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

Early Cretaceous Taconic Lobe Magmatism of the New England-Quebec Igneous Province: Evaluating Crosscutting Structures and Sheet Intrusions

Paper number: 20-9
Program: Technical Sessions
Time: 10:40 AM – 11:00 AM

Authors

Abstract

The passive eastern North American margin records evidence of a dynamic postrift setting. The margin experienced multiple episodes of postrift magmatism, and in New England, magmatism continued until ~100 Ma. Crosscutting structures associated with each episode of magmatism can provide insight into the characteristics of the postrift stress field such as the timing of changes to the stress field, geographic variability, and association with magmatism. These insights into the structural history of the margin provide a better understanding of passive margin evolution and driving mechanisms.

The Taconic Lobe is one of three lobes of magmatism within the Early Cretaceous New England-Quebec (NEQ) Igneous Province. Taconic Lobe magmatism is the youngest episode of postrift NEQ magmatism (~110-100 Ma) and represents an important time marker for reconstructing the postrift structural history of the region. Taconic Lobe magmatism is dominated by lamprophyre dikes, some felsic dikes, and two plutonic complexes. The ~103 Ma Cuttingsville plutonic complex, located in central Vermont, is approximately 20 miles west of the ~122 Ma Ascutney complex.

This investigation focuses on observations of crosscutting structures at the plutonic complexes of the Taconic Lobe as well as the characteristics of Taconic lobe dikes crosscutting or within the vicinity of the plutonic complexes. Both plutons are crosscut by dikes and mesoscale normal faults. The Ascutney complex is crosscut by dikes (Walsh et al., 2020) as well as mesoscale normal faults that are consistent with NW–SE-directed extension after pluton emplacement at ~122 Ma. The Cuttingsville complex is crosscut by mesoscale normal faults and dikes that are consistent with NW–SE extension following pluton emplacement at ~103 Ma. Brittle emplacement characteristics of a NE–SW-trending crosscutting dike at the Cuttingsville complex support the conclusion that NW–SE-extension continued following pluton emplacement and cooling. These observations support previous work in the region (Cooper Boemmels et al., 2025) and suggest NW–SE extension occurred in northern New England throughout the duration of Taconic Lobe magmatism. In addition, the normal faults crosscutting these plutonic complexes are similar in orientation to normal faults observed by others across the northern New England region.

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

doi: 10.1130/abs/2026NE-411411

© 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.