Towards a unified theory for element uptake by minerals over the full range of element concentrations

建立矿物在整个元素浓度范围内吸收元素的统一理论

• 批准号: RGPIN-2020-04173
• 负责人: vanHinsberg, Vincent
• 金额: $ 2.62万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=716824
• 关键词: Towards; unified; theory; element; uptake

Element mobility in the Earth drives global geochemical cycles and concentrates elements into ore deposits. This mobility can rarely be measured directly, especially not for the deep Earth or the earliest history of our planet. Instead, it has to be reconstructed from the rock record, in particular from the chemistry of minerals that formed in the process of interest. Despite huge progress in developing tools to read the mineral record, there is still major ambiguity in derived data because of a lack of understanding in how minerals get their composition. Indeed, no model correctly predicts the uptake of elements by minerals from the tens to thousands of mg/kg. At trace levels, Lattice-Strain Theory (LST) provides a framework to predict the uptake of elements from melts and fluids, showing it to be controlled by an element's mismatch in the crystal lattice in terms of size and charge. However, LST is only valid at “infinite dilution” and strong deviations are observed at higher concentrations. As a result, LST does not provide meaningful concentration data in modeling ore forming systems to their extreme enrichment. Thermodynamic solid solution models allow for modeling of element incorporation at high concentrations from the Gibbs free energy of element substitutions (e.g. Ca+Al = Na+Si in plagioclase). However, uncertainties in thermodynamic data do not permit extrapolations to low concentrations. There is therefore an urgent need for a model to predict element uptake at all concentrations. This research program aims to develop a unified theory to explain and predict element uptake over the full range of concentrations by gaining fundamental insights into how elements are accommodated in minerals. Experiments will be conducted to characterise the response of mineral lattices to mismatching element incorporation. This will be combined with direct measurements of crystal lattice dimensions and elasticity, and with predictive modelling of the local lattice around mismatching elements at the atom-scale by atomistic simulations. The elemental and isotopic composition of minerals contains a treasure trove of information on pressure, temperature, age, and element mobility in the minerals' growth environment. The fundamental insights developed in this research program will permit us to extract this information without the ambiguity that currently cripples this approach. This allows us to address key material and geoscience questions, from subduction zone element cycling, to the compositions of the Early Earth crust and oceans, to ore formation. Moreover, it has direct applications in industry where the desired behaviour of a material, for example as a catalyst, is directly linked to the abundance of functional elements. This research thereby addresses direct concerns to the Canadian general public, including developing novel materials for green technologies, remediating waste, addressing dwindling natural resources, and the impact of climate change.

地球上元素的活动性驱动着全球地球化学循环，并使元素富集成矿。这种流动性很少能被直接测量，特别是对于地球深处或我们星球的最早历史来说。相反，它必须从岩石记录中重建，特别是从感兴趣的过程中形成的矿物的化学成分中重建。尽管在开发读取矿物记录的工具方面取得了巨大进展，但由于缺乏对矿物如何获得其成分的了解，所获得的数据仍然存在很大的模糊性。事实上，没有一个模型能正确预测矿物质对元素的吸收，从几十到几千毫克/公斤。 在痕量水平上，晶格应变理论（LST）提供了一个框架来预测从熔体和流体中吸收元素，表明它是由晶格中元素的尺寸和电荷失配控制的。然而，LST仅在“无限稀释”下有效，并且在较高浓度下观察到强烈偏差。因此，LST不能提供有意义的浓度数据来模拟成矿系统的极端富集。热力学固溶体模型允许从元素置换的吉布斯自由能（例如，斜长石中的Ca+Al = Na+Si）对高浓度的元素掺入进行建模。然而，热力学数据的不确定性不允许外推到低浓度。因此，迫切需要一个模型来预测所有浓度的元素吸收。 该研究计划旨在通过获得元素如何在矿物中被容纳的基本见解，开发一个统一的理论来解释和预测元素在整个浓度范围内的吸收。将进行实验以确定矿物晶格对不匹配元素掺入的响应。这将与晶格尺寸和弹性的直接测量相结合，并通过原子模拟在原子尺度上对失配元素周围的局部晶格进行预测建模。 矿物的元素和同位素组成包含了矿物生长环境中压力、温度、年龄和元素活动性的信息宝库。在这项研究计划中开发的基本见解将使我们能够提取这些信息，而不会出现目前削弱这种方法的模糊性。这使我们能够解决关键的材料和地球科学问题，从俯冲带元素循环，到早期地壳和海洋的组成，再到矿石的形成。此外，它在工业中具有直接应用，其中材料的期望行为，例如作为催化剂，与功能元素的丰度直接相关。因此，这项研究解决了加拿大公众的直接关切，包括开发绿色技术的新材料，修复废物，解决自然资源减少和气候变化的影响。