Science Record

‘SCIENCE RECORD New Ser. Vol. III, No. 1, 1959

GEOLOGY

SOME PALAEOMAGNETIC INVESTIGATIONS ON CHINESE ROCKS* .

CHANG WEN-yYou ( React) A. E. M. Natrnt

(Institute of Geology, Academia Sinica) (Department of Physics, King’s College, : University, Durham, England)

Previous palaeomagnetic investigations"! on European and - North American rocks agree in suggesting that those areas were so positioned that the pole appeared to lie on or near the Chinese mainland from Palaeozoic to late Mesozoic times. If the geology of China is examined for those same periods the climate indicated is more equatorial than polar’. These two apparently contradictory facts make the palaeomagnetic study of Chinese rocks particularly interesting, and account for the publication of the results of the first collection from China despite the small sample size.

The collection was comprised of some eleven samples, of which eight were of the Tertiary Kansu Series collected at three sites in Kansu, while the remaining three were of red Middle Silurian siltstones from the southern part of Yumen, Kansu Province. The Tertiary rocks unfortunately were magnetically unstable, being characterised by low intensities of magnetization and scattered results. The measurements on the Silurian rocks yielded a more consistent pattern (Fig. 1).

The mean declination was N 66.4°W, mean inclination +55.3° with a circle of confidence of 8.5° calculated from 17 measured discs. The mean intensity of magnetization was (8.8 + 3.8) X 10° e.m.u./cm.’

The position of the ancient pole was 168°W, 49°S or 22°E, 49°N which compares with the Silurian pole from North America of 138°E, 19°N and by extrapolation an estimated position of a European pole in 165°E, 22°N. If this Chinese result is confirmed by further collections the following implication, first suggested by Nairn as a result of comparing Permian palacoclimatic and palaeomagnetic data would seem to be valid, namely, that differential movement occurred between Europe and North America and Eastern Asia. This is a significant addition to the Continental Drift theory, for it implies that at the time when Gondwanaland was a single unit, China at least was not part of the Laurasian continent. Further investigation of this possibility is at present in progress.

*Received Dec. 3, 1958. **Member of Academia Sinica, ‘TField work was done by Chang Wen-you and laboratory work by A. E, M. Nairn,