TEXTURAL ANALYSIS OF SOUTH CAROLINA DIKES, CENTRAL ATLANTIC MAGMATIC PROVINCE: INSIGHT INTO A COMPLEX MAGMATIC SYSTEM.

The Central Atlantic Magmatic Province (CAMP) is now one of the most widely distributed large igneous provinces. However, the processes through which it developed are still not well understood. It is associated with dike swarms, of which the best studied are the Carolina Group, in the southeastern US. Despite this, there are still many questions about the province's association with rifting, melt generation, and dike intrusion. This study applied quantitative textural analysis through the calculation of crystal size distributions (CSDs) to evaluate processes of nucleation, growth, and textural equilibration during formation of olivine microgabbro dikes in South Carolina. CSD plot shapes can be used to evaluate processes involved in the development of igneous rocks, from primary crystallization through to textural modification.

This project studied dike samples from Greenville County, South Carolina to assess processes through which they developed. They were divided, on grain size, into coarser (>2 mm), medium (1-2 mm), and finer (<1 mm) groups. Despite variations in grain size, each sample had similar mineralogic and textural characteristics. They are typically 45% plagioclase, 30% clinopyroxene, and 25% olivine. All display ophitic or sub-ophitic textures; plagioclase, clinopyroxene, and olivine phenocrysts, which may be zoned; and stellate plagioclase formations. CSD analysis was performed on plagioclase with linear central portions of plots, indicating in situ crystal growth, with modifications at the smaller and larger crystal sizes. At the smallest crystal sizes, all plots have a downwards curvature. As all plagioclase crystals were easily visible in the thin section images, this is interpreted to be associated with processes of textural equilibration. At the larger sizes plot shapes were interpreted to be kinked, due to the phenocrysts, indicating mixing of crystal populations. Thus, reflecting events associated with magma mixing and mingling. The zoned phenocrysts and the stellate plagioclase likely formed through complex recharge, resorption, nucleation, and growth events, prior to intrusion of the dikes. This indicates a complex deep-level magmatic system fed the Carolina Group dikes.