Collaborative Research: U-Series Isotopic Constraints on the Rates of Magma Genesis Evolution and Degassing at Mt. Erebus, Antarctica

该奖项由极地方案办公室南极地质和地球物理方案提供，为研究埃里伯斯火山系统中活跃的岩浆过程提供资金。岩浆活动是行星内部最基本的动力学过程之一，但我们对玄武岩岩石成因的时变参数（如固体地幔上涌速率、熔融速率、熔体输送速率、岩浆储存时间、结晶速率、岩浆补给速率等）的了解相当有限。岩浆作用，如熔融，分离结晶和岩浆房补充可以破碎母/子比的U衰变系列同位素，从而可以创建同位素不平衡。由于铀系同位素的半衰期与这些过程的时间尺度相当，测量火山玻璃和矿物分离物中的这种同位素不平衡提供了对岩浆过程的持续时间和速率的限制。本项目的目标是收集一个独特的地球化学-同位素-岩石学数据集，并利用它来评估岩浆成因、演化、在南极洲的埃里伯斯山进行脱气。山埃里伯斯火山是南极洲最活跃的火山，包含一个持续对流和脱气的斜长石响岩熔岩湖，每天有2-6次小规模的斯特龙博利火山喷发。熔岩湖为了解岩浆系统提供了一个独特的窗口，并提供了一个难得的机会来研究对流岩浆体深处发生的过程。熔岩湖不断地脱气，正在进行的工作集中在采样和测量气体成分和排放率。小型的斯特龙博利期喷发很方便地喷出火山弹，从而提供了原始的岩浆样品，其中含有大型的、形成良好的斜长石晶体。这些炸弹，加上更古老的放射性测年熔岩流周围的山顶。埃里伯斯提供了一个独特的机会，调查基本的岩浆和火山过程的时间。（以及同位素和主要元素和微量元素的限制）从已知年龄的熔岩，最近爆发的炸弹，并从埃里伯斯山收集的气体，该项目将研究的时间尺度：1）岩浆成因和熔体输运从地幔;（2）岩浆在地壳中储存过程中的演化和结晶过程; 3）岩浆脱气和向当前喷发岩浆房的补给速率。这种利用U系列同位素对气体和伴生岩浆的综合研究将导致对Erebus系统的理解的重大改进，对整个岩浆系统从地幔部分熔融形成岩浆到岩浆演化，再到岩浆湖的脱气和开放系统行为，都有重要意义。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for research on magmatic processes that are active in the Mount Erebus volcanic system. Magmatism is one of the most fundamental dynamic processes of planetary interiors, yet our knowledge of the time-dependent parameters of basalt petrogenesis (e.g. solid mantle upwelling rate, melting rate, melt transport rate, magma storage time, crystallization rate, magma recharge rate) is quite limited. Magmatic processes such as melting, fractional crystallization and magma chamber replenishment can fractionate parent/daughter ratios of U-decay series isotopes and can thus create isotopic disequilibrium. Because the half-lives of the U-series isotopes are comparable to the time-scales of these processes, measurement of this isotopic disequilibrium in volcanic glasses and mineral separates provides constraints on the duration and rates of magmatic processes.The objectives of this project are to assemble a unique geochemical-isotopic-petrological data set, and use this to evaluate the rate dependent parameters of magma genesis, evolution, and degassing at Mt Erebus, Antarctica. Mt. Erebus, the most active volcano in Antarctica, contains a persistent convecting and degassing anorthoclase phonolite lava lake that has 2-6 small Strombolian eruptions daily. The lava lake provides a unique window into the magmatic system and offers a rare opportunity to examine processes occurring deep within the convecting magma body. The lava lake is continuously degassing and on-going work is focused on sampling and measuring the gas compositions and emission rates. The small Strombolian eruptions conveniently eject volcanic bombs thus providing pristine samples of the magma containing large, well-formed anorthoclase crystals. These bombs, plus older radiometrically-dated lava flows around the summit of Mt. Erebus provide a unique opportunity to investigate the timing of fundamental magmatic and volcanological processes.Through measurement of U-series isotopes (as well as isotopic and major- and trace-element constraints) from the known-age lavas, recently erupted bombs, and gases collected from Mt Erebus, this project will examine the timescales of: 1) magma genesis and melt transport from the mantle; 2) magma evolution and crystallization processes during magma storage in the crust; and 3) magma degassing and recharge rates into the current erupting magma chamber.This integrated study of gases and associated magma using U-series isotopes should lead to a major improvement in understanding of the Erebus system, and might yield a significant new insights about the whole magmatic system from magma formation by partial melting in the mantle through its evolution and finally to it degassing and open system behavior in the lava lake.