THE LOWER CRETACEOUS REFERENCE POLE FOR NORTH CHINA, AND ITS TECTONIC IMPLICATIONS

A palaeomagnetic study of Lower Cretaceous continental sediments from the south-southwestern part of the Ordos basin, North China block (NCB), has been carried out. Stepwise thermal demagnetization was used to isolate magnetic components. The low-temperature component is generally removed between 200-degrees-C and 350-degrees-C and corresponds to the Earth's present field direction. A high-temperature component of magnetization, with two polarities, was defined from 10 sites with D = 16.4-degrees, 1 = 50.5-degrees (K = 50.8, alpha95 = 6.8-degrees). The corresponding pole position is located at 75.8-degrees-N, 208.7-degrees-E (d(p) = 6.1-degrees, d(m) = 9.1-degrees). This Lower Cretaceous pole compares well with the hairpin loop of the Eurasian synthetic APW path (Besse & Courtillot 1991) that is inferred from the North American, Eurasian, African and Indian plates. The available late Mesozoic palaeomagnetic data from the NCB and adjacent South China block (SCB) are reviewed. Comparison of these data suggests important intraplate deformation: the area to the east of the Tancheng-Lujiang fault may have undergone local clockwise post-Cretaceous rotations of 10-29-degrees relative to the stable western craton of the NCB. The data also indicate that no palaeomagnetically significant eastward movement of the SCB with respect to the NCB and Eurasia occurred after the Cretaceous.