Tectonic Rotation Pattern at the Northern End of the Red River Fault System in SE Tibet: New Paleomagnetic Evidence From Cretaceous Red Beds

In order to study the rotations of crustal material along the boundary faults in the southeastern Tibetan Plateau, and to better understand the tectonic evolution of this region, in this study we conducted a paleomagnetic study of Cretaceous red beds in the Binchuan and Xiangyun sections near the Chenghai-Binchuan fault, a branch fault at the northern end of the Red River fault in China. Analyses of rock magnetic properties and magnetization components, combined with scanning electron microscopy, show that two types of hematite are present in the Lower Cretaceous rocks: pigmentary hematite and specularite. High-temperature components (HTCs) were isolated by stepwise thermal demagnetization between 300 and 660 degrees C carried by pigmentary hematite and all of the HTCs are of normal polarity. An additional magnetization component carried by specular hematite cannot be isolated efficiently. Progressive unfolding of both the Binchuan and Xiangyun sections shows that the best grouping of the precision parameter was obtained at 75%-80% untilting, indicating that the remanence of syn-folding origin is carried by pigmentary hematite. These syn-folding remanent magnetizations indicate the Binchuan and Xiangyun sections accumulated 20.5 +/- 5.3 degrees of clockwise rotation and 9.9 +/- 4.6 degrees of counterclockwise rotation, respectively, with respect to East Asia since the early Cretaceous, despite the two sections being only similar to 45 km apart. The counterclockwise rotation of the Xiangyun section was likely caused by the left-lateral shear motion of the Red River Fault; and since the Miocene, the Binchuan section experienced integral clockwise rotations, together with most parts of the Chuan-Dian Block.

Automated summary

To understand the tectonic evolution and rotations of crustal material in the southeastern Tibetan Plateau, a paleomagnetic study was conducted on Cretaceous red beds in the Binchuan and Xiangyun sections. Results showed the presence of two types of hematite, with pigmentary hematite carrying syn-folding remanent magnetizations. The rotations of the Binchuan and Xiangyun sections since the early Cretaceous were estimated to be 20.5 +/- 5.3 degrees clockwise and 9.9 +/- 4.6 degrees counterclockwise, respectively, suggesting differential rotations in close proximity.