Abstract
A new paleomagnetic study has been carried out on the Tiaojishan Formation effusives in the Chengde area, North China Block (NCB). The age of the Tiaojishan Formation volcanics was recently dated from 153 Ma to 161 Ma by U–Pb and 40Ar– 39Ar. A total of 154 samples from 16 sites within the Tiaojishan Formation were collected. Detailed stepwise thermal demagnetization allows us to isolate two components from 77 oriented drill-core samples. A low-temperature component identified in most samples falls close to the present local Earth field direction. Characteristic remanent directions obtained from high-temperature pass-reversal test yield a pole position at 240.3°E, 59.9°N with α95 = 6.8°. Combined with coeval paleopoles obtained from the Siberia Block (SIB), these results show a significant paleolatitude displacement between the NCB and SIB, which indicates that the Mongol–Okhotsk Ocean was still open with ~ 3000 km width in its eastern part at ca. 155 Ma.
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