[meteorite-list] Melas Dorsa Reveals a Complex Geological History on Mars (Mars Express)

[Ron Baalke]

http://www.esa.int/esaSC/SEM26D2VW3H_index_0.html

Melas Dorsa reveals a complex geological history on Mars
European Space Agency 
5 July 2012

ESA's Mars Express has imaged an area to the south of the famed Valles Marineris canyon on 
the Red Planet, showing a wide range of tectonic and impact features.
 
On 17 April, the orbiter pointed its high-resolution stereo camera at the Melas Dorsa 
region of Mars. This area sits in the volcanic highlands of Mars between Sinai and 
Thaumasia Plana, 250 km south of Melas Chasma. Melas Chasma itself is part of the 
Valles Marineris rift system.

The image captures wrinkle ridges, some unusual intersecting faults and an elliptical 
crater surrounded by ejecta in the shape of a butterfly and with a strange "fluid-like" 
appearance.  

[Image] 
Melas Dorsa impact crater perspective view
 
Elliptical craters like this 16 km-wide example are formed when asteroids or comets 
strike the surface of the planet at a shallow angle.

Scientists have suggested that a fluidised ejecta pattern indicates the presence of 
subsurface ice which melted during the impact. Subsequent impacts have created a number 
of smaller craters in the ejecta blanket.
 
[Image]	
Zoom view of flooded crater
	
The rim of another large crater is visible in the upper centre part of the image, but 
it appears mostly to have been almost buried during some distant epoch by volcanic dust 
and ash.

This makes any detailed study of it almost impossible. However, its centre shows
concentric deposits that could provide insights into the composition of the volcanic 
material that buried it.
 
[Image] 
Melas Dorsa topography
 
Several wrinkle ridges can be seen across the image. These form when horizontal 
compression forces in the crust pushes the crust upwards.

To the left, the ridges are bisected by crustal displacement faults. These have cut into 
the ridges and the surrounding surface at some later epoch. This highlights the different 
tectonic phases responsible the formation of this region.
 
[Image] 
Melas Dorsa in context
 
[Image] 
Melas Dorsa 3D anaglyph