Seismic Stratigraphy, Tectonic Structure and Extension Factors Across the Dangerous Grounds: Evidence from Two Regional Multi‐Channel Seismic Profiles

Abstract

AbstractTwo recently acquired regional multi‐channel seismic profiles across the Dangerous Grounds, the South China Sea (SCS), are interpreted. One line crosses the entire Dangerous Grounds from the deep oceanic Southwest Subbasin of the South China Sea, along the Spratly Islands to close to Borneo, and the other one runs east of the Reed Bank. Based on the interpretations of these profiles, we worked out the stratigraphic sequences, tectonic structures and extension factors. Five tectonic‐stratigraphic units are determined, together with 7 sequence boundaries. Detailed analyses on the extension factors based on the measurement of fault heaves reveal two episodes of continent extension separated by a distinct unconformity. The main extension occurred during the continental rifting (Early Tertiary), and resulted in the formation of half‐grabens and rotated blocks, controlled by deeply rooted detachment system. During the second extension phase (drifting period, Late Oligocene‐Early Miocene) intensity reduced sharply and focused on the continental‐oceanic transition area. A widespread carbonate platform developed across the Dangerous Grounds concurrent with the spreading period of the SCS. Fault‐related stretching factors (βf ) to the west and east of Reed Bank are found to be comparable and show discrepancy with the whole crust stretching factors (βc) in the study area as derived from gravity modeling. Thus we conclude that the continental crust of the Dangerous Grounds experienced depth‐dependent extension.