The effect of a shallow low viscosity zone on mantle convection and its expression at the surface of the earth

The effect of a shallow low viscosity zone on mantle convection and its expression at the surface of the earth

Thesis (Ph. D.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1987.

Bibliographic Details
Main Author:	Robinson, Elizabeth M
Other Authors:	Barry Parsons.These calculations also predict an asymptotic heat flow on old ocean floor which is higher than the plate model and between 50 and 55 mW/m2 . This value agrees with measurements of heat flow on old seafloor in the Atlantic. In conclusion, we prefer an approximate model for the viscosity structure of the upper mantle which initially has a 125 km thick low viscosity zone that represents a viscosity contrast of two orders of magnitude. The viscosity contrast decreases as the plate ages to one order of magnitude or less by 130 m.y., and the low viscosity zone may also thicken with age. Finally, the Rayleigh number of the upper mantle is at least 105 and may be as large as 107 . With this model, the evolution of the surface plates would initially involve small scale convection which is driven by shear coupling to instabilities downstream and to small scale convection associated with fracture zones. This convective flow would begin at close to 5 m.y. and remain confined to the low viscosity zone until nearly 40 m.y.. As this convective flow cools the upper mantle beneath the low viscosity zone, longer wavelength convection begins throughout the upper (or whole) mantle, and the heat transport from the longer wavelength convection flattens the depth-age curve and may form swells.
Format:	Thesis
Language:	eng
Published:	Massachusetts Institute of Technology 2010
Subjects:	Joint Program in Marine Geology and Geophysics. Earth, Atmospheric, and Planetary Sciences. Woods Hole Oceanographic Institution.
Online Access:	http://hdl.handle.net/1721.1/58496

Internet

http://hdl.handle.net/1721.1/58496