2025-04-25 愛媛大学
シミュレーションで得られた、約30億年前の月内部の温度（右）とマグマ量（左）の描像
＜関連情報＞
- https://www.ehime-u.ac.jp/data_relese/pr_20250425_grc/
- https://www.ehime-u.ac.jp/wp-content/uploads/2025/04/pr_20250424_grc-2.pdf
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL115215
マグマの上昇メカニズムの変化がもたらした月の長期火山活動：マグマ上昇とマントル対流の数値モデルにおける放射性元素濃縮領域の役割 Long-Lasting Volcanism of the Moon Aided by the Switch in Dominant Mechanisms of Magma Ascent: Role of Localized Radioactive Enrichment in a Numerical Model of Magmatism and Mantle Convection
Ken’yo U, Masanori Kameyama, Gaku Nishiyama, Takehiro Miyagoshi, Masaki Ogawa
Geophysical Research Letters Published: 24 April 2025
DOI:https://doi.org/10.1029/2025GL115215
Abstract
Significant volcanic activity continued for billions of years since 3.5–4 Gyr ago in the Procellarum KREEP Terrane (PKT) of the Moon, but not so significant outside the PKT. To understand this volcanic history, we developed a 2-D numerical model of magmatism and mantle convection; the effects of the PKT on lunar evolution are considered by initially imposing a region of localized radioactive enrichment. The calculated volcanism is driven by two different mechanisms. Early volcanism occurs when magma generated in the deep mantle by internal heating ascends to the surface as partially molten plumes. The basaltic blobs in the uppermost mantle formed by this magmatism then sink into the deep mantle, triggering further plumes that cause a resurgence of volcanism in its later history. Our model suggests that later plumes caused by sinking basaltic blobs are the cause of the long-lasting volcanism in the PKT.
Key Points
- To understand the localized long-lasting volcanism of the Moon, we developed a numerical model of magmatism in the convecting mantle
- Partially molten plumes ascend from the deep mantle to the uppermost level to cause the calculated volcanic activity
- Localized radioactive enrichment in the uppermost mantle maintains the plume activity for billions of years to cause volcanism
Plain Language Summary
Geological observations of the Moon have revealed that active volcanism took place at 3–4 Gyr ago and continued for billions of years in the Procellarum KREEP Terrane (PKT), a region enriched in radioactive heat-producing elements (HPEs). Here, we calculated a 2-D model of magmatism and mantle convection, considering a locally HPE-enriched area (EA) beneath the crust to model this localized long-lasting volcanism in the PKT. Localized volcanism continues for billions of years owing to ascending partially molten plumes in our model. However, the mechanism of ascent of plumes changed with time. The early volcanic activity is caused by the ascent of partially molten plumes that are generated by strong internal heating at the base of the mantle. These plumes are globally distributed. The compositionally dense basaltic blobs in the uppermost mantle outside the EA, formed by the earlier magmatism, sink into the deep mantle, triggering counterflows that induce further partially molten plumes. These plumes cause volcanism above the EA from 1.2 to 2.8 Gyr. Our model suggests that the volcanism in the later stage caused by sinking basaltic blobs plays a crucial role in the long-lasting volcanism in the PKT.
