关键词: 龙门山南段, 原生剩磁, 构造旋转, 重磁化

Abstract: In order to study and constrain the tectonic movement characteristics of the southern Longmenshan fold-thrust belt, the paleomagnetic study was carried out on the light purple gray mudstone and siltstone of the lower Triassic Feixianguan formation near Dachuan town and the Permian limestone in Baoxing in the southern Longmenshan fold-thrust belt. Paleomagnetic samples were collected from 10 sampling sites, of which 3 are Permian limestone and 7 are light purple gray mudstone and siltstone of Feixianguan Formation. We have conducted the experiments of stepwise thermal demagnetization, rock magnetism (isothermal remanent magnetization acquisition curves and triaxial isothermal remanent thermal demagnetization) and scanning electron microscope. Based on the stepwise thermal demagnetization experiments of 80 samples, we revealed a stable characteristic remanence from the Feixianguan Formation samples but not from the Permian limestone samples. The high temperature components pass simple generalized fold test, the tilt-corrected mean direction of the characteristic remanence is：Ds=36.9°, Is=16.5°，α95=5.9°, K=33.8, N=18 and the corresponding paleomagnetic pole position plots close to the Early Triassic mean pole of the apparent polar wander path for the south China Block. The results of rock magnetic show that the major magnetic mineral of Feixianguan formation is magnetite, and the scanning electron microscope observation shows that it is clastic iron oxide, and there is no obvious post diagenetic authigenic characteristics. Combined with the characteristics of demagnetization curve, scanning electron microscope, paleomagnetic pole position of characteristic remanence and rock magnetic results, the characteristic remanence of Feixianguan formation is likely to be primary remanence. The results show that there is no obvious relative tectonic rotation between the Longmenshan fold-thrust belt and Sichuan Basin. Since the Late Triassic, the northern and southern Longmenshan fold-thrust belt and Sichuan Basin are unified tectonic units in dynamics.

Key words: southern longmenshan mountain, primary remanence, tectonic rotation, remagnetization