A Cimmerian keystone: Middle-late Triassic paleomagnetic and calcite geochronologic constraints on the South Qiangtang Block

Abstract

The Cimmerian continent was a ribbon-like assemblage of micro-continental blocks that separated from the northern margin of Gondwana at the end of the late Paleozoic. As a keystone at the center of the Cimmerian continent, the South Qiangtang Block of the Qinghai-Tibet Plateau is critical for understanding the kinematic history of the Cimmerian continent, and its influence on the evolution of the Tethyan realm. In this study, we present new in situ carbonate U-Pb geochronologic data and paleomagnetic data from Middle-Upper Triassic limestone and basalt of the Zuoqingco Formation of central South Qiangtang Block. A well-resolved, pre-folding magnetization hosted by magnetite is recovered from 12 limestone sites and 9 basalt sites, and places the South Qiangtang Block at a latitude of ∼20.6 ± 4.8 °N at ∼237–235 Ma. Using this new palaeomagnetic result together with other paleomagnetic data and geologic observations, we argue that the South Qiangtang Block drifted rapidly northwards during the middle Permian to late Middle Triassic and the Longmuco-Shuanghu Ocean is limited expanse but had not completely closed prior to ∼237 Ma. The final closure of two branches of the “Paleo-Tethys” Ocean was likely 230 Ma.