Conduit diameter and buoyant rising speed of mantle plumes: Implications for the motion of hot spots and shape of plume conduits

Abstract

Mantle plumes are expected to be affected by large‐scale flow in the Earth's mantle related to plate motions, subducted slabs, and possibly large‐scale upwellings. Motion of plume conduits will depend on both large‐scale flow and buoyant rising speed of the conduit through the mantle. Here we present a model of depth‐dependent plume conduit temperature, viscosity, radius, and buoyant rising speed and use it to compute plume and hot spot motion. Results support a temperature anomaly of about 500 K at the plume base. In this case, sublithospheric temperature anomaly is about 150 K for the Iceland plume; transition zone anomaly is between 150 and 200 K for Iceland, about 250 K for Samoa, and about 300 K for Hawaii. Thermal plume radii are about 100 km in the upper mantle, increasing to about 200 km in the lower mantle. Beneath the lithosphere, viscosity in the vicinity of plumes is substantially reduced compared to the underlying mantle, and fast‐moving plates deflect plumes by 200 km or less, corresponding to a plume conduit buoyant rise time of about 3 Myr between 400 and 100 km depth, where most of the shear flow due to plate motions occurs. During 100 Myr, plume conduits rise buoyantly from about 1500–2000 km depth. In many cases, computed hot spot motion agrees with previous computations: south‐southeastward motion of the Hawaiian hot spot during the past 100 Myr, Louisville hot spot motion in a similar direction but at slower speed during the past 50 Myr, and westward motion of the Easter hot spot relative to Hawaii and Louisville. However, the previously computed substantial southward motion of the Kerguelen hot spot is not confirmed. If plume sources in the lowermost mantle are assumed to move with large‐scale flow, they are predicted to be displaced toward the two large‐scale upwellings beneath Africa and the Pacific relative to hot spot surface locations. For fixed sources, predicted tilts of the lower part of conduits tend to be opposite to that.

Subduction to the lower mantle – a comparison between geodynamic and tomographic models

“…The correlations are overall similar for all three models, but SMEAN-has somewhat worse performance because the slow anomalies are not predicted that well by mainly slab-driven models. SMEAN+, on the other hand, is almost identical to SMEAN correlations with st12den-1, consistent with the suggestion that we are matching fast A model where tilted mantle plumes with moving source at the CMB according to Becker and Boschi (2007) and based on the modeling procedure described in Steinberger and Antretter (2006) have been added to the slab model st12den-7.…”

“…Finally, because it appears that including upwellings that dynamically form in our model always deteriorates correlation, we consider a model where, instead, we include plumes with surface positions based on hotspots, and tilted plume conduits with moving source at the CMB, as in Boschi et al (2007Boschi et al ( , 2008, based on the modeling approach of Steinberger and Antretter (2006). We find that in this case (Fig.…”

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“…These primary hotspots show very different motions, resulting in increased interhotspot motions, as predicted by mantle flow model calculations (Steinberger, 2002;Steinberger et al, 2004;Koppers et al, 2004;Steinberger and Antretter, 2006;Steinberger and Calderwood, 2006). …”

“…In these models a large-scale mantle flow field is first calculated from mantle density heterogeneities (as derived from seismic S-wave speed anomalies) by applying a radial mantle rheology structure (with a lower mantle assumed to be more viscous) and by using tectonic plate motions as boundary conditions (Steinberger and O'Connell, 2000;Steinberger and Calderwood, 2006). Within the modeled mantle flow field, then, a vertical plume conduit is inserted that gets advected over time, resulting in the sometimes strong tilting of man-tle plumes and the drifting of hotspots (Steinberger and O'Connell, 2000;Steinberger and Antretter, 2006). Advection dominates the motion of a plume at depths where it rises relatively slowly in comparison to the overall mantle flow field, typically in the lower mantle.…”

New Constraints on Temporal Variations in Hawaiian Plume Buoyancy Flux

“…Previous estimates of the plume flux have assumed constant Pacific plate motion over a stationary plume, despite studies that suggest changes in the motion of the Pacific plate [O'Connor et al, 2013] and of the plume itself [Steinberger & O'Connell, 1998;Steinberger & Antretter, 2006;Tarduno et al, 2003;. Both movements result in a change of the observed motion of the plate relative to the underlying plume, which is a key parameter that determines the rate at which plume material accumulates beneath the plate [Christensen & Ribe, 1994], forming the swell.…”