Collaborative Research: Novel Isotopic Tests of the Mechanisms of Non-equilibrium Crystal Growth

天然晶体(矿物)有关于它们生长过程中普遍存在的条件的故事，因此在研究过去的气候、古代和现代火山作用、导致古代山带的板块构造运动等问题上发挥着关键作用。然而，矿物化学必须通过对环境属性如何印在生长中的晶体的成分上的一些了解来解释。一般认为，平衡热力学控制着矿物化学档案。但新出现的证据表明，扩散或不可逆反应等非平衡过程主导着许多关键矿物的化学成分。而且，控制某些矿物成分的可能是对表面热力学性质知之甚少，而不是对散体固体和流体性质的深入研究。加州理工学院-RPI提议的目标是在原子(分子)尺度上理解这些现象。其结果将促进矿物化学作为矿物生长环境的制约因素的解释，从而促进地球-S化学体系和过去环境的研究。本研究将重点关注从天然或合成的富水溶液中生长的矿物石英中的同位素(特别是自然存在的O和Si同位素)和微量元素的分带。氧和硅原子构成了石英(和大多数其他矿物)的三维结构的大部分，以及它们的光？然后呢？重吗？同位素提供了一些最广泛使用的地质历史记录。这些同位素在个别矿物中的分布并不总是一致的。这种不均一性，特别是相邻同时生长的晶面之间的成分差异，告诉我们除了环境因素之外，其他一些因素可能影响了晶体的生长--一些非平衡生长的表现。加州理工学院-RPI的研究将使用分析地球化学的最新进展来记录与晶体内不均一性相关的氧和硅同位素的协变，以及它们与微量元素丰度不均一性的关系。由此产生的化学数据将为非平衡增长的机制提供某种指纹。然后，这项研究将构建矿物生长的第一原理化学物理模型，以复制和解释这些化学指纹。

Natural crystals (minerals) have stories to tell about the conditions that prevailed during their growth, and so play a key role in the study of past climates, ancient and modern volcanism, the plate tectonic motions responsible for ancient mountain belts, among other problems. However, mineral chemistry must be interpreted through some understanding of how environmental properties get imprinted on compositions of growing crystals. It is generally assumed that equilibrium thermodynamics controls the mineral-chemical archive. But emerging evidence indicates that non-equilibrium processes, such as diffusion or irreversible reactions, dominate the chemistry of many key minerals. And, it is possible that the poorly understood thermodynamic properties of surfaces rather than the well-studied properties of bulk solids and fluids control compositions of some minerals. The goal of the Caltech-RPI proposal is to understand these phenomena at an atomic (molecular) scale. Its results will advance interpretations of mineral chemistry as constraints on the environments of mineral growth, and thereby advance the study of Earth?s chemical systems and past environmentsThis study will focus its attention on the zonation of isotopes (particularly naturally occurring isotopes of O and Si) and trace elements in the mineral quartz, grown from natural or synthetic water-rich solutions. Oxygen and silicon atoms make up most of the three dimensional structure of quartz (and most other minerals), and proportions of their ?light? and ?heavy? isotopes provide some of the most widely used records of the geologic past. The distribution of these isotopes in individual minerals are not always uniform. This heterogeneity, particularly differences in composition between adjacent simultaneously growing crystal faces, tells us that some influence other than environmental factors may have affected the growth of the crystal?some manifestation of non-equilibrium growth. The Caltech-RPI study will use the most recent advances in analytical geochemistry to document the co-variations of O and Si isotopes associated with intracrystalline heterogeneities, and their relationship to heterogeneities in trace element abundances. The resulting chemical data will yield a sort of fingerprint for mechanisms responsible for non-equilibrium growth. The study will then construct first-principles chemical-physics models of mineral growth, constructed to replicate and explain these chemical fingerprints.