Unlike the other terrestrial planets, Earth has a substantial silica-rich continental crust with a bulk andesitic composition. A small number of meteorites with andesitic bulk compositions have been identified that are thought to be the products of partial melting of chondritic protoliths, a mode of petrogenesis distinct from that of Earth’s continental crust. Here we show, using geochemical analyses, that unlike other known andesitic meteorites, Erg Chech 002 has strongly fractionated and low abundances of the highly siderophile elements and mineralogy consistent with origin from a melt. The meteorite’s bulk composition, which is similar to terrestrial andesites, cannot be explained by partial melting of basaltic lithologies and instead requires a metal-free chondritic source. We argue that Erg Chech 002 probably formed by ~15–25% melting of the mantle of an alkali-undepleted differentiated asteroid. Our findings suggest that extensive silicate differentiation after metal–silicate equilibration of chondritic parent bodies was already occurring within the first 2.25 million years of Solar System history and that andesitic crust formation does not necessarily require plate tectonics.

与其他类地行星不同，地球拥有大量富含二氧化硅的大陆地壳和大量安山岩成分。少数具有安山岩整体成分的陨石已被确定，它们被认为是球粒质原岩部分熔融的产物，这是一种不同于地球大陆地壳的岩石形成模式。在这里，我们使用地球化学分析表明，与其他已知的安山岩陨石不同，Erg Chech 002 具有与熔体起源一致的高度亲铁元素和矿物学的强烈分馏和低丰度。陨石的整体成分与陆地安山岩相似，不能用玄武质岩性的部分熔融来解释，而是需要不含金属的球粒陨石源。我们认为 Erg Chech 002 可能是由一颗碱金属未耗尽的分化小行星的地幔熔化约 15-25% 形成的。我们的研究结果表明，在太阳系历史的最初 225 万年中，在球粒质母体的金属-硅酸盐平衡后，已经发生了广泛的硅酸盐分化，并且安山岩地壳的形成不一定需要板块构造。