9316277 Johnson The PIs propose to make a combined petrologic, geochemical, Sr-Nd-Pb-Hf isotope and conventional U/Pb zircon study of granulite facies xenoliths from the Davis Mountains-Big Bend region of west Texas and the Camargo basalt field in Chihuahua, Mexico. In addition, they will analyze garnet- bearing metaigneous restites from Kilbourne Hole, New Mexico, for their Hf isotope compositions. Restites from Kilbourne Hole and the other locations have only limited variation in Nd(0) but a wide range of 176Lu/177Hf ratios including extreme values (>0.5). Hf model ages for melt-extraction from garnet-bearing restites should be far less ambiguous than model ages based on Nd. This will be the first systematic study of lower crustal xenoliths that integrates Sr, Nd, Pb, and Hf isotopes, and it will be by far the most detailed conventional U/Pb zircon study to date. Although the immediate goal of this collaborative effort is the study of the lower crust, U.C. Santa Cruz workers will gain valuable experience at U.W. Madison in state-of-the-art Hf isotope analysis, including joint development of new standards and spikes. This approach will allow U.C. Santa Cruz to efficiently start-up a program in Hf isotope work.
