The Li abundances and isotopic compositions of lavas from the McMurdo Volcanic Group (MVG) and the Crary Mountains, Antarctica and selected oceanic islands show Li is sensitive to both the mantle sources of basalts, and the open-system processes that occur during magmatic differentiation. Basaltic MVG lavas have uniform Li isotopic signatures, whereas more evolved lavas have variable δ7Li indicating inputs of altered crustal materials. MVG basalts and those of the Crary Mountains have similar δ7Li, and have compositions broadly consistent with mixing between a MORB-source mantle reservoir and a probable HIMU reservoir with elevated δ7Li.

δ7Li values in ocean island basalt (OIB) samples examined range from +3‰ to +7‰; only two ocean islands were distinguishable from MORBs. None of our OIB samples showed the anomalously low δ7Li that Nishio et al. (2004) have contended is indicative of the EM1 mantle reservoir. Mixing of plume material with a MORB-like upper mantle can serve to mask extreme Li isotopic signatures to a degree, but it may also be the case that the mantle is heterogeneous in δ7Li on the fine scales represented by xenolith hand samples, but relatively homogeneous on the scales of hotspot melting anomalies.