Late Mesoproterozoic to Early Neoproterozoic Tectonic Evolution of the SW Yangtze Block, South China: Evidence from U-Pb Geochronology and Lu-Hf Isotopes of Detrital Zircons from Sedimentary Rocks

In situ zircon U-Pb geochronological and Lu-Hf isotope studies of detrital zircons from Late Mesoproterozoic to Early Neoproterozoic sedimentary units on the southwestern margin of the Yangtze Block have important implications for the tectonic evolution of the Yangtze Block. The Huili Group contains zircons whose ages are mainly Late Archean to Mesoproterozoic (2 650–2 450, 2 100–1 800, and 1 350–1 150 Ma). The Dengxiangying Group has one major age population of 1 900–1 600 Ma, and two subordinate age populations of 1 350–1 100 and 2 300–2 000 Ma. Yanbian Group sedimentary rocks have a zircon age population mainly in the range of 970–850 Ma, contemporaneous with the ages of widespread arc-related magmatism in the western Yangtze Block. Combining these results with previous work, the Huili and Dengxiangying groups were most likely deposited during ca. 1 160 to 1 000 Ma in an intra-continental rift basin setting, while the Yanbian Group accumulated during >920 to 782 Ma in a back-arc basin setting at the southwestern margin of the Yangtze Block. In addition, all these results further suggest a tectonic transition from a continental rift basin to a convergent environment at the southwestern margin of the Yangtze Block at 1 000–970 Ma.