Peering into Past: What Happened to the Moon 3.6 Billion Years Ago (original) (raw)
Related papers
Earth and Planetary Science Letters, 2014
The Moon likely formed as a result of a giant impact between proto-Earth and another large body. The timing of this event and the subsequent lunar differentiation timescales are actively debated. New high-precision Nd isotope data of Apollo mare basalts are used to evaluate the Low-Ti, High-Ti and KREEP mantle source reservoirs within the context of lunar formation and evolution. The resulting models are assessed using both reported 146 Sm half-lives (68 and 103 Myr). The linear relationship defined by 142 Nd-143 Nd systematics does not represent multi-component mixing and is interpreted as an isochron recording a mantle closure age for the Sm-Nd system in the Moon. Using a chondritic source model with present day μ 142 Nd of −7.3, the mare basalt mantle source reservoirs closed at 4.45 +10 −09 Ga (t 1/2 146 Sm = 68 Myr) or 4.39 +16 −14 Ga (t 1/2 146 Sm = 103 Myr). In a superchondritic, 2-stage evolution model with present day μ 142 Nd of 0, mantle source closure ages are constrained to 4.41 +10 −08 (t 1/2 146 Sm = 68 Myr) or 4.34 +15 −14 Ga (t 1/2
Journal of Geophysical Research, 2006
1] The main objective of the present study is to discuss in detail the results obtained from an inversion of the Apollo lunar seismic data set, lunar mass, and moment of inertia. We inverted directly for lunar chemical composition and temperature using the model system CaO-FeO-MgO-Al 2 O 3 -SiO 2 . Using Gibbs free energy minimization, stable mineral phases at the temperatures and pressures of interest, their modes and physical properties are calculated. We determine the compositional range of the oxide elements, thermal state, Mg#, mineralogy and physical structure of the lunar interior, as well as constraining core size and density. The results indicate a lunar mantle mineralogy that is dominated by olivine and orthopyroxene ($80 vol%), with the remainder being composed of clinopyroxene and an aluminous phase (plagioclase, spinel, and garnet present in the depth ranges 0-150 km, 150-200 km, and >200 km, respectively). This model is broadly consistent with constraints on mantle mineralogy derived from the experimental and observational study of the phase relationships and trace element compositions of lunar mare basalts and picritic glasses. In particular, by melting a typical model mantle composition using the pMELTS algorithm, we found that a range of batch melts generated from these models have features in common with low Ti mare basalts and picritic glasses. Our results also indicate a bulk lunar composition and Mg# different to that of the Earth's upper mantle, represented by the pyrolite composition. This difference is reflected in a lower bulk lunar Mg# ($0.83). Results also indicate a small iron-like core with a radius around 340 km.
About age of the lunar surface
Vestnik Otdelenia nauk o Zemle RAN, 2011
Most part of the lunar surface relief was formed during the last 5 Ma. This conclusion was received on the basis of detail analysis of large craters of the Moon, Earth, Mars and Mercury. Falling of the galactic comets in the period 5-0.6 Ma, and the tectonomagmatic processes induced by the comets falling played major role in shaping of the Moon topography. Processes of tectonics and volcanism are occurring on the Moon today also. We found volcano in the Tsiolkovsky crater on the reverse side of the Moon that can serve as good example of that. The volcano has a height of 102 m and is located almost in the bottom center of the crater with a diameter of 180 km on a low oval elevation of plume nature 24-26 km in size.
1996
High-Ti basalts from the Apollo collections span a range in age from 3.87 Ga to 3.55 Ga. The oldest of these are the common Apollo 11 Group B2 basalts which yield evidence of some of the earliest melting of the lunar mantle beneath Mare Tranquillitatis. Rare Group D high-Ti basalts from Mare Tranquillitatis have been studied in an attempt to confirm a postulated link with Group B2 basalts (Jerde et al.,1994). The initial Sr isotopic ratio ofa known Group D basalt (0.69916 ± 3 at 3.85 Ga) lies at the lower end of the tight range for Group B2 basalts (87Sr/86Sr = 0.69920 to 0.69921). One known Group D basalt and a second postulated Group D basalt yield indistinguishable initial ENd (1.2 ± 0.6 and 1.2 ± 0.3) and again lie at the lower end of the range for the Group B2 basalts from Apollo 11 (+2.0 ± 0.4 to +3.9 ± 0.6, at 3.85 Ga). A third sample has isotopic (87Sr/86Sr = 0.69932 ± 2; ENd = 2.5 ± 0.4; at 3.59 Ga; as per Snyder et al., 1994b) and elemental characteristics similar to the Group A high-Ti basalts returned from the Apollo 11 landing site. Ages of 40Ar 3 9 Ar have been determined for one known Group D basalt and a second postulated Group D basalt using step-heating with a continuous-wave laser. Suspected Group D basalt, 10002,1006, yielded disturbed, age spectra on two separate runs, which was probably due to 39Ar recoil effects. Using the "reduced plateau age" method of Turner et al. (1978), the ages derived from this sample were 3898 ± 19 and 3894 ± 19 Ma. Three separate runs of known Group D basalt 10002,116 yielded 40Ar/ 39 Ar plateau ages of 3798 ± 9 Ma, 3781 ± 8 Ma, and 3805 ± 7 Ma (all errors 20). Furthermore, this sample has apparently suffered significant 40Ar loss either due to solar heating or due to meteorite impact. The loss of a significant proportion of 40Ar at such a time means that the plateau ages underestimate the "true" crystallization age of the sample. Modelling of this Ar loss yields older, "true" ages of3837 ± 18,3826 ± 16, and 3836 ± 14 Ma. These ages overlap the ages of Group B2 high-Ti basalts (weighted average age = 3850 ± 20 Ma; range in ages = 3.80 to 3.90 Ga). The combined evidence indicates that the Group D and B2 high-Ti basalts could be coeval and may be genetically related, possibly through increasing degrees of melting of a similar source region in the upper mantle of the Moon that formed >4.2 Ga ago. The Group D basalts were melted from the source first and contained 3-5x more trapped KREEP-like liquid than the later (by possibly only a few million years) Group B2 basalts. Furthermore, the relatively LREE-and Rb-enriched nature of these early magmas may lend credence to the idea that the decay of heat-producing elements enriched in the KREEP-like trapped liquid of upper mantle cumulates, such as K, U, and Th, could have initiated widespread lunar volcanism.
Astronomy & Geophysics
Ian Crawford summarizes a joint RAS/Geological Society Discussion Meeting which examined what the Moon can tell us about the origin and early evolution of our own planet.