Paleomagnetism of Middle Triassic redbeds from Hubei and northwestern Hunan provinces, South China

Paleomagnetic investigations have been conducted on redbeds from the Middle Triassic Badong Formation at Badong, Hubei and Sangzhi, Hunan as well as from the coeval Puxi Formation from Puxi, southeastern Hubei province, South China. The characteristic remanent magnetization (ChRM) determined from Badong and Sangzhi passes the fold test with dual polarity. The tilt-corrected ChRM direction from Puxi is congruent with those from Badong and Sangzhi but is based on a smaller number of samples collected from a monocline. These ChRM directions are believed to be primary. The data indicates that Badong has been rotated clockwise by 13.6 ± 8.5° relative to Sangzhi, which, in turn, has possibly been rotated in the same sense with respect to other parts of the Yangtze Block (YB) except eastern Sichuan based on the bend of the sampled fold axis and the Lower Triassic paleomagnetic data published for the YB. The Lower and Middle Triassic paleomagnetic data together appear to indicate that eastern Sichuan and the border area between Sichuan, Guizhou, Hubei and Hunan provinces have been affected by differential rotations, probably due to oroclinal bending. The paleomagnetic data obtained from this study further constrain the timing of the final suturing of the YB with the North China Block (NCB) to be post-Middle Triassic.