From amalgamation to post-orogenic rifting： Decoded by the Neoproterozoic Shenshan Group, South China

The Shenshan Group provides important geological information which is vital in unraveling the amalgamation and subsequent rifting processes of South China. While conventional studies have asserted its formation in a subduction setting, our distinct investigation reveals the necessity for reassessment. To address this, we employ integrated methods encompassing petrological, zircon U-Pb geochronological, Lu-Hf isotopic and geochemical methods for sedimentary rocks from the upper Shenshan subgroup and Banxi Group. The geochemical results indicate that they were formed through the recycling deposition of intermediate-acidic igneous source material and experienced moderate chemical weathering. Additionally, both sedimentary sequences exhibit characteristics consistent with those formed in an intracontinental extensional rift setting since ca. 810 Ma. The provenance analysis indicates that the upper Shenshan subgroup primarily originates from the Yangtze Domain, while the Banxi Group from both the Yangtze and Cathaysia domains. Synthesizing with previous studies, the Shenshan Group should be subdivided into the lower and upper subgroups which represent distinct tectonic backgrounds. The lower subgroup is inferred to have formed in an Early Neoproterozoic fore-arc setting, akin to the Zhoutan group. The upper subgroup corresponds to the Banxi Group, representing the Middle Neoproterozoic post-orogenic rift setting, responding to the breakup of Rodinia.