Abstract The Planchon Peteroa Volcanic Complex (PPVC) is located on the border of Chile and Argentina, and is one of the most active volcanic systems in the Andes. Holocene activity has included magma-water interaction with an evolving series of crater lakes, mainly sourced from Peteroa volcano. This study examines data from the 2018/19 eruption, together with the volcanic history of the PPVC, to elucidate the complex interplay between magmatic activity and summit water and ice. From February 2016 to mid-2019, three seismic swarms occurred in the PPVC, preceding the explosive eruption from September 2018 to April 2019. The activity originated from a small vent nested within the easternmost crater, the most active portion of the complex (Peteroa). The explosions interacted with a crater lake, producing ash plumes up to 2 km above the crater and building a small tephra cone. To investigate the eruption mechanisms, we performed remote sensing analysis of plume dispersal, thermal anomalies and ground deformation, and characterized the volcanic products, including grain size, componentry, morphology, internal textures, composition and mineralogy. Our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018/19 eruption. The eruption was also preceded by thermal anomalies, geomorphic changes and increased hydrothermal activity at the surface, though without any ground deformation recognized through radar interferometry (InSAR). The eruption initially produced predominantly recycled ash (phreatic activity), then evolved to increasing proportions of juvenile magma (phreatomagmatic) by April 2019. The juvenile clasts had a trachyandesite composition (~59 wt% SiO2), with vesicular and dense scoria containing plagioclase and pyroxene. The ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake. Textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake. Notably, these juvenile particles are distinctive from the pre-2018 products. Ash erupted from 2010/11 did not contain recognizable juvenile material, and is inferred to have been a mainly phreatic eruption. Our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the PPVC during the last three decades. Multi-parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions.

中文翻译：

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将灰分分析与遥感相结合，确定 2018/19 年彼得罗亚火山（南安第斯山脉）小喷发期间的幼年岩浆参与和破碎机制

摘要 普朗雄彼得罗火山群（PPVC）位于智利和阿根廷边境，是安第斯山脉最活跃的火山系统之一。全新世活动包括岩浆-水与一系列不断演化的火山口湖相互作用，主要来自彼得罗亚火山。本研究检查了 2018/19 年喷发的数据以及 PPVC 的火山历史，以阐明岩浆活动与山顶水和冰之间复杂的相互作用。2016 年 2 月至 2019 年年中，在 2018 年 9 月至 2019 年 4 月爆发性喷发之前，PPVC 发生了三个地震群。 该活动起源于嵌套在最东端火山口内的一个小喷口，该火山口是该复合体最活跃的部分 (Peteroa) . 爆炸与火山口湖相互作用，在火山口上方 2 公里处产生灰羽并建造一个小火山锥。为了研究喷发机制，我们对羽流扩散、热异常和地面变形进行了遥感分析，并对火山产物进行了表征，包括粒度、成分、形态、内部结构、成分和矿物学。我们的结果表明，2016 年开始的前兆地震活动与 2018/19 年喷发期间到达地表的新岩浆批次的侵入有关。喷发之前还发生了热异常、地貌变化和地表热液活动增加，但没有通过雷达干涉测量 (InSAR) 识别出任何地面变形。喷发最初主要产生回收灰（潜水活动），然后到 2019 年 4 月演化为幼年岩浆 (phreatomagmatic) 的比例增加。 幼年碎屑具有粗安岩成分（约 59 wt% SiO2），具有包含斜长石和辉石的囊泡和致密熔渣。火山灰表面显示出外部淬火裂纹和阶梯断裂，与活动火山口湖内的岩浆碎裂一致。质地特征还表明，一批缓慢上升的岩浆在与火山口湖中的水相互作用时相对粘稠。值得注意的是，这些幼年颗粒与 2018 年之前的产品不同。2010/11 年喷发的火山灰不含可识别的幼年物质，推测主要是潜水喷发。我们的研究结果表明，在过去 30 年里，由浅层侵入的小批岩浆供给的潜水和潜水岩浆喷发之间的相互作用是 PPVC 喷发行为的主要特征。多参数评估是区分潜水和潜水岩浆喷发的有力工具。