Transcript What alternatives are there to the plume hypothesis?

What alternatives are there to
the plume hypothesis?
Helen Brown
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
Meteorite Impacts
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Catastrophic mechanism
Recognition: shock related effects. Auto-obliterated?
Pressure release or decompression melting
Volume of melt comparable to LIP
Ridge Transform Intersections
3D finite element models
 Seamount formation
Consider effect of lithospheric stress on all hotspots
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
Reheated Slabs
Low velocity anomalies
 Do NOT resemble
plumes
 Ancient slabs
 Velocity inversion
 Radioactive heat
source
 Penetrative
convection=
NO need for plumes!
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
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”
Conclusions
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Common themes:
Fertile mantle
Lithospheric Extension
Decompression melting
Alternatives need further scientific
investigation before they can truly challenge
the long believed “Plume Hypothesis”