[X] My Assistant

[Guest_AlexBlackwell_*]

A Primordial and Complicated Ocean of Magma on Mars

--- Geophysical and geochemical calculations indicate that total melting of Mars during its formation could have led to large-scale heterogeneities in its mantle.

Written by G. Jeffrey Taylor
Hawai'i Institute of Geophysics and Planetology
posted March 31, 2006

[Guest_Richard Trigaux_*]

Yes we all "KNOW" that Hellas IS an impact bassin. There are many other examples of such large bassins on many other bodies. And it really looks like a crater. But:
-it is oval
-it is very deep. There is a law which sets rigorously the ratio between diametre and depth of a crater, as a function of the diametre. Such large craters rather look like "flat" circles showing circular and radial faults and cliffs. And a rim, of course.
-Hellas has no rim, unless we count all the surrounding highlands as a rim.


As for the smaller "umbilics", it is rather difficult to guess what they are exactly, as they are all surrounded by large zones with less craters. It looks as if they were former volcanoes which later subsided into the ground, a rather unique feature.

another strange thing is that the volcanoes (if they are volcanoes) show V shaped radial valleys, as Earth volcanoes which were eroded by rain. Are they so ancient that they bear testimony of a time where rain was occuring on Mars? Arsia Mons also exhibits V shaped valleys.


What I point out is that Hellas and its surroundings show interesting large scale features that we don't yet understand, but which could be subduction zones, like the fossae on Earth. Simply martian subduction zones, being not constrained by horizontal movements, appear more or less circular, while Earth subduction zones, being constrained by plates movement, appear very narrow and elongated.

There was a discution in another thread as what there are magnetic traces of a plate tectonics in the southern highlands. If there was an overturning of the mantle, it could have appeared on the surface like a plate tectonics. But the overturning is a one-time event, while plate tectonics lasts long.


On Earth, the plate tectonics creates magnetic traces which are parallel bands along an extention zone (ocean ridge) where new crust is created. On Mars there are similar features in some parts of the southern highlands. So we may similarly find a ridge where extention occured. There are many elongated ridges in the southern highlands, but we cannot use Google Mars to find which would be a former extention ridge, as it don't give magnetic anomalies.