Constraining 2.0 Ga Volcanism on the Moon via 40Ar/39Ar Dating of Chang'e-5 Basalts

Abstract

The Chang'e-5 landing site provides an important window into the Moon's late Eratosthenian period of volcanism at ∼2 Ga. Clarifying the Moon's history of volcanic activity using radioisotopic dating assists investigations of the evolution of the lunar surface as well as the Moon's internal dynamics. Recent chronological investigations of Chang'e-5 basalts produced ages spanning ∼100 Ma, thereby inhibiting interpretation of the duration of volcanism recorded in the returned samples. We used microcomputed tomography and Back-Scatter Electron imaging to characterize the structure and morphology of nine Chang'e-5 basalt clasts. Several basalt clasts lack shock features and are interpreted to have not been significantly thermally disturbed. ⁴⁰Ar/³⁹Ar incremental heating produced well defined plateaus for four sub-split samples that give a weighted mean age of 2,021 ± 17 Ma (2σ). These are among the youngest mare basalts to be dated thus far by the ⁴⁰Ar/³⁹Ar method and, when combined with most of the published Pb-Pb ages for Chang'e-5 basalts, define a single episode of mare volcanism at ∼2,021 Ma.