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Dynamical consequences of compositional and thermal density stratification beneath spreading centers
Author(s) -
Sotin C.,
Parmentier E. M.
Publication year - 1989
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl016i008p00835
Subject(s) - upwelling , mantle (geology) , geology , buoyancy , geophysics , crust , mantle convection , seafloor spreading , stratification (seeds) , hotspot (geology) , thermal , mantle wedge , oceanic crust , petrology , subduction , tectonics , mechanics , thermodynamics , seismology , oceanography , physics , seed dormancy , germination , botany , dormancy , biology
Extraction of partial melt to form oceanic crust reduces the density of upwelling mantle beneath spreading centers. This compositional buoyancy can significantly affect both the rate of upwelling and the pattern of mantle flow. The relative importance of buoyant upwelling and upwelling due to plate spreading depends on the mantle viscosity. For a low enough mantle viscosity, buoyant upwelling can significantly enhance the thickness of the crust relative to that which would be produced by plate spreading alone. For a mantle viscosity of 10 22 Pa s, upwelling due to plate spreading is dominant, and crustal thickness is predicted to be a strong function of spreading rate. However, for a mantle viscosity of 10 19 Pa s, buoyancy dominates mantle upwelling, and the calculated crustal thickness, like the oceanic crust, is nearly independent of spreading rate. Thermal and compositional density variations result in opposing buoyancy forces that can cause time dependent upwelling. For a mantle viscosity of 10 20 Pa s and a low 1 cm/yr spreading rate this behavior takes the form of undamped crustal thickness oscillations with a single, well defined period. For even slightly lower mantle viscosity, the frequency increases, and crustal thickness oscillations become more complex with two or more frequencies present. While numerical experiments have thus far been carried out only for viscosities significantly greater than that likely to characterize the mantle beneath spreading centers, we speculate that these crustal thickness oscillations may explain important aspects of seafloor structure.