You've got multiple issues here.

The daytime observation has things like shadows etc. The angles involved will produce light and dark areas in a daytime Vis or IR image that will not be there during a Night time IR image.

Secondly - relative to the surroundings - rocks will be 'cold' during the day and 'warm' at night. Things like craters, or rocky gullies, both stand out a lot in Night IR as very bright because they retain the heat they absorbed during the day.

And during the day, because they take longer to warm up relative to things with low thermal inertia such as sand and dust, they appear IR dark.

You've not really found an anomaly of any sort - Mars is covered in rocky features that will do the same.

As for a HiRISE image - you would have to be very very very very lucky. A full HiRISE image is about 5 x 10-15km. In global terms its like a postage stamp on a football field. http://hirise.lpl.arizona.edu/anazitisi.php is the place to search for - I couldn't find one in the area you're asking about.

Ditto THEMIS - http://themis.asu.edu/mars-bin/webmap.pl - nothing in that specific area in the Vis. http://themis-data.asu.edu/img/V05847002.html is nearby and has many similar features to the area you're talking about.



Doug