中国科学院南京地质古生物研究所机构知识库

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 delta V-51) provide insights into this transition because they correlate positively with SiO2 and negatively with MgO contents during igneous differentiation in both subduction zones and intraplate settings. Because delta V-51 is not affected by chemical weathering and fluid-rock interactions, delta V-51 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 delta V-51 values of glacial diamictites systematically increase with time, indicating a dominantly mafic UCC at similar to 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.