Many studies have focused on this topic, often concentrating on minor elements in olivine. These experiments usually mimic Earth's mantle conditions.
For understanding basalt formation on other rocky bodies, including the Moon, Mars, and asteroids, oxygen fugacities during basalt formation vary from 2 log units below the iron-wustite buffer (IW-2) to IW+6. Lunar basalts are generally iron-rich compared to Earth's.
Dr. Jiejun Jing, a JSPS postdoctoral fellow at Ehime University, conducted high-temperature experiments (around IW-2 to IW+5.5) at 1 atm using a gas-mixing furnace. This was done with colleagues from Ehime University and universities in the Netherlands, China, and Germany.
The results indicate most DOl-melt values are insensitive to bulk system iron contents. However, DOl-meltCr is significantly higher in these experiments compared to DOl-meltCr from lunar samples with higher FeO content. DOl-meltNi values remain constant at oxygen fugacities above the IW buffer but drop sharply when the system is iron metal saturated (below the IW buffer).
Using these new partition coefficients, the authors reassessed lunar basalt generation. They concluded that the Cr-rich nature of olivines in lunar basalts compared to terrestrial basalts is due to the Cr-rich cumulate mantle source. This links to the early crystallization of Cr-poor minerals like olivine and orthopyroxene in the lunar magma ocean, resulting in shallow Cr-rich cumulates.
Additionally, higher Co/Ni ratios in olivine in high-titanium lunar basalts compared to low-titanium lunar basalts suggest the former formed under more reduced conditions in the lunar mantle (below the IW buffer, metal-saturated).
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