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
8 - Perspective
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
A fuller picture of mantle convection. Active plates and active plumes. The distinct roles of plates and plumes in heat transport. Plume tectonics cannot replace plate tectonics. How plates and plumes affect each other.
Plumes are not the return mode of plate flow. There is normally no active upwelling under ridges. There is no significant ‘decoupling’ layer. Return flow is not shallow, ‘drag’ is small. There is no seafloor ‘flattening’, though there is some anomalous seafloor elevation. ‘Superswells’ and residual thermal variations. Layered convection?
Rifts and flood basalts. Superplumes? Small-scale modes? Possible, but evidence is marginal. Edge modes. Drips. Mantle wetspots.
Separate but interacting
The picture of mantle convection developed so far is of two thermal boundary layers, each driving a distinctive form of convection. Because the two modes of convection are so different, it has been useful to consider the thermal boundary layers separately. Of course the two modes do interact, but not as strongly as in low-Rayleigh-number ‘textbook’ convection (in which the modes are tightly coupled; Figure 6.2), as we will discuss after a brief assessment of the story so far.
The top thermal boundary layer is very directly implied by all the observations that indicate a steep temperature gradient near the Earth's surface and a shallower gradient further down. The near-surface temperature gradient is directly measured, and the need for a shallower gradient deeper down is implied by the fact that the mantle is not liquid (from seismology) and by temperatures inferred from magmas reaching the surface.
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- Information
- Mantle Convection for Geologists , pp. 104 - 123Publisher: Cambridge University PressPrint publication year: 2011