The existence of basaltic volcanism in McMurdo Sound has been attributed to a mantle hotspot, or alternatively, to structurally controlled eruptions related to continental rifting and extension in the Ross Sea. The goals of this award are to: 1) characterize the mantle source beneath the region and understand its origin, and 2) determine the relationship between the volcanism and the proposed hotspot and/or extension-related tectonic origin. Existing isotopic data suggest that these basalts have unique radiogenic lead and non-radiogenic strontium isotopic compositions that are compatible with derivation from a hypothetical class of mantle called HIMU (meaning high uranium to lead ratio). This type of mantle could be produced by one or more of the following processes; recycling of oceanic crust into the mantle, metasomatic addition of uranium, metasomatic removal of rubidium, or lead loss to the core. Helium isotopes have not yet been used extensively to study HIMU mantle. However, helium isotopes will be useful for characterizing HIMU mantle sources of basalts and identifying the processes involved in its production because helium isotopes can help distinguish between undepleted mantle and mantle that has been involved in mid-ocean ridge or subduction processes. Thus, helium isotopic data from the McMurdo Sound region will help to understand the nature and origin of HIMU mantle sources in Antarctica and elsewhere in the world. In addition, new helium isotopic data from this area, coupled with strontium, neodymium, and lead isotopes, will help determine whether the McMurdo Sound basalts are associated with a hot mantle plume, involving undepleted mantle, or whether they are associated with extension related magmatism that would not require involvement of a mantle plume. Isotopic ages of the volcanic rocks which would be produced in the course of this work will also help document the temporal and tectonic controls on volcanism.
