Yellowstone Plume Conduit Tilt Caused by Large‐Scale Mantle Flow

Abstract

Mantle 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 ≈10 23 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.

Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle

“…In addition, subducting slabs may require up to ∼200 Ma to descend to the bottom of the mantle (Domeier et al., 2016; van der Meer et al., 2010), and it may take another few tens to ∼100 Ma for slab materials to rise to the surface in upwelling plumes. (Such estimates for plume transit times across the mantle—obtained from the plume fluxes as listed (Table ) and a diameter of 100–200 km for the central part of the conduit through which most of the flux occurs—are similar to estimates of plume head rise time (Steinberger et al., 2019; Torsvik et al., in press), and should not be much longer in duration because the conduit would then disconnect from the plume head.) Therefore, even in the limiting case where subducted material is returned to the surface immediately after reaching the bottom of the mantle, some delay (up to ∼300 Ma) is expected between subduction and the appearance of recycled crustal materials in hotspot lavas, and an even longer delay is expected if the subducted materials remain at the bottom of the mantle for any length of time (i.e., a long residence in the mantle for at least some recycled crust is suggested by geochemical signals in OIB; Cabral et al., 2013; Castillo et al., 2018; Chauvel et al., 1992; Eisele et al., 2002; Galer et al., 1985; Hanyu et al., 2011; Hart, 1984; Hauri & Hart, 1993; Hofmann, 2014; Hofmann & White, 1982; Stracke, 2012).…”

“…For each of the four global seismic models, we employ a plume advection model (Steinberger & O'Connell, 1998; Steinberger et al., 2019) to explore how plumes tilt as they upwell through the mantle, which allows us to infer the location of a mantle plume conduit at the core‐mantle boundary (CMB) (Text in supporting information). In order to illustrate the effect of choice of seismic model on conduit paths, conduits are shown beneath all hotspots for all four seismic models in Figure 1.…”

“…For example, the Yellowstone plume is not easily identifiable in any of the four global tomographic models considered; Yellowstone in fact shows the second shortest conduit extent (∼0.25) among the 58 hotspots examined (Figure 2). However, the higher resolution afforded by US Array permitted resolution of the Yellowstone plume in a regional seismic model (Nelson & Grand, 2018), and the imaged plume conduit matches dynamic models for the lateral advection of the plume (Steinberger et al, 2019). The Yellowstone case thus suggests that we cannot exclude the presence of plumes for the 28 hotspots where global seismic models do not resolve a plume (Figure 2) because future, higher‐resolution tomography may yet reveal a deep conduit connection.…”

“…(2019) traced high‐ 3 He/ 4 He hotspot associated plumes and concluded that the high 3 He/ 4 He source region is restricted to the LLSVPs. However, that study excluded Yellowstone, which is a high 3 He/ 4 He hotspot with a likely deep source underneath the Americas (Nelson & Grand, 2018; Steinberger et al., 2019), suggesting high 3 He/ 4 He material is in fact not restricted to the LLSVPs.…”

The Case for a Long-Lived and Robust Yellowstone Hotspot

“…Proponents of a shallow-mantle origin for the Yellowstone hotspot have suggested a variety of mechanisms that include rift propagation (Christiansen et al, 2002), the lateral migration of lithospheric extension (Foulger et al, 2015), and eastward mantle flow driven by sinking of the Farallon slab (Zhou et al, 2018). Other workers attribute the hotspot trend to plate motion over a deep-seated mantle plume (e.g., Hooper et al, 2007, and references therein), an origin reinforced by recent seismic tomography that resolves the Yellowstone hotspot as a high-temperature, low-density conduit that extends through the lower mantle and is sourced at the coremantle boundary (Nelson and Grand, 2018;Steinberger et al, 2019). An energetic plume is suggested by peak excess temperatures of 650-850 °C through the lower mantle (Nelson and Grand, 2018), and by an estimated range in volume flux through the upper mantle of 15 m 3 s -1 to 31 m 3 s -1 (Camp, 2019).…”