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

大陆上的镁铁质火山作用为了解大部分未被板块边界岩浆作用采样的地幔提供了一个关键窗口，也是破译所有非大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。通常被引用来解释这种岩浆作用的羽流模型，随着与这种起源不一致的特征被发现，正越来越多地受到攻击。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，对羽流模型提出了质疑。该项目旨在检验CRBG-SRP岩浆作用是否完全与地柱有关，或者是多个过程的结果，包括减压、上地幔无水部分熔融和由于接近大陆边缘而被俯冲水化而导致的区域控制的通量熔融。这项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套系中选取的样品进行40Ar/39Ar测年，以建立后续地球化学工作和构造解释的年代学框架；(Ii)对薄片进行岩相学和微探针分析，以确定最适合于主元素和微量元素模拟的样品，以确定熔融的程度和深度，同时还要注意任何分离结晶效应；(Iii)确定用于通过傅立叶变换红外光谱(FTIR)和二次电离质谱仪(SIMS)测量橄榄石熔体包裹体中H2O、CO2、S、F和Cl的初级熔体挥发浓度的样品子集；(4)用电子探针测量常量元素，用激光烧蚀电感耦合等离子体质谱(ICPMS)测量与挥发分特征相同的熔融包裹体上的微量元素，以确定以任何形式保存在CRP/SRP LIP中的最原始岩浆的成分，以及(V)测量来自这两个省的40个样品的全套Nd、Sr、Pb和Hf同位素组成，以评估它们可能与岩石圈地幔喷发体积和厚度的任何关系。这项工作将与EarthScope赞助的关于美国西北部大陆岩石圈演化的地球物理研究(USArrow和板块边界天文台)很好地吻合，也将与目前在国际大陆科学钻探计划(ICDP)主持下钻探SRP的计划相吻合。

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).