Abstract
Flood basalts appear to form during the initiation of hotspot magmatism. The Columbia River basalts (CRB) represent the largest volume of flood basalts associated with the Yellowstone hotspot, yet their source appears to be in the vicinity of the Wallowa Mountains1, about 500 km north of the projected hotspot track. These mountains are composed of a large granitic pluton intruded into a region of oceanic lithosphere affinity2. The elevation of the interface between Columbia River basalts and other geological formations indicates that mild pre-eruptive subsidence took place in the Wallowa Mountains, followed by syn-eruptive uplift of several hundred metres and a long-term uplift of about 2 km. The mapped surface uplift mimics regional topography, with the Wallowa Mountains in the centre of a ‘bull's eye’ pattern of valleys and low-elevation mountains. Here we present the seismic velocity structure of the mantle underlying this region and erosion-corrected elevation maps of lava flows, and show that an area of reduced mantle melt content coincides with the 200-km-wide topographic uplift. We conclude that convective downwelling and detachment of a compositionally dense plutonic root can explain the timing and magnitude of Columbia River basalt magmatism, as well as the surface uplift and existence of the observed melt-depleted mantle.
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Acknowledgements
We thank G. Goles for initial conversations regarding this manuscript. Funding for this work provided by National Science Foundation grants to J.J.R. and E.D.H. A review from M. Richards improved the manuscript. We thank J. Riker, D. Clippinger, C. Simmons and M. Giba for field assistance. We also thank N. Fay and J. Crosswhite for help with numerical analysis.
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Supplementary Figure 1
Digital elevation models showing the elevation of each surface interpolated from the current mapped extent of flow interfaces (black dots). The overlapping extent of each flow was then using areas that were well constrained with data and published thicknesses to create a composite surface (Fig 2). Dashed lines show the locations of cross sections. (PDF 2223 kb)
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Hales, T., Abt, D., Humphreys, E. et al. A lithospheric instability origin for Columbia River flood basalts and Wallowa Mountains uplift in northeast Oregon. Nature 438, 842–845 (2005). https://doi.org/10.1038/nature04313
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DOI: https://doi.org/10.1038/nature04313
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