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

这一快速调查将调查智利安第斯山脉南部山顶上的拉古纳德尔莫勒火山田的动乱原因。这个火山场包括地球上最集中的年轻的冰期后(2万到2000年前)流纹岩熔岩流，它们从24个喷口喷发，以23x16.5公里的椭圆形图案排列，中间是拉古纳德尔莫勒湖。湖盆两侧喷发的贫晶流纹岩成分基本相同，与前驱安山岩和流纹质熔岩的结晶-液体分馏作用有关。这种岩石学和构造形态表明，从岩基规模的晶体碎屑储集层中提取的大量高温流纹岩熔体目前位于整个湖盆的下方；一个类似的储集层被推测为560千米3毕晓普凝灰岩超级喷发的来源。从2007年开始，卫星大地测量(InSAR和GPS)表明，流纹岩穹顶的西侧开始以加速上升的速度上升，到2012年底达到300毫米/年。此外，直径20公里的膨胀区正在经历侧向伸展，在膨胀中心上方形成了一系列正断层。目前的抬升速度比最近在黄石或圣托里尼火山口探测到的速度高出4-5倍，这表明动荡可能会导致流纹岩的大规模爆炸性喷发。该项目旨在了解喷发前流纹岩岩浆系统的基本动力学，并评估拉古纳德尔莫勒火山田的火山危险。这将通过用重力和二氧化碳测量来补充现有的观测数据来实现。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出气的范围和程度，这可能反映出最近新的岩浆进入地壳浅层。这两项分析都将与南洛斯安第斯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所有方面，包括在智利的实地考察和数据分析。智利科顿考勒正在进行的流纹岩喷发证明了这一点，该喷发始于2011年6月，即使是轻微的流纹岩爆炸性喷发也可能引发大范围洪水和火山灰坠落，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莫勒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。该项目由地球物理计划、岩石学和地球化学计划以及国际和综合活动办公室提供支持。

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.