Provenance and tectonic setting of the Ordovician sedimentary succession at the southeastern margin of the Yangtze Block, South China: Implications for paleotopographic evolution of northestern Gondwana

Abstract

Abstract Ordovician sedimentary strata at the southeastern margin of the Yangtze Block consist of, from bottom to top, fine-grained siliciclastic rocks, cherts with interlayers of siliceous/carbonaceous slate, and coarse-grained siliciclastic rocks, which are important for understanding the tectono-sedimentary evolution in South China. A combined analysis of petrography, whole-rock geochemistry, and zircon U–Pb dating was carried out on these strata. The cherts with radiolarian fossils have high Al/(Al + Fe + Mn) values (0.38–0.94) and no obvious Ce anomalies (1.09 ± 0.05), suggesting a biogenic origin on a continental margin. The geochemical features of the siliciclastic rocks, including ratios of elements, discriminant functions, and ternary diagram positions, suggest a passive margin setting that received detritus mostly derived from intermediate to felsic igneous rocks and recycled quartzose sedimentary rocks. The source areas of the Ordovician siliciclastic rocks existed in semiarid–arid paleoclimate and moderate weathering conditions. The sandstone modal grain compositions and detrital zircon cumulative curves indicate a collisional setting of the source areas. Zircon age populations have been time-varying during the Early Paleozoic. Based on the above-mentioned evidences, the following basin filling and paleotopographic evolution process has been proposed in research area. In the Cambrian, a bilateral filling pattern reflected a flat and broad basin. In the Early Ordovician, longer transportation of SE-sourced sediments reflected the uplift of Gondwana. In the Late Ordovician, uplift of the Wuyi–Yunkai Orogen blocked some Gondwanan detritus (500–700 Ma) and released recycled (900–1100 Ma) and syn-orogenic detritus. Meanwhile, synchronous uplift of the Jiangnan Orogen led to a steeper and narrower basin, and sediments could reach farther distances in a shorter time. In the Silurian, a unidirectional filling pattern with overwhelming SE-sourced detritus indicated intense uplift of Gondwana and the Wuyi–Yunkai Orogen.