Yellowstone Plume Conduit Tilt Caused by Large‐Scale Mantle Flow

B Steinberger,W Wang,S P Grand,P L Nelson

doi:10.1029/2019gc008490

Abstract

AbstractMantle plumes are hot upwellings of rock thought to originate at the core‐mantle boundary. As they rise through the mantle, their conduits may become tilted due to lateral large‐scale mantle flow. Recent tomographic images have revealed a strongly tilted plume conduit starting at the core‐mantle boundary beneath northern Baja California rising toward the Yellowstone hot spot from the southwest. Here we perform numerical computations of plumes deflected in large‐scale mantle flow with the aim of finding if realistic model parameter ranges exist that yield a good fit with the tomographically observed conduit. We restrict ourselves to models that yield reasonable results for plume conduit tilt and hot spot motion globally. These models require high viscosity ≈1023 Pa s at some lower mantle depths. For a plume head reaching the surface 17 Ma, corresponding to the start of the Columbia River Basalts, our models require rise times ≈80 Myr or longer to match the tilt of the conduit observed by tomography. We used several tomography models to determine mantle density with almost all models predicting southwestward flow in the lowermost mantle beneath the western United States. Exact details of the shape of the predicted conduit's southwesterly tilt vary, depending on the density and viscosity structures we used. In many cases we find comparatively strong tilts in two depth ranges, in the upper and lower portions of the mantle, which is also a characteristic of the tomographically observed conduit. We expect that future models may help to constrain large‐scale flow by matching these corresponding depth ranges.

Highlights

Yellowstone—A Whole-Mantle Plume?Yellowstone National Park, with its geysers and other geothermal activity, and three large volcanic eruptions during the past ≈2 Myr, is often regarded as an intraplate hot spot caused by a deep mantle plume (Pierce & Morgan, 1992, 2009)
We have computed the shape of the Yellowstone plume conduit as the plume rises through the large-scale mantle flow field to see if the tilt magnitude and direction observed by Nelson and Grand (2018) is reasonable
In order to assess the variability and robustness of results, we varied a number of modeling parameters and assumptions: These include the age of the plume, the time it takes the plume head to rise through the mantle, buoyant rising speed of the plume conduit, and mantle density anomalies and mantle viscosity structure

Summary

Introduction

Yellowstone—A Whole-Mantle Plume?Yellowstone National Park, with its geysers and other geothermal activity, and three large volcanic eruptions during the past ≈2 Myr, is often regarded as an intraplate hot spot caused by a deep mantle plume (Pierce & Morgan, 1992, 2009). The Yellowstone plume may be older and the CRB caused by interaction of the plume conduit with the subducting slab (Wells et al, 2014) Despite these features, shown, Yellowstone is a somewhat atypical hot spot candidate: The CRB are rather small compared to other LIPs, and the largest eruption centers of the CRB are located 400 km away from the start of the Yellowstone hot spot track at the McDermitt Caldera. Its location is unusual: Whereas most hot spots (Thorne et al, 2004) classified as deep-rooted plumes, based on tomographic images (French & Romanowicz, 2015)—and corresponding LIP eruption locations (Torsvik et al, 2006) are associated with the margins of Large Low Shear Velocity Provinces (LLSVPs), the Yellowstone hot spot is located far from any LLSVP and instead is located in a region of recent subduction where an upwelling plume would have to circumvent sinking slabs.

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Conclusion