Paleomagnetic Data From Hainan Island And Its Tectonic Implications Since The Late Mesozoic

Hainan Island is situated at the southernmost part of the SCB.It is also at the junction site of the Eurasian Plate,Indian Plate and the Philippine Sea plate and has a complex tectonic evolution history(Zhang et al.,1998;Li et al.,2000;Xia et al., 2004,2005).Hainan contacts the Indo-China Peninsula and the South China block.It can understand the tectonic evolution of them(Chen,2002).Hainan Island also located between the Heihe and eastern extension of part of the Red River.It helps to understand the ancient Tethys eastward extension,continental accretion of the East Asia,continental margin evolution(Yang et al.,1989;Hsu et al.,1990;Metcalfe et al., 1993;Chen et al.,1994).As a sub-topic of the national 973 Project(the South China Sea continental margin dynamics and hydrocarbon resource potential),this paper is about the paleomagnetic research on Hainan since the late Mesozoic.It is used to explore Hainan's tectonic evolution since the late Mesozoic.We present the magnetic and paleomagnetic results of the 975 orieontated drill-core since the late Mesozoic from Hainan Island.Hematite is regarded as the prime remance carrier of Cretaceous sandstone.Thermal demagnetization results showed that the sample group showed 1-2 remanence components.And it indicates that the Curie point is about 675℃.It is consistent with the result of IRM. High-temperature components can pass the fold test,baking tests and consistency tests.The main magnetic mineral of Cenozoic basalts is magnetite.Thermal demagnetization results showed that the sample group showed 1-2 remanence components.And it indicates that the Curie point is at 540-560℃.High-temperature components can pass the reversal test,confirmed the high-temperature components for the primary remanence.The Early Cretaceous yielded a direction of D=8.3°, I=45.2°,a₉₅=5.7°;the Late Cretaceous yielded a direction of D=30.2°, I=39.7°,a₉₅=4.8°.The direction of the Neogene paleomagnetic data is D=3.2°, I=35.8°,a₉₅=4.8;Pleistocene and Holocene are D=3.9°,I=30.4°,a₉₅=3.2;D=8.2°, I=34.0°,a₉₅=9.9.The paleomagnetic results show that Hainan Island drifts southward since the Early Cretaceous to the Late Cretaceous and with a very significant 21.8°counterclockwise rotation.Since the Late Cretaceous to the Neogene,Hainan continues to drift southward.And it accompanies by 27.0°clockwise rotation.Since the Neogene to the Pleistocene,the block continues to drift southward.Since the Pleistocene to the Holocene,land drifts northward.The Holocene to present,it drifts northward while clockwise rotation.This corresponds with the Pacific plate subduction zone retreat of the Eurasian Plate,the eastern part of Hainan Island in a large-scale north-east of the tensile fracture development,as well as volcanic activity.