Radiogenic Isotopic Studies of Magmatism and Crust-Mantle Evolution

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Patchett/VervoortEAR-0003343 We seek to improve the framework for Lu-Hf isotopic studies by redetermination of the Bulk Silicate Earth (BSE) Lu-Hf and Sm-Nd parameters. At present, the array of mantle and crustal samples appears not to contain the BSE point. This may suggest that a very important early differentiation episode is recorded, such that an unseen complementary reservoir exists in the mantle, or was perhaps lost in early Solar System collisions. It may also suggest that the chondritic reference for Lu-Hf is incorrect, or that BSE really differs from chondrites for other reasons. We intend to check the Lu-Hf chondritic parameters by careful analysis of a suite of chondritic meteorites. Sm-Nd characterization will be performed simultaneously, with the goal of ensuring comparability between Lu-Hf and Sm-Nd systems. We will also undertake work to better constrain the decay constant of 176Lu, employing fresh Precambrian dolerites, to obtain internal isochrons and compare ages to those from precise U-Pb dating of baddeleyite or zircon in the mafic intrusions. These investigations should enormously improve the conceptual framework for Lu-Hf isotopic study of Earth differentiation processes.