Download First order of relief

Mars: First Order Landscapes
Geography 441/541
S/16
Dr. Christine M. Rodrigue
C.M. Rodrigue, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Endogenous explanations
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Degree-1 convection
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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, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Endogenous explanations
–
Did Mars have plate tectonics?
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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, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Endogenous explanations
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Evidence for plate tectonics?
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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, 2016
Geography, CSULB
Plate Tectonics: Banded Magnetic Anomalies
C.M. Rodrigue, 2016
Geography, CSULB
Plate Tectonics: Banded Magnetic Anomalies
C.M. Rodrigue, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Endogenous explanations
–
Other explanations for the magnetic anomalies
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-
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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, 2016
Geography, CSULB
Plate Tectonics: Banded Magnetic Anomalies
C.M. Rodrigue, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Endogenous explanations
–
Stagnant lid convection
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-
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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, 2016
Geography, CSULB
Earth Crustal Thickness: Isopach Map
C.M. Rodrigue, 2016
Geography, CSULB
Mars Crustal Thickness: Block Diagram
C.M. Rodrigue, 2016
Geography, CSULB
Mars Crustal Thickness: Hypsometric Isopach Map
C.M. Rodrigue, 2016
Geography, CSULB
Explanations for the Crustal Dichotomy
Exogenous explanations
–
Impact created the Northern Lowlands basin
-
Planetary accretion
Heat
C.M. Rodrigue, 2016
Geography, CSULB
Mars Crustal Thickness
•
•
•
MOLA topography
Crustal thickness
Isostatic root
–
Andrews-Hanna,
Zuber, and Banerdt
2008
C.M. Rodrigue, 2016
Geography, CSULB
Mars Crustal Thickness
•
•
MOLA topography
Modelled ellipse
–
Andrews-Hanna,
Zuber, Banerdt 2008
C.M. Rodrigue, 2016
Geography, CSULB