Lu-Hf systematics of early solar system materials

镥-176到铪-176的β衰变是一个潜在的强大的计时器和行星体化学分化的示踪剂。然而，早期太阳系天体（陨石，eucrites）的Lu-Hf年龄往往超过它们的U-Pb年龄> 2亿年。如果太阳系的年龄是4.57 Ga，而176 Lu的衰变率总是恒定的，那么同位素钟可能在太阳系的最初几百万年内是去耦的。确定负责这一过程的过程是该项目的主要目标，因为1）它可以使我们最终充分利用Lu-Hf时钟/示踪剂，2）它将揭示早期太阳系中普遍存在的物理条件：一些潜在的过程只能在特定的时间范围内运行（例如，Fe-60的自辐射）或在一定尺寸的物体上（例如，宇宙射线的体辐射），这可能会导致对吸积模型的进一步限制。我们的另一个主要目标是测量原始和分化陨石的初始Hf同位素组成以及它们所包含的任何低Lu/Hf相（例如，锆石、斜锆石）。这将提供一个强大的估计初始Hfisotope组成的类地行星用于模拟其硅酸盐分化的历史。

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.