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，为研究埃里伯斯山火山系统中活跃的岩浆过程提供资金。岩浆作用是地球内部最基本的动力学过程之一，但我们对玄武岩成岩作用随时间变化的参数(如固体地幔上涌速率、熔融速率、熔体迁移速率、岩浆储存时间、结晶速率、岩浆补给速率)的了解相当有限。熔融、分离结晶和岩浆房补充等岩浆作用可以使铀衰变系列同位素的母子比分馏，从而造成同位素不平衡。由于U系列同位素的半衰期与这些过程的时间尺度相当，对火山玻璃和矿物分离物中这种同位素不平衡的测量对岩浆作用的持续时间和速率提供了限制。该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，并利用它来评估南极埃里伯斯山岩浆成因、演化和脱气的速率相关参数。Mt.Mt.埃里巴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石熔岩湖，每天有2-6次斯特龙博利亚式的小规模喷发。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。熔岩湖正在持续脱气，正在进行的工作重点是采样和测量气体成分和排放率。小的斯特龙博利亚喷发方便地喷射出火山弹，从而提供了含有大的、结构良好的斜长石晶体的原始岩浆样本。这些炸弹，加上更古老的放射性年代测定的熔岩，在山顶周围流动。Erebus为研究基本岩浆和火山作用的时间提供了一个独特的机会。这个项目将通过测量已知年代的熔岩、最近喷发的炸弹和从Erebus山收集的气体的U系列同位素(以及同位素和主量元素和微量元素约束)，研究以下时间尺度：1)岩浆成因和来自地幔的熔体运输；2)在地壳中岩浆储存期间的岩浆演化和结晶过程；利用U系列同位素对气体和伴生岩浆进行综合研究，将大大提高对Erebus系统的认识，并可能对整个岩浆系统产生重要的新见解，从地幔部分熔融的岩浆形成到熔岩湖中的脱气和开放系统行为。

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.