Title: Viscous stratification of the earth and convection
Abstract: For estimating the vertical distribution of the (linearized) viscosity and thereby the conditions of convection in the mantle, it is convenient to divide the Earth into six layers: lithosphere, asthenosphere, mesosphere, lower mantle, and outer and inner core. The three dividing levels of the mantle are assumed schematically at depths of order 100, 400 and 800 km. On assigning viscosities to the upper layers, one obtains qualitatively a limited number of convective models of the mantle of which the two most significant ones are: shallow convection in the upper mantle and mantle-deep convection. In this paper we discuss mainly the shallow model and collect a variety of geophysical arguments for its correctness and against the existence of deep convection. The main argument is summarized in the proposal that the asthenosphere is less viscous (by a factor of 10 to 100) than has generally been assumed. In this shallow model, the return flow is essentially through the asthenosphere. The dynamical agent is the steep temperature gradient in the upper mantle. Speculations as to the historical variation of this gradient are advanced. The effects on the model of a non-uniform Earth aggregation are considered and shown to favor shallow convection as well as a top convective layer (lithosphere plus asthenosphere) whose depth increases slowly over the Earth's life, leading to a tectonic activity that increases gradually with time.
Publication Year: 1972
Publication Date: 1972-01-01
Language: en
Type: article
Indexed In: ['crossref']
Access and Citation
Cited By Count: 4
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot