20 Mesozoic Magmatism, Postrift Tectonics, and Passive Margin Development of Northeastern North America
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.
Monday, 23 March 2026
8:00 AM - 12:00 PM
CCC, Room 27
Triassic Mafic Magmatism in New England and the Canadian Maritimes
Paper number: 20-2
Program: Technical Sessions
Time: 8:25 AM – 8:45 AM
Authors
-
Martin RossNortheastern University, Boston, Massachusetts
Abstract
Triassic dikes and lava flows in New England and the Canadian Maritimes comprise two provinces – Coastal New England (CNE) and Eastern North America (ENA). The CNE dikes and flows are emplaced between 246 and 222 Ma (the main alkaline magma pulse) followed by a younger alkaline pulse between 209 and 203 Ma. The ENA dikes and flows are emplaced at 201.3 ± 0.4 Ma (the Triassic-Jurassic boundary, CAMP magmatism).
Both CNE and ENA dikes strike NE-SW with steep dips indicating that extension occurred in a NW-SE direction. However, a structural analysis of the CNE dikes presents a more complex picture. Using available data it is possible to distinguish two subprovinces – Cape Ann and Maine. For Cape Ann the majority of the dikes trend 41.2o ± 9.0o. For Maine the majority of the dikes trend 55.4 ± 4o. Based on currently available geochronology, the Maine dikes are younger than Cape Ann dikes, implying that there has been some reorientation of the stress field with time.
There are clear chemical distinctions between the two provinces. On the standard TAS diagram most CNE samples plot in the alkali basalt field while most ENA samples plot in the basalt field. CNE samples range from silica undersaturated to silica saturated while all ENA samples are silica saturated. Nb/Ta and Zr/Hf ratios are higher for CNE samples compared to ENA samples. In general, CNE samples show steeper chondrite normalized REE patterns and higher total REE than the ENA samples. In terms of Nd isotopes, the CNE samples have positive εNd values while the ENA samples have negative εNd. Thus, it is possible to chemically distinguish between these two magma series, which is important when considering the genesis of more evolved magmas.
Thermodynamic modeling and elemental data show that the CNE magmas equilibrated with both spinel lherzolite and garnet lherzolite mantle over a depth range of 190 to 50 km. ENA magmas equilibrated with spinel lherzolite mantle at depths of less than 50 km. The ENA magmas are related to plume which gave rise to the CAMP LIP while current data support the inference that the CNE magmas were derived from the subcontinental lithosphere.
Geological Society of America Abstracts with Programs. Vol. 58, No. 2
doi: 10.1130/abs/2026NE-411444
© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.