Onset of long-lived silicic and alkaline magmatism in eastern North America preceded Central Atlantic Magmatic Province emplacement

The White Mountain magma series is the largest Mesozoic felsic igneous province on the eastern North American margin. Previous geochronology suggests that magmatism occurred over 50 m.y., with ages for the oldest units apparently coeval with the ca. 201 Ma Central Atlantic Magmatic Province, the flood basalt province associated with the end-Triassic mass extinction and the opening of the Atlantic Ocean. We use zircon U-Pb geochronology to show that emplacement of White Mountain magma series plutons was already underway at 207.5 Ma. The largest volcanic-plutonic complex, the White Mountain batholith, was emplaced episodically from ca. 198.5 Ma to ca. 180 Ma and is ∼25 m.y. older than published ages suggest, and all samples we dated from the Moat Volcanics are between ca. 185 Ma and 180 Ma. The Moat Volcanics and the White Mountain batholith are broadly comagmatic, which constrains the age of a key Jurassic paleomagnetic pole. Our data indicate that a regional mantle thermal anomaly in eastern North America developed at least 5 m.y.