Geology of the Blue River Gneiss, Eastern Arbuckle Mountains, Oklahoma

Abstract

The Blue River Gneiss, along with the Burch Granodiorite, Troy Granite, and Tishomingo Granite compose the Proterozoic basement in the eastern Arbuckle Mountains of Oklahoma. The Blue River, in contrast to the other three units, shows the effects of a pervasive regional metamorphism and recrystallization of constituent minerals. This metamorphic overprint produced a foliation and locally a metamorphic layering in those rocks having a sufficiently high color index. In the more leucocratic phases, a mineral orientation defines the foliation. In other rocks, an otherwise homogeneous granitoid contains scattered K-feldspar megacrysts (porphyroblasts or relicts?) that display a preferred orientation.Three main compositional phases characterize the Blue River Gneiss. The most abundant rock type is a metaluminous biotite granite gneiss containing quartz, perthitic microcline, and plagioclase as the essential minerals. The second main rock is a metaluminous hornblende biotite quartz dioritic to granodioritic gneiss composed of quartz, perthitic microcline, and plagioclase. The bulk modal compositions of these granitic and intermediate gneisses are very similar to the Troy Granite and the Burch Granodiorite, respectively, suggesting that they may be the metamorphosed equivalents of these two plutons. A third, apparently minor phase of the Blue River is a weakly foliated leucocratic biotite granofels.Major and trace element geochemistry indicate two compositional groupings of the Blue River Gneiss. Both gneiss groups are I-type granitoids that are subalkaline, metaluminous, and have moderate to high amounts of potassium. One has compositions closely similar to the Troy Granite, the other to the Burch Granodiorite. Geochemical modeling suggests that the Blue River gneisses were probably derived from source regions that were moderately enriched in incompatible elements. They may have formed along an Andean-type continental margin, or alternatively, in an Arbuckle-type setting.KeywordsSource RockContinental MarginIncompatible ElementActive Continental MarginMetamorphic OverprintThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.