The geologic history of the New England hotspot is the subject of much debate among geoscientists. The conventional opinion is that volcanic activity associated with the hotspot results from movement of the
North American Plate over a fixed
mantle plume. During the first major episodes of volcanic activity, the plume created the
igneous intrusions of the
Monteregian Hills in southern
Quebec and the younger set of intrusions of the
White Mountains in
New Hampshire around 124–100 Ma. As the plate moved further west, the plume moved offshore, forming the
New England Seamounts between 103 and 83 Ma. After the formation of the Nashville Seamount around 83 Ma, there was a pause in volcanic activity and the volcanic center shifted north, creating the Corner Rise Seamounts around 80–76 Ma. The Mid-Atlantic Ridge passed over the plume around 76 Ma and renewed volcanic activity produced the Seewarte Seamounts on the African Plate between 26 and 10 Ma. and helium isotope ratios in groundwater in the Monteregian Hills which indicate a deep mantle source. The lack of an obvious hotspot track west of Montreal has previously been ascribed to failure of the plume to penetrate the
Canadian Shield, a lack of recognizable intrusions due to erosion, or strengthening of the plume when it approached the Monteregian Hills, but more recent research has found
kimberlite fields in
Ontario and
New York dated between 180 and 134 Ma and at
Rankin Inlet to the northwest of
Hudson Bay dated between 214 and 192 Ma which may represent an older, continental extension of the hotspot track. Some evidence, such the lack of an initial flood
basalt and age progression along the New England-Quebec volcanic province, is not what is expected for a plume origin, and the case has been made that a shallow,
tectonic mechanism is more plausible. In this view, the two spikes in activity that formed the New England-Quebec volcanic province and New England Seamounts are due to passive, shallow melting associated with
lithospheric extension resulting from tectonic changes in the Atlantic Ocean which reactivated pre-existing zones of structural weakness related to the earlier opening of the
Iapetus Ocean. support this interpretation. ==See also==