AN OVERVIEW OF THE COLD SPRINGS BRECCIA AND THE COMMINGLING ORIGIN OF INTERMEDIATE GRANOPHYRES WICHITA MTNS., SW OKLAHOMA

The Southern Oklahoma Aulacogen (SOA) formed as a result of Early Cambrian rifting that broke up the supercontinent Rodinia and formed the Iapetus Ocean. Exposed in the Wichita Mountains of SW Oklahoma, the bimodal lithology of the Wichita igneous province is typical for intraplate rifting, with a layered mafic complex (Glen Mountain Layered Complex, GMLC) overlain by metaluminous A-type granites (Wichita Granite Group, WGG) and rhyolites. Intruding the mafic anorthosites and troctolites of the GMLC are the enigmatic rocks of the Cold Springs Breccia (CSB). The ~ 25 km² exposure of the CSB S of Roosevelt OK is a network of sills that intrude the GMLC preferentially along cryptic layering horizons. The CSB consists of three primary lithologies: granite, diabase, and intermediate rocks. CSB granophyric granite is geochemically indistinguishable from WGG granites and was the first magma to intrude based on contact relationships seen in the field. The mafic rocks are tholeiitic diabase with Mg# = 51-58, commonly expressed as 3-300 cm lobate pillows with crenulated oxide-dominated margins entrained in the intermediate and granitic rocks. Unique among SOA rocks are tonalite and granodiorite. These hypidiomorphic intermediate rocks contain oligoclase-andesine, Mg-hornblende, orthoclase, and anhedral biotite in a quartz-rich matrix. Magma mingling processes are evident throughout the CSB, demonstrating the coexistence of mafic and felsic magmas. In previous GSA conferences we proposed a magma mixing model for formation of the intermediate rocks which we aim to further support with new data and analyses.