An analysis of 34 lunar lava flows and ponds in the eastern limb Smythii and Marginis basins was undertaken to examine and model the first stages of secondary crustal formation and assess processes involved in magma transport and eruption. In order to isolate the characteristics of single eruptive episodes, we focused on discrete mare ponds adjacent to the major maria. Mean values for areas and volumes of deposits estimated to be good candidates for single eruptive phases are large, approximately 950--1000 km2 and ~200 km3 respectively. These eruptive volumes are commensurate with the largest known terrestrial eruptions (flood basalts). The lack of geomorphological structures indicative of shallow magma reservoirs indicates that deep, probably subcrustal source regions are prevalent. With respect to crustal thickness relationships, the magnitude and frequency of eruptive events are observed to be greatest in areas of thinnest crust. Specifically, regions of major maria (Mare Smythii, Mare Marginis) occur in areas of thinnest crust, while isolated ponds occur where the crust is relatively thicker. This is consistent with the correlation observed globally between crustal thickness and the magnitude and frequency of eruptive events. Ages of volcanic flows and pyroclastic events range from Early Imbrian to Imbrian-Eratosthenian but are concentrated most heavily between 3.80--3.60 Ga, suggesting a period of peak volcanism beginning around 3.85 Ga and lasting approximately 200 Ma. However, the existence of dark-halo crater clusters in non-mare units within the region suggests the presence of cryptomaria, which would indicate an earlier onset of volcanism and a volume of mare material potentially greater than that currently exposed on the surface. Typical nearest-neighbor distances suggest deposits derive from reservoirs <~100 km in diameter. The observations made here are consistent with a magma transport model in which plumes rising diapirically stall at a density boundary under the lunar crust and propagate dikes to the surface through overpressurization. ¿ 1998 American Geophysical Union