CHEMICAL VARIATION OF MESOZOIC DIKES IN THE CAROLINAS

Salters et al. (2003) noted three major trends of Mesozoic dikes in the Central Atlantic Magmatic Province (CAMP). Samples from CAMP dikes were collected from four locations in the Carolinas. The objective of this study is to determine whether there is a systematic relationship between location or trend to the geochemistry within these dikes. The four sampling locations include: 1) west of Greensboro, NC in the Charlotte belt, trending NE, 2) between Raleigh and Durham, NC in the Raleigh belt, trending NS, 3) between Rockingham and Troy, NC, trending both NS and NW, and 4) from the Great Dike near Pageland, SC, trending NW. EDXRF was used to determine the major element compositions of twelve of these samples. Alkali versus silica plots as well as CIPW norms indicate that the magma compositions range from basalt (ol' norm) to basaltic andesite through andesite (qtz' norm). All samples exhibit low titanium (LTi) to intermediate titanium (ITi) values. No high titanium dikes were found. Preliminary results indicate that the dikes in these four locations correspond with the results of Salters et al. (2003). The NS trending dikes are quartz normative, the NE trending dikes are olivine normative, and the NW-SE trending dikes show a wide variation in composition. The Greensboro samples are LTi and low alkali. These samples are located farthest inland and are the most primitive of all dikes studied. The other three sampling localities are farther to the east and parallel to rifting. Their compositions vary widely from LTi to ITi and also from low to high alkali. With the exception of the dikes farther inland, there appears to be little correlation of chemistry to geography. However, perpendicular to rifting, dikes farther inland are more primitive than dikes closer to rifting.