Large Shield Volcanoes on the Moon

[1] The volcanic style of the Moon has long been understood to consist almost exclusively of flood basalts erupted from fissures along with minor pyroclastic activity; large central vent shield volcanoes that characterize basaltic volcanism on the other terrestrial planets appeared to be absent. Small (few kilometers diameter) central vent constructs have long been recognized in the lunar maria and often are found clustered in fields throughout the lunar maria. New global topographic data from the LOLA and LROC instruments on LRO reveal that almost all of these volcanic complexes on the Moon occur on large, regional topographic rises in the lunar maria, tens to hundreds of kilometers in extent and between several hundred to several thousand meters high. We propose that these topographic swells are shield volcanoes and are the lunar equivalents of the large basaltic shields found on the Earth, Venus, and Mars. The newly recognized lunar shields are found peripheral to the large, deeply flooded impact basins Imbrium and Serenitatis, suggesting a genetic relation to those features. Loading of the lithosphere by these basalt-filled basins may be responsible for inducing a combination of flexural and membrane stress, inducing a pressure distribution on vertically oriented dikes favorable to magma ascent. This condition would occur in a zone annular to the large circular loads produced by the basins, where the shield volcanoes occur.