Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum, and Mare Insularum

Abstract

[1] Accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the Moon. We performed new crater size-frequency distribution measurements in order to investigate the stratigraphy of mare basalts in Oceanus Procellarum and related regions such as Mare Nubium, Mare Cognitum, and Mare Insularum. We used high-resolution Clementine color data to define 86 spectrally homogeneous units within these basins, which were then dated with crater counts on Lunar Orbiter IV images. Our crater size-frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses. Our data show that volcanism in the investigated region was active over a long period of time from $3.93 to 1.2 b.y., a total of $2.7 b.y. Volumetrically, most of the basalts erupted in the Late Imbrian Period between $3.3 and 3.7 b.y., and we see evidence that numerous units have been resurfaced. During the Eratosthenian Period, significantly less basalt was erupted. Depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems, five units might be of Copernican age. Younger basalts are generally exposed in the center of the investigated area, that is, closer to the volcanic centers of the Aristarchus Plateau and Marius Hills. Older basalts occur preferentially along the northwestern margin of Oceanus Procellarum and in the southeastern regions of the studied area, i.e., in Mare Cognitum and Mare Nubium. Combining the new data with our previously measured ages for basalts in Mare Imbrium, Serenitatis, Tranquillitatis, Humorum, Australe, and Humboldtianum, we find that the period of active volcanism on the Moon lasted $2.8 b.y., from $4 b.y. to $1.2 b.y. On the basis of the basalts dated so far, which do not yet include the potentially young basalts of Mare Smythii [e.g., Schultz and Spudis, 1983], we conclude that Oceanus Procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface.

Formation of lunar mare domes along crustal fractures: Rheologic conditions, dimensions of feeder dikes, and the role of magma evolution

“…Spectrally, large parts of Mare Insularum are influenced by basalt lavas of low to moderate TiO 2 content on which ejecta of the craters Copernicus, Kepler, and Eratosthenes are superimposed (Hiesinger et al, 2003). The geologic map by Wilhelms and McCauley (1971) shows that most basalts of this region are Imbrian mare materials with some units showing characteristics of Eratosthenian mare (Em) material.…”

Volcanism on Mercury: Evidence from the first MESSENGER flyby for extrusive and explosive activity and the volcanic origin of plains

“…On the Moon, impact melt deposits line the floor and interior of fresh basins (such as Orientale) that have not been subsequently filled extensively with lava (e.g., Head, 1974b;Howard et al, 1974;Spudis, 1993). The majority of lunar basins, however, have been subsequently filled with mare basalts (e.g., Hiesinger et al, 2000Hiesinger et al, , 2003, and one might infer that if the basin appears filled, and the original basin rings buried and obscured, the original deposit of impact melt has been covered by subsequent lava flooding. Calculations strongly suggest, however, that impact melt is proportionally more important in larger basins (Cintala and Grieve, 1998) and at higher impact velocity (Cintala, 1992), specifically that the volume of impact melt formed relative to that of the crater will grow, and proportionally more will be retained inside the basin rim (Cintala and Grieve, 1998;Pierazzo et al, 2007).…”

“…7). MESSENGER data from the first Mercury flyby were of insufficient resolution and illumination geometry to document the morphologic features that might reveal sequential emplacement of plains units over time, and the prominent color contrasts between volcanic units within Imbrium (see Hiesinger et al, 2000Hiesinger et al, , 2003 are not observed in Caloris Robinson et al, 2008). Thus, a major goal for MESSENGER orbital operations will be the acquisition of imaging and spectral data to characterize and date the range of volcanic units in the interior.…”

Emplacement and tectonic deformation of smooth plains in the Caloris basin, Mercury

“…In lunar maria, wrinkle ridges occur predominantly in the basin interior, and graben are found near the margins or outside of mascon mare basins (McGill, 1971;Strom, 1972;Maxwell et al, 1975;Golombek, 1979;Solomon and Head, 1980;Watters and Johnson, in press). Moreover, superposition relationships of lunar graben suggest that they are restricted to the older mare basalt units, whereas wrinkle ridges deform both older and younger mare basalt units (Boyce, 1976;Lucchitta and Watkins, 1978;Hiesinger et al, 2003;Watters and Johnson, in press). Crosscutting relationships between wrinkle ridges and graben in Caloris indicate that extension postdates contraction of the floor, in contrast to the sequence of stresses implied for lunar basins.…”