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

这项提议是为了对阿拉斯加普里比洛夫群岛的火山活动进行综合野外、40Ar/39Ar测年、地球化学、同位素和岩石学研究。两个主要的普里比洛夫群岛，圣保罗和圣乔治，是研究很少的白令海玄武岩省(BSBP)的关键火山田。BSBP是“扩散火成岩省”的一个例子，这是一种新发现的板内火山活动类型，但人们对此知之甚少。之所以选择普里比洛夫群岛进行这项研究，是因为它们允许在岩石圈厚度和成分、离阿留申弧前的距离和其他构造因素基本上不变的情况下调查两个主要的BSBP火山田。这反过来又允许评估是否存在由于诸如构造演化、涉及岩浆作用的地幔和地壳物质平衡以及岩浆储集层和管道系统等因素而导致的中心演化的差异。该项目的具体目标是：1)通过详细的地质填图、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)通过对年龄受到很好限制的样品进行地球化学分析，确定成分的任何时间趋势；3)确定岛屿上断层的几何形状和时间，及其对喷发活动和不同喷口类型定位的影响；获得适当完整的火山岩和包体的化学(XRF和电感耦合等离子体质谱)、同位素(锶、钕、铅、氧)和岩石学数据，以约束地幔、地壳源岩和母岩的性质，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群岛上重要的人类和野生动植物社区。值得注意的是，这些岛屿拥有地球上最大的阿留申群落，是世界上超过一半的北方毛海豹的季节性繁殖地，也是近300万只海鸟的筑巢地点。这些人口在岛屿之间分布的差异可能反映了该地区更新世至全新世火山作用和断层作用的时间和迁移。因此，更好地了解普里比洛夫群岛的地质演变将有助于更深入地了解对每个岛屿不同的地貌及其不同的野生动物和人类种群的主要控制。

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.