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，研究陆源浊积岩融化对弧熔岩中高场强元素（HFSE）丰度和Hf同位素组成的影响。Amlia断裂带（AFZ）比阿留申海沟的其他地方含有更多的沉积物，并将异常数量的沉积物和水直接输送到地幔。太平洋板块的斜向俯冲使AFZ沿着弧形锋面向西移动，先后在大约550万年前、250万年前和100万年前将沉积物和流体脉冲俯冲到Chuginadak岛、Yunaska岛和Seguam岛下面。来自Atka岛的熔岩尚未接收到来自AFZ的沉积物和流体峰值，提供了控制成分。选择阿留申群岛的这一剖面是因为Seguam和Yunaska火山的Sr和Pb同位素组成明显比Atka火山更具有放射性。本研究拟检测这些岛屿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了这些熔岩。由于这种沉积物的添加是在空间和时间上离散的尖峰，因此熔岩中铪元素特征的时间变化限制了高强度强硒向弧岩浆转移的持续时间。由于阿留申群岛的几个火山复群的年龄和岩石成因从未被调查过，因此该项目将对了解这一活跃弧做出重大贡献。该项目将在高丽大学建立PI的研究项目，PI将成为女学生的榜样。该项目将支持Katrina Pekar女士的研究生培训，并部分支持David Bridges先生的研究生培训。该项目将促进KSU地质系与其他机构之间的国内和国际合作。这些合作的一个重要方面包括培训研究生使用KSU （ICP-MS）或堪萨斯州目前没有的分析技术（40Ar/39Ar地质年代学，MC-ICPMS和TIMS的同位素分析）。研究结果将通过国家会议、手稿出版和阿留申弧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.