Non-traditional stable isotope fractionation during magmatic differentiation: In situ Fe-Mg-isotope analyses of phenocrysts by femtosecond laser ablation MC-ICP-MS

在这个项目中，我们的目标是调查非传统的稳定同位素（即铁和镁）的斑晶玄武岩（橄榄石，cpx）的分馏，以提高我们的知识的时间演化的岩浆系统。我们在第一个资助期内获得的结果表明，解决小规模的同位素变化（即同位素分区）中的橄榄石洋中脊玄武岩是可行的，在原位铁和镁同位素分析，使用激光烧蚀等离子体质谱。因此，我们能够追踪岩浆演化过程中矿物尺度上发生的扩散过程，并通过模拟这些过程获得时间信息。在第二个资助期内，我们希望将我们开发的技术应用于大洋中脊玄武岩中的单斜辉石斑晶，以解决以下问题：（1）cpx中Fe和Mg同位素的分带是否与橄榄石中观察到的分带相似，是否与化学分带相关？(2)我们能否利用这种分区来获得岩浆过程的时间信息？(3)从cpx得到的信息与我们通过模拟橄榄石中的扩散分带得到的时间限制相比如何？此外，我们的目标是调查橄榄石斑晶玄武岩从沙茨基海隆海洋高原获得信息的时间演化的岩浆系统非常大的岩浆体积。最后，我们正在开发一个多组分的扩散模型，充分描述了在晶体中的Fe和Mg同位素的耦合运输的稳定同位素在晶体中的扩散分馏的更一般的理解。

In this project we aim to investigate the fractionation of non-traditional stable isotopes (i.e. Fe and Mg) of phenocrysts in basalts (olivine, cpx) to improve our knowledge on the temporal evolution of magmatic systems. Our results obtained during the first funding period show that resolving small-scale isotopic variations (i.e. isotopic zoning) in olivines from mid-ocean ridge basalts is feasible by in situ Fe- and Mg isotope analyses using laser ablation plasma mass spectrometry. We are thus able to trace diffusive processes that occur on the mineral scale during magma evolution and to obtain time information by modeling these processes.During the second funding period, we want to apply our developed technique to clinopyroxene phenocrysts in basalts from ocean ridges to address the following questions: (1) Is the zoning of Fe and Mg isotopes in cpx comparable to that observed in olivines and correlated with a chemical zoning? (2) Can we use this zoning to receive time information on magmatic processes? (3) How do the information from cpx compare to the time constraints we have received by modeling of the diffusion zoning in olivine?Additionally, we aim to investigate olivine phenocrysts in basalts from the Shatsky Rise oceanic plateau to gain information on the temporal evolution of magmatic systems with extraordinarily large magma volumes. Finally, we are working on a more general understanding of diffusive fractionation of stable isotopes in crystals by developing a multi-component diffusion model that adequately describes the coupled transport of Fe and Mg isotopes in a crystal.