The Columbia River Plateau-Snake River Plain Large Igneous Province: Plume, Flux Melting or Both?

大陆上的基性火山活动为研究板块边界岩浆活动未采样的大部分地幔提供了一个关键窗口，是破译所有非海洋岩浆省地幔熔融过程的关键。地球的大部分？S表面是由这种类型的大陆岩浆作用形成的。羽流模型通常被用来解释这种岩浆活动，随着与这种起源不一致的特征被发现，它正日益受到攻击。哥伦比亚河高原(CRP) /蛇河平原（SRP）大火成岩省（LIP）具有许多特征，使羽流模型受到质疑。该项目旨在验证CRBG-SRP岩浆活动是否完全与地幔柱相关，还是多个过程的结果，包括上地幔的减压无水部分熔融，以及由于靠近大陆边缘而导致的区域控制通量熔融，其中地幔因俯冲而水化。这个为期三年的研究项目将涉及几个关键的分析领域：(i)从CRP和SRP组中选择样品进行40Ar/39Ar测年，为后续的地球化学工作和构造解释建立一个年代框架；（ii）薄片的岩石学和显微探针分析，以确定最适合进行主要和微量元素建模的样品，以确定熔化的程度和深度，同时也要注意任何分数结晶效应；（iii）通过傅里叶变换红外（FTIR）光谱和二次电离质谱（SIMS）测量含有橄榄石的熔体包裹体中H2O、CO2、S、F和Cl的初级熔体挥发性浓度，从“ii”中确定样品子集；（iv）用电子探针测量主元素，用激光烧蚀ICP-MS测量痕量元素，以确定在CRP/SRP LIP内以任何形式保存的最原始岩浆的组成；(v)测量一整套Nd， Sr，从两个省收集的40个样品的Pb和Hf同位素组成，以评估其可能与喷发量和岩石圈地幔厚度的关系。这项工作将与earthscope赞助的美国西北部大陆岩石圈演化的地球物理研究（USArray和板块边界观测站）以及目前在国际大陆科学钻探计划（ICDP）主持下钻探SRP的计划很好地吻合。

Mafic volcanism on continents provides a critical window to a large portion of the mantle not sampled by plate-boundary magmatism, and is key to deciphering the mantle melting processes of all nonoceanic magmatic provinces. Much of the Earth?s surface is made from this type of continental magmatism. The plume model, which is commonly invoked to explain such magmatism, is increasingly coming under attack as features inconsistent with such an origin are discovered. The Columbia River Plateau (CRP) / Snake River Plain (SRP) large igneous province (LIP) has numerous features that bring the plume model into question. This project is designed to test the hypothesis of whether CRBG-SRP magmatism is entirely plume-related or is the result of multiple processes, including decompression anhydrous partial melting of the upper mantle, and regionally controlled flux melting attributable to proximity to the continental margin where the mantle has been hydrated by subduction.This three-year research project will involve several key analytical areas: (i) 40Ar/39Ar dating of selected samples from the CRP and SRP suites to establish a chronologic framework for follow-up geochemical work, and for tectonic interpretations; (ii) petrographic and microprobe analysis of thin sections to identify samples best suited for major and trace element modeling to determine the degrees and depth of melting while also being mindful of any fractional crystallization effects; (iii) identify a subset of samples from 'ii' for measurements by Fourier transform infrared (FTIR) spectroscopy, and secondary ionization mass spectrometry (SIMS) of the primary melt volatile concentrations for H2O, CO2, S, F, and Cl in olivine-hosted melt inclusions; (iv) measurement of major elements by electron microprobe and trace elements by laser ablation ICP-MS on the same melt inclusions as those characterized for volatiles to identify the compositions of the most primitive magmas preserved in any form within the CRP/SRP LIP, and (v) measurement of a complete set of Nd, Sr, Pb and Hf isotopic compositions for 40 samples pooled from both subprovinces to assess any relationships there might be with eruption volumes and thickness of the lithospheric mantle. This work will dovetail nicely with EarthScope-sponsored geophysical studies of continental lithosphericevolution in the northwestern U.S. (USArray and the Plate Boundary Observatory), and also with plans currently on the drawing board to drill the SRP under the auspices of the International Continental Scientific Drilling Program (ICDP).