlands of 18‐28/ m.y. over ;100 m.y. Biotite 40