The Mars Dichotomy. Evidence for Plate Tectonics or Erosion?. Theories of the Dichotomy Formation. Giant Impact One major collision resurfaced the region. Multiple Impacts Several large impacts caused resurfacing. Ancient Ocean
Evidence for Plate Tectonics or Erosion?
slope down to the North.
-However, the slopes appear to be impact related.
Note shoreline reversal
(Withers and Neumann, 2001)
Above: Beta Diagram showing the
concentration of great circle intersections
to inferred maximum principle stress
-Note the general E-W trend of the
-Two clusters dominate at Tharsis
and Hesperia Planum.
Plate motion ceases when the rift margin is subducted.
-Yellow outline shows the plate margin at the time of the break up.
-The singular plate breaks into 2 plates, possibly due to subduction angle and different plate velocities.
-New plate geometry after the
-Note the transform fault between
the two plates.
-Plate geometry at the time plate
motion is inferred to have ceased.
East Pacific Rise
(Acuna et. al., 1999).
It is possible multiple large impacts resurfaced the N hemisphere.
However, this is not supported geological or statistically.
There is no evidence of an ocean shore line, only tectonic features and impact ridges.
Plate tectonics provides a possible mechanism for N hemisphere resurfacing.
Magnetic “stripes” are present on Mars, therefore a dynamo may have existed early in Mars history.Summary
Images from Mars show distinct valley networks that flow across the dichotomy from S to N.
These outflow channels may have carried water (or even volcanic materials) into the northern plains
But it would take a large standing body of water to physically form the dichotomy.
Implies episodic flooding.
Valles Marineris: Linear shape implies it was formed tectonically.
Increase in crustal thickness to the south must have formed by internal processes.However, the Northern lowlands may have been resurfaced through water/volcanic outflow.