1. What alternatives are there to the plume hypothesis?
Helen Brown

2. Background! Great variability amongst “hot spots”
Plume theory become progressively elaborate
Question the hypothesis
Investigate alternatives…
should account for what is observed
and be scientifically testable

3. Meteorite Impacts Catastrophic mechanism
Recognition: shock related effects. Auto-obliterated?
Pressure release or decompression melting
Volume of melt comparable to LIP

4. Ridge Transform Intersections
3D finite element models
Seamount formation
Consider effect of lithospheric stress on all hotspots

5. Plate Tectonic Processes
Volcanic anomalies are “by products” of plate tectonics
Unifies convection and volcanism
2 key requirements:
Intraplate Deformation
Upper mantle is compositionally variable
Location + amount of melt

6. Reheated Slabs Low velocity anomalies Do NOT resemble plumes
Ancient slabs
Velocity inversion
Radioactive heat source
Penetrative convection=
NO need for plumes!

7. Lithospheric Delamination
Explain continental volcanism
2 Conditions for delamination:
Gravitationally unstable
Viscosity lowered
How cause magmatism:
Astheno sucked into void
Horizontal T gradients drive convection
Dewatering

8. Edge Driven Convection (EDC)
Instability between thick, stable lithosphere and thinner lithosphere.
Fixed boundaries, mantle mobile.
EDC driven by vertical T variation along the “edge”

9. Conclusions Common themes: Fertile mantle Lithospheric Extension
Decompression melting
Alternatives need further scientific investigation before they can truly challenge the long believed “Plume Hypothesis”