An unusual lunar origin and chondritic refractory Antarctic micrometeorites

Abstract

We report unearthing the first silicate-type (S-type) lunar Antarctic micrometeorites (AMM) spherule and another spherule with a refractory chondritic phase. The lunar spherule is made of Augite with minor Ni magnetite (<1 wt.%), in contrast to other known cosmic spherules. The Augite’s minor oxide range in the spherule are as follows: Wo_37-41En_25-27Fs_34-36, Al₂O₃: 0.7–1 wt.%, Cr₂O₃: 0.01–0.06 wt.%, MnO: 0.32–0.39 wt.% and TiO₂: 0.03–0.09 wt.%. The lunar spherule’s chemical characteristics indicate that it originated from very low Ti lunar basalt (VLT) mare basalts. Chondritic diopside (Wo_46-47En_50-47Fs_5-6, Al₂O₃: 1.7–1.6 wt.%, Cr₂O₃: 0.6–0.63 wt.%, MnO: 0.2–0.4 wt.%, and TiO₂: 0.0–0.02 wt.%) makes up the refractory phase in the second spherule. The chemical composition of diopside is indistinct from those of calcium aluminium inclusion (CAIs) found in both ordinary and carbonaceous chondrites. Our finding reveals that micron-sized lunar impact debris can potentially reach the Earth’s surface, similar to the earliest formed nebulae solid component.