CHARACTERIZING SUBSURFACE GRANITES IN THE SOUTHERN OKLAHOMA AULACOGEN: A FOCUSED ASSESSMENT WITH THE POTENTIAL TO ASSIST A BIG REGIONAL PROJECT

The characterization of Southern Oklahoma Aulacogen (SOA) granite bodies as exposed in the Wichita Mountains remains useful in assessing aulacogen construction and constraining the nature of this prominent basement feature. The study of these shallow sheet plutons has advanced our understanding of crustal construction, magma ascent, pluton cooling, Eocambrian SOA magmatism, and post-emplacement tectonics. But much like an iceberg, the exposed granites represent a small fraction of the total mass; the bulk of the material is buried at depth under younger sedimentary rocks. These are encountered by numerous basement-penetrating wells along the SOA trend. The seminal work of Ham et al., 1964, mapped the general distribution of these granites and other SOA materials by evaluating basement-penetrating wells. Our new study builds on their data by incorporating wells completed in the last half century to define individual pulses of magmatism at a definition roughly equivalent to exposures in the Wichita Mountains. Our study also seeks to understand the attributes of late-Paleozoic deformation and fracture-induced alteration of these bodies.

Basement-penetrating wells are numerous, broadly distributed along the SOA, and sample hundreds of meters of continuous depth. But samples are dominated by rotary drill cuttings, which are voluminous but of small size. We are evaluating and applying relatively inexpensive and rapid analytical techniques for these numerous fragmented samples: Laser Induced Breakdown Spectrometry (LIBS), X-ray powder diffraction Rietveld refinement, and traditional microscopy. These are proving useful for characterizing key attributes of the granites.

The existing basement-penetrating data set is large and under-evaluated, but our work and that of others is revealing numerous gaps in our understanding best solved through additional novel geophysical investigations and targeted drilling. To this end, our investigation could inform a larger project concerning the SOA, as close scrutiny of existing basement penetrations is a necessary step towards locating potential sites for targeted exploration. Our current study also provides a means for rapid (and potentially on-site) assessment of acquired materials that might aid a larger project that incorporates scientific drilling.