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

天然晶体（矿物）讲述了它们生长过程中的条件，因此在研究过去的气候，古代和现代火山活动，造成古代山脉的板块构造运动等问题中发挥着关键作用。 然而，矿物化学必须通过对环境特性如何在生长晶体的成分上留下印记的理解来解释。一般认为平衡热力学控制矿物化学档案。但新出现的证据表明，扩散或不可逆反应等非平衡过程在许多关键矿物的化学性质中占主导地位。而且，有可能是表面的热力学性质知之甚少，而不是大量固体和流体的充分研究性质控制某些矿物的组成。加州理工学院RPI提案的目标是在原子（分子）尺度上理解这些现象。 它的结果将推进矿物化学的解释，作为矿物生长环境的约束，从而推进地球？本研究的重点是从天然或合成富水溶液中生长的矿物石英中的同位素（特别是天然存在的O和Si的同位素）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）的大部分三维结构，它们的比例？光？然后呢？很重？同位素提供了一些最广泛使用的地质过去的记录。这些同位素在个别矿物中的分布并不总是均匀的。 这种异质性，特别是相邻的同时生长的晶面之间的成分差异，告诉我们，一些影响以外的环境因素可能会影响晶体的生长？非均衡增长的一些表现。 Caltech-RPI研究将利用分析地球化学的最新进展，记录与晶内不均匀性相关的O和Si同位素的共同变化，以及它们与微量元素丰度不均匀性的关系。由此产生的化学数据将产生一种负责非平衡增长机制的指纹。然后，该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.