USING NOBLE GASES TO DETERMINE MAGMA SOURCES IN THE WEST ANTARCTIC RIFT SYSTEM

A relationship between lithospheric extension and mantle plumes is often assumed as the force driving rift evolution. Typically, only extension is supported by geological evidence, while the existence of a plume is commonly inferred from a combination of geochemical data and mantle tomography. The West Antarctic Rift System (WARS) is an active continental rift zone within the Antarctic Plate that is approximately 2000 km long. The WARS is associated with several long-lasting magmatic provinces, including the McMurdo Volcanic Group, that are highly alkaline and silica undersaturated with extreme enrichments in light rare earth elements. The mantle source of the magma has been highly debated with multiple proposed models involving contributions from the lithosphere, asthenosphere, or a mixture of both with no universally accepted hypothesis.

Most previous geochemical work in these provinces has focused on bulk classification, modal mineralogy, major element composition, trace element chemistry, and radiogenic isotopes (e.g., Sr, Nd, and Pb isotopes), yet these can be readily recycled between the crust and mantle, meaning rock composition can change with variable mixtures or degrees of partial melting. The limited number of volatile studies conducted on Antarctic volcanic products have focused on carbon dioxide and sulfur emissions and suggest that there are multiple source contributions to Antarctic volcanism. Unlike trace elements and radiogenic isotopes, noble gases are chemically inert and present in low concentrations, making them reliable tracers of magmatic sources and subsurface processes. Here, we present preliminary noble gas isotope (e.g., ³He/⁴He, CO₂/³He, ⁴⁰Ar/³⁶Ar, ⁴⁰Ar*/⁴He) data for a suite of lava samples from the McMurdo Volcanic Group. By coupling noble gas geochemistry with more traditional geochemical techniques from the WARS, we can better constrain a magmatic source and provide geological evidence that could support or oppose the existence of a mantle plume, HIMU plume, or deconvolve mantle-lithosphere interactions.