Paleomagnetic study on the Early Permian Gubaoquan doleritic dike swarm in the southern Beishan area, NW China: Implications for the tectonic and paleogeographic reconstructions of the southern Central Asian Orogenic Belt

To provide further constraints on the tectonic transition and paleogeography of the southern Central Asian Orogenic Belt (CAOB) during the late Paleozoic to early Mesozoic, a paleomagnetic study has been conducted on the Early Permian Gubaoquan doleritic dike swarm in the Beishan region, NW China. Rock magnetic analyses coupled with scanning electron microscope observation show that titanium-poor magnetite is the main magnetic remanence carrier without obvious alteration. Plagioclase Ar-40/Ar-39 dating results reveal that the doleritic dike swarm intruded at similar to 282-286 Ma, having undergone no intense posterior thermal overprint. Characteristic remanent magnetizations with single reverse polarity are isolated, constituting eight independent directional groups. The isolated remanence is suggested to be primary and averages out the paleosecular variation based on several lines of evidence. Hereby, an Early Permian paleomagnetic pole for the Beishan region is calculated at 82.8 degrees N, 285.6 degrees E, A(95) = 9.2 degrees with N = 8 direction groups. This new pole fills spatially the Early Permian paleomagnetic data gap in the southern CAOB. The comparison with published contemporaneous paleomagnetic poles in the southern CAOB indicates that (1) the Early Permian paleomagnetic poles of the Beishan region and Dunhuang Block are indistinguishable, indicating insignificant relative movement since then, negating a broad Early Permian ocean between them; (2) the southern CAOB presented a WNW-ESE distributed paleogeography with either a residual ocean or a rift basin in its eastern part in the Early Permian; (3) large-magnitude strike-slip displacements have played a key role in the tectonic activity of the southern CAOB since the Early Permian.