EAGER: Collaborative Research: Collaborative Investigations of Isotopic Fractionation by Thermal Diffusion and Thermal Migration

这个早期概念探索性研究基金（EAGER）代表了一项跨学科的努力，旨在解决地球化学过程，该过程可能负责最近观察到火成岩（NTSI）中“非传统稳定同位素”的稳定同位素变化。镁和硅同位素的显著分异很难用矿物及其熔体在共同火成岩分异过程中的平衡来解释。令人兴奋的新发现是，在一定温度梯度的熔体中会出现较大的同位素分馏，这为观察到的同位素变化提供了可能的解释。热扩散分馏作用是如此之大，以至于它可以为识别热梯度驱动过程在岩浆分馏中的作用提供一个独特的工具基础。该项目代表了一种协同和新颖的合作，为研究这种NTSI分馏现象带来了实验、分析和理论方法。将开展三项互补工作，包括：1)实验室硅酸盐（完全熔融）实验，使用天然成分和选定的简单系统；2)玄武岩-流纹岩体组成热迁移（部分熔融）实验中主微量元素行为及NTSI分馏分析及镁、硅、铁BetaT测定；3)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。拟议的科学计划汇集了三组研究人员，他们在岩石学/地球化学研究方面具有不同的专业知识，从野外岩石学到实验岩石学再到分子动力学模拟。

This EArly-concept Grant for Exploratory Research (EAGER) represents an interdisciplinary effort to address the geochemical processes that could be responsible for recent observations of stable isotope variations for "non-traditional stable isotopes" in igneous rocks (NTSI). Significant fractionations in the isotopes of Mg and Si are difficult to explain in terms of equilibrium between minerals and their melts during common igneous differentiation processes. The exciting new discovery that large isotopic fractionations occur in melts held within a temperature gradient offers a possible explanation for the observed isotope variations. The fractionation by thermal diffusion is 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 and novel collaboration that brings experimental, analytical, and theoretical approaches to the study of this NTSI fractionation phenomenon. Three complementary efforts will be undertaken that include: 1) Laboratory silicate Soret (fully molten) experiments using both natural compositions and selected simple systems; 2) Analysis of major and trace element behavior and NTSI fractionation in thermal migration (partially molten) experiments on basalt to rhyolite bulk compositions and determination of BetaT for Mg, Si and Fe; and 3) 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. The proposed science plan brings together three groups of researchers with different expertises in petrology/geochemistry research from field petrology to experimental petrology to molecular dynamics simulation.