Time constraints on the closure of the Paleo–South China Ocean and the Neoproterozoic assembly of the Yangtze and Cathaysia blocks: Insight from new detrital zircon analyses

Abstract

The South China Block was built up by the assembly of the Yangtze and Cathaysia blocks along the Neoproterozoic Jiangnan Orogenic Belt. The timing of the Jiangnan Orogeny remains controversial. The widespread orogeny–related Neoproterozoic angular unconformity that separates the underlying folded Sibao (ca.1000–820\u202fMa) and overlying Danzhou (ca.800–720\u202fMa) Groups was investigated. Six sedimentary samples, below and above the unconformity in three distal localities (Fanjingshan, Madiyi, and Sibao) yield detrital zircon with UPb ages ranging from 779\u202f±\u202f16\u202fMa to 3006\u202f±\u202f36\u202fMa, with a prominent peak at ca. 852\u202fMa. The youngest ages of 832\u202f±\u202f11\u202fMa and 779\u202f±\u202f16\u202fMa are revealed for the underlying Sibao and overlying Danzhou Groups, respectively. The detrital zircon UPb age relative probability plot of the Jiangnan Orogen matches well with those of the Yangtze and Cathaysia blocks since ca. 865\u202fMa. Integrating geological, geochemical and geochronological results, we suggest that the Paleo–South China Ocean began to subduct under the Yangtze block at ca. 1000\u202fMa, and was partly closed at ca. 865\u202fMa. Afterwards, the Yangtze and Cathaysia blocks initially collide at 865\u202fMa, forming the Jiangnan Orogen. This collision resulted in not only the folding of the Sibao Group, but also sediment deposition in a syn-collisional setting, which makes the upper part of the Sibao Group. The youngest S-type granite dated at ca. 820\u202fMa that intruded in the Sibao Group marks the late stage of the Jiangnan Orogeny.