Date of Award

Summer 2019

Document Type

Open Access Thesis

Department

Earth and Ocean Sciences

First Advisor

James Kellogg

Abstract

The Central Atlantic Magmatic Province (CAMP) at the Triassic-Jurassic boundary, is the largest known igneous province in the world. However, the geometry and volume of CAMP intrusives under the Coastal Plain of the southeastern United States are poorly known. Under the Coastal Plain sediments of Georgia and South Carolina, the “J” seismic reflector was predicted to be produced by a CAMP lava flow. Recent studies of seismic and well data have shown that the “J” reflector is an unconformity and only locally a CAMP lava flow. In the Clubhouse Crossroads area of South Carolina, seismic reflection, seismic refraction, and well data are available to constrain the shallow structure under the Coastal Plain sediments but have not succeeded in imaging the underlying pluton. We take advantage of a rich potential field dataset to predict the deeper structure of the CAMP mafic intrusive pluton at Clubhouse Crossroads for the first time. The CAMP plutons have both very high densities as well as high magnetic susceptibilities, which makes them ideal for 3-D inversion techniques. We forward modeled the shallow structure with seismic and well control and then inverted for the shape of the deeper structures assuming realistic densities and magnetic properties. The inversion methods used include Fast-Fourier Transform inversion with GMSYS 3D, gravity Fourier Matlab depth inversion, and Oasis Montaj-Voxi earth modeling inversion. The resulting 3-D models show that the Clubhouse Crossroads mafic intrusive is a diabase/gabbro CAMP age laccolith fed by two deep conduits. The laccolith is up to 2 km thick and extends from 1 to 3 km depth over an area of 1900 km2. The volume of the Clubhouse Crossroads laccolith is 1300 km3 or over eight times larger than the Palisades Sill in the Newark Basin. Previous estimates of the Clubhouse Crossroads volumes based solely on drilling and seismic reflection may greatly underestimate the total volumes of CAMP preserved under the Coastal Plain. CAMP laccoliths and basalts under the Coastal Plain may form self-sealing storage reservoirs for CO2 sequestration by injection wells.

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