An Experimental Calibration of the Fractionation of Boron Isotopes among Granitic Melt, Aqueous Fluid, and Tourmaline

花岗岩熔体、水流体和电气石中硼同位素分馏的实验校准

• 批准号: 1623110
• 负责人: David London
• 金额: $ 31.46万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-15 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1623110&HistoricalAwards=false
• 关键词: Experimental; Calibration; Fractionation; Boron; Isotopes

Understanding how the Earth evolves in time is central to the geosciences. Toward that end, there is always a need for analytical tools or methods that may shed light on those processes of change and how these processes operate on the natural environment. The relative abundance of stable isotopes of light elements tend to be fractionated between coexisting phases (i.e., different minerals, gas, magma, biota) by a number of organic and inorganic processes. These natural interactions that fractionate stable isotopes are occurring constantly as the earth and its biosphere evolve. For that reason, stable isotope distributions have played a very large role in elucidating some of the processes operating throughout the earth's chemical history. The stable isotope systematics of H, C, and O are widely studied, calibrated, and utilized. Recent studies have heralded the boron isotopic system, 10B and 11B, as potentially revolutionary. Boron is concentrated in ocean waters, altered oceanic crust, in marine sediments, and in silicate magmas and aqueous fluids that are derived from them. There is a hope among researchers that the fractionation of 10B and 11B among minerals, melts, and aqueous solutions may yield important insights into the chemical evolution of the continental crust. So far, the laboratory analyses of boron isotopes in natural samples have failed to provide an understandable and consistent picture of their chemical behavior. One body of work cites little or no fractionation of boron isotopic composition among coexisting aqueous solution, granitic liquid, and tourmaline, the principal mineralogical carrier of boron in the earth, while other analytical data point to very large ranges in the fractionation of boron isotopes in tourmaline, even within a single geologic occurrence. The goal of this research, therefore, is to complete an experimental program that yields an internally consistent calibration of the partitioning of the boron isotopes among granitic melt, aqueous solution, and tourmaline at elevated pressures and temperatures.Three series of experiments will measure the fractionation of 10B and 11B between granitic melt and aqueous solution. The use of multiple experimental methods, and reversals in the direction of diffusive mixing of the isotopes, will provide robust tests of the attainment of equilibrium distributions. The fractionation of boron isotopes between tourmaline and melt will also be measured through synthesis experiments. These latter experiments will test a hypothesis that the wide range in the isotopic composition of tourmaline stems from diffusion-controlled fractionation of the isotopes of boron attending the crystallization of tourmaline at states far from the mineral-melt equilibrium.

了解地球如何随时间演化是地球科学的核心。为此，始终需要有分析工具或方法来阐明这些变化过程以及这些过程如何对自然环境起作用。轻元素的稳定同位素的相对丰度倾向于在共存相之间分馏（即，不同的矿物、气体、岩浆、生物群）通过许多有机和无机过程形成。随着地球和生物圈的演化，这些自然的相互作用，即不稳定同位素不断发生。因此，稳定同位素分布在阐明地球化学史中的某些过程中发挥了非常重要的作用。氢、碳和氧的稳定同位素系统学被广泛研究、校准和利用。最近的研究已经预示着硼同位素系统，10B和11B，作为潜在的革命性。硼富集在大洋沃茨、蚀变洋壳、海洋沉积物、硅酸盐岩浆和由它们衍生的含水流体中。研究人员希望，10B和11B在矿物、熔体和水溶液中的分馏可能会对大陆地壳的化学演化产生重要的影响。到目前为止，对天然样品中硼同位素的实验室分析未能提供其化学行为的可理解和一致的图像。一个机构的工作引用很少或根本没有分馏硼同位素组成共存的水溶液，花岗岩液体，和电气石，硼在地球上的主要矿物载体，而其他分析数据点非常大的范围内分馏硼同位素在电气石，即使在一个单一的地质发生。因此，本研究的目标是完成一个实验程序，产生一个内部一致的校准花岗岩熔体，水溶液，并在高温高压下tourglycer.Three系列的实验将测量花岗岩熔体和水溶液之间的分馏10B和11B的硼同位素之间的分配。多种实验方法的使用，以及同位素扩散混合方向的逆转，将为平衡分布的实现提供可靠的测试。硼同位素在电气石和熔体之间的分馏也将通过合成实验来测量。这些后面的实验将测试一个假设，即广泛的同位素组成的电气石源于扩散控制分馏的同位素参加的电气石结晶在远离矿物熔体平衡的状态。