Cretaceous palaeomagnetic results from Hainan Island in south China supporting the extrusion model of Southeast Asia

We report the Cretaceous palaeomagnetic results from Hainan Island, south China. In Hainan island we collected the Early Cretaceous redbeds of the Lumuwan Formation at eleven sites. We also describe the tectonic kinematics for and around Hainan Island since the Cretaceous, deduced from our and previous palaeomagnetic results. The palaeolatitude of Hainan Island is 25.9 degrees N (+3.4 degrees/-3.2 degrees), implying that Hainan island was situated about 7 degrees north from the present position during the Cretaceous. The palaeopole of Hainan Island (latitude = 77.7 degrees N, longitude = 162.1 degrees E, k = 65.6, and A(95) = 4.4 degrees) suggests 4.0 +/- 5.8 degrees counterclockwise rotation and 14.1 +/- 5.5 degrees southward translation relative to the suspected coherent part of the south China block (SCB) since the Cretaceous. The rotation and translation of similar sense (18.8 +/- 7.4 degrees and 7.8 +/- 6.9 degrees, respectively) are detected in the existing palaeomagnetic result from the Xinlong Formation in Guangxi, which is situated approximately 400 km north-northwest from Hainan Island. The southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the SCB in a similar pattern to the Indochina block, which had resulted from the indentation of India into Asia. This SW part seems to have slightly rotated counterclockwise, because its extrusion was probably smaller in scale than the Indochina block and therefore it was dragged out by the Indochina block. This hypothesis is supported by the existence of a northwest-southeast-trending fault system parallel to the Red River Fault. (C) 1999 Elsevier Science B.V. All rights reserved.