What is a plume? By Julian Winter

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What is a plume?By Julian Winter
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Introduction

• Aims
• Primarily to confuse you see conclusion
• Briefly look at modeling
• Understand their characteristics evolution
• Conclusion confused?

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Birth of Plumes -Morgan 1971

• Intra plate volcanism failure of plate
  tectonics
• Fixed upward rise of hot, buoyant mantle
• Comes from the deep mantle
• Downward flow dispersed uniformly
• Column shape inferred from swell

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Radiating Dykes

• Centrally located source
• Outward injection of magma
• Plume provides point source
• Found on Venus no tectonics here
• But not all intraplate volcanism has such dykes!

Richard E. Ernst 2004
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Plume Modelling- Whitehead Luther 1975

• Liquids heated from below - TBL
• TBL less dense less viscous
• Head and tail structure entrainment

Griffiths Campbell 1990
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Plumes Refined Flood basalts - Campbell
Griffiths 1990

• A plumes head can-
• Produce 500m-1000m uplift but later subsidence
• Spread gt 2000-2500km
• Melt Flood basalts
• Evolution to plume tail melts
• But wait, flood basalts not found at all hotspots
  e.g. Hawaii!!!

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Geochemistry

• Typically have enrichment in incompatible
  elements
• Higher concentrations of He3 (high RA)
• Typically HIMU, EM-1 2 FOZO
• Isotopic ratio distinguished from DM

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Subduction derived plumes 1.

• Suducted slabs drive convection
• Slabs reheated in lower mantle bouyant
• Accounts for geochemistry

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Subduction derived plumes 2.

• Slab sinks to a 1600km deep TBL
• Slab creates high spot ? Plume
• Interface of TBL irregular
• Depth of plume can therefore be irregular thus
  plume can be both deep shallow?

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Subduction derived plumes 2.
Kellogg et al 1999
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Supersrwells e.g. Polynesia

• Anomalously shallow seafloor several 1000km in
  extent
• Unusually dense concentrations of hotspots
• SUPERPLUMES
• Doming of Superplume ? Plumes

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Superswells
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Plumes a summary

• Plumes from CMB
• Shallower origins subduction driven
• Superswells Superplumes
• Top down models shallow plumes
• Function of plate related stresses
• Shallow mantle upwelling

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Conclusion

• Jules criteria for plume recognition
• LIP but no worries if not.
• Monotic age progression if it suits you.
• A DEEP source but a shallow source will do.
• A superswell e.g. Polynesia Africa- theyre
  just showing off.
• Low seismic velocity? not if you dont want.
• Dare I say radial dykes?

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So a plume is.?
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Questions?
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The plate tectonic paradigm

• Intra plate volcanism failure of plate
  tectonics
• Hotspots
• Linear tracks
• age progression
• Fixed position
• Why a hot mantle? Unrealistic!

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