Evolution of Intraplate Volcanism in a Diffuse Igneous Province: A Case Study of the Pribilof Islands, Alaska

本项目拟对阿拉斯加Pribilof群岛的火山活动进行40Ar/39Ar定年、地球化学、同位素和岩石学研究。两个主要的普里比洛夫岛，圣保罗岛和圣乔治岛，是研究很少的白令海玄武岩省（BSBP）的关键火山场。BSBP是“扩散火成岩省”的一个例子，这是一种新发现的、对板内火山作用知之甚少的类型。之所以选择Pribilof群岛进行这项研究，是因为它们可以在岩石圈厚度和组成、与阿留申弧前缘的距离以及其他构造因素基本不变的情况下，对两个主要的BSBP火山场进行调查。这反过来又可以评估由于结构演化、岩浆活动中涉及的地幔和地壳物质平衡、岩浆储层和管道系统等因素，是否在中心演化中存在差异。该项目的具体目标是：1)通过详细的地质测绘、采样和40Ar/39Ar测年，记录普里比洛夫群岛的火山和地质演化；2)通过地球化学分析确定样品组成的时间趋势，这些样品的年龄受到很好的限制；3)确定岛屿上断裂的几何形状和时间及其对喷发活动和不同喷口类型定位的影响；4)获得相应完整的火山岩及其包体化学（XRF和ICP-MS）、同位素（Sr、Nd、Pb和O）和岩石学数据，从而约束地幔和地壳源岩和母岩浆的性质，估计部分熔融程度，确定岩浆的成因。这项工作的一个重要方面是，有几个广泛的影响远远超出了对火山岩岩石学的理解。这些影响来自普里比洛夫岛上重要的人类和野生动物群落。值得注意的是，这些岛屿拥有地球上最大的阿留申社区，是世界上一半以上的北方海豹的季节性繁殖地，也是近300万只海鸟的筑巢地。这些种群分布的差异可能反映了该地区更新世到全新世火山活动和断裂活动的时间和迁移。因此，更好地了解普里比洛夫群岛的地质演化，将有助于更深入地了解每个岛屿的不同地貌及其不同的野生动物和人类种群的主要控制因素。

This proposal is for an integrated field, 40Ar/39Ar dating, geochemical, isotopic, and petrologic study of volcanism in the Pribilof Islands, Alaska. The two principal Pribilof Islands, St. Paul and St. George, are key volcanic fields in the little studied Bering Sea basalt province (BSBP). The BSBP is an example of a 'diffuse igneous province,' a newly recognized and poorly understood type of intraplate volcanism. The Pribilof Islands have been selected for this study because they allow investigation of two major BSBP volcanic fields in a setting where factors such as lithospheric thickness and composition, distance from the Aleutian arc front, and other tectonic factors are essentially constant. This in turn allows assessment of whether differences exist in the evolution of the centers due to factors such as structural evolution, mantle and crustal mass balance involved in magmatism, and magma reservoirs and plumbing systems. The specific objectives of the project are to 1) document the volcanic and geologic evolution of the Pribilof Islands through detailed geologic mapping, sampling, and 40Ar/39Ar dating; 2) identify any temporal trends in composition through geochemical analyses of samples whose ages are well constrained; 3) determine the geometry and timing of faulting on the islands and its influence on eruptive activity and localization of distinct vent types; and 4) obtain suitably complete chemical (XRF and ICP-MS), isotopic (Sr, Nd, Pb, and O), and petrologic data for the volcanic rocks and included xenoliths so that the nature of the mantle and crustal source rocks and parent magmas can be constrained, the degrees of partial melting estimated, and the petrogenesis of the magmas determined. A significant aspect of this work is that there are several broad impacts that extend well beyond understanding the petrology of the volcanic rocks. These impacts draw from the important human and wildlife communities on the Pribilof islands. Notable aspects are that the islands host the largest Aleut communities on earth, are the seasonal breeding grounds for over half of the world's northern fur seals, and are the nesting sites for nearly three million seabirds. It is likely that differences in the distributions of these populations among the islands reflect the timing and migration of Pleistocene to Holocene volcanism and faulting in the region. Better understanding of the geologic evolution of the Pribilof Islands will therefore permit greater insight into the dominant controls on the contrasting geomorphology of each island and their contrasting wildlife and human populations.