Volumes of lunar lava ponds in South Pole-Aitken and Orientale Basins: Implications for eruption conditions, transport mechanisms, and magma source regions

In an effort to characterize individual eruptive phases and events, 86 isolated mare deposits (ponds) in the lunar South Pole-Aitken and Orientale regions were analyzed to obtain information on areas, volumes, and other characteristics. Deposits likely to represent single eruptive episodes have area mean values of-2000 km 2 in the South Pole-Aitken Basin and -1100 km 2 in the Orientale Basin. Pond volumes range from 35 to 8745 km 3, with a mean value of 860 km 3 for South Pole-Aitken, and 10 to 1280 km 3, with a mean value of 240 km 3 for the Orientale region. No evidence was found for shallow crustal magma reservoirs. The relatively common occurrence of sinuous rilles in Orientale is consistent with very high effusion rates, and the large volumes of individual eruptive pisodes (tens to many hundreds ofkm 3) are comparable toflood basalt eruption volumes on Earth. Pond morphologies are consistent with extrusion from deep, probably subcrustal reservoirs. Distribution of deposits suggests that many ponds may be derived from single reservoirs. Comparison of ponds in both basins shows a higher areal density and average volume of lava ponds in the South Pole-Aitken basin relative to the Orientale area. This is plausibly attributed to the extreme depths of the South Pole-Aitken basin and the correspondingly thinner crust there relative to the Orientale region. These observations are consistent with magma ascent and eruption mechanisms that are strongly dependent on the overpressurization of deepseated source regions, the subsequent propagation of dikes, and the thickness of the intervening lunar crust through which these dikes must rise.