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

这一早期概念探索研究补助金(AGER)代表了一项跨学科努力，以解决可能导致最近观察到火成岩中“非传统稳定同位素”稳定同位素变化的地球化学过程(NTSI)。在常见的火成岩分异过程中，镁和硅同位素的显著分馏很难用矿物与其熔体之间的平衡来解释。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，这为观测到的同位素变化提供了可能的解释。热扩散的分馏是如此之大，以至于它可能为一种独特的工具提供基础，以辨别热梯度驱动过程对岩浆分异的作用。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。将开展三项相辅相成的工作，包括：1)利用自然成分和选定的简单体系进行实验室硅酸盐Soret(全熔融)实验；2)分析玄武岩到流纹岩主体成分的热迁移(部分熔融)实验中的常量元素和微量元素行为以及NTSI分馏；以及3)对MgO-SiO_2体系在温度梯度下的同位素分馏进行分子动力学模拟，以研究热扩散对NTSI分馏影响的物理基础。拟议的科学计划汇集了三组在岩石学/地球化学研究方面具有不同专长的研究人员，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.