PLAINS VOLCANISM ON MARS: TOPOGRAPHIC DATA ON SHIELD AND FLOW DISTRIBUTIONS AND ABUNDANCES, WITH NEW QUANTITATIVE COMPARISONS TO THE SNAKE RIVER PLAIN VOLCANIC PROVINCE

Martian volcanic plains have long been suggested to have a range of terrestrial analogs. A lack of detectable volcanic features on many martian plains has made it difficult to determine possible volcanic origins. However, those plains with mixed low shields and flows were frequently compared to the Snake River Plain and were included in descriptions of "plains volcanism." With recent high resolution Mars Orbiter Laser Altimeter (MOLA) topography data, many martian plains areas thought to have some low shields (like Tempe-Mareotis and Ceraunius) are shown to have dozens, and areas previously thought to have a modest population of shields or constructs (such as Syria Planum, the Borealis Field, and Cerberus) are now seen to have numerous shields, vents, and flows. Many areas previously thought to have few or no small shields at all have now been shown to contain many. A similar situation also applies to the recent detection of lava tube and flow features. This considerably extends the documented regions of plains style volcanism on Mars, and also clarifies the volcanic origins of some previously enigmatic plains regions. Given this and the improved martian data, it is clearly time to re-evaluate plains emplacement quantitatively. In general, the low martian shields display a range of flank slopes and summit crater styles that correlates with latitude. We have previously suggested--on the basis of shield emplacement modeling--that this is well explained by likely local subsurface volatile availability. In addition, a significant proportion of martian low shields display steeper summit areas that are strongly reminiscent of eastern Snake River Plain (ESRP) low shield volcanoes. The outstanding topographic resolution now available with the (MOLA) data allows us to construct detailed topography profiles and grids with sub-meter vertical accuracy. These are then quantitatively compared to recent similar GPS field and map measurements of the ESRP features. Emplacement modeling work as well as extensive recent work on ESRP petrography-topography relationships suggest that these new detailed data sets from both planets may allow us to determine relative states of chemical evolution and possible incompatible element enrichment near vent areas for plains volcanism regions of Mars.