1 New advances in geological and geophysical research on the Appalachian orogen.

We invite contributions that discuss new research on the Appalachian orogen. Submissions should include, but are not limited to, geological or geophysical studies or works comprising a combination of both methods.

Sunday, 22 March 2026
8:00 AM - 12:00 PM
CCC, Room 22/23

Deciphering The Complex Geology of The New Hampshire Connecticut Valley – Gaspé Trough north of The 45th Parallel

Paper number: 1-8
Program: Technical Sessions
Time: 10:20 AM – 10:40 AM

Authors

Abstract

We mapped six 7.5’ quadrangles in the Connecticut Valley – Gaspé trough (CVGT) at a scale of 1:24,000 and are mapping two quadrangles at a 1:100,000 scale through the STATEMAP program between the New Hampshire Geological Survey and United States Geological Survey. This collaboration facilitated useful conversations with neighboring Québec, Vermont and Maine geologists. 

The metasediments are metasandstones, metasiltstones, phyllites and graded graywackes with tuffaceous interbeds and minor carbonates within the Waits River, Gile Mountain (GM), Ironbound Mountain (IBM) and Frontenac (FF) formations. The metaigneous rocks are metabasalts and metagabbros of the FF, metabasalts, metagabbros, and bimodal metavolcanics of the Clinton River Formation (CR) and felsic to intermediate metaintrusives of the East Inlet intrusive complex (EIIC). 

The region was deformed during the Salinic, but primarily during the Acadian, and metamorphosed to greenschist facies. The deformation created extensive folding, formation of two thrust faults, two graben-bounding normal faults as well as a shear zone.  One normal fault separates the CVGT from the Bronson Hill anticlinorium.

Ages of the CVGT rocks are upper Silurian through Early Devonian and show extensive overlap of formation ages. New U-Pb zircon age dating yielded 12 crystallization ages of igneous rocks and 18 detrital zircon age profiles with maximum depositional ages.  Both IBM belts have similar detrital zircon age profiles. Ages of the FF, GM, CR, IBM and EIIC overlap within the range of uncertainties, with some younger IBM ages in the western belt.

New geochemical, lithological and field data support separation of the FF and CR formations – consistent with Québec stratigraphy. Geochemistry of FF mafic rocks indicates a continental crust origin whereas geochemistry of CR mafic rocks indicates a greater oceanic origin.  CR metabasalt dikes and gabbros are intertwined locally and in places, the gabbros are mafic pegmatites.  The felsic meta-intrusives of the EIIC are dominantly tonalites, occurring as a small plutonic body and as thin dikes within the CR metabasalts that extend NE-SW over a large area.  The tonalites may be plagiogranites that formed at the base of oceanic crust.  However felsic metavolcanics of the CR bimodal sequence and of the eastern IBM belt are rhyolites and dacites. Felsic metaintrusives and ignimbrites near Lake Francis are biotite granites and rhyolites, possibly indicating a greater continental crust contribution

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

doi: 10.1130/abs/2026NE-411419

© 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.