Paleomagnetic study of Early Cretaceous red beds from Wulian section,Jiaolai basin in Shandong Province and its tectonic implications
Understanding the Mesozoic vertical-axis rotation of the Jiaodong Peninsula is crucial for constraining the sinistral shearing of the Tan-Lu fault.However,debates still exist regarding whether rotation occurred and,if so,the magnitude of rotation in the Jiaolai basin during the Mesozoic.In this study,we conducted a detailed paleomagnetic investigation of the Early Cretaceous red beds from the Longwangzhuang Formation at the Wulian locality in the southern Jiaolai basin.Detailed rock magnetic results indicate that hematite is the main magnetic carrier,while pyrrhotite and magnetite act as subordinate magnetic carriers in some samples.The Fisherian mean direction of the 8 sampling sites was determined as Ds=169.5°,Is=-33.2°,ks=40.9,and a95=8.8,which is proposed to be the primary remanence acquired during deposition.Our results indicate that the Wulian region underwent an obvious counterclockwise rotation of 22.8°±8.8° relative to stable East Asia.Together with previous paleomagnetic results from the Jiaolai basin,they probably indicate a holistic counterclockwise rotation(10°～20°)of the Jiaolai basin after the Late Cretaceous.Moreover,an increasing magnitude of counterclockwise rotation towards the southwest along the Wulian fault was observed and most likely attributed to the increasing influence of sinistral strike-slip faulting along the Tan-Lu fault to the west.Different rotation senses and magnitudes were observed in different periods along the Tan-Lu fault,which were not only influenced by the sinistral shearing of the Tan-Lu fault but also related to the different nature and tectonic backgrounds of nearby blocks.
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