What is a plume?By Julian Winter

Alexandra Witze (2003)

IntroductionAims• Primarily to confuse you; see

conclusion

• Briefly look at modeling

• Understand their characteristics & evolution

• Conclusion; confused?

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

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

Plume Modelling- Whitehead & Luther 1975

• Liquids heated from below - TBL

• TBL less dense & less viscous

• Head and tail structure & entrainment

Griffiths & Campbell 1990

Plumes Refined: Flood basalts - Campbell & Griffiths 1990

• A plumes head can:-– Produce 500m-1000m uplift but later subsidence – Spread > 2000-2500km – Melt – Flood basalts– Evolution to plume tail melts

• But wait, flood basalts not found at all hotspots e.g. Hawaii!!!

Geochemistry

• Typically have enrichment in incompatible elements

• Higher concentrations of He3 (high RA)

• Typically HIMU, EM-1 & 2 & FOZO

• Isotopic ratio distinguished from DM

Angelo Peccerillo

Subduction derived plumes 1.

• Suducted slabs drive convection

• Slabs reheated in lower mantle; bouyant

• Accounts for geochemistry

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?

Subduction derived plumes 2.

Kellogg et al 1999

Supersrwells e.g. Polynesia

• Anomalously shallow seafloor several 1000km in extent

• Unusually dense concentrations of hotspots

• SUPERPLUMES

• Doming of Superplume Plumes

Superswells

Davaille (1999)

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

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- they’re

just showing off.• Low seismic velocity? not if you don’t want.• Dare I say ‘radial dykes’?

So a plume is…….?

Morgan 1971

Griffiths & Campbell 1990

Kellogg 1999

Ivanov 2004 Daville (1999)

Anderson, Foulger 2004

Questions?

Condie 2003

The plate tectonic paradigm

• Intra plate volcanism – failure of plate tectonics

• Hotspots– Linear tracks – age progression– Fixed position

• Why a hot mantle? Unrealistic!