Geochemical Investigation of Paleocene-Eocene Seafloor Volcanism in the Oregon Coast Range: Products of the Yellowstone Hot Spot?

最近的地球物理数据表明，俄勒冈海岸山脉的厚度可达30公里，其地震结构与海洋高原，洪水玄武岩省相似。OCR苦橄岩中橄榄石的初步He分析表明其为深部地幔柱源。真空破碎的OCR苦橄岩的3He/4He比值（R/Ra 13.0）与蛇河平原熔岩和黄石热点最近的产物的3He/4He比值重叠。该样品的核聚变实验证明，高的3He/4He比值不是宇宙成因的，是苦橄辉岩地幔来源的标志。大量的火山活动和高3He/4He比率是有趣的证据，表明黄石火山对OCR火山活动有贡献，因此，至少从64 Ma以来一直活跃。为了进一步验证这一假设，我们提出对OCR玄武岩进行Sr、Nd、Pb、Ar、He和O同位素的联合研究。我们将重点研究来自Roseburg和Siletz河地层的火山岩：1)确定这些OCR玄武岩的地幔源组成，并评估它们与黄石地幔柱的关系；2)将火山活动的年龄和持续时间限制在OCR范围内。我们还将完成OCR主要元素和微量元素的详细研究，以评估区域融化条件（深度和数量），以了解可能的构造背景的空间分布。

9418458 Pyle Recent geophysical data suggest the Oregon Coast Range reaches thicknesses as great as 30 km and its seismic structure is similar to oceanic plateau, flood basalt provinces. Preliminary He analyses of olivine from an OCR picrite indicate a deep mantle plume source. The 3He/4He ratios of an OCR picrite crushed in vacuo (R/Ra 13.0) overlaps values found for Snake River Plain lavas and more recent products of the Yellowstone hotspot. Fusion experiments on this sample prove that the high 3He/4He ratio is not cosmogenic, and is a signature of the mantle source of the picrite. Voluminous volcanism and high 3He/4He ratios are intriguing evidence that the Yellowstone hospot contributed to OCR volcanism, and therefore, has been active since at least 64 Ma. To further test this hypothesis, we propose a combined Sr, Nd, Pb, Ar, He, and O isotopic study of the OCR basalts. We will focus on volcanic rocks from the Roseburg and Siletz River formations to: 1) determine the mantle source composition for these OCR basalts and evaluate their relationship to the Yellowstone plume; 2) constrain the age and duration of volcanism within the OCR. We will also complete a detailed major and trace element study of the OCR to evaluate regional melting conditions (depth and amount) to understand the spatial distributions of possible tectonic settings.