SEQUENCING AND CATEGORIZING MAGMATIC INTRUSIONS IN THE COLD SPRINGS BRECCIA OF THE WICHITA MOUNTAINS, OKLAHOMA

The Cold Springs Breccia (CSB) is an intrusive complex outcropping over an area of approximately 20 km² outside of Roosevelt, Oklahoma and contains the only known intermediate rocks in the Southern Oklahoma Aulacogen (SOA). Once thought to be a discreet tabular body emplaced during a single intrusion, we now know that it is a network of sills interconnected with subordinate dikes resulting from multiple intrusions. CSB magmas intruded into the Glen Mountain Layered Complex (GMLC), primarily incising the troctolite layers of this cryptic mafic layered complex while being vertically bound by anorthosite. These rocks contain texturally and/or geochemically heterogeneous granite, diabase, and the primary intermediate rock tonalite, a mixing product of the felsic and mafic magmas. This heterogeneity shows evidence of both fractionation and assimilation processes occurring before emplacement. Detailed mapping of the limited CSB outcrops, in addition to petrographic and geochemical analyses, have led to a new method of identifying and categorizing different zones based on mingled and mixed rock relationships. Crosscutting associations and mingled tonalites allow for limited intrusion sequences in some outcrops and provide further evidence for the ingress of mixed intermediate magma rather than in situ mixing. This microcosm of magmatic processes is unique to the CSB and represents the interactions of late-stage fractionated residual magmas of the SOA.