posted on Jun, 8 2011 @ 05:28 PM
reply to post by Arken
size of the polygons in columnar basalt depends on cooling rate, slow cooling on Earth can give columns with maybe a meter polygon width. Not sure
about on Mars, but would suspect a faster cooling rate because of surface Temp.
However, I think they are eroded structural joint sets (three dimensional planes of dilation/weakness) caused by compressional or tensional stresses.
an Earth example upload.wikimedia.org...
The size like you point out is one reason against these being basaltic cooling joints (columns). Another reason, if you look at the image:
there are these columns within impact craters. Hellas Basin is a HUGE impact crater itself, and so these smaller impact craters came after the big
impact (otherwise they would be covered by debris and impact melt (maybe basalt, maybe andesite). The fact that the columns are within the smaller,
later impact craters shows these came after both the Big impact that created Hellas, and the small impacts that created the smaller craters within
Hellas. So my opinion (as geochemist and not structural geologist
is that these columns were created by the regional stresses within the Hellas
Basin resulting from rebounding of the crust in the center of the basin after the Hellas impact.
But like I said Im not a Martian structural geologist, so just my opinion based on Earth geology.
The other option, if you want to buy into these being "man"-made is that they were built within the smaller craters after both the big Hellas Basin
impact and after the small crater impacts
edit on 8-6-2011 by youallcrazy because: (no reason given)