ASSESSING THE GREATER WICHITA GRANITE GROUP OF SOUTHERN OKLAHOMA THROUGH ARCHIVED BASEMENT PENETRATIONS

The Wichita Granite Group (WGG) is a series of lithodemic units and products of magmatism associated with the Cambrian Laurentian margin. The units are reasonably defined as individual intrusive bodies (plutons and dike groups) from exposures within the Wichita Mountains of southwestern Oklahoma. But the bulk of this series is covered by younger strata along a WNW Pennsylvanian uplift trend that stretches across southern Oklahoma and beyond. These products have been intersected by basement-penetrating drill holes. Rotary drill cuttings and a small amount of core are available from the Oklahoma Petroleum Information Center, in Norman.

Potential goals of subsurface analysis of the WGG are to 1.) better constrain the volume of felsic magmatism, and 2.) evaluate potential extents of intrusive bodies. Despite their small size, characterization of the cuttings has proved useful for comparison to the exposed lithodemes. Thus far, we have been able to evaluate samples proximal to the exposures in the Wichita Mountains, and those located 100 km to the ESE within the uplifted block of the Arbuckle Mountains. The WGG is almost exclusively hypersolvus alkali feldspar granite (low plagioclase content), dominated by medium-grained granites with a distinctive granophyre porphyritic microstructure; granites with these latter features are easily identified, even on small (<5 mm) cuttings. A few of the WGG are amphibole-, or more rarely pyroxene-bearing. Given the inherent chemical sensitivity of amphiboles and Ca/Na variability in exposed WGG phases, electron-microbeam analysis of inosilicate phases provides a distinctive characterization for comparison. Sheet silicates are more prevalent throughout the WGG and provide additional constraint and clues to post-emplacement alteration. Lastly, whole-rock geochemical analysis provides further comparison, provided sufficient cutting materials are available.