Collaborative Research: Probing zircon reactivity in aqueous solutions at solubility equilibrium using isotope tracers

矿物锆石提供了地球历史的宝贵信息来源，由于锆石的非凡稳定性，它比任何其他矿物（41亿年）都要早得多。然而，岩石记录提供了地壳和地幔中偶尔的锆石不稳定的证据，这是由辐射损伤和可能与流体相互作用引起的，导致锆石重结晶。虽然有人假设热流体可以使锆石重新结晶，但这一假设尚未在实验室中得到验证。因为锆石的再结晶带可以确定年代，了解这些带是如何形成的可以帮助解释测量的年龄，允许更准确地重建地球和其他行星的历史，我们从中提取含锆石的岩石。了解锆石稳定性的机制和条件也有助于评估在地质储存库中使用锆石安全储存高毒性和放射性污染物的可行性。STEM劳动力实验和分析技术培训将提供给不同的参与者，从高中到实验室和会议研讨会的博士后研究人员。本研究旨在通过创新的锆石-流体混合物同位素示踪实验，在实验室模拟锆石重结晶过程。实验材料将使用最先进的微量分析技术进行表征。以下假设将被验证：1)锆石在水溶液中通过溶解-再沉淀机制再结晶，这可以通过可测量的Si和O同位素交换来检测；2)在相同条件下，小的锆石颗粒会发生再结晶，而大的则不会；3)反应环的发育会阻碍进一步的反应，减慢反应环的生长速度；4)大颗粒的变质锆石会以可测量的速率被结晶锆石取代；5)变质锆石被结晶锆石取代的过程在一定的Si浓度下进行，但其再结晶速率可以通过Si和O同位素的时间变化来测量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The mineral zircon provides an invaluable source of information on Earth's history that extends further back in time than any other minerals (4.1 billion years) due to zircon's extraordinary stability. However, the rock record provides evidence of occasional zircon instability in the Earth's crust and mantle caused by radiation damage and possibly interaction with fluids, resulting in zircon recrystallization. While it has been hypothesized that hot fluids can cause zircon to recrystallize, this hypothesis has not been tested in the laboratory. Because recrystallized zones in zircon can be dated, knowledge of how those zones formed can aid in the interpretation of measured ages, allowing for a more accurate reconstruction of the history of Earth and other planets from which we retrieve zircon-bearing rocks. Knowledge of the mechanisms and conditions of zircon stability should also help evaluate the feasibility of using zircon to safely store highly toxic and radioactive contaminants in geological repositories. STEM workforce training in experimental and analytical techniques will be provided to diverse participants ranging in experience from high school to post-doctoral researchers in laboratories and meeting workshops.This study aims to simulate in the laboratory the process of zircon recrystallization by conducting innovative isotope tracer experiments on zircon-fluid mixtures at high pressures and temperatures. The experimental materials will be characterized using state-of-the-art microanalysis techniques. The following hypotheses will be tested: 1) zircon recrystallizes in aqueous fluid via a dissolution – reprecipitation mechanism that can be detected through measurable Si and O isotope exchange; 2) at the same conditions, small zircon grains will recrystallize, while large grains will not; 3) development of a reaction rim will hinder further reaction, slowing the rate of growth of the reaction rim; 4) large grains of metamict zircon will be replaced by crystalline zircon at a measurable rate, and 5) the replacement of metamict zircon by crystalline zircon proceeds at a constant Si concentration, but the recrystallization rates can be measured with temporal changes in Si and O isotopes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.