SGER-Lu-Hf and Re-Os Systematics of the Earliest Crust in Antarctica: The Napier Complex of Enderby Land

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This award, provided by the Office of Polar Programs, allows a US investigator to participate in integrated geochemical and isotopic investigations of an unusual suite of ancient rocks from East Antarctica. This project entails a Lu-Hf and Re-Os isotopic study of the Archean Napier Complex on the East Antarctic Shield using rock samples collected by two Japanese expeditions to the remote regions of Mt. Riiser-Larsen and Tonagh Island in 1996-97 and 1998. These samples are being made available for a collaborative investigation with Japanese scientists. It is imperative that the work in the US and Japan move ahead simultaneously. The Japanese team is focusing on rock and mineral major oxide compositions, Nd, Sr and Pb isotopic compositions, as well as SHRIMP zircon U-Pb dating on aliquots of these samples. The component of the work supported by this award focuses specifically on Archean crustal and mantle evolution for which the Napier Complex has, potentially, some of the best-preserved rocks on Earth. This project will use the Lu-Hf and Re-Os approach because of increasing recognition that the Sm-Nd system can be perturbed severely by younger metamorphic and metasomatic events. Furthermore, presently the number of data for initial Os isotopic compositions of Archean mafic-ultramafic magmas worldwide is very small, largely because of post-crystallization alteration events and the analytical challenges that have only recently been overcome. In collaboration with Dr. Rick Carlson at the Carnegie Institution, we will attempt to exploit the freshness of Napier Complex ultramafic and mafic rocks and generate Re-Os data on several samples. In addition to providing a means of dating rocks that lack zircon, this approach will yield data critical to the understanding of Os isotopic evolution of the mantle with its implications for the timing and nature of crustal recycling, accretion of a late chondritic veneer and possibly core-mantle exchange through time.