Marie Byrd Land and Ellsworth Land: petrology

• Main Authors: K.S. Panter, T.I. Wilch, J.L. Smellie, P.R. Kyle, W.C. McIntosh
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Geological Society of London 2020
• Subjects: Geology; FOS Earth and related environmental sciences; Antarctic; West Antarctic Ice Sheet; Byrd; Marie Byrd Land; Ellsworth Land; Antarc*; Ice Sheet
• Online Access: https://dx.doi.org/10.6084/m9.figshare.c.5233171.v1; https://geolsoc.figshare.com/collections/Marie_Byrd_Land_and_Ellsworth_Land_petrology/5233171/1

In Marie Byrd Land and Ellsworth Land 19 large polygenetic volcanoes and numerous smaller centres are exposed above the West Antarctic ice sheet along the northern flank of the West Antarctic rift system. The Cenozoic (36.7 Ma to active) volcanism of the Marie Byrd Land Volcanic Group (MBLVG) encompasses the full spectrum of alkaline series compositions ranging from basalt to intermediate (e.g. mugearite, benmoreite) to phonolite, peralkaline trachyte, rhyolite and rare pantellerite. Differentiation from basalt is described by progressive fractional crystallization; however, to produce silica-oversaturated compositions two mechanisms are proposed: (1) polybaric fractionation with early-stage removal of amphibole at high pressures and (2) assimilation–fractional crystallization to explain elevated 87 Sr/ 86 Sr i ratios. Most basalts are silica-undersaturated and enriched in incompatible trace elements (e.g. La/Yb N > 10) indicating small degrees of partial melting of a garnet-bearing mantle. Mildly silica-undersaturated and rare silica-saturated basalts, including tholeiites, are less enriched (La/Yb N <10), a result of higher degrees of melting. Trace elements and isotopes (Sr, Nd, Pb) reveal a regional gradient explained by mixing between two mantle components, subduction-modified lithosphere and HIMU-like plume ( 206 Pb/ 204 Pb >20) materials. Geophysical studies indicate a deep thermal anomaly beneath central MBL suggesting a plume influence on volcanism and tectonism.