GEOLOGIC MAPPING OF THE QUANAH GRANITE, WICHITA MOUNTAINS, SOUTHWESTERN OKLAHOMA

The Wichita Mountains in southwestern Oklahoma are a geologic window into the Cambrian Southern Oklahoma Aulacogen that forms the basement of a large portion of Southern Oklahoma. A U.S. Geological Survey EDMAP grant is supporting the detailed mapping of the main outcrops of one of the youngest and most different of the eleven members of the Wichita Granite suite. Of particular interest are the contacts between the Quanah Granite and its surroundings: the earlier Glen Mountains Layered Complex, the earlier Mount Scott Granite, and the Permian Post Oak Conglomerate.

The Quanah Granite is identified by its blocky cm-scale salmon-pink feldspars and distinctive riebeckitic amphibole and/or annitic biotite. Its intrusive contact with the Mount Scott Granite can be mapped because of its characteristic gray ovoid feldspar phenocrysts, although the contact shows much detailed interdigitation in places. The intrusive contact with the Glen Mountains Layered Complex is distinctive and can easily be followed. The Post Oak Conglomerate contains well-rounded, variably-sized clasts of granite lying unconformably on and against the Quanah.

The goal of this project is to produce a detailed (1:24000 scale) digital geologic map on a modern topographic base for the Quanah Granite. Reconnaissance work shows that the Quanah Granite consists of several different textural and mineralogical facies but these have never been completely mapped out. The contact relations with the abutting finer Mount Scott Granite have also not been mapped sufficiently to show the degree of complexity of the intrusive relations of the Quanah into the Mount Scott. Results from this mapping project will be used in several ways: (1) in the preparation of the Oklahoma Geological Survey's 1:100,000 areal geologic map of the Lawton sheet; (2) in providing geological materials for public use on the hiking and nature trails and entire public sections of the Wichita Mountains Wildlife Refuge; (3) the map will provide a base for models detailing the hydraulic recharge to the local aquifer systems and for more detailed studies of intrusive processes and later imposed deformation.