PETROGRAPHIC COMPARISON OF SUBSURFACE ALKALI-FELDSPAR GRANITES TO THE EXPOSED PLUTONS OF THE SOUTHERN OKLAHOMA AULACOGEN, U.S.A
In the Wichita Mountains, WGG members are A-type, alkali-feldspar granites. Individual plutons are distinguished by location coupled with subtle changes in texture and mineral assemblage, as well as chemical composition. Most have brick- to orange-red weathered surfaces; excavations in two plutons exhibit pink to gray colors with significant depth below the surface. Individual plutons are either fine-to-medium grained porphyry with granophyric to hypidiomorphic-granular texture, or less typically coarser-grained seriate. Alkali feldspars are invariably perthitic. All contain titaniferous oxides ± biotite ± amphibole; zircon ± fluorite ± titanites are common accessory minerals. The mafic and accessory minerals are typically glomerocrystic, also occurring as enclaves in some plutons.
We characterized small (0.1 - 1.0 cm) granite sample chips and thin sections of chips collected from several depths during drilling. Generally, these are orange- and brick-red alkali feldspar granites, with lighter color in some of the deeper samples. Each hole contained chips with granophyre nucleated on medium-grained phenocrysts of perthitic alkali feldspar. Some samples also contained chips exhibiting hypidiomorphic-granular texture. Most chips contain a small amount of glomerocrysts of substantially altered biotite, hornblende, and hematite. Accessory minerals include zircon, titanite, and fluorite. The textures, mineralogy, and alterations seen in these chips are wholly consistent with those seen in plutons from the Wichita Mountains.