Abstract

Work in preparation for a new map of the Wichita Mountains has led to revisions of the surface structure within the exposed igneous rocks. As the presumed faulting pattern will have bearing on the development of regional tectonic models, it is important to document clearly whether major structural discontinuities exist inside this crustal block. Fault distributions within the main igneous outcrops in the eastern Wichitas have been shown on the Oklahoma State Geologic Map (Miser, 1954) and carried forward in Hydrologic Atlas-6 (Havens, 1977). These faults can be grouped into two categories based on stratigraphy: those separating rocks of the same stratigraphic unit, and those separating rocks of different stratigraphic units. Field work over the period 1977-present now shows that most previously accepted faults which allow contact of different igneous lithologies are actually intrusive contacts. Accordingly, such faults do not exist. In fact, no unequivocal major faults (i.e., separations of 100's of meters) have been identified in the igneous rocks although prominent lineaments do exist.

The work described above plus new stratigraphic information on the igneous sequence (Powell, Gilbert, and Fischer, 1980 - Bull. GSA) leads to several speculative ideas on regional deformation associated with the Wichita arch. These ideas follow somewhat the reasoning advanced by Ham, Denison, and Merritt (1964 - O.G.S. Bull. 95), but with modifications as required by new data:

a. The integrity of the main Wichita Mountains horst block results from its underlying gabbroic substrate (Raggedy Mountain Gabbro Group) rather than the covering, thin Wichita Granites, or Carlton Rhyolite.

b. Intrusion of the Roosevelt Gabbros as small plutons into the Glen Mountains Layered Complex Marks the beginning of the Wichita Mountains block as a structural unit. This timing is not yet well-dated but is clearly pre-rhyolite and pre-granite in age.

c. Few faults will be found in areas underlain by much gabbro. For example, faults bounding the south side of the Anadarko Basin may indicate the most northerly extent of gabbro. Basement beneath the Anadarko Basin should have little gabbro.