Geology Reference
In-Depth Information
11
Assimilating mantle convection into geology
The goal of this topic has been to present mantle convection as a topic accessible
to all geoscientists so that it can become a routine part of their thinking. This is
necessary, because it is so fundamental to so many geological processes. It is also
possible, as I hope this presentation has demonstrated.
The understanding of mantle convection that has been developed in the topic is
fairly well established. There remains some debate about a possible layer in the
deep mantle, apart from D
, though the debates usually seem to be conducted in
ignorance of the heat flow constraint given in Chapter 8. There is also some debate
about the existence of mantle plumes, though this persists mainly in circles that
are apparently ignorant of the physics of mantle upwellings given in Chapter 7. In
any case readers should be able to follow the essence of such continuing debates,
which are a normal part of any scientific topic. Hopefully they will be armed with
a better-informed perspective.
Two kinds of implication have also been discussed in this topic: for the tectonic
evolution of the Earth, and for the chemistry of the mantle. The early tectonic
evolution of the Earth is still unclear. Observational constraints are so sparse and
possibilities still so diverse that progress will require a continuing conversation
among all those involved, and a grasp of the essence of mantle evolution models
will be important. Although this topic is still rudimentary in some respects, it is
notable how much more clearly defined it is now compared with, say, two decades
ago.
After a long period of debate and confusion, mantle geochemistry now seems
to be being brought into the fold of mantle dynamics. Hopefully this will focus
debates in more productive directions. Major element heterogeneity emerges as
a particularly important aspect. It leads to much more complicated behaviour in
melting and melt migration, and progress will therefore be more difficult, but some
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