This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports an investigation of Cenozoic volcanic rocks from the western flank of the West Antarctic Rift System. Cenozoic (35 million years ago to presently active) volcanism in West Antarctica has been attributed to: 1) mantle melting by 'passive' rifting that has thinned the crust and mantle lithosphere, 2) mantle melting by 'active' rifting associated with a hot, upwelling mantle plume, and 3) a combined 'active-passive' scenario that involves the melting of an ancient mantle plume source by passive rifting. Making sense of the underlying causes of rifting and volcanism in Antarctica has important implications to our understanding of continental breakup. In this regard the proposed work will engage models of rifting and separation of New Zealand from West Antarctica.
This project will undertake new geochemical research in an attempt to unravel processes of mantle melting and continental breakup using a suite of basaltic volcanic rocks from the foothills of the Royal Society Range, South Victoria Land. Because the basalts represent near-primary melts of the mantle, they will be used as geochemical tracers of the Earth's interior. Basaltic volcanism in the Royal Society Range offers a unique opportunity to study 14 million years of mantle evolution along a major tectonic boundary separating the West Antarctic rift system from the East Antarctic continental shield. The principal objective of this project is to provide the first detailed isotopic and trace-element investigation of basalts in this area. The new results will be integrated into regional studies to build better models for West Antarctic volcanism and rifting.
A preliminary survey of the geochemical data suggests that there has been a change in the degree and depth of melting beneath this portion of the rift. Previous work on basalts in other areas of the rift has shown that variations in the degree and depth of melting correlate with changes in isotopic composition. Because isotopes measured in primary basalts provide a 'fingerprint' of long-lived chemical reservoirs within the Earth's mantle, the variations must indicate that melting of different reservoirs is producing the basalt. A better understanding of the type and origin of distinct mantle reservoirs is critical to models of rifting and volcanism. For instance, previous studies have shown that the isotopic signature of many West Antarctic basalts, as well as some basalts from New Zealand, have a common mantle component; one whose composition is characteristic of a mantle plume source. This has led development of a model for plume-assisted breakup. A complete high-quality geochemical data set for Royal Society Range basalts will allow this project to test theories of mantle plume activity and plume involvement in the breakup of New Zealand from Antarctica. This work is collaborative with investigators at the New Mexico Institute of Mining and Technology and at Royal Holloway, University of London.