Beyond Isoplot: new software for better geochronology.

放射性地质年代学的发展是20世纪世纪地球科学最伟大的成就之一。地质年代学是研究地球历史的基础，并对生物进化的速度提出了基本的限制。大量资源被投入到能够以不断增加的分辨率和灵敏度测量同位素比率的精密质谱仪的开发中。不幸的是，质谱仪数据的统计处理并没有跟上这些硬件的发展，这破坏了放射性地质年代学的可靠性。该建议旨在创建一个“软件革命”的地质年代学，通过建立一个内部一致的生态系统的计算机程序，以考虑样本间的误差相关性。这些对地质年代学的精确度和准确性有一级影响，但在很大程度上被当前的地质年代学数据处理协议所忽略。拟议的软件将修改现有的数据简化平台，并创建全新的平台。它将实施一种数据交换格式，将来自多个计时器的联合收割机数据集结合在一起，同时跟踪它们之间的相关不确定性。新算法将应用于五个重要的地质问题。太阳系的年龄目前被限制在4567.30 +/- 0.16 Ma使用原始陨石。陨石的数据是'undersedised'相对于分析的不确定性。强样本间误差相关性的存在可能是这种分散不足的罪魁祸首之一。考虑到这些相关性，将大大提高这一标志性年龄估计的准确性和精确性。恐龙与古近纪的分界线标志着恐龙在地球历史上最臭名昭著的大灭绝中的消失。我们将使用高精度的40 Ar/39 Ar地质年代学重新评估这一边界周围的关键事件的时间。其他样品的初步结果表明，40 Ar/39 Ar数据倾向于强（r^2 > 0.9）样本间误差相关，并且这些对加权平均年龄估计的精度和准确性有一级影响。一项敏感性测试表明，这可能会改变大灭绝的时间长达200 ka。“Taung Child”是1924年在南非洞穴中发现的著名人类化石。它被认为是世界上第一个南方古猿，但尚未被确定日期。我们从上面的凝灰岩中获得了1.99 ± 0.05 Ma的U-Pb年龄，而在下面的钙质结砾岩存款中获得了1.4 ± 2.7 Ma的不精确年龄上限。这将进一步改善与额外的测量，及时为100周年的Taung儿童的发现。金红石和磷灰石的U-Pb定年深度剖面为研究下地壳岩石的热演化提供了新的思路。然而，用于本研究的激光烧蚀数据容易产生很强的错误相关性，而当前的数据简化协议没有考虑到这一点。这些协议将使用新的软件进行修订，允许更好地解析推断的t-T路径。(5)放射性稀有气体如40 Ar（来自40 K）、4 He（来自U、Th和Sm）和129 I（来自129 I）在高温下通过体积扩散而损失。该研究计划实施的修订后的回归算法将被应用于步进加热“Arrhenius”实验。这将改进对这些气体种类的扩散系数的计算，从而进一步改进（惰性气体）热年代学。

The development of radiometric geochronology is one of the greatest triumphs of 20th century geoscience. Geochronology underpins the study of Earth history and puts fundamental constraints on the rate of biological evolution. Tremendous resources are invested in the development of sophisticated mass spectrometers capable of measuring isotopic ratios with ever increasing resolution and sensitivity. Unfortunately, the statistical treatment of mass spectrometer data has not kept up with these hardware developments and this undermines the reliability of radiometric geochronology.This proposal aims to create a 'software revolution' in geochronology, by building an internally consistent ecosystem of computer programs to account for inter-sample error correlations. These have a first order effect on the precision and accuracy of geochronology but are largely ignored by current geochronological data processing protocols. The proposed software will modify existing data reduction platforms and create entirely new ones. It will implement a data exchange format to combine datasets from multiple chronometers together whilst keeping track of the correlated uncertainties between them. The new algorithms will be applied to five important geological problems.1. The age of the Solar System is presently constrained to 4567.30 +/- 0.16 Ma using primitive meteorites. The meteorite data are 'underdispersed' with respect to the analytical uncertainties. The presence of strong inter-sample error correlations is one likely culprit for this underdispersion. Accounting for these correlations will significantly improve the accuracy and precision of this iconic age estimate.2. The Cretaceous-Palaeogene boundary marks the disappearance of the dinosaurs in the most notorious mass extinction of Earth history. We will re-evaluate the timing of critical events around this boundary using high precision 40Ar/39Ar geochronology. Preliminary results from other samples show that 40Ar/39Ar data are prone to strong (r^2 > 0.9) inter-sample error correlations, and that these have a first order effect on the precision and accuracy of weighted mean age estimates. A sensitivity test indicates that this may change the timing of the mass extinction by up to 200ka.3. The 'Taung Child' is a famous hominin fossil that was discovered in a South African cave in 1924. It is considered to be the world's first Australopithecine, but has not yet been dated. We have a good unpublished U-Pb age of 1.99 +/- 0.05 Ma from a tufa collected above the hominid, and an imprecise upper age limit of 1.4 +/- 2.7 Ma on a calcrete deposit below it. Applying the new algorithms to the latter date will greatly improve its precision. This will be further improved with additional measurements, in time for the 100th anniversary of the Taung Child's discovery.4. Depth profiling of the U-Pb ages in rutile and apatite provides an exciting new way to constrain the thermal evolution of lower crustal rocks. However, the laser ablation data used for this research are prone to strong error correlations that are not accounted for by current data reduction protocols. These protocols will be revised using the new software, permitting better resolution of the inferred t-T paths.(5) Radiogenic noble gases such as 40Ar (from 40K), 4He (from U, Th and Sm), and 129Xe (from 129I) are lost by volume diffusion at high temperatures. The revised regression algorithms implemented by the research programme will be applied to step-heating 'Arrhenius' experiments. This will improve the calculation of diffusion coefficients for these gas species, resulting in further improvement of (noble gas) thermochronology.