Cambrian phreatomagmatic igneous breccia and associated bimodal hypabyssal intrusions in the West Timbered Hills, Arbuckle Mountains, Southern Oklahoma

One of the main outcrop areas of the Cambrian Wichita Igneous Province in southern Oklahoma occurs in the West Timbered Hills, but has never been studied in detail before. New mapping shows that extensive amounts of polymict igneous breccia and microgranite and diabase intrusions occur within the area. Microgranites have A-type compositions similar to other felsic rocks in the Wichita Province. Diabase intrusions have within-plate tholeiitic and alkaline signatures. The breccia forms discordant masses ≤ 1.4 km across cutting older rocks. Felsic and mafic clasts within the breccia are set within a finer grained matrix. Juvenile basaltic pyroclasts in the matrix indicate that the breccia is phreatomagmatic in origin, and it is inferred to fill vent conduits for maar volcanoes. Diabase intrusions in the area are interpreted to represent parts of the magma plumbing system that supplied the phreatomagmatic eruptions.