Cretaceous paleomagnetism of the eastern South China Block: establishment of the stable body of SCB

A paleomagnetic investigation was performed on the Cretaceous red sandstones collected at the eastern side of the South China Block (SCB), China, and attempted to establish the stable part of the SCB since the Cretaceous. Paleomagnetic specimens were collected at 39, 25 and 14 sites from three independent parts: the northern, central and southern regions of eastern SCB, respectively. Characteristic directions of higher temperature components (HTCs) with an unblocking temperature of ∼680 °C were isolated from 69/78 sites. The optimal concentrations of global mean HTC directions calculated using the direction-correction tilt test were achieved at 79±19%, 95±27%, 71±37% and 117±98% untilting for the Early Cretaceous sites from the northern part, Late Cretaceous sites from the northern, central and southern parts, respectively. This treatment gives positive tilt tests or brings the optimal concentration not far from being indistinguishable from positive tilt tests, although this observation can be due to imperfect separation of a primary component (HTC) from a secondary one (lower temperature component). We adopted completely (100%) untilted directions of the HTCs as the paleomagnetic field directions during the Cretaceous, because the mean directions after complete untilting were almost equal to each mean direction after incomplete untilting showing the optimal concentration. The mean paleomagnetic poles for three independent parts were located at almost the same positions and were indistinguishable from that for Sichuan, the western side of SCB at the 95% confidence level. This observation indicates that there is no relative movement between the eastern and western sides of SCB and implies that a large part of the SCB (excluding a 400-km-wide swath along the Red River Fault) has behaved as its coherent (stable) body since the Cretaceous. The Cretaceous paleomagnetic pole for the stable body of the SCB (latitude=80.0°N, longitude=206.7°E, A95=2.5°) is worth using as a reference Cretaceous paleomagnetic pole of the SCB and agrees strongly with the reference Eurasian paleomagnetic pole during the Cretaceous period.