Geoscience Reference
In-Depth Information
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How have the core and geodynamo evolved over time?
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What are the driving forces of plate tectonics and internal circulation?
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When and how did the continents form?
Specific topics for which there are clear opportunities for making progress in
the next decade include (1) appraisal of geochemical heterogeneities in the deep
mantle and their relationship to the dynamic system, (2) quantification of volatile
fluxes and their distribution in the mantle, and (3) determination of core evolution.
All three topics are central to determining the thermo-chemical evolution of Earth.
Progress is being made in these areas by concerted disciplinary and interdisciplinary
efforts. Breakthrough advances that resolve outstanding issues will require enhanced
resolution of fine-scale structures in the interior beyond what can now be achieved,
and efforts to attain higher resolution from seismological, geodynamical, and mineral
physics approaches will need to be undertaken.
Quantification of Geochemical Heterogeneities and Their Role in Mantle
Dynamics
Earth's mantle comprises an immense convective system that circulate heat,
volatiles such as water and carbon dioxide, silicate melts, former lithospheric
material, and a host of other chemical and isotopic species between the interior and
the surface. Throughout Earth's history chemical differentiation has produced
continental and oceanic crust, much of which has been subducted or delaminated,
generating compositional and isotopic mantle heterogeneity. Some chemical
heterogeneities have remained sequestered in the interior for billions of years, while
others have rapidly recycled to the surface. This multicomponent transport constitutes
the primary interaction of the deep Earth with the ocean, atmosphere, and crust over
geological timescales. The internal convective engines provide strain energy for
earthquakes, heat for volcanic activity, and power for the core geodynamo.
Determining the magnitude, spatial distribution, and temporal variability of
geochemical heterogeneities and pinpointing the locations of internal reservoirs
where they are sequestered are key to understanding how the deep interior contributes
to Earth's evolution (NRC, 2008).
A profound task is to fully understand the configuration of global circulation
in the mantle and its capacity to sequester chemical heterogeneities in reservoirs.
Evidence from mantle-derived isotopes has long been interpreted as favoring layering
of the mantle, while most geodynamic interpretations and some seismic
interpretations favor mantle circulation that is at least partially continuous from top to
bottom, with the transition zone providing some degree of resistance. Reconciling
geochemical evidence favoring isolated mantle reservoirs, seismic evidence for
down-welling slab material in the lower mantle, and geodynamic models that tend to
favor extensive, although possibly intermittent, circulation remains at the heart of this
long-standing controversy (Kellogg et al., 2004; Lay, 2009; Olson, 2010).
Quantifying the nature and dynamical influence of deep Earth chemical
heterogeneities will require an interaction of multiple Earth science subdisciplines,
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