Zircon ages of paragneisses from the Sinh Quyen formation in Northwestern Vietnam and their geological significances

Northwestern Vietnam tectonically is an important part of the eastern Tethyan orogenic belt and this terrain has recorded the amalgamation history of the Indochina and South China blocks. Tectonic provenance of the terrain plays a key role for constraints on the location of the suture between these two blocks in NW Vietnam. In this study, detrital zircon ages of the Sinh Quyen Formation as part of the Paleo-to Meso-Proterozoic basement rocks in NW Vietnam are reported for discussion of sedimentary sources and tectonic province of the basement. The rock formation is composed mainly of felsic paragneiss and migmatite. One hundred and sixteen zircon grains separated from three felsic paragneiss samples were analyzed by the LA-ICP-MS U-Pb dating method. Results of a total of 123 analytical spots demonstrate that crystallization ages of the detrital zircons mainly cluster around ~1.8 Ga with minor ~2.2 Ga to ~3.0 Ga, indicating Paleoproterozoic basement rocks as major sedimentary sources of the Sinh Quyen Formation. Basement rocks in northwestern Vietnam are similar to old basements in South China in formation time and so it can be proposed that the Sinh Quyen Formation is of the South China affinity or originated from crustal material of the South China block. Part of detrital zircon grains record ~250 Ma metamorphic overgrowth in the rim, probably related to the collision of South China and Indochina blocks and therefore recording the paleo-Tethyan orogenic event.