Type and evolution of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block: constraints of sedimentary characteristics and provenance tracing based on zircon U-Pb ages

Abstract

To identify its type and evolution features of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block (NMLB) is of great significance for reconstructing its tectonic-paleogeography and assessing the petroliferous basins in the Bangong-Nujiang suture zone (BNSZ) and its adjacent area. This study conducted the sedimentary characteristic analyses and detrital zircon U-Pb dating of the Middle Jurassic–Lower Cretaceous strata exposed in the northern part of Nagqu County (NPNC), Tibet. The Middle–Upper Jurassic Lagongtang Formation was mainly deposited in a steep slope delta and its middle part is characterized by debris flows moving southeastward. The lower part of the Upper Jurassic–Lower Cretaceous Duoni Formation was characterized by molasses formation, and its middle and upper part were primarily deposited on a tidal flat-mixed shelf. The 384 detrital zircons from the debris-flow deposits of the Lagongtang Formation yielded ages of 2800∼210 Ma, except for one yielding an age of 174 Ma. The detrital zircons from the lower part of the Duoni Formation yielded ages of 2744∼152 Ma. Comprehensive research results show that the basin located at the NMLB is a peripheral foreland basin controlled by the BNSZ and had dual source supply, and around 152 Ma, the basin was accompanied by a stronger overthrust event and experienced the conversion from flysch basin to molasses one. Subsequently, a new foreland basin formed marked by the deposition of the Shamuluo Formation in the BNSZ.