Grenvillian S-type granites in the North Qaidam orogenic belt, NW China: Implications for the geodynamic evolution of the Rodinia supercontinent

Abstract

Recognizing tectonic positions and affinity of Precambrian micro-blocks within the Phanerozoic orogenic belts is the key to revealing global paleogeography and the evolution of supercontinents in the early Earth. The Qaidam Block, proposed as a Precambrian continental fragment surrounded by several Paleozoic orogenic belts, has been implicated in the assembly and breakup of the Rodinia supercontinent during the Mesoproterozoic to Neoproterozoic. However, the detailed tectonic position of the Qaidam Block within the Rodinia supercontinent remains poorly constrained. This study presents the integrated research of geochronology, geochemistry, and zircon Lu-Hf isotopes, as well as thermodynamic modeling on the Yuka Grenvillian granite gneiss in the North Qaidam orogenic belt. The protoliths of the Yuka granite gneiss formed at 905–908 Ma. The Yuka granite gneisses are characterized by the enrichment of aluminum with the existence of Al-enriched minerals (e.g., garnet, muscovite, and biotite) and a high aluminum saturation index (1.03–1.20), which belong to S-type granites. Zircon Lu-Hf isotopes display heterogeneous εHf(t) values (−9.7 to + 1.6) and Paleoproterozoic-Mesoproterozoic model ages (2319–1651 Ma), complemented by xenocrystic zircons spanning the Archean-Neoproterozoic (2558–937 Ma). These features collectively suggest they are derived from the partial melting of Neoproterozoic Zr-enriched meta-sedimentary rocks that consist of Archean-Neoproterozoic detritus. Phase equilibrium diagram and trace element modeling further demonstrate that the Yuka 905–908 Ma granite gneisses could result from various degrees of hydrous partial melting (F = 0.12–0.60) of metasediments during 690–820 ℃. Combining with the late Mesoproterozoic to Neoproterozoic magmatic and metamorphic records around the Qaidam Block, we argue that the Qaidam Block experienced Grenvillian-age (1.10–0.85 Ga) subduction-collision followed by 0.85–0.60 Ga anorogenic and continental rifting events. Comprehensive comparisons of the Qaidam Block with other major cratons and continents in the Rodinia supercontinent show that the Qaidam Block may be situated at the core part of southwest Australia, India, and East Antarctica, with no direct affinity with the North China, Tarim, and South China cratons.