PRELIMINARY OBSERVATION AND CLASSIFICATION OF MAFIC ENLAVES IN THE MOUNT SCOTT GRANITE, WICHITA GRANITE GROUP, OKLAHOMA

The Wichita Mountains in southern Oklahoma host exposures of the Cambrian Wichita Granite Group (WGG), the products of roughly a dozen shallowly emplaced sheet plutons resulting from rift-induced magmatism. The Mount Scott Granite is the largest of the WGG lithodemes. Mafic enclaves, dark patches dominated by mafic silicates in the otherwise pink-to-brick-red alkali feldspar granite, are a defining characteristic found throughout its ~200 km² of areal exposure. Although noted by prior workers, their nature and origin remain undefined. Here we report initial findings on classifying their microstructure and dimensions to assist ongoing characterization of mineral assemblages within enclave populations, and to ultimately constrain theories regarding their origins.

This preliminary work measured the apparent Feret diameters on two axes and enclave perimeter on scaled images from in-situ exposures and on collected hand samples; depth was additionally measured on sectioned hand samples. The average measurements are approximately 20 mm for the long and 10 mm for the short axis, the third axis (hand samples only) averaged 13 mm. Perimeters averaged 64 mm. The study placed enclaves into four discrete categories of microstructure: dense mafic minerals with sharp enclave boundary (type I), scattered mafics with sharp boundary (type II), dense mafics with diffuse boundary (type III), and scattered mafics with diffuse boundary (type IV). Additionally, there are two shape categories: ellipsoidal and platy. The bulk of the observed enclaves are of similar dimensions, but categorization includes an additional scaling parameter for uncharacteristically oversized enclaves that have one or more axes that are at least five times the average length.