Petrology and tectonic significance of Mesozoic mafic dikes of the coastal New England igneous province, Massachusetts

The northeast-trending composite swarm of Mesozoic mafic dikes in eastern Massachusetts consists of tholeiitic olivine dolerites, transitional-alkalic dolerites, alkaline dolerites, and alkaline lamprophyres. Chemical subtypes thus far identified among the dolerites include dikes relatively high (>9.00 wt%) or low in MgO as well as dikes having relatively low TiO2(<3.00 wt%) and low P2O5 (<1.00 wt%) contents. The low-MgO dolerites also include high-TiO2 and high-P2O5 varieties.