Trace Elements in Hadean Zircons Reveal the Formation Process of Early Earth's Continental Crust

Abstract

The formation process of continental crust on the early Earth remains unresolved due to a lack of physical evidence. In contrast, Hadean zircons are one of the few clues to the early Earth and are important for understanding the early Earth environment. In this study, we examine the formation process of the continental crust on early Earth using trace elements in Hadean zircons, with a focus on Sc/Yb ratios. Detrital zircons from Jack Hills were used as samples and analyzed for ²⁰⁶Pb-²⁰⁷Pb ages and trace elements using LA-MC-ICP-MS and LA-ICP-MS/MS. The rare-earth patterns showed characteristics similar to igneous zircons. Sc/Yb ratios were below 0.1 before ca. 4.2 billion years, and zircons with ratios above 0.1 appeared after ca. 4.2 billion years. The Zr/Hf ratio exhibited a decreasing trend throughout the Hadean. Based on these results, it can be inferred that there was a transition from high-temperature ocean-island igneous activity in the early Hadean to low-temperature continent-arc igneous activity in the late Hadean.