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

9418458派尔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，其地震结构类似于大洋高原、洪水泛滥的玄武岩省。对OCR苦味石中橄榄石的初步分析表明，它来自深部地幔热柱。在真空中粉碎的OCR苦味岩的3He/4He比值(R/Ra为13.0)与蛇河平原熔岩和黄石热点较新产品的3He/4He比值重叠。在该样品上的聚变实验证明，高的3He/4He比值不是宇宙成因的，而是苦铁矿的地幔来源的特征。巨大的火山活动和高的3He/4He比值是黄石火山活动的有趣证据，因此，至少自以来就一直活跃。为了进一步验证这一假说，我们建议对OCR玄武岩进行锶、钕、铅、Ar、He和O同位素联合研究。我们将重点研究Roseburg和Siletz河组的火山岩，以：1)确定这些OCR玄武岩的地幔来源成分，并评估它们与黄石柱的关系；2)限制OCR内火山活动的年龄和持续时间。我们还将完成OCR的详细常量和微量元素研究，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.