RAPID PROPOSAL: Accelerating unrest within a large rhyolitic magma system: Laguna del Maule, Chile

该 RAPID 将调查智利安第斯山脉南麓拉古纳德尔莫莱火山场动乱的原因。该火山场由地球上最集中的年轻冰川后（20,000 至 2,000 岁）流纹质熔岩流组成，这些熔岩流从 24 个喷口喷发，排列成 23 x 16.5 公里的椭圆形图案，以 Laguna del Maule 为中心。湖盆两侧喷发的贫晶流纹岩的成分几乎相同，通过晶液分馏与前体安山岩和流纹英安岩熔岩有关。这种岩石学和结构构造表明，从岩基规模的晶体糊状储层中提取出的大量高温流纹岩熔体目前位于整个湖盆的下方；据推测，一座类似的水库是 560 平方公里毕夏普凝灰岩超级喷发的源头。从 2007 年开始，卫星大地测量（InSAR 和 GPS）表明，流纹岩圆顶圈的西侧开始隆起，到 2012 年底，该隆起速度已加快至每年 300 毫米。此外，直径 20 公里的膨胀区域正在横向扩展，并且在膨胀中心上方正在形成一系列正断层。目前的抬升速度比最近在黄通岛或圣托里尼火山口检测到的抬升速度高出 4-5 倍，这表明可能会产生大量流纹岩爆炸性喷发。该项目旨在了解喷发前流纹岩浆系统的基本动态，并评估拉古纳德尔莫莱火山场的火山灾害。 这将通过重力和二氧化碳测量补充现有的观测来实现。重力基线将有助于确定地下密度和质量变化。二氧化碳测量将限制岩浆释气的程度和幅度，这可能反映了最近新岩浆添加到浅层地壳中的情况。这两项分析都将与南安第斯火山观测站 (OVDAS) 合作完成。来自威斯康星大学麦迪逊分校的四名研究生将参与该项目的各个方面，包括在智利的实地考察和数据分析。正如2011年6月开始的智利Cordon Caulle正在进行的流纹岩喷发所表明的那样，即使是轻微的流纹岩爆发性喷发也可能引发大范围的洪水和火山灰降落，对智利和阿根廷的基础设施和农业造成相当大的破坏。该项目将提供有关马乌莱湖火山场行为的重要信息，改进对该地区火山灾害的评估，并最终帮助更好地了解喷发（或超级喷发）之前的大型活动流纹岩浆系统。该项目得到了地球物理学计划、岩石学和地球化学计划以及国际和综合活动办公室的支持。

This RAPID will investigate the cause of unrest at the Laguna del Maule volcanic field on the crest of the southern Andes, Chile. This volcanic field comprises the greatest concentration of young, post-glacial (20,000 to 2,000 year old) rhyolitic lava flows on Earth that have erupted from 24 vents, arranged in a 23 x 16.5 km elliptical pattern with Laguna del Maule in the center. Crystal-poor rhyolites erupted on opposite sides of the lake basin are nearly identical in composition and are related to precursor andesitic and rhyodacitic lavas by crystal-liquid fractionation. This petrologic and structural configuration suggests that a large body of high temperature rhyolitic melt, extracted from a batholith-scale crystal-mush reservoir, currently underlies the entire lake basin; a similar reservoir is postulated to have been the source of the 560 km3 Bishop Tuff super-eruption. Beginning in 2007 satellite geodesy (InSAR and GPS) indicates that the western side of the rhyolite dome circle began uplifting at rates that have accelerated to 300 mm/yr by late 2012. Moreover, the inflating region, 20 km in diameter, is undergoing lateral extension and a series of normal faults are forming above the center of inflation. The current rate of uplift is 4-5 times higher than recently detected at the Yellowtone or Santorini calderas and indicates unrest that could produce a large-volume explosive eruption of rhyolite. The project seeks to understand the fundamental dynamics of a rhyolitic magma system prior to eruption and to assess the volcanic hazard in the Laguna del Maule volcanic field. This will be accomplished by complementing the existing observations with gravity and CO2 measurements. The gravity baselines will help determine the subsurface density and mass changes. The CO2 measurements will constrain the extent and magnitude of magmatic outgassing that might reflect a very recent addition of new magma into the shallow crust. Both analysis will be done in collaboration with the Observatorio Volcanológico de los Andes del Sur (OVDAS). Four graduate students from the University of Wisconsin-Madison will participate in all aspects of this project, including fieldwork in Chile, and data analysis.As demonstrated by the ongoing rhyodacite eruption at Cordon Caulle, Chile, that began in June, 2011, even a minor explosive eruption of rhyolite could trigger extensive flooding and ash fall, causing considerable damage to infrastructure and agriculture in both Chile and Argentina. This project will provide important information about the behavior of the Laguna del Maule volcanic field, improving the assessment of the volcanic hazard in the region, and ultimately helping to better understand large active rhyolitic magma systems prior to an eruption (or super-eruption).This project is supported by the Geophysics Program, the Petrology and Geochemistry Program and the Office of International and Integrated Activities.