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

这一RAPID将调查智利南部安第斯山脉山顶上的拉古纳德尔马乌莱火山区动荡的原因。这个火山区是地球上最集中的年轻的冰后期（20，000至2，000年）流纹岩熔岩流，这些熔岩流从24个喷口喷出，以23 x 16.5公里的椭圆形图案排列，中心是拉古纳德尔马乌莱。结晶贫流纹岩喷发对双方的湖盆是几乎相同的组成，并有关前体安山岩和流纹质熔岩的结晶-液体分馏。这种岩石学和结构的配置表明，一个大的机构的高温流纹岩熔体，从一个岩基规模的结晶糊水库提取，目前在整个湖盆的基础上，一个类似的水库被假定为已源的560 km 3主教凝灰岩超级喷发。从2007年开始，卫星大地测量（干涉合成孔径雷达和全球定位系统）表明流纹岩圆顶环的西侧开始上升，到2012年底，上升速度加快到300毫米/年。 此外，直径约20 km的膨胀区正在进行横向伸展，并在膨胀中心上方形成一系列正断层。目前的上升速度比最近在Yellowtone或Santorini火山口检测到的要高4-5倍，表明可能产生流纹岩大规模爆发的动荡。该项目旨在了解流纹岩岩浆系统在喷发前的基本动态，并评估拉古纳德尔马乌莱火山区的火山危险。 这将通过用重力和CO2测量补充现有观测来实现。重力基线将有助于确定地下密度和质量变化。二氧化碳的测量将限制岩浆释气的范围和幅度，这可能反映了最近新的岩浆进入浅地壳。这两项分析都将与南安第斯山脉火山观测站合作进行。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流纹岩喷发所证明的那样，即使是流纹岩的轻微爆炸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。该项目将提供有关拉古纳德尔马乌莱火山区行为的重要信息，改善该地区火山危险的评估，并最终帮助更好地了解大的活跃流纹岩岩浆系统之前的喷发（或超级喷发）。

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.