Chinese scientists studying lunar samples brought back by the Chang’e-5 mission have proposed a new model for the moon’s early crust formation. Contrary to the classical two-stage model, their findings suggest a continuous development process.
The traditional magma ocean model posits that the moon’s crust formed in two distinct stages. The first stage involves the flotation and aggregation of plagioclase minerals during the cooling of the magma ocean, forming the primitive lunar crust. The second stage includes the overturn and melting of the mantle, leading to the formation of magnesian-suite rocks and the reformation of the lunar crust.
However, previous studies on lunar anorthosite—a rock mainly composed of plagioclase—and magnesian-suite rocks indicated they formed almost simultaneously. This simultaneity suggests that the formation and reformation of the lunar crust may be a continuous process, though the exact mechanism has remained unclear.
A research team led by Wang Shuijiong from the China University of Geosciences in Beijing conducted a joint study that sheds light on this mystery. They discovered a melt body resembling magnesian-suite rocks within an anorthosite fragment from the Chang’e-5 lunar regolith.
Published recently in the journal Communications Earth & Environment, their study provides direct evidence that lunar anorthosite and the parent magma of magnesian-suite rocks formed at the same time.
Geochemical and thermodynamic simulations of the melt body revealed that its parent magma originated from the lunar upper mantle. This finding indicates that the formation of the lunar crust is indeed a continuous process.
The researchers propose that during the cooling of the lunar magma ocean, gravitational instabilities triggered a small-scale, in-situ overturn in the upper mantle. This was followed by a large-scale mantle overturn and decompression melting of the lower mantle.
According to the study, the in-situ overturn-induced melting of the lunar upper mantle played a crucial role in linking the building of the lunar primitive crust and its subsequent reformation.
The Chang’e-5 probe, which returned to Earth on December 17, 2020, retrieved 1,731 grams of lunar samples consisting primarily of rocks and soil from the lunar surface. These samples continue to provide invaluable insights into the moon’s geological history.
Reference(s):
Chang'e-5 lunar sample reveals early moon crust formation process
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