Long Zheng-Yu, Moynier Frédéric, Dai Wei, van Zuilen Mark, Deng Jun, Qiu Kun-Feng
Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris 75005, France.
State Key Laboratory of Geological Processes and Mineral Resources, Frontiers Science Center for Deep-time Digital Earth, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
Proc Natl Acad Sci U S A. 2025 Aug 5;122(31):e2510228122. doi: 10.1073/pnas.2510228122. Epub 2025 Aug 1.
The Eoarchean quartz-pyroxene rock from Akilia Island in Greenland has been proposed as one of Earth's oldest banded iron formations (BIF) and a potential host for the earliest biosignatures. However, the origin of its protolith, whether it metamorphosed from an igneous or sedimentary precursor, remains debated. Here, we revisit this longstanding Akilia controversy using potassium isotope analyses, comparing Akilia samples with BIFs and black shales spanning the Eoarchean to Mesoproterozoic. Our results demonstrate that BIFs and black shales show systematic potassium isotope variations correlated with their potassium contents. Potassium-poor BIF layers display heavier isotopic compositions close to seawater values, whereas clay-rich layers exhibit elevated potassium contents and lighter isotopic signatures. The Akilia quartz-pyroxene rock was initially characterized by low potassium concentrations and heavy potassium isotopic compositions consistent with chemical sediments deposited from ancient seawater. It was subsequently modified by metasomatic fluids derived from nearby metamorphosed igneous rocks. These findings support a sedimentary origin for the Akilia quartz-pyroxene rock. Furthermore, our study provides an isotopic framework for interpreting ancient oceanic environments and offers insights into the potassium cycling and habitability of early Earth.
格陵兰阿基利亚岛的早太古代石英辉石岩被认为是地球上最古老的条带状铁建造（BIF）之一，也是最早生物标志的潜在宿主。然而，其原岩的起源，即它是由火成岩还是沉积岩前身变质而来，仍存在争议。在这里，我们使用钾同位素分析重新审视这一长期存在的阿基利亚争议，将阿基利亚样品与从早太古代到中元古代的BIF和黑色页岩进行比较。我们的结果表明，BIF和黑色页岩显示出与它们的钾含量相关的系统钾同位素变化。贫钾的BIF层显示出更重的同位素组成，接近海水值，而富含粘土的层则表现出较高的钾含量和较轻的同位素特征。阿基利亚石英辉石岩最初的特征是低钾浓度和重钾同位素组成，这与从古代海水中沉积的化学沉积物一致。随后，它被来自附近变质火成岩的交代流体改造。这些发现支持了阿基利亚石英辉石岩的沉积起源。此外，我们的研究提供了一个同位素框架来解释古代海洋环境，并为早期地球的钾循环和宜居性提供了见解。
