40 Mesozoic Magmatism, Postrift Tectonics, and Passive Margin Development of Northeastern North America (Posters)

The northeastern region experienced protracted Mesozoic (Triassic-Cretaceous) magmatism associated with continental rifting and subsequent passive margin development. We welcome contributions related to the occurrence, tectonics, or driving mechanisms of these syn- and postrift events.

Tuesday, 24 March 2026
8:00 AM - 12:00 PM
CCC, Ballroom C

New Geochemical and Petrographic Data for Mafic Dikes on Appledore Island, ME

Paper number: 40-5
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Appledore Island is part of the Isles of Shoals, ~15km southeast of Portsmouth, NH. Most of the island is made up of metasedimentary and metaigneous rocks correlated with the Devonian Rye Complex of southeast NH and southern ME. There is also an associated body of diorite caused by partial melting of the Rye Complex rocks during extension following the acadian orogeny (Dorais et al. 2014). A number of mafic dikes of previously unknown origin cut across the island, trending either to the NW or NE. These dikes have three possible origins: the 230-225Ma Coastal New England (CNE) group, the ~200Ma Central Atlantic Magmatic Province (CAMP), or the Cretaceous New England-Quebec (NEQ) province. CNE dikes have a slightly enigmatic origin, currently thought to be caused by hotspot magmatism in the period before the initiation of the rifting of Pangaea (Dorais et al. 2005). They tend to have SiO2 contents between 45-48 wt% and TiO2 of 2.5-3.8 wt%. CAMP dikes are mainly diabases and basalts intruded and erupted during the breakup of Pangaea (Marzoli et al. 2014). Compared to CNE rocks, CAMP rocks are more tholeiitic and tend to be less enriched in REEs. The NEQ province has a more diverse range of magmatic compositions ranging from lamprophyre dikes to alkalic syenite intrusions and stretches from Quebec to southern New Hampshire. NEQ rocks are thought to be caused by the North American plate drifting northwest over the Great Meteor hotspot. This study examines the petrography and geochemistry of 10 mafic dikes on Appledore Island with the goal of learning more about the processes that led to their petrogenesis. Overall, the dikes can be classified as basalt, ranging from porphyritic to diabasic. Phenocrysts in the porphyritic dikes include plagioclase, clinopyroxene, and olivine, though olivine is only present in two samples. Major element compositions for all of the dikes resemble CNE dikes studied by Dorais et al. (2005). Major element data shows at least two populations of dikes, with trace element data showing three. Major element compositions correlate with the orientation of most of the dikes. Continued investigation of these dikes will examine the geochemical and spatial variations to determine their relationship to the magmatic history of New England.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411400

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