Collaborative Proposal: Integrated Investigations of Isotope Fractionation in Magmatic Systems

知识价值。近年来，在火成岩中观察到几种非传统稳定同位素（NTSI）系统的稳定同位素比率有显著变化。这些变异的起源在很大程度上仍然是未知的，尽管这些变异与分化程度相关的关键观察。目前，由于岩浆相之间的分馏因素尚未确定，因此无法评估诸如分馏结晶等传统过程是否可以解释这些观察结果。令人兴奋的新发现是，在温度梯度内的熔体中会发生大的同位素分馏，这为观察到的同位素变化提供了另一种可能的解释，但要充分评估这一机制需要进一步的实验研究。热扩散的分馏作用如此之大，以至于它可以为识别热梯度驱动过程在岩浆分异中的作用提供独特工具的基础。该项目代表了一个协同合作，涉及四个相互关联和互补的研究：1)在实验室硅酸盐（完全熔融）实验中表征NTSI分馏。Soret实验将使用天然成分和选定的简单系统；2)在热迁移（部分熔融）实验中表征主微量元素行为和NTSI分馏；这些将集中于玄武岩到流纹岩的整体组成，并确定Mg、Si和Fe的热扩散分馏；3)利用温度梯度下MgO-SiO2体系中同位素分馏的分子动力学模拟，探讨热扩散对NTSI分馏影响的物理基础；4)用三同位素法确定Mg、Si和Fe的熔体、蒸汽和矿物相之间的平衡分馏因子。拟议的科学计划汇集了四组具有互补专业知识的研究人员。该团队将岩石学/地球化学研究的各个领域结合起来，从野外岩石学到实验岩石学再到分子动力学模拟。该项目将提供火成岩岩石学一级问题的约束，火成岩中NTSI分馏的起源。这将进一步了解热扩散的基本过程及其强烈的质量依赖性，并改进NTSI工具来识别温度梯度在岩浆分异中的作用。更广泛的影响：该项目将支持三名研究生，一名博士后和早期职业教师（UNLV）和一名研究科学家（UCD）参与一个复杂的项目，利用广泛的概念，分析，实验和模拟工具。小组会议和视频会议将促进合作，使学生和博士后参与到研究的各个方面。每个PI期望将这项研究的结果纳入岩石学，地球化学和数值模拟的常规教学中。

Intellectual Merit. Significant variations in stable isotope ratios of several non-traditional stable isotope (NTSI) systems have recently been observed in igneous rocks. The origin of these variations remains largely unknown despite the critical observation that the variations correlate with extent of differentiation. At present, it is not possible to evaluate whether traditional processes such as fractional crystallization may account for the observations, because the fractionation factors among magmatic phases have not been determined. The exciting new discovery that large isotopic fractionations occur in melts held within a temperature gradient offers an alternative possible explanation for the observed isotopic variations, but to fully assess this mechanism requires further experimental investigation. The fractionation by thermal diffusion appears to be so large that it may provide the basis for a unique tool to discern the role of thermal-gradient-driven processes for magmatic differentiation. This project represents a synergistic collaboration involving four interrelated and complementary studies: 1) Characterize NTSI fractionation in laboratory silicate Soret (fully molten) experiments. Soret experiments will use both natural compositions and selected simple systems; 2) Characterize major and trace element behavior and NTSI fractionation in thermal migration (partially molten) experiments; these will focus on basalt to rhyolite bulk compositions and also determine thermal diffusion fractionations for Mg, Si and Fe; 3) Use molecular dynamics simulations of isotope fractionation within a temperature gradient in the MgO-SiO2 system to investigate the physical basis for the effects of thermal diffusion on NTSI fractionation; 4) Determine equilibrium fractionation factors between melts, vapor and mineral phases for Mg, Si and Fe using the three-isotope method. The proposed science plan brings together four groups of researchers with complementary expertise. The team connects diverse areas of petrology/geochemistry research from field petrology to experimental petrology to molecular dynamics simulation. The project will provide constraints on a first-order problem in igneous petrology, the origin of NTSI fractionations in igneous rocks. It will provide further understanding of the fundamental process of thermal diffusion and its strong mass dependence and improve the NTSI tool for discerning the role of temperature gradients in magma differentiation.Broader Impacts: The project will support involvement of three graduate students, a postdoc and early career faculty (UNLV) and a research scientist (UCD) in a complex project utilizing a broad range of conceptual, analytical, experimental and simulation tools. Group meetings and video conferencing will foster the collaboration and involve the students and postdoc in all aspects of the study. Each PI expects to incorporate the results of this study into regular teaching of petrology, geochemistry and numerical modeling.