Detachment-controlled subsidence pattern at hyper-extended passive margin: Insights from backstripping modelling of the Baiyun Rift, northern South China Sea

Abstract

How detachment fault controls the basin subsidence at hyper-extended passive margin remains mysterious. Based on a detailed geological interpretation and backstripping on 29 high-resolution multi-channel seismic profiles, we calculate the basin-scale tectonic subsidence across the Baiyun Rift to study the relationship between tectonic subsidence and detachment faulting. Our results confirm that detachment faulting is the primary factor controlling the syn-rift subsidence. A decaying subsidence rate, or deficit subsidence is observed in the eastern Baiyun Rift from the early to late Eocene, which is in marked contrast to the intensive brittle stretching. We attribute this to the doming of the detachment fault footwall involving the syn-rift magmatism during its hyper-extension process. While in the western Baiyun Rift the average subsidence rate is over 45 m Myr−1 higher than that in the eastern as the response of flexural loading in the late Eocene. During the post-rift stage, the subsidence rate shows a similar oceanward increasing trend, and an anomalous rapid subsidence event during the middle Miocene in the eastern Baiyun Rift, which can be ascribed to the magma-assisted weakened rheological condition of the lithosphere deriving from the syn-rift detachment faulting. We propose that this relationship between subsidence pattern and detachment faulting has global applicability for other hyper-extended rift systems developing detachments and magmatic-related dome structures.