Geographic proximity of Yangtze and Cathaysia blocks during the late Neoproterozoic demonstrated by detrital zircon evidence

Abstract

The late Neoproterozoic (~720–541 Ma) tectonic evolution of South China may have included the development of a paleo-ocean basin (the South China Ocean Basin, SCOB) between the Yangtze and Cathaysia blocks. The Niuhe section in the Yongfu area of northern Guangxi Zhuang Autonomous Region, owing to its location on the southeastern margin of the Yangtze Block and its preservation of an alternating succession typical of both Yangtze- and Cathaysia-type deposits, provides an important window to test if this oceanic basin existed during the late Neoproterozoic. Cryogenian-Ediacaran siliciclastics in the northern Guangxi region were deposited in the intracontinental Xiang-Gui Basin. Detrital zircon assemblages from the Cryogenian Lijiapo Formation at Niuhe yield a prominent UPb age peak of ~774 Ma, with a minor peak of ~891 Ma, indicative of provenance from the Yangtze Block to the northwest. In contrast, zircon samples from the Cryogenian Zhengyuanling Formation of the Laoshan area (Guangxi Zhuang Autonomous Region), which is located closer to the Cathaysia Block than Niuhe, yield a prominent age peak of 959–1112 Ma, consistent with a Cathaysian provenance. Furthermore, three samples of Ediacaran sandstones from Niuhe yield an age peak of ~900–1100 Ma, also demonstrating provenance from the southeast (i.e., Cathaysia). The Cathaysian provenance of Ediacaran sandstones on the southeastern margin of the Yangtze Block does not support the scenario of a broad SCOB between the Yangtze and Cathaysia blocks during the Ediacaran, and the Xiang-Gui Basin is best regarded as an immature intracontinental rift (aulacogen). Uplift of the Cathaysian Block through slab retreat on its external (southeastern) margin (i.e., the ‘top-down’ model of Rodinian breakup) may have been responsible for generation of a massive influx of siliciclastics into the Xiang-Gui Basin during the Ediacaran.