New 40Ar/39Ar and whole-rock geochemical data are used to develop a detailed eruptive chronology for Akutan volcano, Akutan Island, Alaska, USA, in the eastern Aleutian island arc. Akutan Island (166°W, 54.1°N) is the site of long-lived volcanism and the entire island comprises volcanic rocks as old as 3.3 Ma. Our current study is on the 225 km2 western half of the island, where our results show that the focus of volcanism has shifted over the last ∼700 k.y., and that on occasion, multiple volcanic centers have been active over the same period, including within the Holocene. Incremental heating experiments resulted in 56 40Ar/39Ar plateau ages and span 2.3 Ma to 9.2 ka.Eruptive products of all units are primarily tholeiitic and medium-K, and range from basalt to dacite. Rare calc-alkaline lavas show evidence suggesting their formation via mixing of mafic and evolved magmas, not via crystallization-derived differentiation through the calc-alkaline trend. Earliest lavas are broadly dispersed and are almost exclusively mafic with high and variable La/Yb ratios that are likely the result of low degrees of partial mantle melting. Holocene lavas all fall along a single tholeiitic, basalt-to-dacite evolutionary trend and have among the lowest La/Yb ratios, which favors higher degrees of mantle melting and is consistent with the increased magma flux during this time. A suite of xenoliths, spanning a wide range of compositions, are found in the deposits of the 1.6 ka caldera-forming eruption. They are interpreted to represent completely crystallized liquids or the crystal residuum from tholeiitic fractional crystallization of the active Akutan magma system.The new geochronologic and geochemical data are used along with existing geodetic and seismic interpretations from the island to develop a conceptual model of the active Akutan magma system. Collectively, these data are consistent with hot, dry magmas that are likely stored at 5–10 km depth prior to eruption. The prolonged eruptive activity at Akutan has also allowed us to evaluate patterns in lava-ice interactions through time as our new data and observations suggest that the influence of glaciation on eruptive activity, and possible magma composition, is more pronounced at Akutan than has been observed for other well-studied Aleutian volcanoes to the west.

中文翻译：

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美国阿拉斯加东部阿留申群岛长寿阿库坦火山的喷发历史，岩浆演化和冰川冰的影响

使用新的40Ar / 39Ar和全岩石地球化学数据来为美国阿留申群岛弧形山脉的阿拉斯加阿库坦岛，美国阿拉斯加的阿库坦火山制定详细的喷发年代。Akutan岛（西经166°W，北纬54.1°N）是长寿命的火山活动地点，整个岛上都包含早于3.3 Ma的火山岩。我们目前的研究是在该岛西半部225平方公里的地方进行的，研究结果表明，火山活动的重心已转移到最后一个约700 ky，并且有时在同一时期（包括全新世。增量加热实验导致56个40Ar / 39Ar平台期，跨度从2.3 Ma到9.2 ka。所有单位的喷发产物主要是高钾和中等K，范围从玄武岩到钠铁矾。稀有的钙碱性熔岩显示出证据表明它们是通过镁铁质岩浆和演化的岩浆混合形成的，而不是通过钙碱性趋势通过结晶衍生的分化而形成的。最早的熔岩分布广泛，几乎完全是镁铁质岩体，La / Yb比率较高且变化不定，这很可能是部分地幔融化程度较低的结果。全新世的熔岩全部沿单一的玄武岩-达克特演化趋势下落，并且具有最低的La / Yb比率，这有利于更高的地幔熔融程度，并且与这段时间的岩浆通量增加是一致的。在1.6 ka火山口形成喷发的沉积物中发现了一系列涵盖多种成分的异种石。它们被解释为代表了活跃的Akutan岩浆系统的硫级分结晶的完全结晶的液体或结晶残渣。使用新的年代学和地球化学数据以及该岛现有的大地测量和地震解释来开发活跃的Akutan的概念模型岩浆系统。总的来说，这些数据与可能在喷发前储存在5-10 km深度的干热岩浆一致。由于我们的新数据和观测结果表明，冰川对喷发活动和可能的岩浆成分的影响在阿库坦更为明显，因此，阿库坦的长期喷发活动还使我们能够评估熔岩与冰相互作用的模式。西部其他经过深入研究的阿留申火山。