1997/04/10 by Brian P. West, William S. D. Wilcock, Jean‐Christophe Sempéré +1 · 3 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #High-pressure geophysics and materials #earthquake and tectonic studies #Geology #Asthenosphere #Mantle (geology) #Geophysics #Buoyancy #Lithosphere #Upwelling #Radiogenic nuclide #Petrology #Seismology #Tectonics #Mechanics #Physics
paper · pdf · doi:10.1029/96jb03895
openalex publication_date 1997/04/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/23
Both geophysical and geochemical evidence suggests the presence of along‐axis asthenospheric flow toward the Australian‐Antarctic Discordance (AAD) beneath the Southeast Indian Ridge (SEIR). We use a three‐dimensional, finite‐volume formulation of viscous flow to investigate the structure of asthenospheric motion beneath the SEIR. Our results show that simple continental separation in either a constant‐ or variable‐viscosity mantle without horizontal temperature gradients is unable to reproduce the inferred asthenospheric flow velocities and observed geographic distribution of the “Indian” and “Pacific” upper mantle isotopic provinces. The presence of a cooler, more viscous mantle directly beneath the AAD is necessary to reproduce observed constraints. High viscosities beneath the AAD induce significant along‐axis flow beneath the neighboring SEIR that advects warmer material over the cooler, more viscous mantle. In passive flow models, a temperature anomaly of about 300°C at a 400‐km depth is required. Simulations that include the effects of buoyancy forces reduce the required temperature anomaly to 100°–200°C, a result in good agreement with other estimates of the regional temperature anomaly. These models also match observed near‐axis variations in residual depth and crustal thickness. In both passive and buoyant simulations, the presence of high‐viscosity (cooler) upper mantle beneath the AAD results in reduced upwelling, consistent with low extents of decompressional melting inferred from geochemical and geophysical constraints. Along‐axis flow acts to subdue temperature variations within the melting region relative to the deeper mantle and results in a temperature inversion in the subaxial asthenosphere. This effect may also reduce the variations in geochemical parameters such as Na 8.0 and Fe 8.0 with axial depth below those observed in global correlations.