Low-velocity and low-resistivity zone detected in the crust of the passive continental margin of south China
Abstract. Passive continental margin has long been regarded as a tectonically and geo-dynamically inactive region with few discoveries of crustal unconformity and hence lacks scientific attention. However, previous seismic studies have hinted the presence of isolated crustal weak zones characterized by low shear-wave velocities in Guangdong-Hong Kong-Macao Greater Bay Area (GBA), north rim of South China Sea. In order to confirm the crustal heterogeneity, a 100 km-long magnetotelluric (MT) survey (ZHMT) was conducted across Zhuhai and Jiangmen (Guangdong Province) to fill in the blank of resistivity property in the region and to validate the crustal low-velocity zone at the research region. 3D inversion of the ZHMT data reveals a striking low-resistivity anomaly below the township of Shuangshui at the depth of 10–15 km depth. As plausible evidence of on-going or past tectonic activities, the Shuangshui Low-resistivity Anomaly (SLRA) is in a good spatial agreement with the low-velocity feature from the ambient seismic noise tomography. Two geological models are proposed for its origin: a fluid-bearing shear zone associated with deep faulting and fluid migration, or partial melting of mid-crustal material, possibly linked to anomalous heat flow. These findings provide new insights into the tectonic evolution of the passive margin at the research region, revealing previously unrecognized mid-crustal activity.