ObjectiveDuring the opening and closing of the Paleo-Tethys ocean, multiple continental blocks rifted from the northern margin of Gondwana, drifted northward, and eventually merged with the southern boundary of the Asian continent, forming multiple serpentinite belts. As part of the Paleo-Tethys orogenic belt, the Indosinian orogenic belt records the evolution history of the Paleo-Tethys ocean; however, key scientific issues, such as the location of the ocean basin and the subduction polarity, remain controversial. The keys to addressing these questions lie in defining the structural characteristics of the Babu–Cao Bang tectonic belt along the Sino-Vietnamese border and clarifying the tectonic affinity of the North Vietnam terrane. Specifically, it has to be determined, whether the Babu–Cao Bang tectonic belt represents a suture zone of a wide ocean basin, and whether the North Vietnam terrane is a component of the South China block or an independent micro-continental block.

MethodsIn order to clarify these two questions, detrital zircon age data were collected from 31 sedimentary rocks in three tectonic units including the Nanpanjiang basin along the southwestern margin of the South China block, the Babu–Cao Bang tectonic belt, and the North Vietnam terrane. Furthermore, age data of inherited igneous zircon from the Song Chay massif in the North Vietnam terrane were obtained. The zircon age distribution histograms and probability curve peaks were compared within these three tectonic units.

ResultsIt was found that the age spectra of these samples mostly have peaks at 270–250 Ma, 460–420 Ma, and 1000–900 Ma. In addition, the age data are relatively concentrated around 1800 Ma and 2500 Ma, which reflects good consistency in the provenance of the three tectonic units.

ConclusionBased on the stratigraphic correlation between the Nanpanjiang basin and the North Vietnam terrane from the late Paleozoic to the early Mesozoic and the faunal similarities during the same period, this study speculates that an extensional event led to the development of rifts, deep-water sediments, and even oceanic crust in the Babu–Cao Bang tectonic belt during the Permian. However, due to its limited extensional magnitude, this rift failed to evolve into a mature oceanic basin, preserving the tectonic connection between the North Vietnam terrane and the Nanpanjiang basin. The North Vietnam terrane is an important component of the South China block, and the open basin of the Paleo-Tethys ocean should have been located to the south of the North Vietnam terrane. Significance This study provides evidence for the division of tectonic units in the Indosinian orogenic belt, and guides our understanding of Indosinian orogenic processes in the Sino-Vietnamese border area.