Tectonism
Theme Overview:
By Laszlo Keszthelyi
Tectonism is the movement of
rocks under the great forces within a planet's interior. On Earth, the forces of plate tectonics
drive plates together to form mountain ranges like the Himalayas or the Rockies
and tear other plates apart, allowing ocean basins to open. While there are some suggestions that
Mars might have had some plate tectonics in its earliest history, what we see
today is driven mostly by gravity.
The weight of the giant volcanoes presses down on the crust, bending and
breaking it. Smaller ridges rise
where stacks of lava and/or sediment press down and crumple the upper crust. Rising water and/or magma can split
open the ground and form long fissures.
And the ground rebounds and slumps in response to meteorite impacts.
Major Questions:
The primary focus in
tectonics is to understand the forces that are bending and breaking the
rocks. The first step in gaining
this understanding is to measure exactly how and when the rock were
deformed. One idea is that the
global scale tectonism on Mars can be related to the weight of Olympus Mons and
the other volcanoes in the Tharsis area.
This idea makes very specific predictions for how the deformation will
be oriented (cracks will generally be "radial" (point to) Tharsis and ridges
will be "concentric" to (encircle) Tharsis). Another basic question is whether the many fissures that are
seen on the surface of Mars are formed by magma pushing up form underneath or
if they formed first, producing an area of weakness that rising magma could
exploit. Finally, the way the
rocks bend or break tells us a lot about what they are made of. Most sedimentary rocks that have been
laid down in water will bend easier than hard lava, which tends to break more
readily.
Features of interest to
HiRISE
With its ability to see
small details, HiRISE is not the right tool to examine global or regional scale
features. Other existing Mars data
sets, in particular the topographic maps from the Mars Orbiter Laser Altimeter
(MOLA) are ideal for seeing the "big picture". What HiRISE brings to Mars tectonics is the ability to
measure the deformation of rocks in unprecedented precision. Not only can the amount of bending or
sliding be measured, but smaller layers can be matched across zones of
deformation. Also, the more
detailed view will allow us to more clearly see how different cracks and ridges
cross-cut each other letting us better decipher the order in which different
forces acted.
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