MAPPING THE CRATERVILLE FACIES OF THE QUANAH GRANITE, WICHITA MOUNTAINS, SOUTHWESTERN OKLAHOMA

The Wichita Mountains in southern Oklahoma expose the products of intracontinental bimodal magmatism that occurred during Late Ediacaran-Early Cambrian rifting. The Wichita Granite Group (WGG) includes roughly a dozen lithodemes, each thought to arise from separate intrusions of shallowly emplaced magma. Decameter-scale mapping revealed that these plutons exhibit modest differentiation that constrain attributes of emplacement processes. The Craterville granite is a newly studied facies within the mapped Quanah pluton, the second-largest exposure of the WGG and the youngest of those exposed in the eastern Wichitas (530.23 ± 0.14 Ma).

Recent mapping has better defined the extent of the Craterville facies. The easternmost exposures dominate the mountains between McKenzie Hill and Ketch Lake Roads on the Fort Sill Army Base, extending to the west in and around Quanah Mountain within the Wichita Mountains Wildlife Refuge. Sampling identified known and newly-found contacts between the Craterville and the surrounding bodies. A handheld GPS-WAAS unit recorded sample sites and numerous field identification points. Satellite imagery and topographic maps were incorporated to assist in locating accessible contacts and interpolating those inaccessible or unresolvable. Together, these generated a new ArcGIS geologic map with 1:24 000 scale or better resolution.

The Craterville is best characterized in the field by its blocky Ksp grains set in a matrix with glomerocrystic trains of Qz, minor granophyre, and a low mode of mafic silicates. Contacts with the neighboring older Cache and Mount Scott Granites are largely sharp and distinct, as are contacts with a large outcrop of Carlton Rhyolite. Due to similar expression, particularly on weathered surfaces, the transition from Craterville into typical Quanah Granite in the west is enigmatic and perhaps transitional. Furthermore, the Craterville facies exhibits medium to coarse grain sizes throughout its exposure area. Coarse-grained varieties promote tor topography; medium-grained expressions are highly fractured, smoother terrain that is similar to other neighboring bodies and therefore easily mismapped. About a third of the mapped Cache Granite is Craterville facies. This last finding suggests that the Quanah pluton is larger than previously considered.