POTENTIALLY INHERITED INFLUENCES ON LATE PALEOZOIC DEFORMATION IN THE WICHITA GRANITE GROUP, OKLAHOMA

The Wichita and Arbuckle Mountains of southern Oklahoma are exposures of late Paleozoic uplift that largely follow the geometry of an Eocambrian aulacogen. The exposures, along with subsurface uplifts, are products of the Ancestral Rocky Mountains (ARM) orogeny, a basement-involved event contemporary with the Ouachita fold-and-thrust belt. The ARM severely deformed the Lower Paleozoic section of marine carbonates and shelf clastics. These, along with the underlying basement rocks, are offset by regional fault systems, by kilometers of uplift in places. But aside from the large faults, the basement rocks exhibit substantially less evidence of the deformation recorded in the overlying section.

Most of he lithodemes of the Cambrian Wichita Granite Group (WGG) are products of tabular plutons that intruded the volcanics that underlie the strongly deformed Lower Paleozoic cover. The granites are cut by numerous fractures, few with demonstrable offset. Prior work determined these to be late Paleozoic features, products of uplift deformation. At depth, the joints and fractures contain coatings of carbonate, clay minerals, oxides or sulfides. Some accompany adjacent chloritization or hydrolysis of the granite. At the surface, fractures are enhanced by weathering and form prominent features on the landscape.

Directional filtering and thresholding of color satellite imagery produces black and white diagrams that reveal the fabric of the deformation through fractures longer than 3 m. Exfoliation fractures are largely sub-horizontal, with notable exceptions adjacent to the deeper stream cuts. Large non-exfoliation fractures, traceable for tens of meters, largely cut topography and are therefore near-vertical; rare exceptions exhibit high-angle dips. Few fractures have north-south orientation; the fabric is dominated by roughly E-W trends. Preliminary analysis indicates that the fracture sets differ among individual WGG lithodemic units.The direction for Reformatory Granite fractures is predominantly a 115° trend, Mount Scott Granite is 090°, and Quanah Granite is both 065° and 120°. The general E-W trend seems consistent with anticlinal flexure of the upper-most basement of the geometry proposed in Gilbert (1982, OGS GB21). The lithodeme-specific variation suggests influences by preexisting pluton-dependent weaknesses, most likely imparted from emplacement and/or cooling of the granites.