MAPPING OF THE QUANAH PLUTON MARGIN AND ADJACENT DIKES, WICHITA MOUNTAINS, OKLAHOMA

The Wichita Mountains in southwestern Oklahoma expose approximately a dozen granite plutons, all part of A-type silicic magmatism associated with the Southern Oklahoma Aulacogen. The body composed of the Quanah Granite is one such pluton. Contact relationships indicate it to be the youngest of the large intrusive bodies in the eastern Wichita Mountains. The body is 35 km² of nearly continuous exposure. Part of its northern margin is an irregular but roughly E-W contact with the older Glen Mountains Layered Complex (GMLC). Granitic dikes cut the GMLC to the immediate north.

Field reconnaissance and mapping used a handheld GPS-WAAS unit and topographic base map. Within the northern margin of the Quanah Pluton, we marked locations of outcrops and lithologic contacts. The GPS-WAAS unit mapped dike outcrops as we set tracks and waypoints while walking exposed trends. We also recorded orientations of dike walls using a Brunton pocket transit. We employed DeLorme’s Topo North America 10.0 for offloading waypoints and tracks and for marking topography and DOQQ images with boundaries and trends. Those data were plotted on the USGS Quanah Mountain 7.5’ quadrangle topographic map.

Mapping documented the presence and distribution of three facies within the Quanah body. These are 1.) the typical seriate hypidiomorphic coarse-granular facies (CF), 2.) fine-grained allotriomorphic facies (FF), and 3.) fine-grained hypidiomorphic porphyritic facies (PF), which is weakly granophyric. The CF grain size is slightly diminished at the margins compared to exposures in the interior of the pluton, but otherwise the margin CF is identical in texture and mineral content with interior CF. FF and PF are exposed as dike-like bodies with linear and angular contacts. Much of these facies is walled by the CF on one or both sides, At French Lake, the PF contacts the GMLC.

Mapped dike geometries are consistent with an origin from the magmas that gave rise to the facies in the pluton margin. The dikes include a series of small north-trending features seen in the eroded northern contact wall. These demonstrably originate from the Quanah Pluton. Dikes exhibit a variety of orientations, but the prominent dike trends are 045° 33° (both NW and SE), aulacogen-parallel 120° 60°S, and Quanah-margin parallel 090° 60°S.