C.M. Rodrigue, 2014Geography, CSULB

Mars: First Order Landscapes

Geography 441/541S/14

Dr. Christine M. Rodrigue

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Endogenous explanations– Degree-1 convection

- Planetary accretion- Heat accumulation- Magma ocean- Gravitationally unstable crystal accumulation- Mantle overturn- Initiation of upwelling/downwelling plumes- Sinking of cool mantle material intensifies temperature

contrast in outer liquid core- This creates a dynamo/planetary magnetic field

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Endogenous explanations– Did Mars have plate tectonics?

- Upwelling → crustal thinning through tension and ablation (Northern Lowlands?)

- Downwelling → compression and thickening (Southern Highlands?)

- Cerberus Fossæ a spreading zone rift?- South dipping plate south of Cerberus Fossæ- East dipping plate under Tharsis (volcanic arc?)- Or ... could crustal prominence develop above

upwelling plume instead?

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Endogenous explanations– Evidence for plate tectonics?

- No trenches- Crustal thickening in Terra Cimmeria/Sirenum?- Banded magnetization: Could these symmetrical

changes in remanent magnetization be like the bands on Earth's ocean floors in spreading zones, where new lithosphere records the prevailing magnetic field?

- Fault systems- Cerberus Fossæ?- Valles Marineris?- Transform fault-like offsets in magnetic bands

in Noachis Terra

C.M. Rodrigue, 2014Geography, CSULB

Plate Tectonics: Banded Magnetic Anomalies

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Endogenous explanations– Other explanations for the magnetic anomalies

- Not the roughly symmetrical polarity reversals seen on Earth's ocean floors near spreading zones

- Possibly great basaltic dikes that picked up remanent magnetization during solidification as they ascended through joints in country rock

- Maybe the accumulation of terranes with distinct magnetization records due to plate tectonic compression over a downwelling

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Endogenous explanations– Stagnant lid convection

- Earth's crust is < 10 km thick on the ocean floors but ~40 km thick under continents (up to 70 km thick under continental compression zones, e.g., Tibet)

- Mars' crust averages ~ 50 km thick, ranging from ~25 km thick under the Northern Lowlands and Arabia Terra and up to 75 km thick under the Southern Highlands

- Could such a thick crust have prevented Mars' lithosphere breaking into plates and enabling vigorous convection?

- Interestingly, a stagnant lid would be capable of drifting as a unit, perhaps explaining why Tharsis is centered on the equator.

C.M. Rodrigue, 2014Geography, CSULB

Earth Crustal Thickness: Isopach Map

C.M. Rodrigue, 2014Geography, CSULB

Mars Crustal Thickness: Block Diagram

C.M. Rodrigue, 2014Geography, CSULB

Mars Crustal Thickness: Hypsometric Isopach Map

C.M. Rodrigue, 2014Geography, CSULB

Explanations for the Crustal Dichotomy

Exogenous explanations– Impact created the Northern Lowlands basin

- Planetary accretion- Heat

C.M. Rodrigue, 2014Geography, CSULB

Mars Crustal Thickness

• MOLA topography• Crustal thickness• Isostatic root

– Andrews-Hanna, Zuber, and Banerdt 2008

C.M. Rodrigue, 2014Geography, CSULB

Mars Crustal Thickness

• MOLA topography• Modelled ellipse

– Andrews-Hanna, Zuber, Banerdt 2008