MARGINS: The Sr-Nd-Pb-Hf Isotope Evolution of the Mariana Island Arc

马里亚纳岛弧Sr-Nd-Pb-Hf同位素演化火山弧是由先存地壳基底、俯冲板片和邻近地幔储集层形成的复杂混合体。虽然弧岩浆外流（成分和体积）的时间变化必须以某种方式耦合到地球表面和地幔水库的长期变化，目前还不清楚它们如何与俯冲动力学（地壳厚度，板倾角，收敛速度等）变化。该项目旨在调查西北太平洋马里亚纳弧岩浆流出量变化的原因。马里亚纳弧/弧后系统是大约4900万年前开始的大洋内伊豆小笠原-马里亚纳（IBM）弧的一部分。众所周知，随着时间的推移，其可变的K2 O富集率与长期地质变化相匹配。要了解是什么力量，这样的马里亚纳“波动”，建议确定马里亚纳火山岩的化学变化，从渐新世中期到最近的时间。这种岩石记录被火山碎屑沉积物保存在海洋沉积物中，具有很高的时间精度和分辨率（~1 Ma）。虽然早期（~32-48 Ma）和现今弧（1 Ma）的熔岩提供了一个重要的框架，但只有火山熔岩提供了弧演化关键中期的全面信息。新鲜的火山颗粒将从蚀变最小的火山灰层中分离出35米馏分中的碎屑岩（玻璃、火山渣、浮石、幼年岩屑），并将分析这些样品的Sr-Nd-Pb-Hf同位素比率以及新鲜火山玻璃和颗粒的主要和微量元素。“诸如会聚速率和上板块厚度等强迫函数如何调节俯冲工厂的岩浆和流体的产生？'.在区域范围内，新数据将填补IBM系统整体发展的重要空白，为IBM收敛边际的发展提供新的视角。在全球范围内，长期弧演化的研究将有助于了解地球的水库如何相互作用，以及这可能如何与弧岩浆通量和全球环境变化。该项目将促进美国和澳大利亚科学家之间的科学伙伴关系。将进一步支持从事地球科学工作的妇女。斯特劳布是一位残疾女性研究人员，她已经为IBM的发展做出了重大贡献，这是她长期研究目标的一部分。Straub将制作一个在线MARGINS迷你课程，分享她使用火山岩作为成岩工具的专业知识。计划让本科生参与本项目研究。

The Sr-Nd-Pb-Hf isotope evolution of the Mariana Island ArcIntellectual Merit. Volcanic arcs represent a complex blend produced from pre-existing crustal basement, subducting slab and adjacent mantle reservoirs. Although temporal variations in arc magmatic outfluxes (compositions and volumes) must somehow be coupled to secular changes of the Earth's surface and mantle reservoirs, it remains unclear how they vary with subduction dynamics (crustal thickness, slab dip, convergence rate etc.). This project aims to investigate the causes of the variable magmatic outflux of the Mariana arc in the NW Pacific. The Mariana arc/backarc system is part of the intra-oceanic Izu Bonin-Mariana (IBM) arc that initiated ~49 million years ago. It is well known for its variable K2O-enrichment over time at rates that match to secular geological change. To understand what forces such Mariana 'fluctuations', it is proposed to determine chemical variations in Mariana volcanic rocks from the mid-Oligocene to Recent time. This rock record is preserved by tephra deposits in the marine sediments with high temporal precision and resolution (~1 Ma). While the lavas of the early (~32-48 Ma) and present-day arc (1 Ma) provide an essential framework, only the tephras provide comprehensive information on the crucial intermediate period of arc evolution. Fresh volcanic particles (glasses, scoria, pumice, juvenile lithics) from the fraction 35 _m will be separated from minimally altered tephra layers, and these samples will be analyzed for Sr-Nd-Pb-Hf isotope ratios and major and trace elements of fresh volcanic glasses and particles.The project bears on one of the fundamental science themes of the Subduction Factory Initiative: 'How do forcing functions such as convergence rate and upper plate thickness regulate production of magma and fluid from the Subduction Factory?'. On a regional scale, the new data will fill an important gap in the overall evolution of the IBM system that will provide new perspectives on the evolution of the IBM convergent margin. On a global scale, the study of secular arc evolution will aid in the understanding how the Earth's reservoirs interact, and how this may be linked to arc magmatic fluxes and global environmental change.Broader Impacts. The project will promote scientific partnership between U.S. and Australian scientists. The support for women in the geosciences will be furthered. Straub is a female researcher with a disability who has already made substantial contributions to the IBM evolution as part of a long-held goal of her research. Straub will produce an online MARGINS mini-lesson to share her expertise on the use of tephras as petrogenetic tool. It is planned to involve undergraduate students in this project research.