Eastern Asia in the Cretaceous: New paleomagnetic data from South Korea and a new look at Chinese and Japanese data

要旨

Lower Cretaceous continental sediments and volcanic rocks have been sampled in the Gyeongsang basin (South Korea). A detailed analysis of 160 specimens reveals two stable components of magnetization, a postfolding, low‐temperature (LT) component with normal polarity and a stable, high‐temperature (HT) component with both normal and reversed polarities. The blocking temperature of the HT component ranges from 540°C up to the Néel temperature of hematite. This component predates the folding of the series and yields a pole at λ = 68°N, Φ = 205°E, A 95 = 6°. The prefolding magnetization indicates that South Korea stood at a latitude nearly identical to its present‐day latitude in the Lower Cretaceous. Comparison of Korean data with (revised) paleomagnetic data from North and South China and Japan shows that all these blocks of Eastern Asia occupied the same positions in term of latitude and were probably parts of a single craton since at least the Lower Cretaceous. The paleomagnetic directions of the Sino‐Korean block show large discrepancies with respect to the expected directions of the “stable” Eurasian (Siberian) block. An interpretation involving significant N‐S motion (∼1000 km) between either North and South China or between North China and Siberia appears to contradict geological data. A preferred interpretation is that the Siberian data are in serious error and that the combined China/Korea Lower Cretaceous pole provides a valid estimate for the Eurasian plate as a whole.

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