Abstract
The Apollo 15 KREEP basalts—so called because they are rich in trace elements such as potassium, rare-earth elements and phosphorus—are thought to be volcanic rocks1, based on their petrographic characteristics, chemical variations and geological context2. The lavas were extruded ∼3.85 Gyr ago3, and most are represented by only tiny fragments (nearly all less than 1 cm across). Here I report the results of a re-examination of their petrography. Several of them contain yellow residual glasses which cross-cut the crystallized phases; some show more extreme disruption. The features of the glasses appear to be compatible only with impact disruption, ejection and quenching from actively crystallizing flows, indicating a high impact flux immediately after the impact that formed the Imbrium basin. No other example of impacts into active lava flows is known in the Solar System.
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Ryder, G. Quenching and disruption of lunar KREEP lava flows by impacts. Nature 336, 751–754 (1988). https://doi.org/10.1038/336751a0
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DOI: https://doi.org/10.1038/336751a0
