LAUSR

Abstract The Jiangnan orogenic belt in South China, formed by the collision of the Yangtze and Cathaysia sub-blocks, represents a key to reconstruct the assembly of the Rodinia supercontinent. Here we investigated the Fuchuan ophiolite melange and Shexian magmatic units in the eastern Jiangnan belt, and report the first findings of anorthosite and leucogranite that are dated at 848 ± 4 and 840 ± 5 Ma, respectively. The anorthosites yield positive eNd(t) values (2.3–4.2) and lower initial 87Sr/86Sr ratios (0.704616–0.704679), along with zircon eHf(t) of ∼9.2, suggesting a depleted mantle contribution with minor crustal assimilation. The mafic-ultramafic rocks and anorthosite within the Fuchuan ophiolite display N-MORB & E-MORB signatures, likely generated in back-arc marginal sea spreading center and metasomatized by subduction-related fluids. The intermediate-felsic igneous suites from Shexian area in the eastern margin of the Zhanggong Terrane were formed at 850–830 Ma and display continental-arc-related geochemical features. Zircons within these rock suites mostly show eHf(t) values of 3–12, whereas inherited grains yielded negative eHf(t) values with model ages of 2.7–1.9 Ga, implying an active continental marginal environment. Overall relations and data indicate that the disrupted Fuchuan mafic-ultramafic rocks, anorthosite and leucogranite constitute the remnants of an 860–830 Ma ophiolite, whereas the northwestward subduction beneath the Zhanggong terrane occurred at ca. 870–860 Ma to ca. 830 Ma. A ca. 817 Ma muscovite-bearing K-granitic pluton dated at 817 ± 5 Ma emplaced in a post-collisional setting constrains the upper age limit of continental assembly along the Shaoxing- Jiangshan- Pingxiang- Qidong-Quanzhou- Longsheng-Yongfu fault zone. The timing of the final assembly of South China occurred at 830–800 Ma as referred from a collisional-type granitic magmatism ca. 830–815 Ma and an external dynamic process of uplifting-erosion-transpotation-deposition presented by the regional-scale unconformity with ages 820–795 Ma. Age and nature of the Jiangnan orogenic belt, along with sedimentary records and paleomagnetic constraints, indicate that the South China Block was possibly located along the northern Rodinia margin, adjacent to the Tarim and northwestern Australia blocks.