What is a plume By Julian Winter Alexandra

What is a plume? By Julian Winter Alexandra Witze (2003)

Introduction Aims • 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 500 m-1000 m uplift but later subsidence Spread > 2000 -2500 km 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 He 3 (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 1600 km 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 1000 km 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’?

Morgan 1971 Griffiths & Campbell 1990 Kellogg 1999 So a plume is……. ? 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!