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.

Abstract We report new, highly precise, U–Pb and Ar/Ar ages for seven Cretaceous rhyolites, tuffs and granites from across Zealandia spanning a 30 Ma period from arc magmatism to continental break-up. Combined with previously published data, these reveal a strong episodicity in Cretaceous silicic magmatism outside the Median Batholith. 112 Ma tuffs are known only from the Eastern Province in association with a Cretaceous normal fault system. Both 101 and 97 Ma groups of rhyolites and tuffs occur across the entire width and half the length of Zealandia from near the palaeotrench to the continental interior, indicating widespread and effectively instantaneous extension. We attribute an increase in A-type character with time (112–101–97–88–82 Ma) to the progressive thinning of the Zealandia continental crust whereby, with time, there is less opportunity for crustal contamination. Extension directions associated with 101, 97 and 82 Ma magmatism and associated core complex exhumation across Zealandia are all oriented c. 30° oblique to the margin. These observations suggest Zealandia rifting was controlled by either >83 Ma capture of Zealandia by the Pacific Plate and/or <83 Ma Zealandia–West Antarctica spreading, rather than by laterally migrating triple junctions, slab windows or plume heads.