Large Low-Shear-Velocity Provinces

Large Low-Shear-Velocity Provinces
Name	Large Low-Shear-Velocity Provinces
Location	Earth's lower mantle
Type	Deep mantle structure

Large Low-Shear-Velocity Provinces

Large Low-Shear-Velocity Provinces are massive regions in the Earth's lowermost mantle characterized by anomalously low seismic shear-wave speeds. First inferred from seismic tomography and shear-wave studies, they are central to debates involving Alfred Wegener-era plate reconstructions, Harry Hess-style mantle convection models, and modern interpretations tied to Inge Lehmann-era seismology. Their significance spans research by institutions such as United States Geological Survey, Institut de Physique du Globe de Paris, and Massachusetts Institute of Technology.

Overview and Discovery

The first systematic identification of deep, laterally extensive anomalies emerged from global seismic tomography efforts led by groups at California Institute of Technology, Scripps Institution of Oceanography, and Imperial College London, building on datasets from observatories like USArray and networks maintained by Japan Meteorological Agency. Early papers comparing body-wave travel times and shear-wave splitting, notably from researchers at Lamont–Doherty Earth Observatory and National Oceanic and Atmospheric Administration, revealed two antipodal provinces roughly beneath Africa and the Pacific Ocean, prompting cross-disciplinary work involving teams at Stanford University, ETH Zurich, and University of Cambridge.

Physical Characteristics

LLSVPs occupy large volumes of the lowermost mantle adjacent to the core–mantle boundary and display shear-wave velocity reductions of several percent relative to surrounding mantle, as observed in datasets from Inge Lehmann Observatory and processed by groups at Potsdam Institute for Climate Impact Research. Their lateral dimensions span thousands of kilometers, comparable in scale to Sahara Desert or Antarctica, and their tops can be several hundred kilometers above the D″ layer near the CMB. Seismic anisotropy and boundary sharpness inferred by analysts at California Institute of Technology and University of California, Berkeley show complex internal heterogeneity, with interactions noted near regions studied by NOAA and mapped in collaborations with National Aeronautics and Space Administration.

Composition and Origin Hypotheses

Explanations for LLSVP composition include chemically distinct piles enriched in iron and incompatible elements, as proposed by modelers at Princeton University and University of Oxford, recycled oceanic crust assemblages suggested by researchers at Woods Hole Oceanographic Institution, and primordial reservoirs hypothesized by scholars at University of Tokyo and Max Planck Institute for Chemistry. Competing hypotheses invoke dense bridgmanite-rich assemblages, partial melting, or iron-enriched phases evaluated using experimental facilities at Lawrence Livermore National Laboratory and Oak Ridge National Laboratory. Geochemical tracers measured in mantle-derived basalts by teams at University of Hawaii and Smithsonian Institution provide constraints linking LLSVPs to long-lived reservoirs implicated in studies involving Louis Agassiz-era stratigraphy and modern isotope labs at Carnegie Institution for Science.

Geodynamic and Seismic Implications

LLSVPs affect mantle convection patterns in numerical models from groups at California Institute of Technology, University of Michigan, and University of Leeds, altering plume generation zones and whole-mantle circulation scenarios debated at conferences hosted by American Geophysical Union and European Geosciences Union. Their presence influences seismic wave propagation observed by networks such as IRIS and interpreted in tomographic models from Institut de Physique du Globe de Paris and Seismological Society of America-affiliated researchers. Interactions with the core may modulate heat flux at the core–mantle boundary, with implications for geomagnetic field behavior studied by teams at British Geological Survey and Geological Survey of Japan.

Interaction with Mantle Plumes and Surface Volcanism

Locations of LLSVP margins correlate with hypothesized plume generation zones feeding large igneous provinces and hotspot tracks like those examined in studies of Deccan Traps, Siberian Traps, Hawaii, and Iceland. Researchers at University of Hawaii, University of Edinburgh, and Heidelberg University have linked plume locations to LLSVP edges, informing models of Cretaceous and Paleogene magmatism discussed in panels at Royal Society meetings. Geochemical signatures in volcanic rocks analyzed at ETH Zurich and California Institute of Technology laboratories support connections between deep-sourced melts and LLSVP-related reservoirs.

Methods of Detection and Imaging

Imaging of LLSVPs relies on seismic techniques including body-wave tomography, shear-wave splitting, normal-mode analysis, and S-wave delay studies developed by groups at Massachusetts Institute of Technology, Harvard University, and University of California, Santa Barbara. Advanced approaches use adjoint tomography and full-waveform inversion employed by teams at Princeton University and Imperial College London, integrating datasets from networks like USArray, European Seismic Network, and Japan Meteorological Agency. Laboratory experiments on mineral physics at Carnegie Institution for Science and computational studies at Max Planck Institute for Meteorology complement seismic observations to infer temperature, composition, and phase behavior in LLSVPs.

Category:Geophysics