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Durham University GEOL 4061 Frontiers of Earth Science. Do Plumes Exist?. Gillian R. Foulger. What is a plume?. A plume is a bottom-heated convective upwelling that rises through its own thermal buoyancy.

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Do plumes exist

Durham University

GEOL 4061

Frontiers of Earth Science

Do Plumes Exist?

Gillian R. Foulger


What is a plume
What is a plume?

  • A plume is a bottom-heated convective upwelling that rises through its own thermal buoyancy.

  • Plumes almost certainly must rise from a “thermal boundary layer”, i.e., from material that lies just above a hot body.


1971 plumes were invented to explain
1971: Plumes were invented to explain:

  • excess volcanism

  • “hot spots” fixed relative to one-another

  • linear island chains

Morgan (1971)


Later the plume head plume tail model developed
Later the “plume-head, plume-tail” model developed

Griffiths & Campbell (1990):

Plumes created by injecting syrup/water mix (to be less dense) into the tank.


Problems
Problems

  • There is little evidence that “hot spots” are hot

  • Some have very small melt volumes

  • They are not fixed relative to one-another

  • Many chains not time-progressive

  • Seismology does not reliably detect them in the lower mantle


An unfalsifiable hypothesis
An unfalsifiable hypothesis

However, study of melting anomaly origins has not progressed because of “plume belief”


Are hot spots hot
Are “hot spots” hot?

What does “hot” mean?

200 - 300 K is the minimum required for a plume

How hot are “hot spots”?




Modeling lip volumes
Modeling LIP volumes

Cordery et al. (1997)



Hot spots are not fixed1
“Hot spots” are not fixed

Hawaii relative to Atlantic “hot spots”



Example whole mantle tomography iceland
Example:whole-mantle tomography: Iceland

Ritsema et al. 1999



Plate tectonic processes
Plate Tectonic Processes

  • lithospheric extension

  • mantle heterogeneity

    = variable magmatic fecundity


Ptp lithospheric extension
PTP: Lithospheric extension

  • Intraplate deformation

  • Mid-ocean ridges (1/3 of all “hot spots”)


Ptp mantle heterogeneity
PTP: Mantle heterogeneity

  • Possible sources:

    • recycling of subducted slabs in upper mantle

Peacock (2000)


Ptp mantle heterogeneity1
PTP: Mantle heterogeneity

  • Possible sources:

    • delamination of continental lithosphere

Bertram Schott et al. (2000)


Melt fraction temperature
Melt fraction : Temperature

A 30/70 eclogite-peridotite mixture can generate several times as much melt as peridotite

Yaxley (2000)


Ptp model iceland
PTP model: Iceland

  • Geochemistry indicates recycled Iapetus crust in source

  • Eclogite more fertile than peridotite

  • Geochemistry & melt volume could come from recycled Iapetus slabs

Closure of Iapetus



Plate boundary junctions
Plate-boundary junctions

Extensional stresses occur at RT and RRR intersections and can permit volcanism

e.g., Amsterdam/St. Paul, Easter


Meteorite impacts
Meteorite impacts

Recent modeling suggests that meteorites 10 - 30 km in diameter could form LIPs

e.g., Bushveldt, Ontong Java


Lithospheric delamination
Lithospheric delamination

Overthickening of the crust causes eclogitisation, delamination and triggers LIP volcanism

e.g., Siberian Traps


Edge convection
EDGE convection

e.g., Tristan


Current problems
Current problems

  • Origin of excess melt

    • source consistent with geochemistry

    • energy budget to melt large volumes: must either

      • accumulate melt over long period of time and retain in the mantle, or

      • melt very rapidly - a melt-as-erupted basis

  • Hawaii


Student seminars
Student seminars

  • What is a plume?

  • Are plumes predicted by realistic convection experiments and numerical simulations?

  • What is the origin of ocean island basalt (OIB)?

  • Are the predictions of the plume hypothesis borne out by observation? 1. Temperature

  • Are the predictions of the plume hypothesis borne out by observation? 2. Uplift

  • What is the origin of high 3He/4He?

  • Have plumes been detected seismologically?

  • What alternatives are there to the plume hypothesis?

  • Can the plume hypothesis be tested, and if so how?

  • How can the Plate Tectonic Processes theory be tested?