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

CAMP Intrusions in Southeastern Pennsylvania: 1) Morphologic Variability, Interaction, and Magmatic Pathways

Paper number: 20-3
Program: Technical Sessions
Time: 8:45 AM – 9:05 AM

Authors

Abstract

The Morgantown/Adamstown/Jacksonwald (AMJ) intrusive complex is part of the Central Atlantic Magmatic Province (CAMP, 201.5 Ma). The complex developed at the eastern end of the early Mesozoic ‘Narrow Neck’ rift basin in SE Pennsylvania (USA) during the final stages of rifting.  We have integrated field, lidar, aeromagnetic, petrologic, and subsurface core and mine data to define the 3D geometry of the complex today and at emplacement time. Additionally, we have used the emplacement geometry to predict magmatic pathways based on observations from 3D seismic data supporting predominantly up-dip magmatic flow.

 

Our work shows that each intrusion within the AMJ complex had a distinct morphology during emplacement. 1) The Morgantown intrusion was the largest (>700 km2) and thickest (up to 500 m). It had a concave-upward shape with a moderately dipping north side subparallel to the underlying rift-basin border-fault zone, a gently dipping south side, and a steeply dipping NE side subparallel to the Birdsboro fault zone. Its SW side had a complex shape, reflecting development of a secondary concave-upward intrusion sourced from the main Morgantown intrusion. The sides of the Morgantown intrusion converge at depth within pre-rift Paleozoic and Precambrian rocks beneath the rift basin at a likely feeder-dike location. From this location, magma spread laterally (up to 20 km) and upward (up to 7 km) through the syn-rift Triassic sedimentary rocks. Magma emplacement was strongly influenced by pre-existing structures, suggesting high magmatic pressures. 2) The smaller and thinner Adamstown intrusion was a gently dipping (~20°SW) sheet emanating from a likely feeder-dike location in the SW at ~6 km depth. The intrusion propagated to the north and northeast (up to 10 km) where it intersected/joined the Morgantown intrusion. 3) The Jacksonwald intrusions are small and thin (< 200 m). The two deeper intrusions formed at ~2 and 3 km depth in the axis of the developing Jacksonwald syncline and were likely fed by a dike between them. The two shallow intrusions (<1 km depth), located just south of the border-fault zone, were fed either by magma propagating up the border-fault zone or by magma flowing eastward from the Morgantown intrusion. The morphologies and emplacement dynamics of the intrusions within the AMJ intrusive complex closely resemble those observed on 3D seismic data.

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

doi: 10.1130/abs/2026NE-411256

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