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Mars: First Order Landscapes

Explore the geological mysteries of Mars' crustal dichotomy through theories of plate tectonics, magnetic anomalies, and crustal thickness. Discover the unique landscapes and potential explanations for Mars' surface features.

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Mars: First Order Landscapes

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  1. Geography 441/541 F/19 Dr. Christine M. Rodrigue Mars: First Order Landscapes C.M. Rodrigue, 2019 Geography, CSULB

  2. C.M. Rodrigue, 2019 Geography, 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

  3. C.M. Rodrigue, 2019 Geography, 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?

  4. C.M. Rodrigue, 2019 Geography, 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

  5. C.M. Rodrigue, 2019 Geography, CSULB Plate Tectonics: Banded Magnetic Anomalies

  6. C.M. Rodrigue, 2019 Geography, 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

  7. C.M. Rodrigue, 2019 Geography, 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.

  8. C.M. Rodrigue, 2019 Geography, CSULB Earth Crustal Thickness: Isopach Map

  9. C.M. Rodrigue, 2019 Geography, CSULB Mars Crustal Thickness: Block Diagram

  10. C.M. Rodrigue, 2019 Geography, CSULB Mars Crustal Thickness: Hypsometric Isopach Map

  11. C.M. Rodrigue, 2019 Geography, CSULB Explanations for the Crustal Dichotomy Exogenous explanations • Impact created the Northern Lowlands basin • Planetary accretion: lots of bombs • Large one may have hit obliquely • But even pretty oblique impacts create spherical craters (impact is a detonation process) • Hard to trace great dichotomy under the Tharsis lump • Andrews-Hanna, Zuber, Banerdt team tried modeling topography, gravimetry, and how the pre-existence of Tharsis would have redistributed crustal thickness • Their results yielded a pretty clear oval of 10,600 km by 8,500 km centered around 67° N and 208° E in Vastitas Borealis (Arcadia Planitia) northwest of Alba Mons

  12. Mars Crustal Thickness • MOLA topography • Crustal thickness • Isostatic root • Andrews-Hanna, Zuber, and Banerdt 2008 C.M. Rodrigue, 2019 Geography, CSULB

  13. Mars Crustal Thickness • MOLA topography • Modelled ellipse • Andrews-Hanna, Zuber, Banerdt 2008 C.M. Rodrigue, 2019 Geography, CSULB

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