Tectonics and Convection

Transcription

1 Tectonics and Convection 1. Historical introduction 2. Surface kinematics 3. Subduction dynamics 4. Subduction dynamics in their ecosystems 5. A world tour of horizontal tectonics 6. Going vertical: Dynamic topography

2 I am not claudio faccenna. I am not nico coltice. (although I ll talk about glucose syrup and camembert)

3 1. Historical introduction (short)

4 History was driven by a Naturalist viewpoint (continental drift) and a Physicist viewpoint (mantle convection) Milestones: * 16th century! Continental drift by Abraham Ortelius

5 Milestones: * 16th century! Continental drift by Abraham Ortelius * 1910 s: Continental drift by A. Wegener

6 Milestones: * 16th century! Continental drift by Abraham Ortelius * 1910 s: Continental drift by A. Wegener * 1910 s: Continents are carried by the flow of the mantle on which they sit (A. Holmes, 1919)

7 Milestones: * 16th century! Continental drift by Abraham Ortelius * 1910 s: Continental drift by A. Wegener * 1910 s: Continents are carried by the flow of the mantle on which they sit (A. Holmes, 1919) * 1920 s: Mountain belts caused by continental collision, oceans by continental rupture (E. Argand) * 1960 s: Mid-oceanic ridges found (Harry Hess, 1962) * 1960 s: Oceanic magnetic stripes (Fred Vine and Drummond Matthews, 1963 and Morley, 1963)

8 Milestones: * 16th century! Continental drift by Abraham Ortelius * 1910 s: Continental drift by A. Wegener * 1910 s: Continents are carried by the flow of the mantle on which they sit (A. Holmes, 1919) * 1920 s: Mountain belts caused by continental collision, oceans by continental rupture (E. Argand) * 1960 s: Mid-oceanic ridges found (Harry Hess, 1962) * 1960 s: Oceanic magnetic stripes (Fred Vine and Drummond Matthews, 1963 and Morley, 1963) * Late 60 s until today: Refining the theory (Wilson, Morgan, McKenzie, etc.)

9 Milestones: 21 st century * 16th century! Continental drift by Abraham Ortelius * 1910 s: Continental drift by A. Wegener * 1910 s: Continents are carried by the flow of the mantle on which they sit (A. Holmes, 1919) * 1920 s: Mountain belts caused by continental collision, oceans by continental rupture (E. Argand) * 1960 s: Mid-oceanic ridges found (Harry Hess, 1962) * 1960 s: Oceanic magnetic stripes (Fred Vine and Drummond Matthews, 1963 and Morley, 1963) * Late 60 s until today: Refining the theory (Wilson, Morgan, McKenzie, etc.)

10 History was driven by a Naturalist viewpoint (continental drift) and a Physicist viewpoint (mantle convection)

11 2. Surface kinematics

12 Relief noaa * topography / bathymetry * Plate boundaries: Convergence Divergence Transform

13 Relief noaa A variety of morphologies at convergence zone. Plateaus, mountain ranges, oceanic basins A variety of plate pairs: * ocean / continent, les Andes * ocean / ocean, Marianas * continent / continent, Himalaya * blurry mix: the Med

14 Any$systema*cs$to$plate$boundary$relief?$$ noaa Mountains associated to convergence? Mountains associated to continent / continent? Mountains to continental upper plates? NO! E.g. W pacific No! The Andes NO! Java or Aegean

15 Stresses?$ world stress map extension Compression strike-slip

16 noaa Trench$mo*on:$any$systema*cs$in$trench$kinema*cs?$

17 An old story (Chase, 1978) (Uyeda Kanamori, 1979)

18 noaa noaa Convergent$boundaries$:$ *$include$advancing$and$retrea*ng$trenches$ *$are$extensive/compressive$regardless$of$mountain$belts/back$arc$

19 We need: Upper plate velocity, lower plate velocity Insights$from$plate$kinema*cs$ NUVEL1A-HS3

20 Absolute$plate$mo*on$in$the$hotspot$reference$frame$ Ou en inversant les SKS

21 Kinema*cs:$the$reference$frame$issue$$

22 Kinema*cs:$the$reference$frame$issue$$

23 Upper plate velocity (Vsup) Lower plate velocity (Vinf) Trench velocity (Vtrench) kinema*cs$

24 Vup > Vtrench: mountain Vup < Vtrench: back-arc basin kinema*cs$

25 Vup > Vtrench: mountain Vup < Vtrench: back-arc basin kinema*cs$

26 3. Subduction dynamics

27 driving dorsale dorsale ridge push slab pull / slab suction) mantle drag MANTEAU resisting subduction Forces need to cancel out. Need for resisting forces mantle drag - interplate coupling MANTEAU

28 (Becker & O Connell, 2001)

29 General wisdom from the 90 s say slab pull does everything. Really?

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35 Subducting plates

36 slab$pull$ (Conrad and Lithgow-Bertelloni)

37 Quan*fying$slab$pull$ α= K -1 Tm=1300 K T0= 0 K ρ0=3000 kg m -3 F sp $=$Δρ$g$V$ Δρ$~$(Tm@T0)/2$x$α x $ $ $ $$ V=$z um $x$h $ $ F sp $=$Δρ$g$V $ $ $ $~$x$10 13 $ $ => $BIG! $

38 Subduc*ons$and$rollback$ $ $ Trench (e.g. Malinverno migration & Ryan, in the 86; Mediterranean Royden, 96) (Funiciello et al.)

39 @ $ $ $ Seismic$anisotropy$ Slab$curvature$ (Pearce et al., 2005)

40 @ $ $ $ Seismic$anisotropy$ Slab$curvature$ (Long & Silver, 2008)

41 Slab$curvature$ $ $ $ (Gudmundson & Sambridge, 1998)

42 Slab$curvature$ $ $ $ deviatoric stresses around a retreating slab (Schellart et al., 2004) (Morra and Regenauer-Lieb, 2006) (Gudmundson & Sambridge, 1998) (Loiselet et al., 2009) η slab < 100 x η mantle

43 (e.g. Malinverno & Ryan, 86; Royden, 96)

44 driven by gravity resisted by the viscous dissipation in the mantle toroidal flow poloidal flow (Piromallo et al., 2005)

45 Faccenna style subductions : rollback seems to be the natural behaviour of slabs (exp Francesca Funiciello)

46 Trench retreat rates range from +130 mm/yr to -50 mm/yr (Schellart et al., 07 Heuret & Lallemand 05) Some trenches advance! Some slabs are curved the other way around!

47 - slab viscosity - mantle viscosity - slab width - slab thickness predict slab - rollback buoyancy! - H sediments Models almost always (Funiciello, Bellhasen, Capitanio, Schellart, Stegman, Billen, Royden, Enns, di Giuseppe, Conrad, Faccenna )

48 Slab$pull$vs$slab$suc*on$ (Conrad and Lithgow-Bertelloni, 2004)

49 Slab buoyancy and slab rollback$ Slab Slab buoyancy is is an an obvious obvious candidate to to explain explain the the variations in in trench trench migration migration rates rates Trenches Trenches retreats retreats faster faster when when negative negative buoyancy increases.

50 Trench retreat rates negative buoyancy Trench retreat rates decrease when negative buoyancy increases Trench retreat rates decrease when negative buoyancy increases

51 Trench retreat rates decrease when negative buoyancy increases Trench retreat rates decrease when negative buoyancy increases

52 (Jarrard, 1986)

53 Cri*cal$age$of$subduc*on$zones$ $ $ $ Boundary layer theory says that the lithosphere subducts when old and dense enough. there should be a critical age of subduction (~80 Ma). V ridge D=constant??

54 Cri*cal$age$of$subduc*on$zones$ $ $ $ Plates subduct regardless of the intrinsic properties of subduction zones. Boundary layer theory says that the lithosphere subducts when old and dense enough. there should be a critical age of subduction (~80 Ma). applied to the Earth, there should be no rollback! V ridge D=constant??

55 - slab viscosity - mantle viscosity - slab width - slab thickness predict extension! - slab buoyancy - H sediments Models almost always (Funiciello, Bellhasen, Capitanio, Schellart, Stegman, Billen, Royden, Enns, di Giuseppe, Conrad, Faccenna )

56 Upper$plate$strain$ (Kreemer et al. 2014)

57 Upper$plate$strain$ (Kreemer et al. 2014)

58 Upper$plate$strain$ (Kreemer et al. 2014)

59 Theory says : 1. Slabs rollback => failed! 2. The older the faster the rollback => failed! 3. Subductions at a critical age => failed! 4. Subductions cause extension => failed! - Why is everything going wrong? Slab buoyancy is an obvious candidate - Are subducting to explain the slabs variations really the in prime drivers of trench plate migration tectonics? rates - Trenches Can subduction retreats faster zones when be more sophisticated? negative buoyancy increases.