Mesozoic igneous rocks in New England and adjacent areas can be divided into four provinces, on the basis of their ages, distribution, physical aspects, and petrology. These provinces represent intraplate magmatism that is correlated with successive stages in the opening of the Atlantic Ocean. The Coastal New England province includes three alkalic complexes and possibly some olivine dolerite dikes, Late Permian to Early Triassic in age, that are located in southern Maine and coastal New Hampshire and that were formed during uplift and early rifting in the Gulf of Maine region. Early Jurassic dolerite dikes occur in most of New England and are part of the Eastern North America province that extends along the eastern Appalachians from Alabama to Newfoundland, correlated with maximum rift-basin formation and continental breakup. Plutons of the classic White Mountains Magma Series are mainly Early Jurassic syenitoids and granitoids in central and northern New Hampshire. This elongate north-south province may have formed along an ancient transform or rift fault in the New England basement crust. After a relatively nonmagmatic period during the Late Jurassic, the Early Cretaceous New England–Quebec province of alkalic syenite-gabbro plutons and lamprophyre dikes formed in a large area of northern New England and adjacent Quebec. Similar magmas created seamount chains southeast of the New England coast, possibly along an extension of transverse Appalachian fracture zones. The Mesozoic New England igneous intrusions and tectonic activity represent incipient rifting in the continental platform, related to mantle convection and plate motions in the North Atlantic basin.

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