A Natural Experiment to Examine Hafnium Mobility in Subduction Zones

该项目旨在利用阿留申弧中部作为一个自然实验来考察陆源浊积岩熔体对弧熔岩中高场强元素丰度和Hf同位素组成的影响。AMLia断裂带(AFZ)包含的沉积物比阿留申海沟中的其他地方更大，并将异常数量的沉积物和水直接输送到地幔。太平洋板块的倾斜俯冲使AFZ沿着弧前向西移动，随后分别在约5、2.5和100万年前的丘吉纳达克岛、尤纳斯卡岛和塞冈岛下俯冲了一波沉积物和流体脉冲。来自阿特卡岛的熔岩提供了对照成分，该岛尚未收到来自AFZ的沉积物和流体尖峰。之所以选择这段阿留申火山，是因为塞冈火山和尤纳斯卡火山的锶和铅同位素组成明显比阿特卡火山具有更强的放射性。这项研究建议研究这些岛屿15个熔岩中HFSE和Hf同位素组成的变化，以测试岩浆源中由俯冲断裂带输送的沉积物脉冲是否影响这些熔岩。由于这种沉积物添加是作为一个在空间和时间上离散的尖峰发生的，熔岩中Hf特征的时间变化限制了HFSE向弧状岩浆转移的持续时间。由于阿留申山脉中几个火山杂岩的年龄和岩石成因从未被研究过，该项目将对了解这一活动弧度做出重大贡献。该项目将在KSU建立PI的研究计划，在那里PI为女学生提供一个榜样。该项目将支持Katrina Pekar女士的研究生培训，并部分支持David Bridges先生的培训。该项目将促进KSU地质系和其他机构之间的国家和国际合作。这些合作的一个重要方面包括培训研究生使用KSU(电感耦合等离子体质谱仪)或堪萨斯州目前没有的分析技术(40Ar/39Ar年代学、MC-ICPMS和TIMS的同位素分析)。这项研究的结果将通过国家会议、手稿出版和阿留申弧线数据系统档案与地质界分享。

This project is designed to use the central Aleutian arc as a natural experiment to examine the influence that melts of terrigenous turbidites has upon the abundances of high field strength elements (HFSE) and Hf isotopic compositions in arc lavas. The Amlia Fracture Zone (AFZ) contains sediment in greater volume than elsewhere in the Aleutian trench and delivers anomalous quantities of sediment and water directly to the mantle. Oblique subduction of the Pacific plate has moved the AFZ westward along the arc front, sequentially subducting a pulse of sediment and fluid beneath the islands of Chuginadak, Yunaska and Seguam circa 5, 2.5 and 1 million years ago, respectively. Lavas from Atka Island, which has not yet received the sediment and fluid spike from the AFZ provides control compositions. This section of the Aleutians was selected because Sr and Pb isotopic compositions are markedly more radiogenic at Seguam and Yunaska volcanoes than at Atka. This study proposes to examine the variation of HFSE and Hf isotopic compositions in fifteen lavas from these islands to test whether a pulse of sediment in the magma source, delivered by a subducted fracture zone, affected these lavas. Because this sediment addition occurred as a spatially and temporally discrete spike, temporal variation in the hafnium characteristics of the lavas constrains the duration of HFSE transfer to arc magmas. Because the ages and petrogenesis of several of the volcanic complexes in the Aleutians has never been investigated, this project will contribute significantly to the understanding of this active arc. This project will establish the research program of the PI at KSU, where the PI provides a role model for women students. The project will support the graduate training of Ms. Katrina Pekar and partially support that of Mr. David Bridges. The project will foster national and international collaborations between the KSU geology department and other institutions. An important aspect of these collaborations includes training graduate students in the use of analytical techniques not currently available at KSU (ICP-MS) or in the state of Kansas (40Ar/39Ar geochronology, isotope analysis by MC-ICPMS and TIMS). The results of the study will be shared with the geologic community through national meetings, manuscript publication and archive on the Aleutian Arc Data System.