POST CAMP MAGMATISM: THE WHITE MOUNTAIN AND MONTEREGIAN HILLS IGNEOUS PROVINCES, EASTERN NORTH AMERICA

The Central Atlantic Magmatic Province (CAMP) extends approximately 5000 km north to south on both sides of the Atlantic Ocean. The magmatic activity occurred at the Triassic-Jurassic boundary (~200 Ma). In New England and the Maritime provinces this magmatic event is represented by two major suites of Mesozoic dikes emplaced between 225 and 230 Ma (Coastal New England, CNE) and at ~200 Ma (CAMP). In New England the CAMP magmatism is immediately followed by the emplacement of a distinctly different suite of igneous rocks (the older White Mountain Igneous Province, OWM) between ~200 Ma and 160 Ma. In the Cretaceous (~122 Ma) a more diverse group of rocks, ranging from carbonatites to alkaline granites, here referred to as the Monteregian Hills White Mountain Igneous Province (MHWM), are emplaced in Quebec and New England.

The OWM is dominated by feldspathic silica-saturated rocks (syenites, quartz syenites, and granites), but silica-undersaturated rocks are found at Red Hill and Rattlesnake, Maine. The rarity of mafic rocks inhibits direct comparison with CAMP magmas. However, the most primitive OWM samples have elemental and isotopic characteristics that are similar to the CNE and MHWM magmas but distinctly different from the CAMP magmas. Mafic rocks are much more abundant in the MHWM series and previous models suggest that these magmas were derived from a depleted mantle source and are related by variable degrees of melting and crustal contamination. The same models can be extended to the OWM and CNE. Thus one possible conclusion is that the CNE, OWM and MHWM magmas were derived from a similar source and represent a spectrum of magma compositions related by variable degrees of partial melting and crustal contamination. The CAMP magmas represent a totally different source and have a different petrogenetic history.