THE LOWER CRETACEOUS REFERENCE POLE FOR NORTH CHINA, AND ITS TECTONICIMPLICATIONS

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 generall y removed between 200-degrees-C and 350-degrees-C and corresponds to t he Earth's present field direction. A high-temperature component of ma gnetization, with two polarities, was defined from 10 sites with D = 1 6.4-degrees, 1 = 50.5-degrees (K = 50.8, alpha95 = 6.8-degrees). The c orresponding 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 pol e compares well with the hairpin loop of the Eurasian synthetic APW pa th (Besse & Courtillot 1991) that is inferred from the North American, Eurasian, African and Indian plates. The available late Mesozoic pala eomagnetic data from the NCB and adjacent South China block (SCB) are reviewed. Comparison of these data suggests important intraplate defor mation: the area to the east of the Tancheng-Lujiang fault may have un dergone local clockwise post-Cretaceous rotations of 10-29-degrees rel ative to the stable western craton of the NCB. The data also indicate that no palaeomagnetically significant eastward movement of the SCB wi th respect to the NCB and Eurasia occurred after the Cretaceous.