Evolution of the Paleo-Tethys Ocean: Constraints from detrital zircons of the Paleozoic to Triassic clastic rocks in the Qiangtang terrane, Tibetan Plateau

Abstract

• The Longmuco-Shuanghu-Lancangjiang suture zone represents an in situ relic of the Paleo-Tethys Ocean. • The northward subduction of the Paleo-Tethys oceanic lithosphere was continuous at least during the Late Devonian to Triassic. • The collision between the North and South Qiangtang subterranes began at ∼ 225 Ma. The Qiangtang terrane, which is divided into the North and South Qiangtang subterranes, is a key unit to study the evolution of the Paleo-Tethys Ocean in the Tibetan Plateau. Here we present new detrital zircon U-Pb and Lu-Hf isotopic data from a Paleozoic-Triassic sedimentary succession in the Qiangtang terrane. This new dataset is used to unravel the tectonic affinity of the North and South Qiangtang subterranes and the evolution of the Paleo-Tethys Ocean. Detrital zircons from the Paleozoic-Triassic sedimentary succession in the North Qiangtang subterrane are generally poorly rounded, indicating short transported distance. They yielded variable U-Pb ages ranging from 3399 Ma to 233 Ma with major age peaks of 358 Ma and 266–248 Ma, and ε Hf (t) values of −18.6 to 19.3. These features reveal that these detrital zircons were most likely derived from arc magmatic rocks, which were associated with the subduction of the Paleo-Tethys oceanic lithosphere. By contrast, detrital zircons from the Paleozoic sedimentary succession in the South Qiangtang subterrane are characterized by sphericity and ellipsoid, with most Th/U values > 0.1. They yielded U-Pb ages of 3624–321 Ma and three consistent age peaks of 549–527 Ma, 973–940 Ma and 2504–2470 Ma. They display ε Hf (t) values ranging from –33.4 to 26.2, with a cluster of −20.0 to 10.0. These features are similar to those of the detrital zircon grains from the South Qiangtang, Lhasa, and Himalaya terranes, as well as the Indian Gondwana. Detrital zircon ages data suggest that the North and South Qiangtang subterranes were derived from the Yangtze block and Gondwana, respectively. Available data indicate that the northward subduction of the Paleo-Tethys oceanic lithosphere was continuous at least during the Late Devonian to Triassic. The collision between the North and South Qiangtang subterranes was initiated at ∼ 225 Ma.