Constraints on the Jurassic swing of the apparent polar wander path for the North China Block

Abstract

In order to better constrain the Mesozoic apparent polar wander path for the North China Block, Late Triassic and Early Jurassic sandstones in the Ordos Basin and Early Jurassic sandstones in the Datong area were collected at 37 sites. Thermal demagnetization isolated a high-temperature magnetization component with unblocking temperatures of 500-580°C from five sites of the Early Jurassic Yongdingzhuang Formation in the Datong area. Palaeomagnetic directions from the five sites yielded a positive fold test at the 95 per cent confidence level. These directions combined together with previously reported ones give a new Early Jurassic mean direction (D = 358.0°, I = 50.6°, α95 = 4.4°) and corresponding palaeomagnetic pole (81.5°N, 302.5°E, A95 = 5.5°). The palaeomagnetic pole is regarded as representative of the North China Block because this pole is derived from two localities in the undisputed part of the North China Block. Comparisons of the Early Jurassic pole for the North China Block with coeval ones for the South China Block identify significant differences between the poles from the two regions. At Early Jurassic times, the North China Block was at the peak of rotational motion associated with the collision of the North and South China Blocks. The North China Block underwent a counterclockwise rotation of 12°-32° with respect to the South China Block since the Early Jurassic, at least 17 per cent of the total rotational motion remaining at that time.