Chinese Academy of Sciences, Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Anhui 230026, China.
Chinese Academy of Sciences, Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei 230026, China.
Proc Natl Acad Sci U S A. 2023 Mar 14;120(11):e2220563120. doi: 10.1073/pnas.2220563120. Epub 2023 Mar 9.
The transition from mafic to felsic upper continental crust (UCC) is crucial to habitability of Earth, and may be related to the onset of plate tectonics. Thus, defining when this crustal transition occurred has great significance for the evolution of Earth and its inhabitants. We demonstrate that V isotope ratios (reported as δV) provide insights into this transition because they correlate positively with SiO and negatively with MgO contents during igneous differentiation in both subduction zones and intraplate settings. Because δV is not affected by chemical weathering and fluid-rock interactions, δV of the fine-grained matrix of Archean to Paleozoic (3 to 0.3 Ga) glacial diamictite composites, which sample the UCC at the time of glaciation, reflect the chemical composition of the UCC through time. The δV values of glacial diamictites systematically increase with time, indicating a dominantly mafic UCC at ~3 Ga; the UCC was dominated by felsic rocks only after 3 Ga, coinciding with widespread continental emergence and many independent estimates for the onset of plate tectonics.
从镁铁质到长英质上大陆地壳（UCC）的转变对地球的宜居性至关重要，并且可能与板块构造的开始有关。因此，确定这种地壳转变何时发生对于地球及其居民的演化具有重要意义。我们证明，V 同位素比值（报告为 δV）提供了对此转变的深入了解，因为它们在俯冲带和板内环境中的火成岩分异过程中与 SiO 和 MgO 含量呈正相关。由于 δV 不受化学风化和流体-岩石相互作用的影响，太古宙至古生代（3 至 0.3 Ga）冰川砾岩复合岩样中细粒基质的 δV 值反映了 UCC 在冰川作用时期的化学成分。冰川砾岩的 δV 值随时间系统增加，表明在~3 Ga 时 UCC 主要为镁铁质；只有在 3 Ga 之后，UCC 才主要由长英质岩石组成，这与大陆广泛出现和许多独立估计的板块构造开始时间相吻合。
