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

矿物锆石提供了关于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)都要追溯到更早的时间。然而，岩石记录提供了证据，表明地壳和地幔中偶尔会出现锆石不稳定的情况，这是由于辐射损伤以及可能与流体的相互作用造成的，导致锆石重结晶。虽然人们假设热的流体会导致锆石重结晶，但这一假设还没有在实验室中得到验证。由于锆石中的重结晶带可以确定年代，了解这些带是如何形成的有助于解释测量的年龄，从而能够更准确地重建地球和其他行星的历史，我们可以从这些行星上提取含锆石的岩石。对锆石稳定性机理和条件的了解还应有助于评估使用锆石在地质储存库中安全储存剧毒和放射性污染物的可行性。实验和分析技术方面的培训将提供给不同的参与者，从高中到实验室和会议车间的博士后研究人员。这项研究旨在通过在高压和高温下对锆石-流体混合物进行创新的同位素示踪实验，在实验室模拟锆石重结晶的过程。实验材料将使用最先进的微观分析技术进行表征。将检验如下假设：1)锆石在水溶液中通过溶解-再沉淀机制再结晶，可通过可测量的Si和O同位素交换检测到；2)在相同条件下，小的锆石颗粒将重结晶，而大的颗粒不再重结晶；3)反应边缘的发展将阻碍进一步的反应，减缓反应边缘的生长速度；4)大颗粒的变质锆石将以可测量的速度被结晶锆石取代，5)变质锆石被结晶锆石取代的过程是在恒定的硅浓度下进行的，但重结晶速度可以通过硅和氧同位素的时间变化来测量。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势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.