New Late Cretaceous and Palaeogene paleomagnetic results from south China and their geodynamic implications

Abstract

To better understand the tectonic evolution of South China Block (SCB) in response to the India-Asia collision, we present new paleomagnetic results from Late Cretaceous and Paleogene red bed formations of the Hengyang basin of Hunan province, in the interior part of the SCB. Stepwise thermal demagnetization of the rocks isolated a high-temperature component. The tilt-corrected mean direction from the Late Cretaceous rocks is D = 15.6°, I = 29.9° with a95 = 5.7°, N = 26 sites, corresponding to a paleopole at 71.9°N, 236.3°E with A95 = 4.7°, which passes reversal tests. The tilt-corrected mean direction (D = 358.9°, I = 35.4° with a95 = 5.0°, N = 22 sites) from the Paleogene rock, which passes the reversal test, gives a pole at 82.6°N, 300.6°E with A95 = 4.4°. The low-field anisotropy of magnetic susceptibility results suggest that the red beds have not experienced significant strain due to compaction or tectonic stress, while the anisotropy of isothermal remanence results suggest that postdepositional compaction in these red beds produced no more than 3°-4° of inclination shallowing. These paleomagnetic and rock magnetic tests imply that the remanence is primary. On the basis of paleomagnetic results obtained from coeval basalts in Mongolia and Siberia, we suggest that no significant latitudinal motion has taken place between the SCB and Siberia since the Late Cretaceous. The significant latitudinal discrepancy between the SCB and European block could be due to nonrigid behavior of the Eurasian plate since the Late Cretaceous. A 16.7 ± 5.0° clockwise rotation of the SCB during the Late Cretaceous to the Paleogene could be related to the collision of India and Asia in the west and the subduction of the circum-Pacific plate to eastern Asia in the east. Copyright 2006 by the American Geophysical Union.