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

大陆上的基性岩火山活动提供了一个重要的窗口，大部分的地幔不采样板边界岩浆作用，是关键的破译所有非海洋岩浆省份的地幔熔融过程。地球的大部分？地球表面就是由这种大陆岩浆作用形成的。通常用来解释这种岩浆活动的地幔柱模型，由于发现了与这种起源不一致的特征，正日益受到攻击。哥伦比亚河高原（CRP）/斯内克河平原（SRP）大火成岩省（LIP）有许多特点，使烟羽模型的问题。该项目旨在验证CRBG-SRP岩浆活动是否完全与地幔柱有关或是多种过程的结果，包括上地幔减压无水部分熔融，以及可归因于大陆边缘附近地幔因俯冲而水化的区域控制的通量熔融。该三年研究项目将涉及几个关键分析领域：㈠对CRP和SRP套件中选定的样品进行40 Ar/39 Ar年代测定，以便为后续地球化学工作和构造解释建立年代框架; ㈡对薄片进行岩相学和微探针分析，以确定最适合进行主元素和微量元素建模的样品，从而确定熔融程度和深度，同时也注意到任何分离结晶效应;（iii）从“ii”中确定一个样本子集，用于通过傅里叶变换红外（FTIR）光谱和二次电离质谱（西姆斯）测量橄榄石托管熔体包裹体中H2O、CO2、S、F和Cl的初始熔体挥发物浓度;（iv）用电子探针测量主要元素，用激光烧蚀ICP-对与挥发分特征相同的熔体包裹体进行MS，以确定CRP/SRP LIP中以任何形式保存的最原始岩浆的成分，以及（v）测量一套完整的Nd，Sr，铅和铪同位素组成的40个样品汇集从两个次省，以评估任何关系，可能有喷发量和岩石圈地幔厚度。这项工作将很好地配合地球探测器赞助的美国西北部大陆岩石圈演化的地球物理研究（美国阵列和板块边界观测站），也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).