AN EXAMPLE OF INTRUSION RELATIONSHIPS ALONG THE NORTHERN MARGIN OF THE QUANAH GRANITE, WICHITA LIP, SOUTHWESTERN OKLAHOMA
Mapping the FF and PF revealed these to have dike-like geometries that cut the CF, suggesting that both are late intrusions. To resolve relationships, we assessed the three facies through petrography, X-Ray Diffractometry (XRD), and Electron Probe Microanalysis (EPMA). Prior researchers noted CF’s sodic amphiboles (confirmed as arfvedsonite) that make the Quanah unique among the Wichita granite plutons. PF contains biotite and/or calcic amphibole, both occuring as anhedral interstitial crystals. In our samples, FF contains only biotite. The pegmatitic bodies are quartz ± orthoclase ± biotite or arfvedsonite.
The textures and mafic mineral assemblages of the different facies imply that the voluminous CF magma first intruded this area, followed by the magma(s) that gave rise to the FF and PF. The difference in texture suggests a change in the local thermal profile over the time interval. As such, the FF and PF facies may record one of the last gasps of felsic magmatism in the province.