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Re: More Seriously... LPSC abstracts
Posted by Jill England (64.24.187.135) on 8/28/2001 2:42:38 PM
In Reply to: More Seriously... LPSC abstracts posted by Justin Kelly on 8/27/2001 3:26:17 AM
I don't know if anyone thinks it's important or not but,
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1698.pdf
Contains a rather serious graph labeling error;
Their Longitude scale goes from 0 to 360, in the wrong direction.
Their actual Map is the one with 0,0 in the center of the map and then moving out to 180 degrees on the edges, not the middle.
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Thanks for the catch. I had been thinking that the smaller concentration near the center of their fig. 4 was in Amazonis based on their coordinate labeling, rather than its actual location in Arabia Terra.

The latitudinal concentration might support the idea that water is involved with the origin of the dark streaks, as Bara and Hoagland suggest in their Tides report. Also, there was a recent report that there are active glaciers in Tharsis which might indicate a source for the water near surface. However, I don't see why there would need to be a concentration in Arabia.
Another possibility is that the volcanic activity in Tharsis is the cause. Recent research indicates that volcanism in the Tharsis region extends to geologically recent times, and perhaps currently. Then perhaps the supporting factor of the streaks is a gas release due to volcanic activity. Albin and King in their report "ORIGIN OF DARK SLOPE STREAKS WITHIN THE SCHIAPARELLI IMPACT BASIN, MARS.", http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1395.pdf , proposed a CO2 gas release to support the long flows of the streaks that can extend over a kilometer.
Why again in Arabia then? There was a paper in Science that suggested the Arabia uplift was due to Tharsis:

Ancient Geodynamics and Global-scale Hydrology on Mars
"Members of the MOLA Team used Mars Global Surveyor topography and gravity data to address loading of the lithosphere of Mars by the Tharsis rise. Tharsis is a BIG load on the surface of Mars and when it was emplaced it deformed the whole surface of the planet, just like what would happen if you punched a beach ball. By developing models, we showed that loading of Mars by Tharsis explains much of the global shape and long-wavelength gravity field of the planet. Loading by Tharsis also explains a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity-anomaly and topographic highs centered in the Arabia Terra region and extending northward toward the Utopia basin. We showed that the Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch, the earliest stratigraphic epoch in Martian history (about 4 billion years ago)."
http://ltpwww.gsfc.nasa.gov/tharsis/tharsis_paper.html

There are some nice images from the Science paper and a link to the full text paper on this page.
Question: would you also expect ongoing volcanic activity or gas release from Arabia for this reason? If so then the low latitude concentration may only be an accident having to do with the location of the Tharsis volcanos.

Note also that this Science paper gives an alternative explanation of the Arabia rise to the one proposed by Bara and Hoagland. The authors suggest it is due to lithospheric deformation due to the Tharsis load.

Bob Clark