Isotopic Studies of Mantle-Crust Evolution

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9614471 DePaolo The primary proposed research is aimed at further developing a new approach to U-Th-Pb geochronology, and assessing its applicability to ocean floor basalts. The new technique may allow for improved understanding of the temporal framework of deep sea volcanism. The proposed work involves precisely measuring 206Pb/207Pb and 208Pb/207Pb, and U/Pb and Th/Pb in mineral, glass and groundmass separates of selected submarine basalts to determine the applicability of the method. The plan is to evaluate whether the necessary initial condition of uniform 206Pb/207Pb and 208Pb/207Pb is satisfied in oceanic basalts, and to compare the U-Pb and Th-Pb dates from the same rocks to Ar-Ar age determinations to establish its reliability. Two other secondary projects will be pursued. The first will use stratigraphic time-series data from basaltic lavas to quantitatively assess the hydrological properties of partial melt zones to better understand the role of melt zone dispersion and chromatography in the study of isotopic variations in the mantle. The second project is aimed at verifying the evidence for fractionated mantle reservoirs in the early Archean mantle and quantifying approaches for reconstructing the initial isotopic and chemical compositions of metamorphosed Archean rocks.