COMPARISON OF GEOCHEMICAL FINGERPRINTS OF NON-CUMULATE MAFIC ROCKS IN THE SOUTHERN OKLAHOMA AULACOGEN WITH THOSE OF OTHER LARGE IGNEOUS PROVINCES

The Southern Oklahoma Aulacogen (SOA) stretches WNW from southern Oklahoma through the Texas panhandle westward into Colorado and New Mexico and formed as a result of Early Cambrian rifting that broke up the supercontinent Rodinia and formed the Iapetus Ocean. The total volume of igneous rock emplaced within the rift is estimated to be > 250,000 km³, qualifying it as a large Igneous Province (LIP). Exposed in the Wichita Mountains of SW Oklahoma, the bimodal lithology of the Wichita igneous province is typical for plutonic rocks associated with continental rifting, with a layered mafic complex (Glen Mountain Layered Complex, GMLC) overlain and intruded by hydrous gabbros, metaluminous A-type granites (Wichita Granite Group, WGG), and rhyolites. Late diabase and basalt dikes crosscut all of these units, but these late dikes provide little insight into the nature of the SOA LIP. Slightly older diabases in the Cold Springs Breccia (CSB) provide a glimpse of SOA mafic magmas, which group into two distinct populations delineated clearly by a Mg# = 40 divide. High-magnesian diabases consist of magnesio-hornblende, unaltered plagioclase, and discreet K-feldspar crystals. Low-magnesian diabases are biotite dominated with ≈5% ferro-hornblende. They contain sericitized plagioclase and K-feldspar as a sub-poikilitic interstitial host. These diabases have broad geochemical ranges that exceed those of other non-cumulate mafic rocks in the SOA and reflect a higher degree of fractionation and crustal assimilation than mafic rocks of other well studied LIPs. Trace element ratios span tholeiitic intra-plate basalts and intraplate alkali basalts, both calc-alkalic and shoshonitic, on mafic discrimination diagrams. REE concentrations of high-magnesian CSB diabases are more depleted than SOA non-cumulate mafics while the low-magnesian CSB diabases are enriched. The goal of this study is to compare and contrast the SOA non-cumulate mafic rocks with those of other well-studied LIPs to better understand how the SOA LIP is similar and different from other LIPs.