Geochemistry, geochronology, and Sr-Nd isotopic compositions of Permian volcanic rocks in the northern margin of the North China Block: implications for the tectonic setting of the southeastern Central Asian Orogenic Belt

The southeastern part of the Central Asian Orogenic Belt (CAOB), which records the collision of the North China Block (NCB) with the South Mongolian microcontinent, is a key area for reconstructing the tectonic history of the CAOB. Controversy persists regarding the timing of the final structural amalgamation of the region; therefore, it remains unclear whether the Late Paleozoic thick volcanic successions were generated in a subduction or post-orogenic environment. Redefining the age of the formation and analyzing the geochemical compositions of these volcanic rocks can provide clues regarding the regional tectonic evolution during the Late Paleozoic and place constraints on the closure time of the Paleo-Asian Ocean. In this study, we present geochemical, geochronologic, and Sr-Nd isotopic data for 29 volcanic rock samples from the Elitu Formation in Xianghuangqi, central Inner Mongolia. The Elitu volcanic rocks have latest early-to-middle Permian ages between 272 and 268 Ma. Most of the mafic-intermediate and felsic rocks show K-normal and high-K calc-alkaline characteristics. Melting is considered to be due to large scale upwelling of the metasomatic lithospheric mantle and different degrees of melting of the thickened lower crust. The northern margin of the NCB, which represents the southeastern boundary of the CAOB, records transtensional and, subsequently, extensional tectonics associated with late Carboniferous to middle Permian volcanic activity.