Lecture 2: Tectonics of Rocky Planets

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Arnold Dixon
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1 Lecture 2: Tectonics of Rocky Planets

2 Lithosphere is a thermal boundary layer where heat transport is Lithosphere is a dominated by conduction. On Earth, this layer is treated as a rigid layer from which plate kinematics can be derived. T o C Depth (km) Thermal boundary layer (heat transport by conduction) Crust Mantle Lithosphere Conduction Convection (nearly isothermal)

3 Discrete deformation along plate boundaries and recycling of the thermal boundary layer on Earth

4 Earth has a unified and kinematically linked GLOBAL plate-tectonics network, but this network probably did not start all at once. The thermal boundary layer is recycled by subduction and seafloor spreading. Twiss and Moores (2010)

Plate Tectonics The shell is so broken that

5 Plate Tectonics The shell is so broken that the mantle rises to the surface! Fragments of shells move great distance relative to one another. Stagnant-lid Tectonics Shell may be slightly broken, but no significant motion of individual fragments with one another.

6 Plate Tectonics Global plate tectonics (Earth and possibly Mars in its first 500 Ma history) Local plate tectonics (possibly on Venus and Mars) Brittle deformation: formation of fractures and small motion (relative to lithosphere thickness) along fracture planes (Mercury, Earth s Moon, and parts of Mars). Stagnant-lid Tectonics Ductile deformation: lithosphere deforms like a flowing fluid. Again, the magnitude of the flow is small compared to the lithosphere thickness (most of Venus, some parts of Earth such as the Tibetan plateau and the western U.S.).

7 Styles of Planetary Tectonics Plate Tectonics Local plate tectonics/primitive plate tectonics (e.g., local subduction on Mars and Venus and local rigid-plate motion on Mars) Global plate tectonics (Earth s s oceanic domain) Stagnant-lid Tectonics Deforming lid Distributed deformation (Venus, Enceladus) Discrete deformation (some parts of Europa, Mercury) Rigid lid (e.g., the Moon, Callisto) Plume (Venus) and heat pipe (Jupiter s moon Io) tectonics Vertically Detached Plate Tectonics Upper lithosphere experiences distributed deformation whereas the lower part subducts into the mantle (e.g., continents on Earth and some parts of Venus)

8 From Byrne et al. (2014 Nature Geoscience)

9 Comparison of global topography between Mars and Mercury. Mars Mercury

10 Comparison of global topography between Mars and Venus. Venus Mercury

11 Caloris Basin View of Caloris Basin from MESSENGER mission

$Weird terrain is highly fractured region at the antipodal point to the large Caloris basin.$ point, breaking down the lithosphere.

12 Weird terrain is highly fractured region at the antipodal point to the large Caloris basin. The shock wave produced by the Caloris impact may have been reflected and focused to the antipodal point, breaking down the lithosphere. Weird terrain has also been thought to the source of sodium and potassium. It lies in the opposite side of the Caloris basin on Mercury. The area covered is about 800 km

13 Scarp of a thrust fault (yes, just like our Santa Monica thrust you see on the Westwood Bl A long profile across Mercury surface From Preusker et al. (Planetary and Space Science, 2011)

14 Rembrandt impact basin is the second largest impact crater on Mercury, with a diameter of 715 km.

15 Crater basin (180 km in diameter) is covered by smooth material interpreted as volcanic flows. Rims and interior are wrinkled, interpreted as folds due to contraction of the crust.

16 They are the same picture with one rotated 180 degrees in case you cannot see the crater depressions like me! Thrust scarp From Byrne et al. (2014 Nature Geoscience)

17 From Byrne et al. (2014 Nature Geoscience)

18 From Byrne et al. (2014 Nature Geoscience)

19 Venus Formation of a corona

20 Rifts on Venus and Earth Beta regio rift on Venus East Africa Rift: longest rift system on Earth

21 Plateaus on Venus and Earth Tibetan plateau on Earth Ishtar Terra on Venus

22 An Yin Department of Earth and Space Sciences, UCLA

23 Earth has a unified and kinematically linked GLOBAL platetectonics network, but did it probably did not start all at once. Twiss and Moores (2010)

24 Main Points of this Talk: (1) Tharsis Rise on Mars was generated by impactinduced slab rollback subduction; (2) Martian plate tectonics is local vs. Earth s plate tectonics that is global. Mars Early Earth (3) Hadean and early Archean may have local plate tectonics, reconciling conflicting evidence for and against plate tectonics.

25 Previous work on plate tectonics on Mars: 1.Sleep (1992): use plate tectonics to explain dichotomy 2.Cornerney et al. (2004): use plate tectonics to explain patterns of magnetized Martian crust. 3.Baker (2006): use plate tectonics to explain hydrologic cycles on Mars. All existing models emphasize plate tectonics in the first Ma of Martian history. My study suggests that plate tectonics has been operated continuously since about 4 Ga at a very slow pace (~3 orders of magnitude slower than that on Earth).

26 Baker (2006)

27 Baker (2006) Yin (2012a, Lithosphere)

28 MOLA topographic map Mars (Smith et al., 2001) Tharsis Rise Valles Marineris Magnetic map of Mars (Lillis et al., 2008) Argyre Basin Tharsis Rise Valles Marineris Argyre Basin

29 Size of Tharsis rise and terrestrial comparisons

30 Main Tharsis Graben System

32 HiRISE Images across the thrust front of the Thaumasia Highlands

33 Central Tharsis graben zone is a right-slip transtensional fault zone: Right-slip offset of early NWtrending grabens (Yin 2012b, Lithosphere). N

35 Valles Marineris is a large left-slip transtensional fault zone: Left-slip fault zone on plateau margin north of Coprates Chasma. Yin (2012 Lithosphere)

36 Valles Marineris is a large left-slip transtensional fault zone: Offset of headless debris flows. Yin (2012b, Lithosphere)

37 Valles Marineris is a large left-slip transtensional fault zone: NW- trending folds in east-trending trending trough zone (Ius Chasma). Yin (2012 Lithosphere, in press)

38 Purucker et al. (2000) Yin (2012 Lithosphere)

39 Dead Fault Zone VM Fault Zone 500 km 500 km

40 Olympus aureole zone is a thrust belt

41 Noachian basement thought to be unrelated to the aureole zone Olympus Aureole Zone From Geologic Map of Mars (Skinner et al., 2006)

42 Noachian basement Olympus Aureole Zone From Geologic Map of Mars (Skinner et al., 2006)

43 Back thrust involving basin deposits Thrust front of the aureole zone

44 Left-slip reverse fault zone bounding topographic front of the basement uplift

45 Left-slip reverse fault zone bounding topographic front of the basement uplift

46 Frontal thrust links with normal faults at north and south ends N 5 km

47 Frontal thrust links with normal faults at north and south ends

Summary of Tharsis structural geology: 1.Tharsis Rise is dominated by NW-SE trending main Tharsis graben system (interpreted as result of back-arc extension). 2.

48 Summary of Tharsis structural geology: 1.Tharsis Rise is dominated by NW-SE trending main Tharsis graben system (interpreted as result of back-arc extension). 2.Valles Marineris is a left-slip transtensional fault zone with km (interpreted as accommodation zone during back-arc extension). 3.NW Tharsis margin bounded by a thrust belt (interpreted as a subduction zone of a rollback slab).

(2) Absolute ages of volcanic zones are based on crater statistics and assumptions

49 Timing of Tharsis volcanism Skinner et al. (2006) (1) Relative ages of volcanic zones are based on cross-cutting relationships. (2) Absolute ages of volcanic zones are based on crater statistics and assumptions about the flux rate of impact meteorites and its relation to that on the Moon. Crater counts mainly based on Scott and Tanaka (1986)

50 1850 km 750 km (4) (3) (2) (1) Zone 4: Volcano spacing is ~1850 km. Zone 3: (a) Early stage volcano spacing is km; (b) Late stage volcano spacing is ~ 750 km. Zone 2: Volcano spacing is km. Zone 1: Effusive eruption without central volcanoes. Argyre Impact Basin

51 Eruption style: effusive without volcanic centers (1) (1) 2 km P13_005967_1401_XI_39S092WCAVX6XB8

52 Eruption style: close spaced central volcanoes (2) Baptista et al. (2008) (1) Baptista et al. (2008)

53 Change in Tharsis volcano spacing as function of time Zone 4 Zone 3 Zone 2 Zone 4: Volcano spacing is ~1850 km. Zone 3: (a) Early stage volcano spacing is km; (b) Late stage volcano spacing is ~ 750 km. Zone 2: Volcano spacing is km. Zone 1: Effusive eruption without central volcanoes.

54 Relationship between volcano spacing and viscosity ratio (Marsh, 1979) Mantle viscosity ratio of different stages of volcanism

55 Tharsis volcanism : 1.Volcanism is zonal and trends northeast; 2.Zones of eruption migrate from SE to NW; 3.Volcano spacing increases from SE to NW, indicating an increase in mantle viscosity with time.

56 Why did Tharsis volcanism start from SE? Major impact basins are associated with large volcanic fields, asymmetrically distributed on basin sides. Argyre Impact

57 nitiation of volcanism occurred ~ Ma after nearby major impact events; Volcanic fields lie on one sides of the large impacts.

58 Zone-1 volcanism Distribution of volcanic field may be related to oblique impact Inferred oblique direction of impact

59 I II I (Schultz and Anderson, 1996) II

60 Volcanic load may helped break the lithosphere, leading to subduction. Short-lived subduction (hot side subduction) Sustainable Subduction (cold side subduction)

61 Unsustainable subduction Sustainable subduction

62 Due to the large crust thickness, impact-induced loading could not lead to subduction of lithosphere in the southern highlands. Argyre Impact

63 Argyre impact induced mantle melting, causing emplacement of thick volcanic piles at the dichotomy boundary zone. Argyre Impact

64 Feedbacks of volcanic loading and volcanic eruption caused lithospheric foundering (Kemp and Stevenson, 1996; Schubert and Zhang, 1997). (1)

65 Establishing subduction zone below zone 2 of volcanic eruption (i.e., Syria Planum) (2)

66 1. Establish stable subduction configuration first at Tharsis Montes volcanic chain (zone 3) 2. Slab Breakoff and rapid migration of volcanic arc to zone 4. (4) (3)

67 Subduction-driven delamination (?) may have created different shapes of volcanoes Flat and short volcanos Tall and thin volcanos

68 Strip subduction model predicts normal faulting at lateral edges of the down-going slab

69 Juvenile Tharsis Crust Explains Lack of Remanent Magnetic Anomalies Lillis et al. (2009)

70 Foreland basin and Forebulge Te = ~ 280 km, a factor of 3-20 greater than estimated Te across the Tharsis rise.

71 Tharsis volcanism probably a result of combined slab roll back (western Pacific ocean style) and long-term stable subduction (the Andean style)

72 Tonga trench in western Pacific Ocean and high topographic regions in the over-riding plate. 660 km Slab Retreat Schellart et al. (2006)

73 If Mars is an analogue of early Earth, then the global plate-tectonics network must have evolved from linking local systems Tharsis strip-subduction zone lies in a single plate shell

74 Conceptual model for evolution of global plate tectonics network via interactions of local slab rollback zones

75 Necessary Conditions for Initiation of Plate Tectonics on Rocky Planets by Large Impacts ρ L > ρ A ρ L Assuming thickening rate of lithosphere = 10 km/ma ρ A Following formulation by Davies (1992)

76 Main conclusions: (1) Tharsis Rise on Mars may have been generated by impact-induced slab rollback subduction; (2) This plate tectonic process on Mars is localized, with the rest of the lithosphere behaving as a single plate; (3) Local operation of plate tectonics reconciles conflicting observations for and against the occurrence of plate tectonics on the early Earth at various geographic locations.

77 Example of recycling of thermal boundary layer without rigid-block motion Dominantly juvenile crust 660 km Creation of new arc crust during slab rollback Schellart et al. (2006)

78 Modern plate tectonics: two processes at global scale and Primitive plate tectonics: one of the two processes at local scale or 660 km Slab Retreat Schellart et al. (2006)

79 Korenaga (2013 Ann. Rev. Earth. Planet Sci.)

80 Slow cooling of Earth due to inefficient conductive cooling Rapid cooling of Earth due to recycling of thermal boundary layer Korenaga (2013 Ann. Rev. Earth. Planet Sci.)

81 Korenaga (2013) 850 Ma

82 Korenaga (2013.) 4200 Ma

83 Earth has a kinematically linked GLOBAL plate-tectonics network NOW Twiss and Moores (2010)

84 Overnight process? No Plate Tectonics Korenaga (2013.)

85 Transitional stage

Tectonics. Planets, Moons & Rings 9/11/13 movements of the planet s crust

Tectonics. Planets, Moons & Rings 9/11/13 movements of the planet s crust Tectonics Planets, Moons & Rings 9/11/13 movements of the planet s crust Planetary History Planets formed HOT Denser materials fall to center Planet cools by conduction, convection, radiation to space