Book contents
- Frontmatter
- Contents
- 1 Introduction
- 2 Context
- 3 Why moving plates?
- 4 Solid, yielding mantle
- 5 Convection
- 6 The plate mode of convection
- 7 The plume mode of convection
- 8 Perspective
- 9 Evolution and tectonics
- 10 Mantle chemical evolution
- 11 Assimilating mantle convection into geology
- Appendix A Exponential growth and decay
- Appendix B Thermal evolution details
- Appendix C Chemical evolution details
- References
- Index
4 - Solid, yielding mantle
Published online by Cambridge University Press: 03 May 2011
- Frontmatter
- Contents
- 1 Introduction
- 2 Context
- 3 Why moving plates?
- 4 Solid, yielding mantle
- 5 Convection
- 6 The plate mode of convection
- 7 The plume mode of convection
- 8 Perspective
- 9 Evolution and tectonics
- 10 Mantle chemical evolution
- 11 Assimilating mantle convection into geology
- Appendix A Exponential growth and decay
- Appendix B Thermal evolution details
- Appendix C Chemical evolution details
- References
- Index
Summary
The mantle is solid and deforming, not molten. How do we know? Viscosity. Estimating the viscosity of the mantle. Temperature dependence of deformation of solids. Inevitable convection.
Prior to the twentieth century, geologists had deduced that the interior of the Earth had to be yielding, in order to accommodate the uplift of mountains. Some geologists assumed the interior was molten, but others acknowledged that a yielding solid would be sufficient. The clearest expression of the latter viewpoint is in the famous 1855 paper by Airy [35] in which he proposed an explanation for mountains being approximately in isostatic balance, namely that mountains have thickened crust beneath them. However, Airy also cited a key observation to support the idea of a deformable, solid interior [35]:
This fluidity may be very imperfect; it may be mere viscidity; it may even be little more than that degree of yielding which (as is well known to miners) shows itself by changes in the floors of subterraneous chambers at a great depth [emphasis added] when their width exceeds 20 or 30 feet [7 or 10m]; and this degree of yielding may be sufficient for my present explanation.
There had been debate about whether the interior is presently fluid or whether it had only been fluid when the Earth was forming. It was Hall [36] in 1859 who established that continuing deformation was required, through his observations that sediments throughout thick sedimentary formations had all been deposited in shallow water.
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- Chapter
- Information
- Mantle Convection for Geologists , pp. 26 - 37Publisher: Cambridge University PressPrint publication year: 2011