10-13 A Tale of Two Plutons: the Mount Scott and the Quanah Granites of the Wichita Igneous Province, Oklahoma

Session: How are Plutons Made? Physical and Chemical Records of Pluton Construction and Evolution

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Cambrian magmatism along the Laurentian Margin produced the Wichita Granite Group (WGG), a series of A-type plutons along a WNW trend cutting across southern Oklahoma and the Texas panhandle. All are likely shallow crustal intrusions. They are exposed in the Wichita Mountains, where late Paleozoic uplift stripped the WGG of older rhyolite overburden. The Mount Scott and the Quanah Granites are the two best-exposed plutons. Despite zircon crystallization dates separated by only 220 kyr and relatively similar whole-rock composition, these differ greatly in their expression.

The Mount Scott Granite is the most extensively exposed WGG. Measured along and perpendicular to trend, outcrops extend 52 by 15 km, 34 km of which is continuous. Detailed mapping places the total exposure area at 192 km². Exposures reveal a largely homogenous medium-grained porphyritic body marked throughout by perthitic rapakivi and quartz phenocrysts, magmatic plagioclase, and mafic enclaves. Only the abundance of granophyre and corresponding changes in accessory mineral populations varies with location. Quartz pockets, veins, and vugs are rare and located near the roof. It is geochemically related to three adjacent but distinct bodies: the Rush Lake, Medicine Park, and Saddle Mountain Granites.

In contrast, the Quanah pluton is strongly heterogeneous. Exposed nearly continuously, with trend dimensions of 22 by 4 km, its most consistent attributes are an allotriomorphic texture, abundant vugs, and splotchy red staining in most expressions. Four facies have been documented. It is dominated by two, each a coarse-grained pink granite with strongly perthitic feldspar and albite present only as exsolution-induced rims. An arfvedsonite-bearing granite with glomerocrystic quartz is 38 km² of exposure; this Type facies is geochemically heterogeneous. A further 22  km² is the Craterville facies, an amphibole-free, compositionally-homogenous granite. Roughly 1% of mapped exposure is the Fine-grained facies that forms decameter-wide dike-like features. Expressions are concentrated along the northern and southern margins, as is a fourth facies, the French Lake, a porphyritic expression that is roughly 5% of mapped exposure and compositionally akin to the Mount Scott Granite. Pegmatitic pods and dikes are common.

The behavior of volatiles seems key to the differences. Elevated fluorine reduced viscosity of the relatively dry WIP magmas, permitting extensive emplacement. Vapor saturation in the Quanah pluton may have been promoted by intrusion geometry and timing.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9890

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