LINKING STRUCTURAL GEOLOGY AND PETROLOGY AT MULTIPLE SCALES TO BETTER UNDERSTAND THE EVOLUTION OF THE MORGANTOWN (AND OTHER) CAMP INTRUSIONS

The Morgantown intrusion (SE PA) lies within the narrow rift basin between the larger Gettysburg and Newark basins of the eastern North American rift system. It is part of the Central Atlantic Magmatic Province (CAMP) formed by a global-scale igneous event at ~201 Ma. We have integrated field, lidar, aeromagnetic, petrologic, and subsurface core and mine data from the kilometer to the micrometer scale to define the Morgantown intrusion’s 3D geometry and to relate this geometry to magma flow.

Today, its north side (near the border-fault zone), west side, and south side dip moderately to gently inwards toward each other, whereas its NE side is a steeply-dipping, >200 m-wide dike parallel to the Birdsboro fault zone. These sides connect at depth within the pre-rift Paleozoic and Precambrian rocks beneath the rift basin. The western side also connects to another gently dipping sheet to the west. The geometry of the intrusion at the time of emplacement (i.e., after correcting for syn- and post-CAMP folding, faulting, regional NW tilting, and erosion) differed significantly from its current shape. Its northern side dipped much more steeply than its southern side (~70°SE vs. ~20°NW). Emplacement depths ranged from <1 km in the north to >5 km within the Paleozoic and Precambrian rocks beneath the rift basin. From this likely feeder-dike location, magma spread laterally (up to 10 km) and upward (up to 5 km) into the syn-rift Triassic sedimentary rocks.

The variety and spatial distribution of diabase rock types in the Morgantown intrusion (e.g., pyroxene-rich vs. chemically evolved) are similar to those in other CAMP intrusions from VA to NY. We have used the reconstructed geometry of the intrusion to quantify the spatial pattern of different rock types both vertically (emplacement level) and laterally to improve previous models of lateral-flow differentiation. Importantly, the northern and eastern sides that contain the most evolved, hydrothermally altered diabase had the steepest dips and intruded along fault zones. We propose that lateral and vertical flow during emplacement distributed crystal cargo primarily in gently-dipping segments, whereas convection after emplacement in dike-like segments enhanced the transport of evolved liquids and fluids to shallow levels or the surface, affecting degassing and eruptive behavior.