The continental extension discrepancy and anomalous subsidence pattern in the western Qiongdongnan Basin, South China Sea

Zhao, Zhongxian; Sun, Zhen; Liu, Jianbao; Pérez‐Gussinyé, M.; Zhuo, Haiteng

doi:10.1016/j.epsl.2018.08.048

Cited by 30 publications

(36 citation statements)

References 44 publications

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“…We analyzed multiple sections through the northern margin of the South China Sea, as shown in Figure . To obtain the subsidence process that fully reflects the deep variation, we used the 1‐D unloaded subsidence formula (Sclater & Christie, ; Zhao et al, ):

italicUTS = italicST \frac{ρ_{m} - ρ_{s}}{ρ_{m}} + italicPWD \frac{ρ_{m} - ρ_{w}}{ρ_{m}} - normalΔ italicBL

where UTS is the unloaded tectonic subsidence, ρ m , ρ s ,and ρ w are the average density of the asthenospheric mantle (3,185 kg/m 3 ), sedimentary layer (2,500 kg/m 3 ), and seawater (1,030 kg/m 3 ), respectively, ST is the decompacted sediment thickness, PWD is paleowater depth, and ∆ BL is the base level change. The method of Sclater and Christie () is used to calculate the decompacted sediment thickness, which is determined from the sediment lithology and relationship between porosity and depth.…”

Section: Methods and Datamentioning

confidence: 99%

“…Thus, according to the location of each section, different values of the PWD and ∆BL are adopted for the calculations. Data from the Qiongdongnan Basin (Zhao et al, ) are used for sections on the western side of the continental margin, and Pearl River Mouth Basin data (Dong et al, ) are used for sections on the eastern side of the continental margin.…”

Section: Methods and Datamentioning

confidence: 99%

“…Assuming that the continental margin is always in equilibrium, the mass above the compensation surface is always equal to that in the initial condition, either during the stretching phase or the stage of lithospheric cooling after extension (Figure ). Therefore, the unloaded tectonic subsidence can be expressed by the following formula at any time (Hasterok & Chapman, ; Zhao et al, ):

\begin{matrix} lefttrue \\ L (0) = ρ_{uc 0} \cdot g \int_{0}^{{UC}_{i}} [1 - αT (z, t_{0})] d z + ρ_{lc 0} \cdot g \int_{{UC}_{i}}^{{LC}_{i}} [1 - αT (z, t_{0})] d z + ρ_{m 0} \cdot g \int_{{LC}_{i}}^{a} [1 - αT (z, t_{0})] d z \\ L (t) = ρ_{uc 0} \cdot g \int_{0}^{{UC}_{t}} [1 - αT (z, t)] d z + ρ_{lc 0} \cdot g \int_{{UC}_{t}}^{{LC}_{t}} [1 - αT (z, t)] d z + ρ_{m 0} \cdot g \int_{{LC}_{t}}^{a} [1 - αT (z, t)] d z \\ S (t) = \frac{L (0) - L (t)}{ρ_{m 0} \cdot g \cdot (1 - αTm)}, \end{matrix}

where L (0) represents t...…”

Section: Methods and Datamentioning

confidence: 99%

“…The seismic profile shows that the number of fragile faults and their growth rate decreased significantly after ~23 Ma. This indicates that the upper crust did not stretch and thin thereafter (Zhao et al, ). Therefore, lower crustal flow was proposed to explain the rapid postrift subsidence in the margin of the South China Sea.…”

Section: Geological Settingmentioning

confidence: 99%

“…Therefore, lower crustal flow was proposed to explain the rapid postrift subsidence in the margin of the South China Sea. But previous studies only focused on a single basin and did not define the amount of the lower crustal flow (Clift et al, ; Zhao et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

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Quantifying Postrift Lower Crustal Flow in the Northern Margin of the South China Sea

et al. 2020

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Postrift subsidence of sedimentary basins in the northern margin of the South China Sea exceeds more than 2,.000 m, which points toward anomalous postrift crustal deformation. Previous studies have proposed lower crustal flow to explain this observation; however, this hypothesis has never been confirmed quantitatively. Here, we calculate the initial crustal structure and thermal lithospheric thickness of the northern margin of the South China Sea on the basis of recently measured heat flow data, tectonic subsidence curves, and present‐day crustal structure. Crustal thinning processes during rifting and reduced thickness of the lower crust in the postrift are also calculated by the strain rate inversion method and thermal isostasy. Our results show that the initial (Early Cenozoic) crustal thickness of the northern margin of the South China Sea varies between 27.7 and 36.3 km, and the average proportion of the lower crust is 67%. The initial thermal lithospheric thicknesses decrease from ~118 to ~81 km from the shelf to the sea, which indicates that the offshore margin has high temperatures and low strength and is more easily stretched and deformed. The average stretching factor the margin during rifting is 1.24. The lower crust reduces in thickness during the postrift phase by values between 1 and 11 km, which increases gradually from the shelf to deep water. We suggest that the thicker weak crust and hot lithospheric structure therefore make positive contribution to the lower crustal flow, the direction of which is from the oceanic basin to the shelf.

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