Abstract

The Neoproterozoic (830–815 Ma) Shuangqiaoshan (SQS) and (833–817 Ma) Xikou (XK) groups are two of a series of sedimentary sequences in the Jiangnan Orogen, which are located in the southeastern Yangtze Block, South China and witnessed the assemblage and breakup of the supercontinent Rodinia. Through a multidisciplinary approach, including petrology and geochemistry of the clastic sedimentary rocks, we reconstruct the sedimentary provenance and paleoweathering of the sedimentary basin and characterize the formation and evolution of the Jiangnan Orogen and its role in Rodinia. The SQS Group consists of texturally immature sandstones composed of unsorted and angular to subangular clastic grains dominated by lithic fragments (54–80%) (mostly chert, metasedimentary, and sedimentary grains) accompanied by variable amounts of quartz (14–40%) and feldspar (0–18%). Sandstones from the XK Group are characterized by lower quartz (5–16%) but higher feldspar (16–47%) and lithic fragments (47–78%) (mostly volcanic detritus). All samples lie along a provenance-dependent compositional trend, suggesting that hydraulic sorting and recycling of heavy minerals were insignificant. Moderate Eu/Eu* (0.6–1.0) and (La/Yb)n (4.8–8.4) values and predominant Neoproterozoic euhedral detrital zircons indicate that sedimentary detritus was largely sourced from locally distributed Neoproterozoic intermediate to felsic igneous rocks. Potential sources include the ca. 930–900 Ma Pingshui plagiogranite, the ca. 930–890 Ma Shuangxiwu andesite, and the ca. 850 Ma Zhenzhushan dacite and basalt. The modeled average composition of the SQS detritus consists of 80% dacite, 10% andesite, and 10% basalt, whereas the XK detritus consists of 70% dacite, 20% andesite, and 10% basalt.

The SQS and XK rocks record mild to moderate chemical weathering in their source areas. Some samples plot away from the predicated weathering trend in the A-CN-K diagram, reflecting replacement of the detrital calcic plagioclase by authigenic albite during postdepositional metasomatism. Textural and chemical immaturity, non-steady-state weathering, and signatures of immobile elements are indicative of a tectonically active setting, likely a continental arc environment, for deposition of the SQS and XK groups. The Yangtze Block is thus considered to be located in the periphery of Rodinia during ca. 833–815 Ma.