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 and Cretaceous magmatism along the Southwestern Maine Mesozoic Igneous Corridor: A record of both pre- and post- CAMP/White Mountain Batholith igneous activity

Paper number: 20-7
Program: Technical Sessions
Time: 10:00 AM – 10:20 AM

Authors

Abstract

In a relatively narrow (~10 km wide) north-northwest (340o) trending corridor extending ~100 km from the southern Maine coast to the southeastern margin of the Early Jurassic White Mountain Batholith are nearly a dozen small Mesozoic magmatic complexes.  The igneous rocks along the transect fall into Triassic (239-207 Ma) and Cretaceous (122-115 Ma) age bins, and include impressive compositional variability (e.g., from layered gabbronorite to granite to nepheline syenite).  This study integrates previously published and new petrologic, geochemical, and geochronological data from these igneous rocks in Maine that both pre-date and post-date CAMP (~201 Ma) and White Mountain Batholith (~199-180 Ma) magmatism.   

 

Triassic intrusions along the transect include the largest (area ~75 km2) and oldest (238.9 ± 0.3 Ma, Hussey et al., 2016) of the intrusions, the Agamenticus Complex exposed near the Maine coast.  This complex consists largely of granite, alkali granite and syenite.  About 50 km to the north-northwest are two smaller Triassic intrusions, Picket Mtn. (~35 km2) and Abbott Mtn. (~15 km2).  The Picket Mtn. intrusion is dominated by biotite granite and new U-Pb zircon ages reveal a crystallization age of 231.1 ± 1.9 Ma.  The Abbott Mtn. intrusion consists largely of fayalite-bearing alkaline syenites and new LA-ICP-MS U-Pb zircon ages indicate crystallization at 211.6 ± 1.6 Ma.  Finally, at the northern end of the transect within 10 km of the White Mountain Batholith, Kinney et al. (2022) report a 207.4 ± 0.1 Ma age for granite in the Whales Back intrusion (~15 km2).

 

Cretaceous magmatism is also distributed along this narrow transect and from south to north these include the Cape Neddick (<1 km2), Tatnic (~10 km2), Alfred (~10 km2), Randall Mtn. (~1 km2) and Burnt Meadow Mtn. (~12 km2) igneous complexes.  The southern three of these complexes (Cape Neddick, Tatnic, Alfred) are all dominated by alkaline and LREE enriched mafic rocks and previously reported 40Ar/39Ar biotite ages indicate all three were intruded at roughly the same time (122.5 ± 1 Ma, Hubacher and Foland, 1991).  In contrast, further to the north, the Randall Mtn. and Burnt Meadow Mtn. complexes are dominated by LREE-enriched alkaline syenite and trachyte (Na2O+K2O = 10-14 wt.%).  New LA-ICP-MS U-Pb zircon ages indicate both alkaline complexes crystallized at 115 ± 1.0 Ma.         

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

doi: 10.1130/abs/2026NE-411219

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