Dynamic analysis on rifting stage of Pearl River Mouth basin through analogue modeling

The Pearl River Mouth basin (PRMB) is a marginal sedimentary basin of the South China Sea. It trends NE and is divided into three segments from west to east by two NW-trending faults. Changing dramatically in structures along and across strike, the PRMB is a good example to analyze main factors that might control the process of a continental rift basin’s extension. Through five series of analogue experiments, we investigate the role of different factors, such as pre-existing discontinuities of crust, rheological profiles of lithosphere, kinematics of extension and presence of magmatic bodies and strong crustal portions (rigid massifs) on the development of basin’s structures. After being compared with the architecture of the natural prototype, the results of the analogue models were compared with the architecture of the natural prototype and used to infer the role of the different factors controlling the formation and evolution of the PRMB. The main conclusions are as follows. (1) Affected by pre-Cenozoic structures, the PRMB was controlled by crosscut NE- and NW-trending initial faults, and the NW-trending Yitong’ansha (一统暗沙) fault may be a through-going fault along dip and offset the NE-trending rift and faults, while the Enpingdong (恩平东) fault might exist only in the middle and south. (2) The NW-trending faults may orient WNW to be sinistrally transtensional under SE to nearly NS extension. (3) The thickness ratio of brittle over ductile crust in Baiyun (白云) sag is less than normal, suggesting an initially hot and weak lithosphere. (4) The magma must have taken part in the rifting process from early stage, it may occur initially upon or slightly south of the divergent boundary in the middle segment. The flow of magma toward rift boundary faults caused extra vertical subsidence above the initial magma reservoir without creating a large extensional fault. (5) The rigid massif contributed to the strain partition along and across basin strike.