30 New advances in geological and geophysical research on the Appalachian orogen. (Posters)

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.

Monday, 23 March 2026
1:30 PM - 5:30 PM
CCC, Ballroom C

Geologic Mapping and Kinematic Analysis of a ~330 Ma Gabbro and Adjacent Migmatitic Shear Zone, Androscoggin Riverlands State Park, South Central Maine

Paper number: 30-3
Program: Technical Sessions
Time: 1:30 PM – 1:30 PM

Authors

Abstract

The Norumbega Fault System is a long-lived, crustal scale, right lateral shear zone system that is exposed from the southeast corner of New Hampshire and Southern Maine to New Brunswick, Canada. The main fault was active as a shear zone from the Late Devonian to Late Carboniferous. Near Casco Bay, the main fault bends slightly, and an extensive array of secondary restraining bend shear zones have been mapped coastward of the Norumbega Fault. However, no analogous secondary shear zones have been mapped inland. This study presents geologic mapping, geochemistry, and electron backscatter diffraction (EBSD) data for a partially deformed 330 Ma gabbro intrusion and an adjacent high-temperature shear zone in the Androscoggin Riverlands State Park north of Lewiston, Maine. The intrusion and shear zone are hosted in the Devonian Leeds Pluton. Detailed mapping reveals the intrusion is a subvertical tabular feature that has undergone horizontal boudinage at the 100-m scale, with pegmatite filling boudin necks. The high-temperature shear zone dips subvertically and strikes N-S. It wraps around one side of the gabbro boudins and extends beyond the gabbro in both directions. EBSD analysis reveals that the kinematics of the shear zone are predominantly dextral and west-side down. We explore the relationship between gabbroic magmatism and shear zone development and suggest that the shear zone was active concurrently with post-intrusion boudinage, which is significantly later than high-temperature activity at the current exposure level of the main fault strand.

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

doi: 10.1130/abs/2026NE-411366

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