Analog modelling for pit craters and its relation to extensional features on Mars

SPAGNUOLO, M. G; PIO ROSSI, A.

Texas

Congreso; 40th Lunar and Planetary Science Conference; 2009

           Pit craters are conical collapse structures widelyoccurring on the surface of Mars. Main morphologicaldifferences with impact craters are the lack of the craterrim and impact ejecta [1,2].    Terrestrial counterparts for these structures arerather scarce. Recent studies associate these structureswith dilatational fractures related to normal faults un-der tensional regimes and they would be related to thepresence mechanical strong layers where a void is gen-erated and unconsolidated material from above col-lapses [3,4]. Interestingly not all extensional featuresshow these kinds of structures (Fig. 1). Following [5]in order to evaluate the hypothesis of pit crater forma-tion we have performed analog modeling probing different arrays of internal layers, changingthickness and mechanical parameters. We considerthose experiments could be useful to constrain Marsinternal structure and subsurface mechanical parame-ters along different areas. Preliminary results show thatpit craters in fact form in the presence of unconsoli-dated material over hard layers (e.g. possibly lavaflows and piroclastic and/or non volcanic material inthe case of Mars) but no faults are developed, so amixed array should be tested in order to have both,grabens and associated pit craters. We also evaluatedthe depth of the structures to probe recently proposedrift models like Tempe Fossae, Tratcus Fossae andThaumasia regions.