Lu-Hf systematics of early solar system materials

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The beta decay of lutetium-176 to hafnium-176 is potentially a powerful chronometer and tracer of the chemical differentiation of planetary bodies. However, the Lu-Hf ages of early solar system objects (chondrites, eucrites) often exceed their U-Pb counterparts by >200 million years. If the solar system age is ~4.57 Ga and the rate of decay for 176Lu was always constant, then the isotopic clocks were likely decoupled within the first few million years of the solar system. Identifying the processes responsible for this is a major goal of the project because 1) it may allow us to finally exploit the Lu-Hf clock/tracer to its fullest potential, and 2) it will shed light on prevalent physical conditions in the early solar system: Some potential processes could only operate within specific time frames (e.g., self-irradiation by Fe-60) or upon bodies of a certain size (e.g., bulk irradiation by cosmic rays) and this may lead to further constraints on accretion models. Our other primary aim is to measure initial Hf isotopic compositions of primitive and differentiated meteorites and any low-Lu/Hf phases they contain (e.g., zircon, baddeleyite). This will provide a robust estimate of the initial Hfisotope composition of the terrestrial planets for use in modeling their silicate differentiation histories.