Preliminary early cretaceous paleomagnetic results from the Gansu Corridor, China

We report results from our paleomagnetic study of Lower Cretaceous redbeds from the Gansu Corridor, northwestern China. The characteristic remanent magnetization (ChRM) resides in hematite, often at very high unblocking temperatures (> 660°C). The directions associated with this component exhibit only reversed polarities from locality A (Sunan area), but the samples from locality B (Lanzhou area, 480 km to the southeast) show roughly antipodal normal and reversed polarities. The combined sample directional data from both localities pass a fold test at the 99% confidence level. The mean paleomagnetic pole is located at 48.7°N, 199.7°E, with A95 = 4.1°, which is discordant with poles of similar age elsewhere from neighboring regions in China. Although represented by relatively few samples (N = 21) this pole suggests that significant post-Cretaceous motion may have occurred between the Gansu Corridor and adjacent blocks. Relative to Eurasia or North China, the discordance corresponds to 28.1 ± 5.2° or 35.6° ± 9.7° clockwise rotation and 9.5° ± 4.5° or 9.8° ± 8.2° northward displacement respectively. The rotations support, but do not yet distinguish between, several neotectonic models assumed to have acted over the past 15–40 m.y. The displacement is not predicted by any of these models; if real, it may have occurred early in the history of the India-Asia collision, or even before.