Completion of lunar magma ocean solidification at 4.43 Ga

Area of Science:

• Lunar geology and planetary science
• Radiometric dating and isotope geochemistry
• Early Solar System evolution

Background:

• The lunar magma ocean (LMO) is a key concept explaining the Moon's chemical evolution.
• KREEP (Potassium, Rare Earth Elements, Phosphorus) is a unique chemical component resulting from LMO crystallization.
• Previous estimates for LMO crystallization completion varied significantly.

Purpose of the Study:

• To precisely determine the age of lunar magma ocean crystallization.
• To constrain the Moon's formation age.
• To investigate the origin and timing of the KREEP component.

Main Methods:

• Analysis of the ¹⁷⁶Lu-¹⁷⁶Hf decay system in lunar zircons.
• Radiometric dating of lunar samples to determine U-Pb ages.
• Comparison of isotopic data with thermal and accretion models.

Main Results:

• The Moon achieved >99% crystallization at 4,429 ± 76 million years ago.
• This indicates a lunar formation age of approximately 4,450 Ma or older.
• The KREEP-rich reservoir formed ~140 million years after solar system formation with a low ¹⁷⁶Lu/¹⁷⁷Hf ratio.

Conclusions:

• Lunar magma ocean crystallization occurred early in the Moon's history, overlapping with planetary accretion.
• The timing of mare basalt sources may relate to impact events rather than LMO crystallization.
• Further analysis of South Pole-Aitken basin samples can clarify KREEP distribution and its early lunar significance.