Lu-Hf systematics of early solar system materials

镥-176向铪-176的衰变可能是一种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（球粒陨石、绿长岩）的Lu-Hf年龄通常比它们的U-Pb对应物高出2亿年。如果太阳系的年龄是~4.57 Ga，并且176Lu的衰变速率一直是恒定的，那么同位素时钟很可能在太阳系的最初几百万年里就解耦了。识别过程负责这个项目的一个主要目标,因为1)它可能让我们最后利用Lu-Hf时钟/示踪剂充分发挥作用,和2)它将揭示普遍的物理条件在早期太阳系:一些潜在过程只在特定的时间框架(例如,自辐照Fe-60)或在一定规模的尸体(例如,大部分由宇宙射线照射),这可能会导致进一步限制吸积模型。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，以及它们含有的任何低lu /Hf相（例如，锆石，坏辉石）。这将为类地行星的初始氢同位素组成提供一个可靠的估计，用于模拟它们的硅酸盐分化历史。

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.