Paleomagnetism and U-Pb Geochronology of Early Cretaceous Volcanic Rocks from the Qiangtang Block, Tibetan Plateau: Implications for the Qiangtang-Lhasa Collision

Abstract

The collision between the Qiangtang and Lhasa blocks is a critical factor in understanding the geodynamics of the central Tibetan Plateau. However, the process of the Qiangtang-Lhasa collision remains contentious. A direct way to study the history of the Qiangtang-Lhasa collision would be to determine the evolution of the paleolatitude positions of the Qiangtang and Lhasa blocks during the Jurassic-Cretaceous. In this study, we present a combined paleomagnetic and geochronological study of the Early Cretaceous volcanic rocks dated at ~120–115 Ma in the western Qiangtang block. Stepwise thermal demagnetization succeeded in isolating the high-temperature characteristic directions of the samples. The tilt-corrected mean direction of the 16 sampling sites was Ds = 60.9°, Is = 45.9° with ɑ95 = 4.4°, which indicates that the Qiangtang block was situated at 27.6 ± 5.0°N during the Early Cretaceous (~120–115 Ma) (reference point: 32.9°N, 83.5°E). Our new data combined with previous reliable Cretaceous paleomagnetic results for the Lhasa block indicate that the collision between the western parts of the Qiangtang and Lhasa blocks may occur later than 115 Ma. The extent of the western segment of the Bangong-Nujiang Tethys Ocean was ~825 ± 600 km (7.5° ± 5.5° in latitude) at 120–115 Ma.