Viscous flow within the Earth's mantle
ultimately drives plate tectonics and most of the time-dependent
geological deformation that we observe at the Earth's
surface. Seismic constraints on mantle structure, coupled with
improved computational abilities, have allowed us to constrain
patterns of flow presently occurring in the Earth's mantle. My
research group has been constraining such models of global
mantle flow using various geological and geophysical
observations. This effort has led to a greater understanding of
how surface tectonic and mantle dynamics interact to drive
geological deformation and modulate mantle convection.
Observations of Global Mantle Flow
The tectonic plates are part of the mantle, and their
motions represent the surface expression of the mantle deformation
occurring beneath them. We have explored the link between plate motions and
mantle flow in a variety of ways.
Global Tectonics and Mantle Flow
Crameri‡, F., C.P. Conrad, L. Montési, and C.R. Lithgow-Bertelloni (2019) The dynamic life of an oceanic plate,
Tectonophysics, 760, 107-135, doi:10.1016/j.tecto.2018.03.016.
[Torsvik Special Issue]
- Becker, T.W., A.J.
Schaeffer, S. Lebedev, and C.P. Conrad (2015), Toward a generalized plate motion reference
frame, Geophysical Research Letters, 42,
- Conrad, C.P., B. Steinberger, and T.H.
Torsvik (2013), Stability of active mantle upwelling revealed
by net characteristics of plate tectonics, Nature,
498, 479-482, doi:10.1038/nature12203.
[Comment and Reply, reprint ]
- Combes, M., C. Grigné, L. Husson, C.P. Conrad,
S. Le Yaouanq, M. Parenthoën, C. Tisseau, and J. Tisseau (2012),
Multiagent simulation of evolutive plate
tectonics applied to the thermal evolution of the
Earth, Geochemistry, Geophysics, Geosystems,
13, Q05006, doi:10.1029/2011GC004014.
- van Summeren‡, J., C.P. Conrad, and
C. Lithgow-Bertelloni (2012), The importance of
slab pull and a global asthenosphere to plate
motions, Geochemistry, Geophysics, Geosystems,
13, Q0AK03, doi:10.1029/2011GC003873.
- Steiner†, S.A., and
C.P. Conrad (2007), Does active
mantle upwelling help drive plate motions?,
Physics of the Earth and Planetary Interiors, 161,
Stresses from mantle flow can cause uplift or subsidence at
the Earth's surface. In a continental region, dynamic topography can
cause regional transgression or regression events as as the land
surface moves relative to sea level. If an oceanic region, dynamic
topography changes the volume of the ocean basins, and can cause
eustatic sea level change. Observations of uplift and subsidence are
prevalent in the geologic record, and therefore useful for
constraining past dynamic topography.
Steinberger, B., C.P. Conrad, A. Osei Tutu, and M.J. Hoggard (2019) On the amplitude of dynamic topography at spherical harmonic degree two,
Tectonophysics, 760, 221-228, doi:10.1016/j.tecto.2017.11.032.
[Torsvik Special Issue]
Watkins†, C.E., and C.P. Conrad (2018), Constraints on dynamic topography from
asymmetric subsidence of the mid-ocean ridges,
Earth and Planetary Science Letters, 484,
- Conrad, C.P., and L. Husson (2009), Influence of dynamic topography on sea level
and its rate of change, Lithosphere, 1,
[dynamic topography model]
- Husson, L., and C.P. Conrad (2006), Tectonic velocities, dynamic topography, and relative sea level, Geophysical Research Letters, 33, L18303, doi:10.1029/2006GL026834.
- Conrad, C.P., C. Lithgow-Bertelloni, and
K.E. Louden (2004), Iceland, the Farallon slab,
and dynamic topography of the North Atlantic, Geology,
32, 177-180, doi:10.1130/G20137.1
- Conrad, C.P., and M. Gurnis (2003), Mantle flow, seismic tomography and the breakup of Gondwanaland: Integrating mantle convection backwards in time, Geochemistry, Geophysics, Geosystems, 4, 1031, doi:10.1029/2001GC000299.
When subjected to shearing deformation, olivine grains in the Earth's
upper mantle acquire a texture that can be detected using seismic
observations. This texture is called seismic anisotropy, and
it can be used to constrain the pattern of mantle deformation that
produced it. The texture may also be viscously anisotropic, which can
affect deformation. We have developed models of mantle flow that we have
been able to link directly to observations of seismic anisotropy.
Anisotropy and Asthenosphere Deformation
Hansen, L.N., C.P. Conrad, Y. Boneh, P. Skemer, J.M. Warren, and D.L. Kohlstedt (2016), Viscous anisotropy of textured olivine
aggregates, Part 2: Micromechanical model, Journal
of Geophysical Research, 121, 7137-7160, doi: 10.1002/2016JB013240.
- Becker, T.W., C.P. Conrad, A.J.
Schaeffer, and S. Lebedev (2014), Origin of azimuthal seismic anisotropy in
ocean plates and mantle, Earth and Planetary
Science Letters, 401, 236-250, doi:10.1016/j.epsl.2014.06.014.
- Natarov†, S.I., and
C.P. Conrad (2012),
The role of Poiseuille flow in creating
depth-variation of asthenospheric shear,
Geophysical Journal International, 190 , 1297-1310, doi:10.1111/j.1365-246X.2012.05562.x.
- Conrad, C.P., and M.D. Behn (2010), Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy, Geochemistry, Geophysics, Geosystems, 11, Q05W05, doi:10.1029/2009GC002970.
[mantle flow model]
- Conrad, C.P., M.D. Behn, and P.G. Silver (2007), Global mantle flow and the development of seismic anisotropy: Differences between the oceanic and continental upper mantle, Journal of Geophysical Research, 112, B07317, doi:10.1029/2006JB004608.
[flow model and anisotropy code]
- Behn, M.D., C.P. Conrad, and P.G. Silver (2004),
Detection of upper mantle flow associated with
the African superplume, Earth and Planetary Science
Letters, 224, 259-274, doi:10.1016/j.epsl.2004.05.026.
The mantle features exotic structures such as
the Large Low Seismic Velocity Provinces (LLSVPs) at the base of the
mantle and mantle plumes that are thought to arise from
the lowermost mantle. These structures interact with the overall flow
occurring within the mantle We have been able to link the dynamics of parts
of the mantle interior to the overall dynamics of the rest of the mantle.
Mantle Structures: Plumes, LLSVPs, and the CMB
Heyn†, B.H., C.P. Conrad, and R.G. Trønnes (2018), How thermochemical piles can (periodically) generate plumes at their edges,
Journal of Geophysical Research, 125, e2019JB018726, doi:10.1029/2019JB018726.
Heyn†, B.H., C.P. Conrad,
and R.G. Trønnes (2018), Stabilizing effect of compositional viscosity
contrasts on thermochemical piles,
Geophysical Research Letters, 45, 7523-7532, doi:10.1029/2018GL078799.
- Husson, L., and C.P. Conrad (2012), On the location of hotspots in the framework
of mantle convection, Geophysical Research
Letters, 39, L17304, doi:10.1029/2012GL052866.
- Métivier‡, L., and
C.P. Conrad (2008), Body tides of a convecting, laterally heterogeneous, and aspherical Earth, Journal of Geophysical Research, 113, B11405, doi:10.1029/2007JB005448.