M1_-_Geomorphology_-_Tectonic_Geomorphology

TECTONIC GEOMORPHOLOGYBenjamin Guillaume

GEOMORPHOLOGY

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[from greek gê, Earth and morphê, shape and logos, speech] «the branch of geology that is concerned with the

structure, origin, and development of the topographical features of the Earth's surface»

TECTONICS

[from greek tektonikos, relating to building] «the branch of geology relating to the structure of the Earth’s

crust and the large-scale processes which take place within it»

TOPOGRAPHY

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Topography (ETOPO1)

-10.9 km <elevation< 8.9 kmMariannes trench Everest

PLATE TECTONICS

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Chamot-Rooke et Rabote (2006)

Morgan, McKenzie et Le Pichon (1967)Wegener (1912)

• diverging plate boundaries (spreading ridges)• transform plate boundaries (transform faults)• converging plate boundaries (subduction-collision)

PLATE TECTONICS

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Chamot-Rooke et Rabote (2006)

Morgan, McKenzie et Le Pichon (1967)Wegener (1912)

~1 cm/yr <convergence velocity< ~25 cm/yr

PLATE TECTONICS

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John Nelson, IDV Solutions

maximum released energy and deformation at convergent plate boundaries

“Pacific ring of fire“

The shape of the EARTH is controlled at first-order by plate tectonics and modulated by surface processes

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60˚S 60˚S

30˚S 30˚S

0˚ 0˚

30˚N 30˚N

60˚N 60˚N

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Tectonics act at different time-scales

sec

10’s of Myr

earthquakes

mountain building

Burbank and Anderson (2012)

SHORT-TERM DEFORMATION

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Some theory

ß = 45° + Ω/2Ω : internal friction angle

ß = 45° - Ω/2

π = 45° - Ω/2

SHORT-TERM DEFORMATION

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Some theory

right-lateralstrike-slip fault

2-stages process

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Example : Nankaido (Japan) December 1946 Mw : 8.1

after Hyndman and Wang (1995)opposite vertical motions during coseismic and interseismic stages

subduction thrust fault

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Models for earthquake recurrence

after Shimaki and Nakata (1980) and Friedrich et al. (2003)

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Earthquake nucleation

after Zielke and Arrowsmith (2008)

controlled by the difference between coefficients of dynamic and static friction= maximum slip where Δt is largest

Slip propagates toward the surface : a few 10’s mm to 10’s cm

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Length-displacement ratios on faults

after Scholz (1990), Schlische et al. (1996), and Davis et al. (2005)

Maximum displacement ranges from 0.3% to 30% of fault length

GEOMORPHIC EXPRESSION OF FAULTS

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Strike-slip fault zones(maximum compressive stress is horizontal + horizontal deviatoric tensile stress)

Garlock fault (California)

• Offset drainage channel• Beheaded stream• Linear valley

➜ Location of fault trace and direction of relative motion

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Strike-slip fault zones

Right-lateral / left-lateral?

San Andreas fault (California)

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Right-lateral strike-slip fault!

San Andreas fault (California)

Strike-slip fault zones

Normal faults(maximum compressive stress is vertical + horizontal deviatoric tensile stress)

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2D

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3D

East African rift system

after Morley (1989)

Transfer of displacement between adjacent major faults

Normal faults(maximum compressive stress is vertical + horizontal deviatoric tensile stress)

2D

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after Stein et al. (1988)

Example : Lost River Range (Idaho) 1983 - M = 7.0

Asymmetry during coseismic phase

Persists during interseismic phase

Thrust faults : the most destructive earthquakes

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Since 1960’s : • Great Chilean (1960 ; Mw = 9.5)• Alaska (1964 ; Mw = 9.2)• Sumatra-Andaman (2004 ; Mw = 9.1)• Tohoku-Oki (2011 ; Mw = 9.0)

Thrust faults(maximum compressive stress is horizontal + vertical deviatoric tensile stress)

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short-term

long-termafter Stein et al. (1988)

Example : Kern County (California) 1952 - M = 7.3

Thrust faults : model of deformation during earthquake cycle

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after Davis et al. (2005)

Different models of folds (see your textbooks...)

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GEOMORPHIC EXPRESSION OF FOLDS

after Hubert-Ferrari et al. (2007)

Surface expression of slip gradients

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Displacement variations in the subsurface fault are directly related to the magnitude of rock uplift at the surface.

Lateral fold growth

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Example : Wheeler Ridge anticline

after Burbank et al. (1996)

Lateral fold growth

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Example : Wheeler Ridge anticline

• Intense dissection on the steeply dipping flank of the fold

• Deflection of streams toward the east by the growing fold

after Burbank et al. (1996)

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EARTHQUAKE-TRIGGERED EROSION : LANDSLIDES

Papua - New Guinea (courtesy of N. Hovius)

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Landslides triggered by earthquakes develop preferentially close to crests and channels

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Amplification of seismic shaking near crests

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Amplification of seismic shaking near crests

Higher pore pressures + local steepening of hillslopes by river incision near channels

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METHODS FOR MEASURING SHORT-TERM DEFORMATION AND TOPOGRAPHY

• Trilateration arrays (horizontal)• Tide gauges (vertical)• Tropical corals (vertical)• GPS (horizontal + vertical)• Radar interferometry (horizontal)• Lidar imaging (vertical)• ASTER imagery (vertical)• ....

See Burbank and Anderson, Tectonic geomorphology, 2012

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DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES

Intermediate time-scales?

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Holocene-Pleistocene boundary (11.6 ky) ➜ 300-400 ky

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Landscape = episodic + continuous tectonic and geomorphic processes

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• Allows determining long-term mean rate of deformation• Needed to compare with shorter-term record

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• Allows determining long-term mean rate of deformation• Needed to compare with shorter-term record

Mean vertical uplift of 1 mm/yr and horizontal deformation of 1 cm/yr gives 400 m of vertical motion and 4 km of horizontal motion

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At these time-scales : • Pristine tectonic forms become degraded by erosion• Major glacial-interglacial cycles : specific geomorphic markers (marine terraces, fluvial terraces)

after Porter (1989) and Lisiecki and Raymo (2005)

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CALIBRATING RATES OF DEFORMATION

Marine terraces : formation

Terraces form during highstand sea-level and are abandoned during lowstand sea-level

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Marine terraces : formation

Regard et al. (2010)

Uplift rate from age-elevation relationship

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Marine terraces : extracting uplift rates

Steady Uplift rate = Elevation / Age

after Lajoie (1986)

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Unsteady Uplift rate = Elevation / Age

after Merritts and Bull (1989)

northern California

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UpliftRateΔi0 = (ShAi −Ei)/ Agei

Mean uplift rate over a time interval ti–t0 (Δi0) between each marine terrace (i) and present sea level (0)

If age of the surface is known directly (cosmogenic datation, U-Th,...) or indirectly (relative to Marine

Isotopic Stage)

ShAi : present-day elevation of the shoreline angle of the marine terrace (time ti)Ei : sea-level elevation at ti compared to the present sea level

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UpliftRateΔij = [(ShAi - Ei) - (ShAj - Ej)]/ [Agei - Agej]

Incremental uplift rate over a time interval ti–tj (Δij) between two successives marine terraces

ShAi : present-day elevation of the shoreline angle of the marine terrace (time ti)Ei : sea-level elevation at ti compared to the present sea level


If age of the surface is known directly (cosmogenic datation, U-Th,...) or indirectly (relative to Marine

Isotopic Stage)

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A CASE STUDY : SOUTH AMERICA

Tectonic framework

Espurt et al. (2008)

• Subduction of the Nazca plate beneath the South American plate for 10’s of Myr

• Present-day convergence velocity = 8 cm/yr

• Subduction of ridges (topographic anomalies = thickenned crust produced by hot spot volcanism)

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A CASE STUDY : SOUTH AMERICA

Tectonic framework

Espurt et al. (2008)

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Shore morphology

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Methodology : example of Punta Choros (Chile)

• DEM from aerial stereophotos• Identification of terraces = break-in-slope on cross-sections

• Sampling for cosmogenic dating (10Be)

> 400 ky

> 400 ky

➜ Uplift rate J. Maison (M1, 2013)

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Rasa age evaluation - lower level (~110 m)

Regard et al. (2010)

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Main results

The Central Andes coast morphology (rasa) seems to indicate that uplift is:• Recent (Quaternary, with evidences of preexisting subsidence)• Wide (most probably due to subduction)• MIS 11 (~400 kyrs BP) appears to have been particularly marked: variation in uplift rate or greater efficiency in erosion?

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MIS 5e uplift rates (~100 ky)

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Taux de soulèvement(MIS 5e)

Ride de Carnegie

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Higher uplift rates related to topographic anomalies within the subducting plate

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Marine terraces : determining slip rates on faults

San Juan (Chile)

Saillard et al. (2011)

Loma Fault

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Saillard et al. (2011)

SlipRateΔij = (ShACEHi −ShACTHi) - (ShACEHj −ShACTHj) / (Agei −Agej)

Marine terraces : determining slip rates on faults

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Marine terraces : folding and shortening rates

Melnick et al. (2009)

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Fluvial terraces : formation

Unlike marine terraces, fluvial terraces are not necessarily horizontal

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Fluvial terraces : are diachronous

Terrace T6 at Cajon Creek (California)

after Weldon (1986)

4 ky

7 ky

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Fluvial terraces : displacement across faults

Wellington Fault (New-Zealand)

after Van Dissen et al. (1992)

Increase of the amount of offset with age

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Fluvial terraces : displacement across faults

Ventura River (California)

• Asymmetry in faulting rate• Maximum faulting rate at the core of the fold• Increase of the amount of offset with terrace age• Variable faulting rate on single fault

after Rockwell et al. (1984)

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Stream gradient : principle

For a uniform lithology, anomalously steep or gentle profile may be interpreted in term of ongoing tectonism

after Duvall et al. (2004)

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Stream gradient : physical modeling

Adaptation of the river profile to a change in tectonic uplift rate : knickpoint

knickpoint sweeps upstream

courtesy of D. Lague

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Stream gradient : knickpoints

Uplift rate x2

after Whipple and Tucker (1999)

Formation of a knickpoint that sweeps upstream- lower channel steepens - upper channel retains its initial gradient

Same concavity but different steepness

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Stream gradient : extracting uplift history from river profiles

Rate of change of elevation ∂z/∂t along a river profile :

∂z/∂t = U(x,t) + E(x,t)

x : distance along river profileU : rate of rock upliftE : rate of erosion

E(x,t) = -vAm (∂z/∂x)n + k (∂2z/∂x2)

n and m : constants affecting the concavity of a river profile (n generally taken = 1)Am : related to average discharge along a riverv and m : control the value of the advective term, which governs the transient form of a river profile and the knickpoint retreat velocitiesk : erosional diffusivity (10-107 m2 Ma-1)

➜ U(x,t)

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Inverse modeling testing plausible parameters values (2x102 <k< 7x102 ; 200<v<210 ; 0.19 <m< 0.21; 1<n<1.05)

Roberts et al. (2012)

In gray : observed profileIn black : best-fitting profile

Colorado catchment

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Roberts et al. (2012) Colorado catchment

Getting uplift rate history for different parameters

best-fit to river profile

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Roberts et al. (2012) Madagascar

Applying to a large number of rivers to get spatial uplift history

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Madagascar

Maps of cumulative uplift

Roberts et al. (2012)

Drawback : only works for uplifted areas

TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES

Larger time-scales?


Larger time-scales?

Time required for the growth and decay of a mountain chain = 10’s of Myr


Larger time-scales?


Currently observable deformation patterns, climate and erosion rates may have only tangential relevance to a range’s overall evolution


Larger time-scales?



At these time-scales, detailed interactions of short-term deformation and surface processes are often obscured


Larger time-scales?



At these time-scales, detailed interactions of short-term deformation and surface processes are often obscured

Larger spatial framework: 100’s to 1000’s of km

Climate and tectonics

Climate(through erosion)

Tectonics



Tectonics

Erosion-controlled isostatic uplift (Molnar and England, 1990)



Tectonics


Widening/narrowing of orogens in response to erosion (e.g., Whipple and

Meade, 2006)



Tectonics



Meade, 2006)

Enhanced deformation where rainfall is high (e.g., Willett, 1999)

...



Tectonics



Meade, 2006)

Problems of dataset (often use of proxy, e.g. cooling and not erosion rate) and time-frame of correlations

Enhanced deformation where rainfall is high (e.g., Willett, 1999)

...


Cooling age = Age at which a rock crosses the closure temperature of a

specific thermochronometer

Zr FT : 220°CAp FT : 110°CAp He : 60°C

Proxy for erosion rate : younger age = faster erosion


Two possible scenari :

Acceleration of erosion rates into a increasingly narrow zone over the last 5 My (B)

vs. Spatially focused erosion pattern persisting for Myr (C)


TectonicsClimate(through erosion)


Tectonics

Orographic rainfall (Burbank et al., 2003)

Loci of high rainfall develop on the upwind side of a range vs rain shadow develop on the downwind side



Example : summer monsoon in the Himalayas

Bookhagen and Burbank (2010)


Example : summer monsoon in the Himalayas

Bookhagen and Burbank (2010)

Monsoon rainfall produces a peak associated with each topographic step

Latitudinal gradients in climate and tectonics

Elongate N-S oriented ranges can span latitudinal bands with contrasting climate regimes

Latitudinal gradients in climate and tectonics

Elongate N-S oriented ranges can span latitudinal bands with contrasting climate regimes

Montgomery et al. (2001)

Example : the Andes

the Andes : latitudinal gradients in climate and tectonics




Variable amount of sediments provided to the trench


Lamb and Davies (2003)

Central Andes : - low precipitation- low trench fill thickness (deep trench)- high interplate coupling- high topography

Northern and Southern Andes : the opposite

It’s a model...

Dynamic topography

WHEN MANTLE FLOW IS INVOLVED...

«Surface deformation associated with density driven convection in the sub-lithospheric mantle»

Dynamic topography

WHEN MANTLE FLOW IS INVOLVED...

«Surface deformation associated with density driven convection in the sub-lithospheric mantle»

Large-scale signal (100’s of km) and moderate amplitude (~100‘s of m)

Dynamic topography

Well expressed in areas with no recent tectonic activity (e.g., Africa)

Present-day topography

F. Guillocheau

Moucha and Forte (2011)

Signature of a plume

Tomography

Dynamic topography

Well expressed in areas with no recent tectonic activity (e.g., Africa)

Present-day topography

F. Guillocheau

∆ Dynamic topo (10 Ma-0 Ma)

Moucha and Forte (2011)

Dynamic topography

Inverse signal of equal amplitude above high density anomalies (subduction zones)

Steinberger (2007)

Dynamic topography

Inverse signal of equal amplitude above high density anomalies (subduction zones)

but signal convoluted with isostatic response of the lithosphere to convergence (generally of higher amplitude)

Steinberger (2007)

Dynamic topography

Control the fraction of inundated continents

60˚S 60˚S

30˚S 30˚S

0˚ 0˚

30˚N 30˚N

60˚N 60˚N

−10000 −8000 −6000 −4000 −2000 0 2000 4000 6000 8000

m

Present-day elevation

Dynamic topography

Control the fraction of inundated continents

60˚S 60˚S

30˚S 30˚S

0˚ 0˚

30˚N 30˚N

60˚N 60˚N

−10000 −8000 −6000 −4000 −2000 0 2000 4000 6000 8000

m

Present-day elevation -200m

Dynamic topography : tilting of the Australian continent

Sandiford (2007)

Subduction to the North : downward deflection

Mid-ocean ridge to the South : upward deflection

Dynamic topography : tilting of the Australian continent

Sandiford (2007)

Subduction to the North : downward deflection

Mid-ocean ridge to the South : upward deflection

Down to the north tilt of the continent!

(as recorded by shoreline migration for the last 15 Myr)

M1_-_Geomorphology_-_Tectonic_Geomorphology

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