Unravelling the volcanic history of the enigmatic lunar farside is essential for understanding the hemispheric dichotomy of the Moon^1-3. Cratering chronology established for the lunar nearside has been used to suggest long-lived volcanism on the farside of the Moon^3,4, but without sample verification. Here we report two newly recognized episodes of basaltic volcanism with Pb-Pb dating for basalt fragments returned by the Chang’e-6 mission. One high-Al basalt fragment dated at 4,203 ± 4 million years ago (Ma) has a source ²³⁸U/²⁰⁴Pb ratio (µ value) of ~1,620, implying a KREEP-rich (K, rare earth elements, and P) source for this oldest-known occurrence of basaltic volcanism among returned samples. The main volcanic episode of the Chang’e-6 basalt documents a surprisingly young eruption age of 2,807 ± 3 Ma, which is not recognized from the nearside of the Moon. The initial Pb isotope compositions of these younger basalts indicate derivation from a source with a µ value of ~360, indicating a KREEP-poor mantle source. Mare volcanism on the lunar farside thus persisted for >1.4 billion years even with a shift to a source depleted in heat-producing elements. The consistency between the 2.8-billion-year basalt age and its crater-counting age indicates that the cratering chronology model established for the lunar nearside is also applicable to the farside of the Moon.

解开神秘的月球背面的火山历史对于理解月球^1-3 的半球二分法至关重要。为月球近侧建立的火山口年代学已被用来表明月球背面存在长寿的火山活动^3,4，但没有样本验证。在这里，我们报告了两个新发现的玄武岩火山活动事件，对嫦娥六号任务返回的玄武岩碎片进行了 Pb-Pb 测年。一块测年为 4,203 ± 400 万年前 （马） 的高铝玄武岩碎片的来源为 ²³⁸U/²⁰⁴Pb（μ值）为 ~1,620，这意味着在返回的样本中，已知最古老的玄武岩火山作用来源是富含 KREEP（K、稀土元素和 P）的来源。嫦娥六号玄武岩的主要火山喷发事件记录了令人惊讶的年轻喷发年龄，为 2,807 ± 3 马，这在月球的近侧是无法识别的。这些年轻玄武岩的初始 Pb 同位素组成表明来源于 μ 值为 ~360 的来源，表明 KREEP 贫地幔来源。因此，月球背面的海火山活动持续了 >14 亿年，即使转移到产热元素耗尽的源头。28 亿年玄武岩年龄与其陨石坑计数年龄之间的一致性表明，为月球近侧建立的陨石坑年代学模型也适用于月球背面。