TECTONIC GEOMORPHOLOGY. Benjamin Guillaume

Transcription

1 TECTONIC GEOMORPHOLOGY Benjamin Guillaume

2 GEOMORPHOLOGY [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» 1 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» -1

3 TOPOGRAPHY km <elevation< 8.9 km Mariannes trench Everest -1 Topography (ETOPO1)

4 PLATE TECTONICS Wegener (1912) Morgan, McKenzie et Le Pichon (1967) 1 Chamot-Rooke et Rabote -1 (26) diverging plate boundaries (spreading ridges) transform plate boundaries (transform faults) converging plate boundaries (subduction-collision)

5 PLATE TECTONICS Wegener (1912) Morgan, McKenzie et Le Pichon (1967) 1 Chamot-Rooke et Rabote -1 (26) ~1 cm/yr <convergence velocity< ~25 cm/yr

6 PLATE TECTONICS 1-1 John Nelson, IDV Solutions maximum released energy and deformation at convergent plate boundaries Pacific ring of fire

7 The shape of the EARTH is controlled at first-order by plate tectonics and modulated by surface processes 1 6 N 6 N 3 N 3 N 3 S 3 S 6 S 6 S -1

8 Tectonics act at different time-scales mountain building 1 s of Myr 1-1 earthquakes sec Burbank and Anderson (212)

9 SHORT-TERM DEFORMATION Some theory 1 ß = 45 + Ω/2 Ω : internal friction angle ß = 45 - Ω/2-1 π = 45 - Ω/2

10 SHORT-TERM DEFORMATION Some theory 1 right-lateral strike-slip fault 2-stages process -1

11 Example : Nankaido (Japan) December 1946 M w : subduction thrust fault opposite vertical motions during coseismic and interseismic stages -1 after Hyndman and Wang (1995)

12 Models for earthquake recurrence 1-1 after Shimaki and Nakata (198) and Friedrich et al. (23)

13 Earthquake nucleation 1 controlled by the difference between coefficients of dynamic and static friction = maximum slip where Δt is largest Slip propagates toward the surface : a few 1 s mm to 1 s cm -1 after Zielke and Arrowsmith (28)

14 Length-displacement ratios on faults 1-1 Maximum displacement ranges from.3% to 3% of fault length after Scholz (199), Schlische et al. (1996), and Davis et al. (25)

15 GEOMORPHIC EXPRESSION OF FAULTS 1 Strike-slip fault zones (maximum compressive stress is horizontal + horizontal deviatoric tensile stress) Offset drainage channel Beheaded stream Linear valley Garlock fault (California) -1 Location of fault trace and direction of relative motion

16 Strike-slip fault zones 1-1 San Andreas fault (California) Right-lateral / left-lateral?

17 Strike-slip fault zones 1-1 San Andreas fault (California) Right-lateral strike-slip fault!

18 Normal faults (maximum compressive stress is vertical + horizontal deviatoric tensile stress) 2D 1-1

19 Normal faults (maximum compressive stress is vertical + horizontal deviatoric tensile stress) 2D 1 East African rift system 3D Transfer of displacement -1 between adjacent major faults after Morley (1989)

20 Example : Lost River Range (Idaho) M = 7. 1 Asymmetry during coseismic phase Persists during interseismic phase -1 after Stein et al. (1988)

21 Thrust faults : the most destructive earthquakes Since 196 s : Great Chilean (196 ; Mw = 9.5) Alaska (1964 ; Mw = 9.2) Sumatra-Andaman (24 ; Mw = 9.1) Tohoku-Oki (211 ; Mw = 9.) 1-1

22 short-term Thrust faults (maximum compressive stress is horizontal + vertical deviatoric tensile stress) 1 Example : Kern County (California) M = after Stein et al. (1988) long-term

23 Thrust faults : model of deformation during earthquake cycle 1-1 after Davis et al. (25)

24 GEOMORPHIC EXPRESSION OF FOLDS Different models of folds (see your textbooks...) 1-1 after Hubert-Ferrari et al. (27)

25 Surface expression of slip gradients Displacement variations in the subsurface fault are directly related to the magnitude of rock uplift at the surface. 1-1

26 Lateral fold growth 1 Example : Wheeler Ridge anticline -1 after Burbank et al. (1996)

27 Lateral fold growth 1 Example : Wheeler Ridge anticline Intense dissection on the steeply dipping flank of the fold Deflection of streams toward the east by the growing fold -1 after Burbank et al. (1996)

28 EARTHQUAKE-TRIGGERED EROSION : LANDSLIDES 1 Papua - New Guinea (courtesy of N. Hovius)

29 EARTHQUAKE-TRIGGERED EROSION : LANDSLIDES Landslides triggered by earthquakes develop preferentially close to crests and channels 1-1

30 EARTHQUAKE-TRIGGERED EROSION : LANDSLIDES Landslides triggered by earthquakes develop preferentially close to crests and channels 1 Amplification of seismic shaking near crests -1

31 EARTHQUAKE-TRIGGERED EROSION : LANDSLIDES Landslides triggered by earthquakes develop preferentially close to crests and channels 1 Amplification of seismic shaking near crests -1 Higher pore pressures + local steepening of hillslopes by river incision near channels

32 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, 212

33 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES Intermediate time-scales? 1-1

34 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES Intermediate time-scales? 1 Holocene-Pleistocene boundary (11.6 ky) 3-4 ky -1

35 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES Intermediate time-scales? 1 Holocene-Pleistocene boundary (11.6 ky) 3-4 ky Landscape = episodic + continuous tectonic and geomorphic processes -1

36 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES Intermediate time-scales? 1 Holocene-Pleistocene boundary (11.6 ky) 3-4 ky Landscape = episodic + continuous tectonic and geomorphic processes Allows determining long-term mean rate of deformation Needed to compare with shorter-term record -1

37 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES Intermediate time-scales? 1 Holocene-Pleistocene boundary (11.6 ky) 3-4 ky Landscape = episodic + continuous tectonic and geomorphic processes Allows determining long-term mean rate of deformation Needed to compare with shorter-term record -1 Mean vertical uplift of 1 mm/yr and horizontal deformation of 1 cm/yr gives 4 m of vertical motion and 4 km of horizontal motion

38 DEFORMATION AND GEOMORPHOLOGY AT INTERMEDIATE TIME-SCALES At these time-scales : Pristine tectonic forms become degraded by erosion Major glacial-interglacial cycles : specific geomorphic markers (marine terraces, fluvial terraces) 1-1 after Porter (1989) and Lisiecki and Raymo (25)

39 CALIBRATING RATES OF DEFORMATION Marine terraces : formation 1 Terraces form during highstand sea-level and are abandoned during lowstand sea-level -1

40 CALIBRATING RATES OF DEFORMATION Marine terraces : formation 1 Uplift rate from age-elevation relationship -1 Regard et al. (21)

41 Marine terraces : extracting uplift rates 1-1 after Lajoie (1986) Steady Uplift rate = Elevation / Age

42 Marine terraces : extracting uplift rates 1 northern California -1 after Merritts and Bull (1989) Unsteady Uplift rate = Elevation / Age

43 Marine terraces : extracting uplift rates If age of the surface is known directly (cosmogenic datation, U-Th,...) or indirectly (relative to Marine Isotopic Stage) 1 Mean uplift rate over a time interval ti t (Δi) between each marine terrace (i) and present sea level () UpliftRate Δi = (ShA i E i )/ Age i -1 ShA i : present-day elevation of the shoreline angle of the marine terrace (time t i ) Ei : sea-level elevation at t i compared to the present sea level

44 Marine terraces : extracting uplift rates If age of the surface is known directly (cosmogenic datation, U-Th,...) or indirectly (relative to Marine Isotopic Stage) 1 Incremental uplift rate over a time interval t i t j (Δij) between two successives marine terraces UpliftRate Δij = [(ShA i - E i ) - (ShA j - E j )]/ [Age i - Age j ] -1 ShA i : present-day elevation of the shoreline angle of the marine terrace (time t i ) Ei : sea-level elevation at t i compared to the present sea level

45 A CASE STUDY : SOUTH AMERICA Tectonic framework 1 Subduction of the Nazca plate beneath the South American plate for 1 s of Myr Present-day convergence velocity = 8 cm/yr Subduction of ridges (topographic anomalies = thickenned crust produced by hot spot volcanism) -1 Espurt et al. (28)

46 A CASE STUDY : SOUTH AMERICA Tectonic framework 1-1 Espurt et al. (28)

47 Shore morphology 1-1

48 Methodology : example of Punta Choros (Chile) DEM from aerial stereophotos Identification of terraces = break-inslope on cross-sections > 4 ky 1 > 4 ky Sampling for cosmogenic dating ( 1 Be) -1 Uplift rate J. Maison (M1, 213)

49 Rasa age evaluation - lower level (~11 m) 1-1 Regard et al. (21)

50 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 (~4 kyrs BP) appears to have been particularly marked: variation in uplift rate or greater efficiency in erosion? 1-1

51 MIS 5e uplift rates (~1 ky) Ride de Carnegie 1 Higher uplift rates related to topographic anomalies within the subducting plate Taux de soulèvement (MIS 5e) mm/an.6.5 Ride de Nazca after Pedoja et al. (211)

52 Marine terraces : determining slip rates on faults San Juan (Chile) 1 Loma Fault -1 Saillard et al. (211)

53 Saillard et al. (211) Marine terraces : determining slip rates on faults SlipRate Δij = (ShA CEHi ShA CTHi ) - (ShA CEHj ShA CTHj ) / (Age i Age j ) 1-1

54 Marine terraces : folding and shortening rates 1-1 Melnick et al. (29)

55 CALIBRATING RATES OF DEFORMATION Fluvial terraces : formation 1-1 Unlike marine terraces, fluvial terraces are not necessarily horizontal

56 CALIBRATING RATES OF DEFORMATION Fluvial terraces : are diachronous 1 Terrace T6 at Cajon Creek (California) 7 ky 4 ky -1 after Weldon (1986)

57 Fluvial terraces : displacement across faults Wellington Fault (New-Zealand) 1 Increase of the amount of offset with age -1 after Van Dissen et al. (1992)

58 Fluvial terraces : displacement across faults 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 1-1 Ventura River (California) after Rockwell et al. (1984)

59 CALIBRATING RATES OF DEFORMATION Stream gradient : principle 1-1 after Duvall et al. (24) For a uniform lithology, anomalously steep or gentle profile may be interpreted in term of ongoing tectonism

60 Stream gradient : physical modeling Adaptation of the river profile to a change in tectonic uplift rate 1: knickpoint knickpoint sweeps upstream -1 courtesy of D. Lague

61 Stream gradient : knickpoints Uplift rate x2 1 Formation of a knickpoint that sweeps upstream - lower channel steepens - upper channel retains its initial gradient Same concavity but different steepness after Whipple and Tucker (1999) -1

62 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) 1 x : distance along river profile U : rate of rock uplift E : rate of erosion E(x,t) = -va m ( z/ x) n + k ( 2 z/ x 2 ) n and m : constants affecting the concavity of a river profile (n generally taken = 1) A m : related to average discharge along a river v and m : control the value of the advective term, which governs the transient form -1 of a river profile and the knickpoint retreat velocities k : erosional diffusivity (1-1 7 m 2 Ma -1 ) U(x,t)

63 Stream gradient : extracting uplift history from river profiles Inverse modeling testing plausible parameters values (2x1 2 <k< 7x1 2 ; 2<v<21 ;.19 <m<.21; 1<n<1.5) 1 In gray : observed profile In black : best-fitting profile -1 Roberts et al. (212) Colorado catchment

64 Stream gradient : extracting uplift history from river profiles Getting uplift rate history for different parameters 1 best-fit to river profile -1 Roberts et al. (212) Colorado catchment

65 Stream gradient : extracting uplift history from river profiles Applying to a large number of rivers to get spatial uplift history 1-1 Roberts et al. (212) Madagascar

66 Stream gradient : extracting uplift history from river profiles Maps of cumulative uplift 1 Madagascar Drawback : only works for uplifted areas -1 Roberts et al. (212)

67 TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES Larger time-scales?

68 TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES Larger time-scales? Time required for the growth and decay of a mountain chain = 1 s of Myr

69 TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES Larger time-scales? Time required for the growth and decay of a mountain chain = 1 s of Myr Currently observable deformation patterns, climate and erosion rates may have only tangential relevance to a range s overall evolution

70 TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES Larger time-scales? Time required for the growth and decay of a mountain chain = 1 s of Myr Currently observable deformation patterns, climate and erosion rates may have only tangential relevance to a range s overall evolution At these time-scales, detailed interactions of short-term deformation and surface processes are often obscured

71 TECTONIC GEOMORPHOLOGY AT LARGER TIME-SCALES Larger time-scales? Time required for the growth and decay of a mountain chain = 1 s of Myr Currently observable deformation patterns, climate and erosion rates may have only tangential relevance to a range s overall evolution At these time-scales, detailed interactions of short-term deformation and surface processes are often obscured Larger spatial framework: 1 s to 1 s of km

72 Climate and tectonics Climate (through erosion) Tectonics

73 Climate and tectonics Climate (through erosion) Tectonics Erosion-controlled isostatic uplift (Molnar and England, 199)

74 Climate and tectonics Climate (through erosion) Tectonics Erosion-controlled isostatic uplift (Molnar and England, 199) Widening/narrowing of orogens in response to erosion (e.g., Whipple and Meade, 26)

75 Climate and tectonics Climate (through erosion) Tectonics Erosion-controlled isostatic uplift (Molnar and England, 199) Widening/narrowing of orogens in response to erosion (e.g., Whipple and Meade, 26) Enhanced deformation where rainfall is high (e.g., Willett, 1999)...

76 Climate and tectonics Climate (through erosion) Tectonics Erosion-controlled isostatic uplift (Molnar and England, 199) Widening/narrowing of orogens in response to erosion (e.g., Whipple and Meade, 26) Enhanced deformation where rainfall is high (e.g., Willett, 1999)... Problems of dataset (often use of proxy, e.g. cooling and not erosion rate) and time-frame of correlations

77 Climate and tectonics Cooling age = Age at which a rock crosses the closure temperature of a specific thermochronometer Zr FT : 22 C Ap FT : 11 C Ap He : 6 C Proxy for erosion rate : younger age = faster erosion

78 Climate and tectonics

79 Climate and tectonics 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)

80 Climate and tectonics Climate (through erosion) Tectonics

81 Climate and tectonics Climate (through erosion) Tectonics Orographic rainfall (Burbank et al., 23) Loci of high rainfall develop on the upwind side of a range vs rain shadow develop on the downwind side

82 Climate and tectonics Example : summer monsoon in the Himalayas Bookhagen and Burbank (21)

83 Climate and tectonics Example : summer monsoon in the Himalayas Monsoon rainfall produces a peak associated with each topographic step Bookhagen and Burbank (21)

84 Latitudinal gradients in climate and tectonics Elongate N-S oriented ranges can span latitudinal bands with contrasting climate regimes

85 Latitudinal gradients in climate and tectonics Elongate N-S oriented ranges can span latitudinal bands with contrasting climate regimes Example : the Andes Montgomery et al. (21)

86 the Andes : latitudinal gradients in climate and tectonics Montgomery et al. (21)

87 the Andes : latitudinal gradients in climate and tectonics Variable amount of sediments provided to the trench Montgomery et al. (21)

88 the Andes : latitudinal gradients in climate and tectonics 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... Lamb and Davies (23)

89 WHEN MANTLE FLOW IS INVOLVED... Dynamic topography «Surface deformation associated with density driven convection in the sub-lithospheric mantle»

90 WHEN MANTLE FLOW IS INVOLVED... Dynamic topography «Surface deformation associated with density driven convection in the sub-lithospheric mantle» Large-scale signal (1 s of km) and moderate amplitude (~1 s of m)

91 Dynamic topography Well expressed in areas with no recent tectonic activity (e.g., Africa) Present-day topography Tomography Moucha and Forte (211) Signature of a plume F. Guillocheau

92 Dynamic topography Well expressed in areas with no recent tectonic activity (e.g., Africa) Present-day topography Dynamic topo (1 Ma- Ma) F. Guillocheau Moucha and Forte (211)

93 Dynamic topography Inverse signal of equal amplitude above high density anomalies (subduction zones) Steinberger (27)

94 Dynamic topography Inverse signal of equal amplitude above high density anomalies (subduction zones) Steinberger (27) but signal convoluted with isostatic response of the lithosphere to convergence (generally of higher amplitude)

95 Dynamic topography Control the fraction of inundated continents 6 N 6 N 3 N 3 N 3 S 3 S 6 S 6 S Present-day elevation m

96 Dynamic topography Control the fraction of inundated continents 6 N 6 N 3 N 3 N 3 S 3 S 6 S 6 S Present-day elevation -2m m

97 Dynamic topography : tilting of the Australian continent Subduction to the North : downward deflection Mid-ocean ridge to the South : upward deflection Sandiford (27)

98 Dynamic topography : tilting of the Australian continent 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) Sandiford (27)