Neoproterozoic granitoids along the Ailao Shan-Red River belt: Zircon U-Pb geochronology, Hf isotope analysis and tectonic implications

Abstract

The Ailao Shan-Red River belt (ASRRB) is a complex tectonic collage of Archean to Miocene geological units, located between two major tectonic domains, i.e., the South China domain to the east and the Tethys domain to the west. Although general agreements have been reached on that the Ailao Shan suture zone along the ASRRB represents a Silurian to middle Triassic subsidiary ocean in the eastern Paleo-Tethyan system and the Ailao Shan-Red River shear zone within the belt occurred as the northeastern boundary of the Cenozoic extrusion of the Indochina block during the Indian-Eurasian collision, the Precambrian tectonic attributes of the belt remain controversial. This study presents new zircon U–Pb ages, whole-rock geochemical and Hf isotopic data of Neoproterozoic granitoids along the ASRRB.Neoproterozoic granitoids along the ASRRB are located to the east of the Jinshajiang-Ailao Shan suture zone. Samples from the granitoids have zircon 206U/238Pb ages between 799Ma and 724Ma, implying the existence of extensive Neoproterozoic granitic magmatism along the ASRRB. Their basement rocks share similar characteristics (e.g. Paleo- to meso-Proterozoic protolith ages) to those of the western Yangtze block. Evidences suggest that the Neoproterozoic intrusions and their metamorphic basement rocks along the ASRRB were derived from the southwest margin of the Yangtze block.Zircon εHf (t) values of the granitoid samples range from −10.22 to 0.64, with Hf crustal model ages of 1632.2–2335.9Ma. It is suggested, combining the present results and regional geology data, that the Neoproterozoic granitic magmatism along the ASRRB is dominantly of crustal origin, and contributions from mantle sources are common. They are possibly attributed to partial melting of ancient lower crust and addition of mantle fluids related to oceanic subduction. The results support a scenario that arc magmas were generated by continued oceanic subduction beneath the southwestern margin of the Yangtze block, instead of the northeastern margin of the Indochina block, lasted from 799Ma to 724Ma.