New paleomagnetic result of Early Triassic rocks from the Longmenshan belt and its tectonic implications

This paper reports new Early Triassic paleomagnetic results from Jiange County (32.2°N, 105.3°E) in the Longmenshan belt. Based on the stepwise thermal demagnetization of limestone and argillaceous limestone specimens from 9 sampling sites, the au-thors revealed a characteristic remanent magnetism (ChRM). Both normal and reversal polarities were observed in the study section, and the high temperature components pass reversal tests at the 95% confidence level. This indicates that the ChRM may represent the primary remanent magnetism of the Early Triassic limestone. The tilt-corrected mean direction for the Early Triassic is D_s/I_s=42.3°/12.6° with α₉₅=9.4° and N=9 sites, corresponding to a paleopole at 42.9°N, 219.3°E, d_p/d_m=4.9°/9.6°. A comparison with the Early Triassic poles from the Sichuan basin shows that insignificant post-Early Triassic motion may have occurred between the Longmen-shan belt and the Sichuan basin. It is thus considered that the Sichuan basin has not experienced whole-scale vertical axis rotation since the Early Triassic.