The recycling of supracrustal materials, and in particular hydrated rocks, has a profound impact on mantle composition and thus on the formation of continental crust, because water modifies the physical properties of lithological systems and the mechanisms of partial melting and fractional fractionation. On the modern Earth, plate tectonics offers an efficient mechanism for mass transport from the Earth's surface to its interior, but how far this mechanism dates back in the Earth's history is still uncertain. Here, we use zircon oxygen (O) isotopes to track recycling of supracrustal materials into the magma sources of early Archean igneous suites from the Kaapvaal Craton, southern Africa. The mean δ18O values of zircon from TTG (tonalite–trondhjemite–granodiorite) rocks abruptly increase at the Paleo-Mesoarchean boundary (ca. 3230 million years ago; Ma), from mantle zircon values of 5‰–6‰ to approaching 7.1‰, and this increase occurs in ≤3230 Ma rocks with elevated Dy/Yb ratios. The 18O enrichment is a unique signature of low-temperature water–rock interaction on the Earth's surface. Because the later phase was emplaced into the same crustal level as the older one and TTG magmas would derive from melting processes in the garnet stability field (>40 km depth), we suggest that this evident shift in TTG zircon O isotopic compositions records the onset of recycling of the mafic oceanic crust that underwent seawater hydrothermal alteration at low temperature. The onset of the enhanced recycling of supracrustal materials may also have developed elsewhere in other Archean cratons and reflects a significant change in the tectonic realm during craton formation and stabilization, which may be important processes for the operation of plate tectonics on early Earth.

中文翻译：

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古-中太古代边界表层物质深度循环的开始


表壳物质，特别是水合岩石的再循环，对地幔成分以及大陆地壳的形成具有深远的影响，因为水改变了岩性系统的物理性质以及部分熔融和分馏的机制。在现代地球上，板块构造为从地球表面到内部的质量传输提供了一种有效的机制，但这种机制可以追溯到地球历史多久仍然不确定。在这里，我们使用锆石氧 (O) 同位素来追踪南非卡普瓦尔克拉通早期太古代火成岩套岩浆源中的表壳材料的回收情况。 TTG（英闪长岩-长辉长岩-花岗闪长岩）岩石中锆石的平均 δ18O 值在古中太古代边界（约 32.3 亿年前；Ma）突然增加，从地幔锆石值的 5‰-6‰ 增加到接近 7.1‰，这种增加发生在 ≤3230 Ma 且 Dy/Yb 比率升高的岩石中。 18O 富集是地球表面低温水-岩石相互作用的独特特征。由于后期阶段与较老阶段位于同一地壳水平，并且 TTG 岩浆源自石榴石稳定场（>40 km 深度）的熔化过程，因此我们认为 TTG 锆石 O 同位素组成的这种明显变化记录了起始阶段低温下经历海水热液蚀变的镁铁质洋壳的循环利用。表壳物质强化循环的开始也可能在其他太古宙克拉通的其他地方发展起来，反映了克拉通形成和稳定期间构造领域的重大变化，这可能是早期地球板块构造运行的重要过程。