Using clinopyroxene chemistry to constrain magma plumbing systems in a 1.2 ga andesitic to shoshonitic volcanic arc, Barby Formation, Namibia

Abstract

The 1.2 Ga Barby Formation located in SW Namibia is composed of basaltic andesites and shoshonites erupted in a volcanic arc setting. Clinopyroxene (cpx) from samples of pyroclastic rocks and hypabyssal intrusions previously collected by TCU graduate students was analyzed using an electron microprobe at Fayetteville State University, North Carolina. Correlations between cpx and whole-rock chemistry are used to provide additional insights into the complex magma plumbing system feeding the Barby Formation. Cpx compositions and cation ratios were also used in an attempt to constrain pressure and temperature conditions in the source magma chambers using geothermobarometry. Cpx data from hypabyssal intrusions in one part of the study area provide evidence of a different magma reservoir compared to the other samples.