Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc
Eocene to Pleistocene magmatic evolution of the Delarof Islands, Aleutian Arc
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阿留申岛弧德拉罗夫群岛始新世至更新世岩浆演化
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发表时间：
2016
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通讯作者：
A. Tibbetts
中科院分区：
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作者：
A. Schaen;B. Jicha;S. Kay;B. Singer;A. Tibbetts
位于西经 179° 附近的阿留申群岛弧上的德拉罗夫群岛记录了大约 3700 万年的不连续弧岩浆活动，沿着从海沟附近到活火山前缘的西南-东北跨弧横断面。该地区更新世前火山记录的地球化学和地质年代学数据有限，这里提供的 40Ar/39Ar、同位素和微量元素数据是第一个来自比更新世-全新世火山（Tanaga、Gareloi）更古老的单位的数据。 22 个新的 40Ar/39Ar 年龄建立了地球化学数据的时间框架，并揭示了德拉罗夫地区的岩浆活动与晚始新世/早渐新世和晚中新世/上新世的两次弧宽岩浆爆发同时发生。德拉罗夫群岛南部的镁铁质熔岩和岩体给出的 40Ar/39Ar 高原年龄范围为阿马提尼亚克岛的 36.8±±0.2 至 26.9±±0.6 Ma，乌拉克岛的 37.0±±0.2 至 29.3±±1.0 Ma。向北25公里处，德拉罗夫群岛中部、卡瓦尔加岛、奥柳加岛和斯卡古尔岛的40Ar/39Ar年龄为晚中新世（6.28±0.04 Ma）至上新世（4.77±0.18 Ma），东北部年龄较年轻。更新世期间，弧化学发生了重大转变，与靠近海沟的旧德拉罗夫岛单元相比，来自活火山 Gareloi 和 Tanaga 的熔岩表现出更高的沉积物和含水流体特征（Th/La、Cs/Ta、La/Sm、LILE 丰度）和更低的 143Nd/144Nd。从阿姆奇特卡到埃达克的始新世-中新世熔岩中的类似发现表明，先前较小的沉积物熔融成分在第四纪变得更加明显。
The Delarof Islands in the Aleutian Arc near 179º W record ∼37 million years of discontinuous arc magmatism along a SW‐NE cross‐arc transect from near the trench to the active volcanic front. Geochemical and geochronologic data from the pre‐Pleistocene volcanic record in this region are limited and the 40Ar/39Ar, isotopic, and trace element data presented here are the first from units older than the Pleistocene‐Holocene volcanoes (Tanaga, Gareloi). Twenty‐two new 40Ar/39Ar ages establish a temporal framework for geochemical data and reveal that magmatism in the Delarof region was coincident with two arc‐wide magmatic flare ups in the late Eocene/early Oligocene and latest Miocene/Pliocene. Mafic lavas and plutons in the southern Delarofs give 40Ar/39Ar plateau ages ranging from 36.8 ± 0.2 to 26.9 ± 0.6 Ma on Amatignak Island and 37.0 ± 0.2 to 29.3 ± 1.0 Ma on Ulak Island. To the north 25 km, 40Ar/39Ar ages from the central Delarof Islands, Kavalga, Ogliuga, and Skagul are late Miocene (6.28 ± 0.04 Ma) to Pliocene (4.77 ± 0.18 Ma) with younger ages to the northeast. A significant transition in arc chemistry occurs in the Pleistocene where lavas from active volcanoes Gareloi and Tanaga exhibit higher sediment and hydrous fluid signatures (Th/La, Cs/Ta, La/Sm, LILE abundances) and lower 143Nd/144Nd than older Delarof Island units closer to the trench. Similar findings from Eocene‐Miocene lavas from Amchitka to Adak suggest that a previously minor sediment melt component became more pronounced in the Quaternary.