SUSTAINED MARGINAL DIKES IN THE WICHITA LIP, SOUTHWESTERN OKLAHOMA

The Quanah Granite is one of roughly a dozen granitic plutons that are products of the Eocambrian Southern Oklahoma Aulacogen (SOA) or Wichita Large Igneous Province. Unlike the other plutons, it uniquely contains arfvedsonite. Recent research indicates that biotite ± hornblende-bearing granites intrude the northern margin. Adjacent to this margin lies a series of granitic dikes that transect a gabbroic layered complex. These features vary in width and length across a three square kilometer area. We examined the variation of distribution, orientation, and composition of the dikes.

Mapping revealed three principal dike orientations: 090° 60°S, 120° 60°S, and 045° 33°; the 120° trend is parallel to SOA rifting. We collected samples from six dikes spaced proportionally across the research area (two from each of these prominent orientations). We evaluated samples petrographically and by X-Ray Diffractometry (XRD) with an emphasis on characterizing mafic silicates. We noted that all samples are dominated by perthitic alkali feldspar, and in one sample amazonite. Grain sizes vary from fine- to coarse-grained. The dikes are aplitic, seriatic, granophyric, and pegmatitic (including vugs); the textures vary among and within the dikes. Mafic mineral modes range from 0-7%. Common mafic assemblages are biotite ± hornblende ± magnetite ± xenocrystic clinopyroxene. Biotite occurs as acicular grains (13 x 1 mm), small books (3 x 1 mm), or similar to smaller crystals disseminated with other mafic grains. At least one dike exhibits mafic schlieren. Surprisingly our sample set is dominated by biotite-, not arfvedsonite-bearing granitoids. The composition and textures indicate that dikes of our three primary orientations may have arisen from the later marginal fluids as well as the magma that gave rise to the Quanah Granite.