Superplumes Flashcards
Hot spots - different types reference Hotspots are 125,000 type 1, type 2, type 3 Examples
(Koppers, 2011)
Hotspots are hot plumes, stationary in mantle, heat up crust above.
125,000 seamount over 1km high
type 1 - results from long lived pulses from mantle plume from as deep as core mantle boundary, creates chain as plate moves e.g. Hawaii
Type 2 - result of short lived plume or offshoot from bigger plume, e.g. French Polynesia
Type 3 - third end member, no plume, caused by cracks in lithosphere due to tectonics e.g. Puma Puma ridge in Pacific
Convective mantle circulation
Reference
Episodic so?
First circulation system - tectonic movement? Continental growth? Upper and lower mantle?
Second circulation model - cold material? Large plumes? Effect? Oceanic plateaus? Upper mantle?
Stein and Hofmann, 1994
Episodic fluctuations in continental crust growth, two different connective mantle circulations
WIlsonian periods, normal tectonic movement, open, close sea, continental growth by arc-accretion, upper and lower mantle separate, shallow plumes from upper mantle, depleted in incompatible elements, concentrated now in crust
MOMO, cold material breaks through 660km boundary, multiple large plumes from CMB rise causing mantle overturn, oceanic plateaus created from plumes and may become continental crust by accretion or underpaying. Newly created crust is composed of upper and lower mantle, upper mantle partially replenished in incompatible elements
Superplume cause Reference 670km below, barrier for? If endothermic phase with? Then mantle? When 670km thermal boundary layer penetrated? Almost at same time? Slab penetration event was coincident with? Triggered? Issue?
Larson and Kincaid, 1996
Boundary between upper and lower mantle, leaky interface and can be barrier for vertical mass movement
If boundary is an endothermic phase with significant temp discontinuity then mantle has layered convection punctuated by slab penetration and mass flux
When thermal boundary layer penetrated, triggers deep mantle upwelling moving boundary to shallower depths causing near surface melting. Almost same time slab material reaches CMB increasing heat loss across CMB. Slab penetration coincident with break-up of gondwana, triggered formation of oceanic plateaus (ontong-java)
Issue - very short gap between penetration of CMB and rise of superglue (10-15ma) speed of movement in mantle unknown
Effect of superplumes on climate - Cambrian explosion
Reference
Shift in true north caused?
Force continents and mantle to? Why does mantle under supercontinent heat up?
Mantle bulge upward effect? fate of bulge?
cause of Cambrian biodiversity, why?
Controversial, why?
Irion, 2001
Shift in true north caused planet to spin off balance, forced continents and mantle to slide upto metre per year for millions of years, doesn’t cool as no subduction, mantle bulges causing earth to be asymmetrical and unbalanced. Bulge then sheared off within mantle by motion of earth rotation migrates towards equator to rebalance mass
Cambrian biodiversity caused by changes in ocean circulation, sea level rise and new biomes with migration of bulge.
Controversial as evidence limited and palaeomagnetic data may be unreliable, no guarantee seamount data is solid rock
cretaceous spreading rates Reference Major control on eustasy? Mid cretaceous nightstand correlated with? Evidence for? However ecstasy accounted for by? Main evidence? 3 things conclusion
Heller et al, 1996
Major control on eustasy is sea floor spreading rate differences, mid cretaceous high stand correlated to pulse of rapid spreading and used as evidence for superglue (Larson, 1991)
However eustasyaccounted for by breakup of supercontinent+variations in distribution of crust consumed at subduction zones. Evidence is no evidence of hydrothermal flexes during mid cretaceous, evidence of ridge jumping indicating more sea floor of age may be preserved, Mesozoic so timescale revised so spreading rates over longer time, not so rapid
Since rapid spreading rate was evidence for superglue, superplume not necessary
