New early Cretaceous paleoagnetic results from the Haiyuan area and its tectonic implications

The paleomagnetic results are presented for 13 sites from lower Cretaceous red beds in the Haiyuan area, northwest of Ninxia province. Thermal demagnetization of the samples allows us to isolate a high-temperature component which passed postive reversal test. The preliminary magnetosratigraphic result from Liwaxia and Heshangpu sections seems to correlate with the globe lower Cretaceous magnetic polarity. It is suggested that the high-temperature component possibly represents the primary magnetization. The corresponding paleople lies at 78.2 degreesN, 218.0 degreesE (d(p) = 5.7 degrees, d(m) = 8.4). The tectonic-corrected data are D = 12.7 degrees, I = 50.2 degrees alpha (95) = 6.3 degrees. Comparing with the lower cretaceous poles from the Ordos basin in the west of North China Block, we conclude that Haiyuan area could suffered a non-significant northward motion and rotation with respect to the stable Ordos basin since the lower Cretaceous. The result indicates that Haiyuan fault zone does not yield a large-scale left-slip eastward movement in the southeast end, and that the effect of collision between India and Asia on Haiyuan area diminished.