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 Ori entale regions were analyzed to obtain information on areas, volumes, and other characteristics. Deposits likely to represent single eruptiv e episodes have area mean values of similar to 2000 km(2) in the South Pole-Aitken Basin and similar to 1100 km(2) in the Orientale Basin. P ond 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 24 0 km(3) for the Orientale region. No evidence was found for shallow cr ustal magma reservoirs. The relatively common occurrence of sinuous ri lles in Orientale is consistent with very high effusion rates, and the large volumes of individual eruptive episodes (tens to many hundreds of km(3)) are comparable to flood basalt eruption volumes on Earth. Po nd morphologies are consistent with extrusion from deep, probably subc rustal reservoirs. Distribution of deposits suggests that many ponds m ay be derived from single reservoirs. Comparison of ponds in both basi ns shows a higher areal density and average volume of lava ponds in th e South Pole-Aitken basin relative to the Orientale area. This is plau sibly 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 erupti on mechanisms that are strongly dependent on the overpressurization of deep-seated source regions, the subsequent propagation of dikes, and the thickness of the intervening lunar crust through which these dikes must rise.