Basement Characteristics and Late-Stage Tectonic Evolution of the Qiangtang Terranes

Abstract The Qiangtang terrane is composed of several small blocks that formed since the Rodinia supercontinent period. Previous studies have shown that the Longmu Co-Shuanghu suture zone divides the Qiangtang terrane into the South and North Qiangtang terranes. However, the tectonic affinities and evolution histories of the North and South Qiangtang remain debated. We conducted geochemical and geochronologic analyses on gneiss rocks from the Ningduo and Jitang groups in the North Qiangtang terrane and the Youxi Group in the South Qiangtang terrane. The results of major and trace element analysis indicate the protoliths are lithic arkose, lithic greywacke, and granite (rhyolite), respectively. The isotopic analysis results further suggest that the gneisses have undergone a long-term crustal material cycle and had different ancient crustal source regions. Zircon U-Pb dating results reveal that the detrital zircons from the Ningduo Group are predominantly concentrated in two age ranges: 951–998 Ma and 1100–1148 Ma. The Jitang Group mainly exhibits three distinct age clusters: 226–249 Ma, 952–998 Ma, and 1052–1093 Ma. The Youxi Group mainly displays three prominent ages: 213–249 Ma, 402–449 Ma, and 1055–1098 Ma. These ages indicate that the ancient plate basement has been overprinted by multiple stages of deformation and magmatism and that both the South and North Qiangtang terranes exhibit records of the closure of the paleo-Tethyan Ocean. We propose that the North Qiangtang tends to be Cathaysian provenance, and the South Qiangtang tends to be Gondwana provenance. The investigation of gneiss in this article presents a novel perspective on the tectonic evolution of the Qiangtang area.