OLIGOCENE PALEOMAGNETIC ROTATION STUDY OF THE NANGQIAN BASIN AND ITS IMPLICATIONS ON REGIONAL TECTONIC EVOLUTION
The southeastern Tibetan Plateau has undergone clockwise rotation and southeastward extrusion in response to the India-Eurasia collision during the Cenozoic.This process has played a crucial role in accommodating the uplift and deformation of the plateau.However,the relationship between these tectonic deformation processes,such as rotation and southeastward extrusion,remains unclear.To gain better insight into the Cenozoic tectonic deformation of the southeastern Tibetan Plateau,we conducted a new paleomagnetic study in the Nangqian Basin,located in the northern part of this region.We set up two sampling sections,Baerqu(BEQ:32.2°N,96.0°E)and Tuotuohe(TTH:32.0°N,59.9°E),in the western part of the Nangqian Basin,from which we collected a total of 225 paleomagnetic samples from 25 sampling sites.Rock magnetic analysis indicates that the main magnetic carriers are pseudo-single domain(PSD)magnetite and single domain(SD)hematite.Through detailed thermal demagnetization analysis,we successfully isolated 188 characteristic remanent magnetic directions from 21 sites.Their mean direction is Dg=168.1°±10.8°,Ig=-21.1°±19.1°,α95=11.8°,k=8.3 in geographic coordinate,and Ds=171.0°±7.4°,Is=-33.3°±10.8°,α95=6.8°,k=22.7 in stratigraphic coordinate.Detailed rock magnetic and field test analyses indicated that this mean direction is likely primary magnetization.The studied strata are speculated to be Oligocene based on comparisons of lithology and spores with strata from adjacent areas.Compared with the Eurasian apparent polar wander path reference pole,this paleomagnetic declination yields a 17.2°±8.1° counterclockwise rotation of the Nangqian Basin since the Oligocene.Combined with oroclinal analysis and other geological evidence,this study proposes that the Nangqian,Gonjo,Mangkang and Lanping basins have exhibited an increasing degree of clockwise rotation from north to south in an oroclinal bending manner since the Late Eocene.Additionally,the Nangqian Basin has experienced a superimposed counterclockwise local rotation after the Neogene.
万方数据
维普
