Isotopic dating indicates the most active
magmatic phase of the NAIP was between and c. 54.5
Ma (million years ago) (mid-Paleocene to early Eocene) – further divided into Phase 1 (pre-break-up phase) dated to c. 62–58 Ma and Phase 2 (syn-break-up phase) dated to c. 56–54 Ma. Continuing research also indicates that
tectonic plate movement (of the
Eurasian,
Greenland, and
North American plates), regional
rifting events, and
seafloor spreading between
Labrador and Greenland may have begun as early as c. 95–80 Ma, c. 81 Ma, and c. 63–61 Ma respectively (late
Cretaceous to early Paleocene). Studies have suggested that the modern day
Iceland hotspot corresponds to the earlier 'North Atlantic mantle plume' that would have created the NAIP. Through both
geochemical observations and reconstructions of
paleogeography, it is speculated that the present day Iceland hotspot originated as a mantle plume on the
Alpha Ridge (
Arctic Ocean) c. 130–120 Ma, migrated down
Ellesmere Island, through
Baffin Island, onto the west coast of Greenland, and finally arrived on the east coast of Greenland by c. 60 Ma. Extensive outpourings of lava occurred, particularly in East Greenland, which during the Paleogene was then adjacent to Britain. Little is known of the
geodynamics of the opening of the North Atlantic between Greenland and Europe. As the Earth's crust was stretched above the
mantle hotspot under stress from plate rifting, fissures opened up along a line from Ireland to the
Hebrides and
plutonic complexes were formed. Hot
magma over 1000 °C surfaced as multiple, successive and extensive
lava flows covered over the original landscape, burning forests, filling river valleys, burying hills, to eventually form the Thulean Plateau, which contained various volcanic landforms such as
lava fields and
volcanoes. Volcanic activity would have started with
volcaniclastic accumulations, like
volcanic ash, quickly followed by vast outpourings of highly
fluid basaltic lava during successive eruptions through multiple volcanic vents or in linear fissures. As
mafic low
viscosity lava reached the surface it rapidly cooled and solidified, successive flows built up layer upon layer, each time filling and covering existing landscapes.
Hyaloclastites and
pillow lavas were formed when the lava flowed into lakes, rivers and seas. Magma that did not make it to the surface as flows froze in conduits as
dikes and
volcanic plugs and large amounts spread laterally to form
sills.
Dike swarms extended across the British Isles throughout the
Cenozoic. Individual central complexes developed with arcuate intrusions (cone sheets,
ring dikes and
stocks), the intrusions of one centre cut through earlier centres recording magmatic activity with time. During intermittent periods of erosion and change in sea levels, heated waters circulated through the flows altering the basalts and deposited distinctive suites of
zeolite minerals. One hypothesis is that the uplift caused by the NAIP hotspot caused
methane clathrates to dissociate and dump 2000 gigatons of carbon into the atmosphere. ==Igneous landforms==