BASALTIC "PLAINS-STYLE" VOLCANISM IN SOUTHWESTERN ARIZONA AS A POSSIBLE PLANETARY ANALOGUE

The Sentinel Plains lava field and proximate small shields, collectively referred to as the Sentinel-Arlington Volcanic Field (SAVF) are composed of Pliocene-Pleistocene alkali olivine basaltic lavas and located ~75 km southwest of Phoenix, Arizona. The SAVF covers ~600 km² and consists of more than 2 dozen volcanic centers ranging from 4-6 km in diameter and 30-200 m in height. The two northeastern isolated small shields have volumes ranging from 0.3-0.4 km³ and median slopes ranging from 1.8º-2.5º. Preliminary results from geologic mapping and remote sensing data indicate that the volumes of the remaining SAVF eruptive centers are comparative to these, but that the median slopes within the contiguous lava field are possibly lower due to embayment of eruptive centers. The SAVF lies on the eastern terminus of the Gila River graben and a series of northwest-trending normal faults cuts across the surrounding terrain, indicating that the loci of the SAVF eruptive centers could be controlled by structural trends. The volcanic centers of SAVF erupted near the Gila River channel, damming and diverting the river at least once and potentially several times, forming small ephemeral lakes. The SAVF basal contact is ~30 m above the Holocene surface. The SAVF lavas are eroded and lightly mantled by aeolian dust and basaltic rubble, with a few areas covered by alluvium. SAVF represents basaltic plains-style volcanism, an emplacement style of volcanism intermediate between classic flood volcanism and large shield-building volcanism. The SAVF is similar in morphology, composition and eruptive style to the Snake River Plain in Idaho and the Cima Volcanic Field in California. The SAVF could serve as an analog site for planetary investigations, especially for investigations of similarly mantled small-volume effusive volcanic centers on Mars, such as those identified in the Mars Express High Resolution Stereo Camera (HRSC) images of the southern flank of Pavonis Mons (See Bleacher et al., this volume).