Igneous petrology through the lens of non-traditional stable isotopes

人们早就认识到，地质作用可以引起元素同位素比率的变化。然而，对于C、H、O、N、S以外的元素，同位素变化在高温下被认为是微不足道的。大约20年前，这种看法发生了巨大变化，当时质谱法的进步表明，较重元素的同位素（例如，事实上，镁、铁）在其同位素组成中确实显示出可分辨的变化。这些同位素变化（或分馏）为化学分析提供了补充，并且在化学分析提供模糊解释的情况下特别有用。 大多数研究都涉及平衡同位素分馏，其中所研究的熔体和晶体的化学和同位素组成不随时间变化。然而，我的研究项目主要集中在动力学同位素分馏上。这是当系统向平衡态移动时发生的同位素分馏。动力学分馏通常比平衡分馏大。我的研究计划将利用这些记录在单晶中的独特动力学特征，来确定火山下的岩浆是如何随时间演变的。 晶体内的化学变化记录了岩浆条件（温度、压力和成分）的变化，在某些情况下，可以提供有关导致火山爆发的事件的时间轴的关键信息。使用诸如激光烧蚀多收集器电感耦合等离子体质谱（LA-MC-ICPMS）的原位技术测量晶体内的同位素分布可以提供关于晶体如何以及在什么时间尺度上获得其化学分布的基本约束。稳定同位素也可以阐明在这些晶体中发现的包裹体的历史。使用稳定同位素，可以重建火山的管道结构-地表下岩浆运动的几何形状和时间尺度-可以充满信心。为了实现这一目标，我的团队将在同位素地球化学和实验岩石学的交叉点上工作，通过在实验室中模拟岩浆条件并将我们所学到的应用于自然样品。我的研究计划将有助于对活火山内部运作的基本了解。

It has long been recognized that geological processes can cause variations in the isotopic ratios of an element. For elements other than C, H, O, N, S, however, isotopic variations were thought to be insignificant at high temperatures. This perception changed dramatically about two decades ago, when advances in mass spectrometry revealed that isotopes of heavier elements (e.g., Mg, Fe) do, in fact, show resolvable variations in their isotopic compositions. These isotopic variations (or fractionations) provide a complement to chemical analyses and are especially useful in instances where chemical analyses provide ambiguous interpretations. Most studies are concerned with equilibrium isotope fractionations, in which the chemical and isotopic composition of the melts and crystals being studied do not change with time. My research program, however, focuses on kinetic isotope fractionation. This is the fractionation of isotopes that occurs as a system moves towards its equilibrium state. Kinetic fractionations are often large compared to equilibrium fractionations. My research program will use these unique kinetic signatures recorded within a single crystal, to determine how magmas beneath volcanoes evolve through time. Chemical variations within a crystal records changes in magmatic conditions (temperature, pressure, and composition) and, in some cases, can provide key information regarding the timeline of events leading up to an eruption. Measuring isotope profiles within a crystal using in-situ techniques, such as laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS), can provide fundamental constraints on how, and on what timescale, a crystal obtained its chemical profile. Stable isotopes can also illuminate the history of inclusions found in these crystals. Using stable isotopes, the plumbing structure of a volcano - the geometry and timescales of magma movement below the surface - can be reconstructed with confidence. To achieve this goal, my group will work at the intersection of isotope geochemistry and experimental petrology, by simulating magmatic conditions in the laboratory and applying what we learn to natural samples. My research program will contribute to a fundamental understanding of the inner workings of active volcanoes.