As an important transition domain between the thinnest continental crust and the initial oceanic crust, the ocean–continent transition zone (OCT) preserves a wealth of information on the processes of lithospheric extension and breakup. The northern margin of the South China Sea (SCS) is a non‐typical, magma‐poor passive continental margin with a particular structural pattern and sedimentary formation. The OCT in the northern margin of the SCS was developed by a series of continental rifting and seafloor spreading. Based on several multi‐channel seismic reflection profiles, crustal‐scale structural profiles extracted from gravity data and ocean‐bottom seismometers (OBS) data, this paper studies the deep crustal structures, deformation and geodynamics of the OCT to further understand the structural patterns and tectonic process from the lithospheric extension to its breakup. The OCT of the northern margin of the SCS is characterized by a crustal thinning and high‐velocity layer (HVL) in the lower crust. The OCT has three structural units: rift depression, volcanic zone and tilted fault blocks. The HVL is mainly limited in the eastern portion of the northern SCS. The HVL is distributed essentially within the OCT but does not clearly develop everywhere in the OCT. We propose a hybrid model of rifting to fit characteristics of the northern margin of the SCS. A crustal‐scale largely symmetric process predominated at the initial rifting stage. The basin‐controlling faults subsequently penetrated the entire crust, resulting in asymmetric tectonic evolution. Then, the OCT occupied this asymmetric location. Copyright © 2016 John Wiley & Sons, Ltd.

A magnetic quiet zone (MQZ) is located in the ocean–continent transition zone in the northern South China Sea (SCS), according to ΔT magnetic anomaly data. Features of the gravity and magnetic anomalies in the MQZ are discussed by the multi‐scale wavelet decomposition method. Comprehensive boundary identification and fault analysis by analytic signal and normalized total horizontal derivative methods achieve some good effects in the northern SCS. The inversion results suggest a deep magnetic basement, a shallow Curie isothermal interface and thin magnetic layers. The average depth of the Curie isothermal interface is about 14–28 km in the northern SCS, and the thickness of the magnetic layer is about 6–10 km in the MQZ. The formation mechanism of the MQZ is discussed, and the thinning of the magnetic layer is considered as the origin of the MQZ in the northern SCS. The deep hot mantle materials were upwelled during the extension of the SCS, and the magnetic layer was demagnetized. In addition, the magnetic anomaly caused by thick Mesozoic sediments was very weak, and the NW–SE‐trending faults made the magnetic bodies fragmental. The distribution of major faults is consistent with the fluctuating changes of the Curie isothermal interface, and the faults in the MQZ are the upward intrusion channels of the deep hot materials. Copyright © 2016 John Wiley & Sons, Ltd.