Earth's mantle

Earth's mantle
CharlesC · CC BY-SA 3.0 · source
Name	Earth's mantle
Caption	Cross-section of Earth showing mantle location
Thickness	~2,900 km
Composition	silicate peridotite, oxides
Density	~3.3–5.7 g/cm³
Temperature	~500–4,000 °C
Viscosity	10^18–10^24 Pa·s (approx.)

Earth's mantle is the thick silicate shell between the crust and the Outer core that dominates Earth's volume and controls long-term geological evolution. The mantle's composition, rheology, and thermal state influence Plate tectonics, Volcanism, Earthquakes, and the geochemical differentiation that produced the Continental crust and Oceanic crust. Observational constraints derive from Seismology, high-pressure experiments at institutions like the Carnegie Institution for Science and Lawrence Livermore National Laboratory, and sample studies from Mid-ocean ridges, Ophiolites, and volcanic provinces such as Hawaii and Iceland.

Composition and Mineralogy

Mantle composition is inferred from Peridotite xenoliths, Basalt chemistry, and high-pressure experiments by groups at Max Planck Institute for Chemistry and ETH Zurich, suggesting a bulk dominated by Olivine, Orthopyroxene, Clinopyroxene, and Garnet phases. Major-element budgets are constrained relative to models like Bulk silicate Earth and isotopic systems studied by laboratories at Scripps Institution of Oceanography and Massachusetts Institute of Technology, using isotope ratios of Strontium-87/Strontium-86, Neodymium-143/Neodymium-144, Lead isotopes, and Oxygen isotopes. Trace elements and volatile inventories (e.g., Water (H2O), Carbon) are probed through melt inclusions from Mount St. Helens, Mount Etna, and Kilauea as well as experiments at University of California, Berkeley. High-pressure polymorphs such as Wadsleyite and Ringwoodite occur in the transition zone and relate to signatures found in Kachchh and Rupelo inclusions.

Structure and Layers

The mantle is classically divided into the upper mantle, transition zone, and lower mantle; boundaries correspond to phase transitions identified by seismic discontinuities at ~410 km and ~660 km observed by networks like USArray and international observatories such as the International Seismological Centre. Uppermost mantle plus crust form the Lithosphere which overlies the mechanically weaker Asthenosphere implicated in plate motions studied since the work of Alfred Wegener and later formalized by researchers at California Institute of Technology and University of Cambridge. The lower mantle extends to the D'' layer atop the Core–mantle boundary, where anomalous structures like the Large Low-Shear-Velocity Provinces and ultra-low-velocity zones have been imaged by collaborations including IRIS and interpreted in studies from Princeton University and University of Oxford.

Physical Properties and Dynamics

Mantle density and elastic properties derive from mineral physics experiments at facilities such as the European Synchrotron Radiation Facility and Argonne National Laboratory using diamond anvil cells and shock compression. Viscosity estimates, informed by post-glacial rebound observed since analyses by James Hutton-era thinkers and modern studies at National Center for Atmospheric Research, range many orders of magnitude and control mantle strain rates beneath regions like the East African Rift and San Andreas Fault. Anisotropy revealed beneath regions including Japan, Alaska, and Tibet links mantle flow to slab dynamics documented by research teams at Tokyo University and Columbia University.

Thermal State and Heat Transport

Mantle temperatures are constrained by geotherms derived from heat flow measurements at sites such as TOPEX/Poseidon-era surveys, mantle xenolith thermobarometry, and mantle convection models developed at Princeton University and Geological Survey of Canada. Heat transport occurs via conduction in boundary layers, advection within convective cells under continents like Laurasia and Gondwana remnants, and shear heating near slabs such as those beneath Iberia and Japan Trench. Radiogenic heat production from isotopes including Uranium-238, Thorium-232, and Potassium-40 contributes to mantle heat budget evaluated by teams at Oak Ridge National Laboratory and Centre National de la Recherche Scientifique.

Mantle Convection and Plate Tectonics

Convective patterns in the mantle drive Plate tectonics and are constrained by mantle tomography from projects like EarthScope, studies of mantle plumes beneath Hawaii and Iceland debated in literature from Harvard University and University of Cambridge. Subduction zones such as the Mariana Trench and Peru–Chile Trench record slab penetration into the lower mantle or stagnation in the transition zone, topics explored by researchers at GFZ Potsdam and USGS. Numerical models developed at Los Alamos National Laboratory and Princeton University simulate plume-lithosphere interaction, slab rollback, and continental rifting exemplified by the East African Rift and breakup of Pangea.

Geochemical Cycles and Mantle Reservoirs

The mantle participates in long-term cycles of volatiles and incompatible elements via magmatism at mid-ocean ridges like the Mid-Atlantic Ridge, arc volcanism at systems such as the Aleutian Islands, and intraplate volcanism exemplified by Yellowstone and Réunion. Isotopic heterogeneities—e.g., distinct HIMU, EM1, and EM2 reservoirs—are catalogued from samples analyzed at institutions like Australian National University and Lamont–Doherty Earth Observatory. Recycling of crustal material through subduction influences mantle composition beneath regions such as the Mediterranean and Indonesia, with geochemical flux estimates constrained by work from International Ocean Discovery Program expeditions.

Seismic Imaging and Exploration Methods

Seismic tomography from networks including IRIS, USArray, and the European Seismological Commission images mantle structure using body waves, surface waves, and receiver functions; techniques advanced at Massachusetts Institute of Technology and ETH Zurich resolve slabs, plumes, and anisotropy. Experimental petrology, electrical conductivity studies at GFZ Potsdam, and mineral physics using Advanced Photon Source complement seismic constraints; active-source experiments like those near Iceland and passive-array deployments across Tibet and Alaska provide regional resolution. Geodynamic inversions and machine-learning approaches from teams at Google DeepMind-affiliated collaborations and university groups refine models of mantle flow and composition.

Category:Geology