New palaeomagnetic data supporting the extent of the stable body of the South China Block since the Cretaceous and some implications on magnetization acquisition of red beds

Abstract

Previous palaeomagnetic studies have demonstrated that a large part of the South China Block (SCB) has behaved as a stable body since the Cretaceous. We undertook a palaeomagnetic investigation of Lower Cretaceous red sandstones at 24 sites within the Ganzhou and Xingguo basins in southern Jiangxi Province in China. The aim of this study was to further constrain the extent of the SCB, which has been stable since the Cretaceous. We isolated the characteristic directions of higher temperature components (HTCs) with an unblocking temperature from 650 to 700 °C, by progressive thermal demagnetization and principal component analysis. The optimal concentration of site mean HTC directions calculated using the direction-correction tilt test was achieved at 51.2 ± 32.4 per cent untilting, indicating syntilting magnetization, suggesting that the remanences were not acquired immediately after sedimentation. Most Cretaceous sedimentary basins on the eastern part of the SCB were controlled by fault movement (extensional basins). Most tilting in such an extensional basin is thought to have progressed contemporaneously with the structural and stratigraphic development of the basin. We concluded that the remanence acquisition of red sandstones on the Ganzhou and Xingguo basins occurred during synsedimentary tilting. We adopted 51.2 per cent untilted directions of the HTCs as the palaeomagnetic field directions during the Early Cretaceous. The mean palaeomagnetic pole (76.3°N, 224.3°E, α95 = 3.3°), calculated using virtual geomagnetic poles from 23 sites (excluding site 20, which has an insufficient number of samples showing a stable magnetic component), is in good agreement with the Late Cretaceous palaeomagnetic poles from the same region and also with most of Cretaceous poles previously reported from the stable body of the SCB. This agreement indicates that the Jiangxi region has been part of the stable body of the SCB since the Cretaceous. This result also demonstrates that the tectonic influence of the India-Asia collision did not destroy the rigidity of most of the SCB. The global mean pole position (78.8°N, 214.4°E, α95 = 2.6°), calculated using sixteen Cretaceous poles from the stable body of the SCB, is suitable for use as the reference Cretaceous palaeomagnetic pole of the stable SCB. © 2009 The Authors Journal compilation © 2009 RAS.