Hotspots, mantle plumes and intra-plate volcanism

Question 1

Intra-plate volcanism

Answer 1

occurs away from plate margins

Question 2

Most volcanoes occur at plate margins

Answer 2

• constructive mid ocean ridges

- destructive island arcs and ocean-continent subduction zone

Question 3

Hawaii

Answer 3

• linear increase in age with distance along the Hawaii emperor chain
• gradual decrease in elevation with increasing distance from the active volcano
• the oldest seamounts are found at the end, ready to be carried down in the subduction zone beneath the Aleutian volcanic arc

Question 4

Hot Spots

Answer 4

• where stationary columns of magma, originating deep within the mantle, slowly rise to the surface

Question 5

Mantle melting

Answer 5

• upper mantle is essentially made up of peridotite
• peridotite is made of: olivine + orthopyroxene + clinopyroxene + spinel and/or garnet
• this is the region where magmas are sourced

Question 6

Mantle plume model

Answer 6

• originate at the lower mantle
• bulbous head as the plume rises, long tails and also flattened plume heads as they spread out at the base of the lithosphere
• volcanic islands are produces by plumes rising through the mantle
• the plumes come from the lower mantle and are therefore fixed

Question 7

Hawaiian chain

Answer 7

• the sea floor surrounding the chain is anomalously shallow, over an area about 1,200km wide and 3,000km long

Question 8

Parallel problen

Answer 8

portions of island chains of similar age are parallel to each other suggests that the hotspots themselves remain mostly fixed with respect to each other

Question 9

Hotspot tracks: hawaii

Answer 9

• eruption rate for Hawaiian volcanoes has remained quite constant over most of the 65million years of preserved activity
• this suggests that as volcanic material being erupted, new material is being supplies more or less continuously from below
• for the 10 million years following the bend, very little lava erupted

Question 10

Palaeo-magnetic data

Answer 10

strongly suggests that all of the lava solidified at 19.5 degrees north latitude, precisely the latitude of the hotspot today
Hawaiian hotspot has been nearly fixed for at least 65 million years

Question 11

Arguments supporting the notion of hotspot location

Answer 11

Palaeo-magnetic data and:
Portions of island chains of similar age are parallel to each other suggests that the hotspots themselves remain mostly fixed with respect to each other

Question 12

Plume model summary

Answer 12

• a rigid plate moves over a deeply rooted mantle plume
• the straightness of the hotspot tracks and the linear increase in volcanic ages along the track
• topographic expression
• nearly constant eruption rate (new material being supplied more or less continuously from below)
• distinct chemistry for the ocean island basalts suggest deeper origin for the magma source
• seismic tomography