The formation of a unified basement of the Yangtze Craton

Abstract

The Yangtze Craton has a long evolution history since the Eoarchean. With the increasing number of studies on the Yangtze Craton, ten Archean-Paleoproterozoic basements, separated from each other, have been identified. These basements may represent independent microcontinental blocks before they were amalgamated into a unified basement. To decipher their affinities with each other and when these microcontinental blocks joined together to form the basement of the Yangtze Craton, we compiled the Archean-Mesoproterozoic magmatic and metamorphic events and zircon U-Pb ages with Hf isotope data of magmatic rocks in these basements. Magmatic activities of basements in the Yangtze Craton mainly occurred within nine periods: approximately 3.7 Ga, 3.1–2.9 Ga, 2.9–2.7 Ga, 2.7–2.6 Ga, 2.5–2.4 Ga, 2.4–2.2 Ga, 2.1–1.9 Ga, 1.9–1.7 Ga, 1.7–1.6 Ga. By comparing the timings of tectono-thermal events and calculating the likeness of igneous zircon Hf isotopes between them, we reconstructed the assembly history of these microcontinental blocks and the formation time of the unified basement of the Yangtze Craton. The amalgamation history can be briefly summarized as: Yangkou was assembled with Dabie at ca. 3.7 Ga; Cuoke was merged with Phan Si Pan during 3.1–2.9 Ga to form the proto-south Yangtze Craton; Zhongxiang and Kongling were assembled during 2.9–2.8 Ga; Yangkou-Dabie, Zhongxiang-Kongling, and Yudongzi were assembled during 2.7–2.6 Ga; Feidong and Douling joined the Yangkou-Dabie-Zhongxiang-Kongling-Yudongzi assemblage during 2.5–2.4 Ga, constituting the proto-north Yangtze Craton. The coeval development of ca. 2.0 Ga metamorphism in the proto-south and the proto-north Yangtze Craton suggests that the amalgamation of the Yangtze Craton may have occurred as early as approximately 2.0 Ga. The occurrence of 1.9–1.7 Ga A-type granites and mafic dykes indicative of extension in both the northern and southwestern blocks marks the final assembly of the Yangtze Craton. The development of late Paleoproterozoic-Mesoproterozoic sedimentary strata with sporadic interlayered mafic volcanics in most parts of the Yangtze Craton suggests the stability of the Yangtze Craton. Based on the aforementioned evidence, we propose that a unified basement of the Yangtze Craton was formed no later than the late Paleoproterozoic, coeval with the final assembly of the supercontinent Columbia (Nuna).