GSA Connects 2021 in Portland, Oregon

Paper No. 192-7
Presentation Time: 2:30 PM-6:30 PM


NEWMAN, Jordan, Department of Geosciences, University of Texas at Dallas, 800 W Campbell RD, ROC 21, Richardson, TX 75080, LEYBOURNE, Matthew I., Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, ON K7L 3N6, Canada and STERN, Robert, Department of Geosciences, The University of Texas at Dallas, FO 21, 800 West Campbell Rd, Richardson, TX 75080

The Wichita Mountains in southwest Oklahoma preserve excellent exposures of bimodal igneous rocks produced as a result of Early Cambrian rifting that formed the Southern Oklahoma Aulacogen. Layered anorthosites of the Glen Mountain Layered Complex (GMLC) and hydrous gabbro are overlain by metaluminous A-type granites of the Wichita Granite Group (WGG) and Carlton rhyolites. The ≈25 km2 Cold Springs Breccia (CSB) located west of the Wichita National Wildlife Refuge demonstrates that mafic and felsic magmas co-existed in time and space and give clues to their interactions. The CSB is not a breccia but reflects co-mingling and incomplete mixing of magmas. Three lithologies comprise the CSB: A-type granite that is geochemically similar to the WGG, within-plate tholeiitic diabase and diorite with Mg# = 51-58 and Ni = 40-60 ppm, and a hypidiomorphic intermediate rock containing oligoclase-andesine, Mg-hornblende, orthoclase, and anhedral biotite in a quartz-rich matrix. The granite is always in contact with GMLC, commonly as a fine-grained upper horizon separating CSB and GMLC. The diabase forms lobate pillows of varying size (3-100 cm in largest dimension) with crenulated oxide-dominated margins enclosed in sinuous channels of intermediate rock between mafic pillows. In previous presentations we proposed that a granitic magma intrusion within the GMLC was followed by an energetic pulse of diabase magma and proposed that the intermediate rock is a product of magma mixing of these two end-members. Field observations of limited exposures, many of which are on private land, reveal a complex network of sills ranging in thickness from 5 cm to 20 m, although the lack of exposed bottom contacts suggests that some units could be thicker. The CSB is highly variable with thicker units displaying some stratigraphic zonation. In addition, a new georeferenced geologic map of the CSB has been produced.