Metamorphism on the Moon: A terrestrial analogue in the Vredefort dome, South Africa?

A new model is proposed to explain the origin of enigmatic fine-grained granulite facies rocks sampled from the Moon, based on observations from the Vredefort dome, South Africa. The dome is the deeply eroded central uplift of the ;300-km-diameter Vredefort impact structure. In the dome, fine-grained granulites displaying poikilitic or granoblastic microstructures were formed by relatively slow cooling of shock 6 friction melts derived at T . 1350 8C. Slow cooling was achieved owing to the .7 km depth of burial of the rocks following the impact. At least some of the lunar granulitic impactites may also have formed by shock heating and slow cooling at deep levels within the central uplifts of large impact structures, without the need for additional heating by younger intrusive or impact melt bodies.