Isotopic Studies of Mantle-Crust Evolution

9614471 DePaolo拟议的主要研究旨在进一步发展一种新的U-Th-Pb年代学方法，并评估其对海底玄武岩的适用性。这项新技术可能有助于更好地理解深海火山活动的时间框架。拟议的工作包括精确测量所选海底玄武岩的矿物、玻璃和基质分离中的206Pb/207Pb和208Pb/207Pb，以及U/Pb和Th/Pb，以确定该方法的适用性。该计划将评估大洋玄武岩中是否满足统一的206Pb/207Pb和208Pb/207Pb的必要初始条件，并将来自相同岩石的U-Pb和Th-Pb年龄与Ar-Ar年龄进行比较，以确定其可靠性。还将开展另外两个次要项目。第一个将利用玄武岩熔岩的地层时间序列数据来定量评估部分熔融带的水文性质，以更好地了解熔融带弥散和层析在地幔同位素变化研究中的作用。第二个项目旨在验证早太古宙地幔中存在分馏地幔储集层的证据，并量化重建太古代变质岩石的初始同位素和化学成分的方法。

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.