Lecture 2: Tectonics of Rocky PlanetsLecture 2: Tectonics of Rocky Planets

Lithosphere is a Lithosphere is a thermal boundary layer thermal boundary layer where heat transport is where heat transport is dominated by conduction.dominated by conduction.

On Earth, this layer is treated as a rigid layer from which platOn Earth, this layer is treated as a rigid layer from which plate e kinematics can be derived. kinematics can be derived.

T oC

Dep

th (k

m)

Thermal boundary layer (heat transport by conduction)

Convection (nearly isothermal)

Crust

Mantle Lithosphere Conduction

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

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

Stagnant-lid Tectonics

Shell may be slightly broken, but no significant motion of individual fragments with one another.

The shell is so broken that the mantle rises to the surface! Fragments of shells move great distance relative to one another.

Plate Tectonics

Global plate tectonics (Earth and possibly Mars in its first 500 Ma history)

Local plate tectonics (possibly on Venus and Mars)

Stagnant-lid Tectonics

Brittle deformation: formation of fractures and small motion (relative to lithosphere thickness) along fracture planes (Mercury, Earth’s Moon, and parts of Mars).

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.).

Plate Tectonics

Stagnant-lid Tectonics

Local plate tectonics/primitive plate tectonicsLocal plate tectonics/primitive plate tectonics(e.g., local subduction on Mars and Venus and local rigid-plate motion on Mars)

Global plate tectonics (EarthGlobal plate tectonics (Earth’’s oceanic domain)s oceanic domain)

Deforming lidDeforming lid

Rigid lid Rigid lid (e.g., the Moon, Callisto)

Distributed deformation(Venus, Enceladus)

Discrete deformation (some parts of Europa, Mercury)

Vertically Detached Plate Tectonics

Upper lithosphere experiences distributed Upper lithosphere experiences distributed deformation whereas the lower part subducts into deformation whereas the lower part subducts into the mantle the mantle (e.g., continents on Earth and some parts of Venus)

Styles of Planetary Tectonics

Plume (Venus) and heat pipe (Jupiter’s moon Io) tectonics

From Byrne et al. (2014 Nature Geoscience)

Mars

Mercury

Comparison of global topography between Mars and Mercury.

Mercury

Comparison of global topography between Mars and Venus.

Venus

Caloris Basin

View of Caloris Basin from MESSENGER mission

• 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

From Preusker et al. (Planetary and Space Science, 2011)

A long profile across Mercury surface

Scarp of a thrust fault (yes, just like our Santa Monica thrust you see on the Westwood Blvd.)

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

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.

From Byrne et al. (2014 Nature Geoscience)

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)

From Byrne et al. (2014 Nature Geoscience)

Venus

Formation of a corona

Rifts on Venus and Earth

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

Plateaus on Venus and Earth

Ishtar Terra on Venus

Tibetan plateau on Earth

An YinAn YinDepartment of Earth and Space Sciences, UCLADepartment of Earth and Space Sciences, UCLA

Earth has a unified and kinematically linked GLOBAL plate-tectonics network, but did it probably did not start all at once.

Twiss and Moores (2010)

Main Points of this Talk:

(1) Tharsis Rise on Mars was generated by impact-induced slab rollback subduction;

(2) Martian plate tectonics is local vs. Earth’s plate tectonics that is global.

(3) Hadean and early Archean may have local plate tectonics, reconciling conflicting evidence for and against plate tectonics.

Early Earth

Mars

Previous work on plate tectonics on Mars:

1.Sleep (1992): use plate tectonics to explain dichotomy2.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 300-500 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).

Baker (2006)

Baker (2006)

Yin (2012a, Lithosphere)

Argyre Basin

Tharsis Rise

Tharsis Rise

Argyre Basin

Magnetic map of Mars (Lillis et al., 2008)

MOLA topographic map Mars (Smith et al., 2001)

Valles Marineris

Valles Marineris

Size of Tharsis rise and terrestrial comparisons

Main Tharsis Graben System

HiRISE Images across the thrust front of the Thaumasia Highlands

Central Tharsis graben zone is a Central Tharsis graben zone is a rightright--slip transtensional fault zone: slip transtensional fault zone: Right-slip offset of early NW-trending grabens (Yin 2012b, Lithosphere).

N

Valles Marineris is a large leftValles Marineris is a large left--slip slip transtensional fault zone: transtensional fault zone: Left-slip fault zone on plateau margin north of Coprates Chasma.

Yin (2012 Lithosphere)

Valles Marineris is a large leftValles Marineris is a large left--slip slip transtensional fault zone: transtensional fault zone: Offset of headless debris flows.

Yin (2012b, Lithosphere)

Valles Marineris is a large leftValles Marineris is a large left--slip slip transtensional fault zone: NWtranstensional fault zone: NW--trending folds in easttrending folds in east--trending trending trough zone (Ius Chasma).trough zone (Ius Chasma).

Yin (2012 Lithosphere, in press)

Purucker et al. (2000)

Yin (2012 Lithosphere)

Dead Fault Zone VM Fault Zone

500 km500 km

Olympus aureole zone Olympus aureole zone is a thrust belt is a thrust belt

From Geologic Map of Mars (Skinner et al., 2006)

Olympus Aureole Zone

Noachian basement thought to be unrelated to the aureole zone

From Geologic Map of Mars (Skinner et al., 2006)

Olympus Aureole Zone

Noachian basement

Thrust front of the aureole zoneThrust front of the aureole zone

Back thrust involving basin deposits

LeftLeft--slip reverse fault zone bounding slip reverse fault zone bounding topographic front of the basement uplifttopographic front of the basement uplift

LeftLeft--slip reverse fault zone bounding slip reverse fault zone bounding topographic front of the basement uplifttopographic front of the basement uplift

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

N

5 km

Frontal thrust links with normal faults at north and south endsFrontal 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.Valles Marineris is a left-slip transtensional fault zone with 150-160 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).

Timing of Tharsis volcanismSkinner et al. (2006)

Crater counts mainly based on Scott and Tanaka (1986)

(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.

(4) (3)

(2)

(1)

Zone 4: Volcano spacing is ~1850 km.

Zone 3: (a) Early stage volcano spacing is 130-170 km; (b) Late stage volcano spacing is ~ 750 km.

Zone 2: Volcano spacing is 20-30 km.

Zone 1: Effusive eruption without central volcanoes .

1850

km

750 k

m

Argyre Impact Basin

(1)(1)

Eruption style: effusive without volcanic centers

P13_005967_1401_XI_39S092WCAVX6XB8

2 km

(1)

(2)

Baptista et al. (2008)

Baptista et al. (2008)

Eruption style: close spaced central volcanoes

Change in Tharsis volcano spacing as function of time

Zone 2

Zone 3

Zone 4

Zone 4: Volcano spacing is ~1850 km.

Zone 3: (a) Early stage volcano spacing is 130-170 km; (b) Late stage volcano spacing is ~ 750 km.

Zone 2: Volcano spacing is 20-30 km.

Zone 1: Effusive eruption without central volcanoes .

Relationship between volcano Relationship between volcano spacing and viscosity ratio (Marsh, spacing and viscosity ratio (Marsh, 1979) 1979)

Mantle viscosity ratio of different Mantle viscosity ratio of different stages of volcanismstages of volcanism

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.

Why did Tharsis volcanism start from SE?

Major impact basins are associated with large volcanic fields, asymmetrically distributed on basin sides.

Argyre Impact

Initiation of volcanism occurred ~200-250 Ma after nearby major impact events; Volcanic fields lie on one sides of the large impacts.

Inferred oblique direction of impact

Distribution of volcanic field may be related to oblique impact

Zone-1 volca

nism

(Schultz and Anderson, 1996)I

II

III

Sustainable Subduction (cold side subduction)

Short-lived subduction (hot side subduction)

Volcanic load may helped break the lithosphere, leading to subduction.

Unsustainable subduction

Sustainable subduction

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

Argyre Impact

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

Argyre Impact

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

(1)

(2)

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

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.

(3)

(4)

Subduction-driven delamination (?) may have created different shapes of volcanoes

Flat and short volcanos

Tall and thin volcanos

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

Lillis et al. (2009)

Juvenile Tharsis Crust Explains Lack of Remanent Magnetic AnomalJuvenile Tharsis Crust Explains Lack of Remanent Magnetic Anomalies ies

Foreland basin and ForebulgeForeland basin and Forebulge

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

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

660 km Slab Retreat

Schellart et al. (2006)

Tonga trench in western Pacific Ocean and high topographic regions in the over-riding plate.

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

Conceptual model for evolution of global plate tectonics networkvia interactions of local slab rollback zones

Necessary Conditions for Initiation of Plate Tectonics on Necessary Conditions for Initiation of Plate Tectonics on Rocky Planets by Large ImpactsRocky Planets by Large Impacts

ρ L > ρ A

ρ A

ρ L

Following formulation by Davies (1992)

Assuming thickening rate of lithosphere = 10 km/Ma

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.

Example of recycling of thermal boundary layer without rigid-block motion

660 km

Schellart et al. (2006)

Creation of new arc crust during slab rollback

Dominantly juvenile crust

Primitive plate tectonics: one of the two processes at local scaPrimitive plate tectonics: one of the two processes at local scale le

or 660 km Slab Retreat

Schellart et al. (2006)

Modern plate tectonics: two processes at global scale Modern plate tectonics: two processes at global scale

and

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

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

Rapid cooling of Earth due to recycling of thermal boundary layer

Slow cooling of Earth due to inefficient conductive cooling

Korenaga (2013)

850 Ma850 Ma

Korenaga (2013.) 4200 Ma4200 Ma

Earth has a kinematically linked GLOBAL plate-tectonics network NOW

Twiss and Moores (2010)

Korenaga (2013.)

No Plate TectonicsNo Plate Tectonics

““OvernightOvernight”” process? process?

Transitional stage