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| Asthenosphere | |
|---|---|
| Name | Asthenosphere |
| Type | Mantle layer |
| Depth | variable |
| Composition | peridotite, partial melt |
| State | ductile, convecting |
Asthenosphere is the mechanically weak, ductile layer of the upper mantle that underlies the rigid lithosphere and participates in mantle convection and plate motions. It is implicated in processes studied by geologists, geophysicists, and planetary scientists and appears in models developed by institutions such as United States Geological Survey, California Institute of Technology, and Max Planck Institute for Chemistry. Observations from expeditions like the Challenger expedition and missions including Seismic Array deployments have refined its conceptualization.
The layer is defined in relation to the Lithosphere and the deeper mesosphere using seismic, rheological, and thermal criteria recognized by organizations such as the American Geophysical Union, Royal Society, and International Seismological Centre. Classical definitions reference the transition from elastic to viscous behavior observed in studies by researchers affiliated with Massachusetts Institute of Technology, University of Cambridge, and University of Tokyo. Its properties include low seismic shear velocity contrasts identified in tomographic models by teams at Scripps Institution of Oceanography and ETH Zurich, and attenuated seismic phases catalogued by the Incorporated Research Institutions for Seismology.
Mineralogical models derive from peridotite compositions measured in ophiolites like the Semail Ophiolite and mantle xenoliths curated by museums such as the Natural History Museum, London. Principal minerals include olivine, orthopyroxene, clinopyroxene, and spinel or garnet in compositions constrained by experimental petrology at Woods Hole Oceanographic Institution, Carnegie Institution for Science, and Geological Survey of Canada. Geochemists from University of Oxford and Université Paris-Saclay use trace-element and isotopic systems exemplified by studies of Hawaiian Islands basalts and Iceland lavas to infer melt fractions and volatile contents.
Rheological behavior is informed by laboratory deformation experiments led by groups at ETH Zurich, Stanford University, and Pennsylvania State University that explore dislocation creep, diffusion creep, and grain-boundary sliding. Models incorporate viscosities comparable to those used in simulations at Princeton University and California Institute of Technology, and account for partial melt effects demonstrated in work by teams at University of British Columbia and Utrecht University. This ductile solid exhibits viscoelastic response important for interpretations of post-glacial rebound data from studies by Scott Polar Research Institute and sea-level reconstructions by National Oceanic and Atmospheric Administration.
Seismic discontinuities and low-velocity zones are mapped by tomographic inversions conducted by Harvard University, Columbia University, and National Academy of Sciences-affiliated projects, showing variable depth from beneath cratons like the Canadian Shield to thinner regions beneath mid-ocean ridges such as the Mid-Atlantic Ridge. The depth to the layer's top correlates with lithospheric thickness as documented in datasets from Lamont–Doherty Earth Observatory and British Geological Survey, while thickness estimates derive from seismic anisotropy studies published by researchers at IRIS and Geological Survey of Japan.
The layer facilitates relative motion between tectonic plates studied since the formulation of plate theory by proponents associated with University of Cambridge and Wegener-related historical debates recorded in archives of the Royal Geographical Society. Mantle convection cells modeled at NASA Goddard Space Flight Center, Los Alamos National Laboratory, and university consortia link downwellings at subduction zones like the Mariana Trench to upwellings beneath hotspots such as Yellowstone National Park and Hawaii (island), implicating the layer in geodynamic coupling documented in publications from the European Geosciences Union.
Investigative methods include seismic tomography developed by groups at Caltech Seismological Laboratory and University of Michigan, magnetotelluric surveys used by teams at University of Edinburgh and University of Western Australia, experimental petrology carried out at Geophysical Laboratory (Carnegie Institution), and geodetic measurements from networks like Global Positioning System arrays and International GNSS Service. Additional constraints derive from laboratory high-pressure experiments at facilities such as Diamond Light Source and Argonne National Laboratory and petrological analyses of mantle-derived xenoliths collected during field campaigns led by Geological Survey of India and Instituto Geofísico del Perú.
Thermal structure is constrained by heat-flow compilations from the International Heat Flow Commission and mantle potential temperature estimates used in models at Pacific Northwest National Laboratory and University of Leeds, while chemical heterogeneity is evident from isotope systems studied at Massachusetts Institute of Technology and University of California, Berkeley. Variations include melt-rich zones beneath Iceland and depleted regions beneath old shields like the Baltic Shield, with implications for volatile cycling investigated by researchers at ETH Zurich and Max Planck Institute for Chemistry.