A Late Devonian Magmatic Link between Rhode Island and Nova Scotia

• Published in: The Journal of geology 2018-09, Vol.126 (5), p.511-530
• Main Authors: Dorais, Michael J., Gibson, David, Bothner, Wallace A.
• Format: Article
• Language: English
• Subjects: Basins; Coastal environments; Coexistence; Composition; Convergence; Deposition; Devonian; Dikes; Diorite; Embankments; Eruptions; Geological faults; Heat flux; Heat transfer; Igneous rocks; Lava; Magma; Orogeny; Petrogenesis; Plutons; Ponding; Rock; Rocks; Studies
• ISSN: 0022-1376; 1537-5269
• DOI: 10.1086/699266

Several Late Devonian plutons across southeastern New Hampshire, coastal Maine, and north-central Massachusetts have within-plate compositions distinct from the 400–410 Ma calc-alkaline plutons related to the Acadian Orogeny in the same region. The ages of these plutons range from 380 to 360 Ma. The mafic portions of these plutons are compositionally similar to within-plate tholeiites of the same age in Maritime Canada, the Narragansett Basin in Rhode Island, and the Coastal Maine Magmatic Belt. Coastal New England and Maritime Canada experienced extensional magmatism resulting from oblique convergence of Meguma accreting to Laurentia during the Neoacadian Orogeny. A transtensional zone along dextral transcurrent faults allowed the formation of the Maritimes Basin of Nova Scotia and New Brunswick and the eruption of the 373 ± 4 Ma Fisset Brook Formation into the basin, as well as the eruption of similar-aged rocks in the Narragansett Basin. The petrogenesis of Late Devonian peraluminous and metaluminous granitic plutons associated with these mafic rocks across central/coastal New England is problematic because the compositions of the mafic plutons and lavas from Maritime Canada to the Narragansett Basin indicate that the region was undergoing extension during this time period, yet the felsic rocks lack the within-plate compositions of granitic rocks of this age in central New England. The association of granitic rocks and within-plate mafic rocks as composite dikes in the Deer Isle Pluton, quenched dioritic enclaves in the granitic phase of the Appledore Island Diorite, and the coexistence of mafic-felsic magmas of the Hardwick Pluton indicates that the two magma types were coeval. The plutonic rocks of this study mark the region of transpression between these basins, and ponding of these within-plate mafic magmas may have provided the heat flux for partial melting of the crust and may account for the variety of compositions of granitic magmas emplaced across New England at this time.