The following blog has been written by our colleague Abigail Calzada-Diaz from Birkbeck College about a new collaborative paper between Birkbeck College, the Univeristy of Manchester and the Natural History Musuem London published in Meteoritics and Planetary Science.
Most of what we know about the composition of the Moon is thanks to the rocks returned from NASA´s Apollo missions and the Luna soviet robotic mission. These samples were collected in areas within the nearside so, they represent just a small portion of the lunar surface. Fortunately, we have an additional source of material from the Moon that provide us with lots of valuable information: lunar meteorites.
The lunar meteorites Miller Range (MIL) 090036 and MIL 090070 were found in the Miller Range Icefield area of Antarctica by the 2009 Antarctic Search for Meteorites (ANSMET) campaign. They both are fused ancient soil samples – called regolith breccias – formed by rocks, impact melts and mineral fragments. These fragments, called clasts, were created previously to the formation of the breccia and they are the result of the fragmentation and melting of rocks by impacts on the lunar surface. The chemistry of both meteorites are feldspathic, with high contents of Al2O3 and low FeO, indicative of a possible origin in the feldspathic highlands of the Moon.
To investigate the source of these meteorites, the bulk rock compositions of the meteorites obtained in the laboratory were compared to the measurements obtained by the NASA´s Lunar Prospector Gamma-Ray Spectrometer. Three compositions were compared: FeO to distinguish between highlands and mare materials, TiO2 to differentiate among different types of basalts and Th an element that have their higher abundances in the Procellarum KREEP Terrane. These study shows that, although they are very similar, these two meteorites likely originally derive from different areas of the Moon.
MIL 090036 contains slightly higher Th abundances than MIL 090070, indicating that the former derives from a region in the nearside, relatively close to the Procellarum KREEP Terrane.
MIL 090070 contains two types of rocks: ferroan anorthosite rocks and metamorphosed rocks derived from magnesian anorthosites called magnesian granulites. The results of this study suggest that the sample was launched from the farside of the Moon, far from the dark mare areas and also far from the Procellarum KREEP Terrane on the nearside (see figure, yellow). This interpretation has implications for understanding the diversity and formation of the lunar crust suggesting that both ferroan and magnesian anorthosites may coexist in a geographically similar region and are sampled by different feldspathic lunar meteorites. The ages obtained for MIL 090070 indicate that the rock suffered an impact formation event at ~3.9 Ga and subsequent impacts that affected differently to the different materials of the MIL 090070 breccia.
Every new lunar meteorite sample we have has the potential to unlock key information about the Moon’s geological past, and we look forward to seeing what new lunar meteorites will be discovered in the future.
The full paper can be accessed at:
Calzada-Diaz A., Joy K. H., Strekopytov S. and Crawford I.A. (In Press) The petrology, geochemistry, and age of lunar regolith breccias Miller Range 090036 and 090070: Insights into the crustal history of the Moon. Meteoritics and Planetary Science DOI: 10.1111/maps.12737
More information about lunar meteorites:
- Scientific importance of lunar meteorites
- Randy Korotev’s Lunar Meteorite List
- NASA Lunar Meteorite Compendium