Juxtaposed Mesozoic diabase dike sets from the Carolinas: A preliminary assessment

Aeromagnetic anomaly maps of the North Carolina Piedmont provide confirming evidence of juxtaposed Mesozoic diabase dike sets. Dikes in North Carolina may be divided into four domains, on the basis of dike orientations. Most dikes are olivine normative, but there are apparent systematic differences in chemical compositions that are reflected in different orientations and ages. Two orientations dominate: northwest and north-south. The northwest-trending set dominates in the South Carolina Piedmont, and the north-south set extends through much of the central Virginia Piedmont and under the Coastal Plain in South Carolina. The north-south dikes are part of a set that converges near Charleston and Georgetown, South Carolina, and diverges northward into Virginia. Preliminary information suggests that the north-south dikes are younger than the more common northwest-trending dikes. Current models proposed for stress regimes associated with the breakup of Pangea can accommodate the northwest set, but not the north-south convergent set. This convergent set may be evidence for crustal deformation above a mantle plume centered near Charleston and Georgetown in Middle Jurassic time. It is possible that presumed mafic plutons under the Coastal Plain near Charleston, regional seismicity patterns, and orientations of the diabase dikes are all related to an intersection of zones of crustal weakness inherited from mid-Mesozoic time. The western margin of northwest-trending dikes may be related to tectonic features inherited from pre-Mesozoic time.