ANOMALOUS GRANITES WITHIN THE QUANAH GRANITE PLUTON, WICHITA MOUNTAINS, OKLAHOMA

The Wichita Mountains in southwestern Oklahoma expose roughly a dozen granite plutons associated with the Cambrian Southern Oklahoma Aulacogen. The Quanah Granite is one of two coarse-grained plutons within the Wichita Granite Group (WGG); it uniquely contains arfvedsonite, and is the youngest of the plutons in the Eastern Wichita Mountains.

The pluton’s boundaries as defined by Meyers et al., (1981, Ok. Geo. Notes), contains several anomalous granite bodies (including their facies B and C). The northern margin exhibits their contrast against typical Quanah Granite. The anomalously fine-grained (B) and medium-grained porphyritic rocks (C) have distinct mafic assemblages. The latter contains granophyre and hornblende ± biotite, and the other is fine-grained granular with biotite. Lacking arfvedsonite, coarse crystals, miarolitic cavities, and hematitic patches, both rock types are more typical of WGG units. Their dike-like geometries suggests that these are intrusions of later magma(s), and they are mappable based on texture and mafic assemblage. We have designated these marginal expressions the French Lake Granite.

Anomalous granites within the interior to southern margin of the Quanah Granite pluton differ from the French Lake. The largest of these comprises a portion of the mountains on and adjacent to Ft. Sill; the western portion crosses Oklahoma Highway 115 near Quanah Mountain. We refer to this as the Craterville unit. Like the Quanah, it can be relatively coarse-grained with miarolitic cavities and hematite staining, and weathers into boulders and grus, causing relatively steep topography. However, it contains sparse to abundant granophyre and contains hematite ± chlorite. Geochemically, the Craterville shares the Quanah’s relatively low-Ba (<200 ppm) signature. Although significantly different in texture, the Craterville bears more similarity to its adjacent unit to the east, the Cache Granite; in addition to low Ba, it has similar elevated SiO₂, lower modified alkali-lime index, and scant mafic silicates. Its relationship with these units remains enigmatic; most likely younger than Cache and older than Quanah.