Lithospheric dynamics and mantle sources of alkaline magmatism of the Cenozoic West Antarctic Rift System

Abstract

Lithospheric extension in the West Antarctic Rift System and the Ross Sea embayment is related to Cenozoic alkaline volcanism. Basanites and alkali basalts define the two endmembers of primary magmas with distinct petrographic, chemical and isotopic compositions. Basanites are generally more primitive and significantly more enriched in incompatible trace elements than alkali basalts. Parallel incompatible trace-element distribution patterns in both rock types but slightly different isotopic compositions suggest a derivation by different degrees of partial melting from different mantle sources. Sr-, Nd- and Pb-isotopes allow the identification of distinct magma sources: asthenospheric mantle, enriched lithospheric mantle and a HIMU plume component which is widespread beneath the entire area. Spatial and temporal variations in isotopic compositions suggest a relationship between the dynamics of lithospheric extension and changing mantle sources of related magmas. Geothermobarometry on mantle xenoliths documents a pressure–temperature–time evolution of the mantle lithosphere which is related to rifting, uplift and cooling of mantle below the Ross Sea Rift–Transantarctic Mountain transition. This paper reviews existing data and ideas but is biased towards the author's own working area, the Western Ross Sea.