Makushin stratovolcano, Alaska, produced three, highly explosive, andesitic eruptions between ~ 9292 and 6215 yBP. Those eruptions are informally named the CFE (“crater-forming eruption”), Nateekin, and Driftwood Pumice, and they deposited significant tephra fallout in the present-day port of Dutch Harbor and City of Unalaska area. The focus of this study is to examine the geochemistry and petrology of those eruptions to better understand Makushin volcano hazards, andesite petrogenesis and eruption triggering by mafic recharge processes. The CFE, Nateekin, and Driftwood Pumice samples range from basaltic andesite to dacite but are predominantly andesitic (SiO2 = 55.6 to 63.5 wt%). The CFE deposits are slightly compositionally stratified, with the top CFE samples slightly more mafic (55 to 60 wt% SiO2) than the basal deposits (58 to 60 wt% SiO2). Disequilibrium mineral compositions and textures in the CFE, Nateekin, and Driftwood Pumice samples, combined with two pyroxene thermometry and An-rich plagioclase microlites (An80) found only in the top of the CFE deposits, provide evidence for repetitive mafic recharge triggering those eruptions, consistent with prior studies. We compare the Makushin geochemical data with data from select satellite vents and cones in the Makushin Volcanic Field (MVF) from prior studies, to examine possible genetic relationships. The geochemical data and Rhyolite-MELTS models run at crustal storage conditions (2 kbar, fO2 = Ni-NiO, and 1.5 and 3.5 wt% H2O) indicate that no single parental magma supplies the MVF satellite cones and Makushin volcano. Instead, two component mixing models better fit the MVF geochemical array. Our Makushin results compare well with models of predominantly andesitic volcanoes that require mafic recharge to mobilize the andesites and trigger eruptions.

中文翻译：

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阿拉斯加马库申火山 3 次早期全新世喷发的岩石学和地球化学

阿拉斯加的 Makushin 成层火山在约 9292 年和 6215 年 yBP 之间产生了三次高度爆炸性的安山岩喷发。这些喷发被非正式地命名为 CFE（“火山口形成喷发”）、Nateekin 和 Driftwood Pumice，它们在现今的荷兰港港口和乌纳拉斯卡市地区沉积了大量的火山灰。本研究的重点是检查这些喷发的地球化学和岩石学，以更好地了解 Makushin 火山的危害、安山岩成因和由基性岩补给过程引发的喷发。CFE、Nateekin 和 Driftwood Pumice 样品的范围从玄武岩安山岩到英安岩，但主要是安山岩（SiO2 = 55.6 至 63.5 wt%）。CFE 沉积物在成分上略微分层，顶部 CFE 样品的镁铁质（55 至 60 wt% SiO2）比基底沉积物（58 至 60 wt% SiO2）略多。CFE、Nateekin 和 Driftwood Pumice 样品中的不平衡矿物成分和质地，结合两种辉石测温法和仅在 CFE 矿床顶部发现的富含 An 的斜长石微晶石 (An80)，为重复的镁铁质补给触发这些喷发提供了证据与先前的研究一致。我们将 Makushin 地球化学数据与来自先前研究的 Makushin 火山场 (MVF) 中选定卫星喷口和锥体的数据进行比较，以检查可能的遗传关系。在地壳储存条件（2 kbar，fO2 = Ni-NiO，以及 1.5 和 3.5 wt% H2O）下运行的地球化学数据和流纹岩-熔体模型表明，没有单一的母岩浆供应 MVF 卫星锥和 Makushin 火山。相反，两个组分混合模型更适合 MVF 地球化学阵列。