Terminal Neoproterozoic (Ediacaran) granitoid rocks underlie most of the Southeastern New England Avalon Zone. Major- and trace-element analyses on representative samples from Massachusetts and Rhode Island corroborate earlier interpretations that these rocks were formed in a subduction-related setting. New crystallization ages from the same suite are 609.5 ± 1.1 Ma, 609.1 ± 1.1 Ma, and 608.9 ± 1.2 Ma for units of the Dedham Granite; 606.3 ± 1.2 Ma for the Milford Granite; 604.4 ± 1.2 Ma for the Fall River Granite; and 599 ± 2 Ma for the Esmond Granite (2σ errors, including internal and external uncertainties). The Avalonian magmatic interval defined by these and other reliable dates is ca. 610–590 Ma, which is considerably shorter and younger than previously thought. These dates provisionally link the southeastern New England Avalon zone with the Antigonish and Cobequid Highlands in northern mainland Nova Scotia as distinctive blocks in the Northern Appalachian Avalonian collage.