Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
Citation:
Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
Citation:
Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
The southern continental margin of the South China Sea has documented multiphase continental rifting corresponding to the propagation of seafloor spreading. Here we investigate three multi-channel seismic reflection profiles across different segments of the Dangerous Grounds with a NE-SW direction. Stratigraphic correlation reveals that the Cenozoic tectono-stratigraphic framework in the Dangerous Grounds is featured with diachronous rifting, which records the successive spreading of East Subbasin and Southwest Subbasin, South China Sea. By reconstructing the tectono-sedimentary evolution history in different segments, we combine the quantification of the brittle extension, tectonic subsidence, as well as the crustal thinning. Results provide evidence that the extensional stress migrated from northeast to southwest with the progressive propagation of the seafloor spreading in the oceanic basin. Besides, the impact of the tectonic propagation persists even after the cessation of seafloor spreading, evidenced by a longer stretching duration in the West-Dangerous Grounds than that in the eastern area. Moreover, a temporary syn-rift subsidence delay synchronously to the spreading of the adjacent oceanic basin is observed along the southern margin. This observation proves the secondary mantle convection during the seafloor spreading in the southern continental margin, which is related to the propagating rift.
As one of the largest marginal basins in the western Pacific region, the SCS has experienced almost all the fundamental elements of Wilson Cycle, including the continental rifting since the Late Cretaceous, the seafloor spreading during Early Oligocene to Middle Miocene, the subsequent collision with Borneo to the south, and subduction under the Luzon to the east (Franke et al., 2014; Cullen, 2010; Briais et al., 1993). In topographic map view, the width of the passive margin of the SCS increases westward from 400 to 900 km as the age of the seafloor decreases (le Pourhiet et al., 2018), including the contribution from the Dangerous Grounds lying between the oceanic basin and the Sunda continental shelf.
Constrained by the geological and geophysical data, detailed studies were carried out in different segments of the Dangerous Grounds. In the eastern segment, Yao et al. (2012) analyzed the Cenozoic structural characteristics and sedimentary evolution of the Reed Bank Basin. Ding et al. (2014) further discussed the carbonate platform development. In the center segment of the Dangerous Grounds near the Zhenghe Massif, Chang et al. (2017a) characterized the stratigraphic features and discussed the nature of the carbonate platform deposit. Besides, Zhang et al. (2020) investigated the extensional tectonics and post-rift magmatism through newly obtained multi-channel seismic reflection data. In the southwestern segment, Li L et al. (2014) reconstructed the subsidence history and explored the crustal-mantle strain accommodation using a combination of back-stripping technique and forward modelling. These previous studies suggest that the structural pattern, sedimentary process, as well as deep crustal structure in different segments of the southern SCS are complicated and distinct. Along the rifting strike in the entire Dangerous Grounds, a comparison of the extensional deformation and spatial-temporal distribution analysis of tectonic subsidence are important yet poorly discussed, which hinders our understanding of the propagated rifting process and its geodynamic attribution.
In this study, we present three seismic profiles across different segments of the Dangerous Grounds from NE to SW. Efforts include the correlation of the along-strike variation in seismic stratigraphy and the restoration of the deformation pattern during rifting, seafloor spreading and final collision. In addition, we reconstruct the tectonic subsidence history in different geological time, and analyze the crustal stretching factors dominated by the featured subsidence in different segments. This study aims to provide an implication for the spatial-temporal pattern of the Cenozoic tectonics in the Dangerous Grounds and place constraints on the understanding of the propagated rifting dynamics of the SCS area.
Figure
1.
Morphological features and major tectonic units in the Dangerous Grounds, southern continental margin of the South China Sea. Three seismic profiles, L1 (Ding et al., 2014) across Reed Bank area, L2 (Ding et al., 2013) across the Center-Dangerous Grounds and L3 (Sun et al., 2011) across the West-Dangerous Grounds have been selected to demonstrate the structural changes along the southern margin. The yellow solid line shows the location of previous Ocean bottom seismometers profile OBS-PR2 (Pichot et al., 2014). Drilling holes are after ODP Shipboard Scientific Party (2000) and Schlüter et al. (1996).
Figure
2.
Stratigraphy, lithology, eustatic sea level curve and major tectonic events of the study area (summarized from Peng et al., 2019; Ding et al., 2016; Savva et al., 2014; Franke et al., 2011; Yan and Liu, 2004). DG. Dangerous Grounds; BRU-E. breakup unconformity of the East Subbasin; BRU-SW. breakup unconformity of the Southwest Subbasin; MMU. Middle Miocene unconformity.
The wide southern continental margin of the SCS preserves a polyphase rifting process recorded by different structural styles and crust configurations. The eastern segment of the Dangerous Grounds includes the Reed Bank and is bounded in the east by the Ulugan fault. Regional multi-channel seismic data reveal that the morphology is characterized by a serious of half-grabens, which are controlled by low angle normal faults tilting towards the ocean (Fig. 3) (Ding et al., 2014). From SE to NW, the individual fault locks gradually decrease in width and thickness due to the increasing lithospheric stretching (Benes et al., 1994). The thickness of the continental crust is approximately 20 km in the Reed Bank and decreases to less than 10 km towards the NW (Franke et al., 2011; Qiu et al., 2011).
Figure
3.
Seismic profile L1 across the Reed Bank (a), geological interpretation of L1 modified from Ding et al. (2014) (b), and the depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~23.8 Ma; T40. ~16 Ma; T0. seabed. The dash line marks the area for tectonic subsidence modelling.
The Center-Dangerous Grounds, represented by the Zhenghe Massif and its adjacent rift basins, is dominated by low angle normal faults running parallel to the coast and dissecting the region (Fig. 4) (Savva et al., 2014). These large-scale normal faults are rooted in the lower crust and control the major tilted fault blocks (Ding et al., 2013; Hutchison and Vijayan, 2010). According to an Ocean Bottom Seismometers (OBS) profile covering the Zhenghe Massif (Fig. 1), high velocity lenses (2–3 km thick, 7.0–7.7 km/s) are imaged within the lowermost crust (Pichot et al., 2014). Based on the integrated data offshore north of Taiping Island in the Zhenghe Massif, these high velocity materials are probably associated with the volcanic structural highs on the profile, suggesting the limited post-rift volcanism in the southern continental margin (Sun et al., 2021; Chang et al., 2017b).
Figure
4.
Seismic profile L2 across the Center-Dangerous Grounds (a), the geological interpretation of seismic profile L2 modified from Ding et al. (2013) (b), and its depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~21 Ma; T40. ~16 Ma; T0. seabed. The dash line marks the continental-ocean transition (COT) area.
The West-Dangerous Grounds is located at the tip of the Southwest Subbasin. This segment includes Nanweixi Basin and Beikang Basin, which is bounded in the southwest by the Lizhun-Tinjia fault zone (Fig. 1). Rifting in the West-Dangerous Grounds was intense comparing to the central and eastern segments during the seafloor spreading of the SCS (Sun et al., 2011). The continental crust ranges from 10 to 25 km within this area (Gozzard et al., 2019; Peng et al., 2019). Horsts and grabens bounded by steep normal faults can be observed (Fig. 5). Thick sediments with relatively shallow water are widely distributed on the fluctuant basal surface (Peng et al., 2019; Li et al., 2013).
Figure
5.
Seismic profile L3 across the West-Dangerous Grounds (a), geological interpretation of seismic profile L3 modified from Sun et al. (2011) (b) and its depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~18.5 Ma; T40. ~16 Ma; T0. seabed.
Three published multi-channel seismic profiles, L1 (Ding et al., 2014), L2 (Ding et al., 2013), and L3 (Sun et al., 2011), are used in this study (Fig. 1). Seismic profiles L1 and L2 were collected in 2009 with the R/V "TANBAO" during the Project 973 Cruise. The data were acquired through 480 channels with a 6 237.5 m streamer in total length and were recorded at a sampling interval of 2 ms. The total capacity of the air gun is 5 080 in3; SO27-04 was joint with L2 in the Southeast, which was obtained by the Federal Institute for Geosciences and Natural Resources (BGR), Germany in 1983 during the SONNE 27 Cruise. The seismic profile L3 was collected in 1990 by the R/V "Shiyan Ⅱ" of the South China Sea Institute of Oceanology, Chinese Academy of Sciences. The total capacity of the air gun is 1 380 in3. The data were recorded at 2 ms sampling intervals and in 50 m space for both shot and receiver intervals. The three seismic profiles are arranged at approximately equal intervals from NE to SW, which can effectively reflect the structural changes along the strike in the study area (Table 1).
Table
1.
Acquisition parameters for seismic profiles used in this study
The stratigraphic successions on rift-related passive margins correspond to the distinct environment and different tectonic phases. In this study, five sequence boundaries (unconformities) marking the key tectonic events have been identified, including Tg, T70, T60, T40 and T0 (Table 2). Geological interpretations of the three seismic profiles across the Reed Bank, the center and western part of the Dangerous Grounds are shown in Figs. 3–5.
Table
2.
Seismic reflection pattern of the main unconformities with tentative ages
Sequence boundary
Age
Seismic line
Typical seismic image
Reflection feature
T40
~16 Ma
L1
Strong amplitude, moderate-good continuity
L2
Strong amplitude, good continuity, parallel above and truncation below
L3
Strong amplitude, good continuity, truncation below
T60
~23.8 Ma
L1
Strong amplitude, good continuity, truncation below
~21.0 Ma
L2
Strong amplitude, good continuity, onlap above and truncation below
~18.5 Ma
L3
Moderate-srong amplitude, patchy continuity, onlap above and truncation below
Tg (basement of Cenozoic), featured with moderate-strong, continuous amplitude (Figs. 3–5), is the base of the wedge-shaped syn-rift infill on the seismic profiles. With locally erosional truncation below, Tg represents the onset of rifting. Drilling samples from the Dangerous Grounds encountered the Mesozoic strata (Schlüter et al., 1996). The pre-rift unit is composed of sandstones, siltstones with plant debris and dark-green claystones with Upper Triassic to Lower Jurassic shells deposited in fluvial or coastal to shallow marine environment (Schlüter et al., 1996). We suggest an age of 65 Ma for this horizon referring to Ding et al. (2013) and Sun et al. (2011).
T70 (~32 Ma, BRU-E) is a widely distributed regional unconformity corresponding to the initiation of seafloor spreading in the East Subbasin of the SCS (e.g., Franke et al., 2014). The reflectors show moderate-strong amplitude and good continuity in the study area (Figs. 3–5). Regional truncation beneath T70 indicates an erosional event, which is related to the rising asthenosphere during the initiation of seafloor spreading (Falvey, 1974). We propose that T70 represents the breakup unconformity of East Subbasin with an age of 32 Ma (e.g., Sun et al., 2019).
T60 (~23.8– ~18.5 Ma, BRU-SW) is another regional unconformity denoting the diachronous interface related to the propagated spreading of the Southwest Subbasin (Ding et al., 2016; Franke et al., 2014; Savva et al., 2014). Li C F et al. (2014) suggested that a ridge jump in the SCS occurred at about 23.6 Ma according to the modeling results of the deep tow magnetic transects close to the continental-ocean transition (COT) of seismic profile L2. The model fits well with the age constraints based on microfossils in recovered cores from IODP Expedition 349. Across the Dangerous Grounds, T60 shows strong and continuous reflectors (Figs. 3–5). It represents an erosional phase and forms the top of a clastic succession (Jamaludin et al., 2018; Steuer et al., 2014) in the Center-Dangerous Grounds and southwestern area. In the northeastern Dangerous Grounds, T60 marks the top boundary of the widespread carbonate platform (Ding et al., 2014, 2013; Schlüter et al., 1996; Kudrass et al., 1986). Dredging samples from the carbonate platform developed in the southwest of the Reed Bank were dated from Late Oligocene to Early Miocene (Steuer et al., 2014; Schlüter et al., 1996; Kudrass et al., 1986). The development of carbonate platform offshore and onland Palawan continued into the Early Miocene (e.g., Steuer et al., 2013). Hence, we suggest an age of 23.8 Ma in the Reed Bank area, 21 Ma in the Center-Dangerous Grounds, and 18.5 Ma (Ding et al., 2016) in the western part, corresponding to the diachronous age of the top of the carbonates and the progressive spreading in the Southwest Subbasin.
T40 (ERU) is referred to as the end-rift unconformity separating the underlying rifted terrane and overlying draping strata (Franke et al., 2014). Most faults terminate upwards at this unconformity. The reflectors are nearly parallel to the seafloor and show a moderate-strong amplitude with local onlap above and truncation below. Locally the carbonate deposition ended up to this interface which is merged with T60 (Song and Li, 2015; Steuer et al., 2014; Schlüter et al., 1996). This prominent reflector coincides with the major tectonic events in the Middle Miocene, including the initiation of the Palawan/Mindoro-Central Philippines collision (Yumul et al., 2003), the collision between Dangerous Grounds and Borneo (Cullen, 2010; Hutchison and Vijayan, 2010), and the cessation of seafloor spreading in the SCS (e.g., Li C F et al., 2014; Briais et al., 1993). Therefore, T40 was also described as the Middle Miocene unconformity (MMU) with an age of 16 Ma and there is a depositional hiatus of 3–5 Ma in the Dangerous Grounds area (Hutchison, 2004). After the Middle Miocene, the sedimentary environment changed from shallow-marine to abyssal facies (Steuer et al., 2013; Williams, 1997).
2.3
Seismic Units
Cenozoic infill of the Dangerous Grounds is characterized by four seismic units corresponding to distinct tectonic phases. The seismic units are described as follows.
2.3.1
Syn-rift unit (Tg–T70, Paleocene to Early Oligocene)
Massive faults offsetting the sequence between Tg–T70 suggests an intense continental rifting episode. Referring to Ding et al. (2013), syn-rift unit is defined mainly by the wedge-shaped sediments thickening to the major faults, which suggests that it is syn-tectonic and deposited during the extensional rift deformation. The sequence is widespread in the southern continental margin of the SCS and the thickness of the sediments gradually decreases with a NE-SW direction (marked by blue in Figs. 3–5). In the three seismic profiles, the initial syn-rift sequence is characterized by chaotic (locally subparallel) reflectors with low frequency and various intensities. Close to the COT, a wedge-shaped graben bounded by a remarkable detachment is well-imaged (Fig. 4). The lower parts of this unit between 6.5–8 s, show discontinuous and chaotic reflections, indicating the proximal provenance and turbulent environment at the very early rifting stage (Song and Li., 2015).
2.3.2
E-Drift unit (T70–T60, Early Oligocene to Early Miocene)
The E-Drift unit was developed simultaneously with the opening of the East Subbasin of the SCS. The overall thickness is thinner than the syn-rift unit in the three seismic profiles. This unit generally fills half-grabens in a wedge-shaped succession with subparallel reflectors of high-intermediate continuity and moderate intensity. The top of this unit is T60 formed by ridge jumps (e.g., Briais et al., 1993). Afterwards, the East Subbasin continues spreading and the Southwest Subbasin shows dinstinct propagated spreading feature (Li et al., 2012). In the Dangerous Grounds, T60 marks the top of the widespread Oligocene to Early Miocene carbonate platforms, particularly in the Reed Bank area (Fang et al., 2017; Franke et al., 2014).
2.3.3
SW-Drift unit (T60–T40, Early Miocene to Middle Miocene)
With the propagated seafloor spreading in the Southwest Subbasin, SW-Drift unit was deposited. The internal reflectors are parallel layered with immediate-high continuity and slightly varying frequency. Locally the reflections are seismically transparent. The strata (marked by orange in Figs. 3–5) changes thicken than the prior two units in the West-Dangerous Grounds (Fig. 5), but ultra-thin or even absent in the Reed Bank (Fig. 3) and Center-Dangerous Grounds area (Fig. 4). The top of this unit corresponds to the cessation of rifting. Locally some faults continue their activities and reach to the seafloor, but do not control the deposition. This unit is assumed to consist of a transitional phase between shallow-water and bathyal depositional settings (Ding et al., 2013).
2.3.4
Post-drift unit (T40–present)
The post-drift unit above T40 is characterized by continuous, subparallel-parallel reflectors with low-moderate intensity. ODP Site 1143 penetrated the Upper Miocene to present post-drift strata and recovered 500 m of claystones, sandstones and highly calcareous nanofossil ooze with foraminifera in slope bathyal or foreshore alluvial to open marine environments (Shipboard Scientific Party, 2000). The upper parts of the half-graben (above T40) closed to the COT in seismic profile L2 (Fig. 4) show clear erosion, indicating a hemipelagic sedimentary environment (Peng et al., 2019; Franke et al., 2014). According to the velocity model of this graben, large horizontal velocity variations can be observed in the unit under T40, while the post-drift unit shows rather uniform interval velocities (Song and Li, 2015). A small number of normal faults are still active during this unit in the seismic profile L3 close to the tip of the propagator in the southwest, indicating a very recent extensional event (Fig. 5).
3.
METHODS
3.1
Time-Depth Conversion
By integrating previous seismic interpretation (Ding et al., 2013; Sun et al., 2011), we construct the Cenozoic sequence stratigraphic framework.The time-depth conversion of the three seismic profiles is carried out following function (1)which is provided by China National Offshore Oil Corporation (CNOOC) and applicable for the Dangerous Grounds,
h=−5.1578t3+133.48t2+721.06t−2.4356
(1)
where t represents the two-way travel time starting from the seafloor (TWT, in seconds), and h represents the depth below the seafloor (in meters).
3.2
Restoration and Tectonic Subsidence Modeling
Under the assumption that all pre-tectonic layers were horizontal and continuous before rifting (Sutra et al., 2013), we apply flexural back-stripping technique (Watts and Ryan, 1976) to restore the extensional deformation in different domains by using the software 2D Move in the study. Decompaction, fault displacement removing and horizon flattening are processed in sequence to the three seismic profiles. Then we obtain the deformation structure of each depositional stage (Fig. 6).
Figure
6.
Structural evolution of seismic profiles L1, L2 and L3. During continental rifting, faults were widely developed in all three profiles. Syn-rift sequence (marked by blue) in Reed Bank with the largest thickness suggests the basin subsidence and deposition were focused on the northeastern Dangerous Grounds area. After the formation of the seafloor spreading sequence (marked by green and orange), the tectonics related to the extension and subsidence apparently migrated and focused on L3, southwest of the southern continental margin.
After the structural restoration, we further analyze the tectonic subsidence history on the basis of Airy isostasy (e.g., Steckler and Watts, 1978).The tectonic subsidence history can be quantified by removing the effects of sediments, paleo-water depth and eustatic sea-level changes from the basement subsidence. We correct the decompaction thickness of sediments according to the porosity-depth relationship (Table 3). The lithology parameters refer to previous drilling data and studies (Fang et al., 2017; Ding et al., 2014; Steuer et al., 2014; Zhao et al., 2011; Kudrass et al., 1986).
The deposition thickness cannot represent the depth of subsidence when the sedimentary interface remains underwater (Fang et al., 2017). Thus, the estimation of the water depth is significant in the tectonic subsidence analysis. We use several wells with bio-stratigraphic data in the Reed Bank area and offshore Palawan (e.g., wells Sampaguita-1, Santiago-1, Nido-1; see Fig. 1 for locations) to constrain the range of paleo-water depths (Steuer et al., 2014; Schlüter et al., 1996; Kudrass et al., 1986). The sedimentary facies in different geological periods are mainly used to determine the paleo-water depth in the study area (Xie et al., 2014). The sediments in the Mesozoic were composed of sandstones and shales, with coal and show lacustrine and delta facies (Ding et al., 2014), so we assume that the paleo-water depth is zero for the initial rifting age (~65 Ma). Between the Paleocene to Early Oligocene (~65– ~32 Ma), the paleo-water depth is determined from 0–100 m based on the neritic facies. During the drifting stage, a widespread carbonate platform in the northeastern Dangerous Grounds (Franke et al., 2014; Steuer et al., 2014) indicates a paleo-bathymetry of shallow water (less than 50 m). After 16 Ma the water depth rapidly increased, and the linear interpolation is applied to estimate the depth of paleo-water. The correction of the eustatic sea-level changes referring to Haq et al. (1987) is made to improve the accuracy of the results.
3.3
Quantification of Extension
3.3.1
Upper crustal extension
The Dangerous Grounds is a privileged site to quantify extension due to the absence of main magmatic additions. The extension ratio for each evolution period (R) can be quantified by the proportion of the deformed length of each layer (Ll - L0) in the total extension amount since the Cenozoic (ΔL). The extension rate (V) is calculated with the extension amount in each evolution period (Ll - L0) divided by the depositional duration (ΔT). The functions are as following.
R=(L1−L0)/ΔL
(2)
V=(L1−L0)/ΔT
(3)
where L0 and L1 are the length of a section before and after stretching in a certain period, respectively.
3.3.2
Whole crustal stretching factor
The first-order interfaces can be used to estimate the crustal thickness evolution linking with lithosphere and subsidence history (Roberts et al., 2013; Kusznir and Karner, 2007). The crustal stretching factor β, defined as the ratio of original crustal thickness and extended crustal thickness at rifted continental margins, quantitatively describes the thinning variations of lithosphere with pure shear deformation (McKenzie, 1978). The larger β value indicates the higher degree of the crustal thinning. The stretching factor derived directly from the crustal thickness has been widely used in deep water areas lack of drilling data. For presenting geographically, we calculate γ (γ = 1 - 1/β) to demonstrate the crustal thinning factor. The γ ranges from 0 to 1 representing no crustal thinning to complete crustal thinning.
The initial crustal thickness has been determined by the thickness of the South China Block, which is 30 km (e.g., Yan et al., 2001). The crustal thickness after rifting is calculated by the Moho depth subtracting the depth of the Cenozoic basement. In the seismic profile L1, the Moho depth was obtained by wide-angle seismic data inversion in the Reed Bank area (Ruan et al., 2011). In profile L2, we refer to the Moho depth with the interpretation results of deep crustal architecture in the southern continental margin of the SCS (Franke et al., 2014). For L3, the Moho depth is after the inversion of free-air gravity anomaly (Gozzard et al., 2019).
4.
RESULTS
4.1
Cenozoic Tectonic Subsidence
Based on the structural restoration (Fig. 6), the tectonic subsidence history of the three seismic profiles across Reed Bank (L1), Center-Dangerous Grounds (L2) and West-Dangerous Grounds (L3) are shown in Fig. 7. Ten artificial wells are extracted at equal intervals to present the changes of tectonic subsidence along each seismic profile. Results show the tectonic subsidence changes regularly along the Dangerous Grounds both spatially and temporally.
Figure
7.
An overview of the back-stripping tectonic subsidence curves. (a) The tectonic subsidence rate of Reed Bank area (L1), Center-Dangerous Grounds (L2) and West-Dangerous Grounds (L3). (b) The average subsidence rate curves in the Dangerous Grounds. (c) Ten equally-distributed artificial wells are extracted from profiles L1, L2 and L3, respectively to show the tectonic subsidence change.
During this stage the overall tectonic subsidence amounts and rates of the Dangerous Grounds are small. The average tectonic subsidence rate of seismic profiles L1, L2 and L3 is 12.02, 5.74, and 6.21 m/Ma, respectively. L1 in the east shows a relatively higher subsidence rate than the other two profiles, suggesting the initial rifting in the Eocene was focused on the Reed Bank area.
4.1.2
E-Drift stage
During the seafloor spreading of the East Subbasin, the subsidence rates across the study area show significant differences. In the Reed Bank area, the average tectonic subsidence rate drops slightly to 9.94 m/Ma comparing to the initial rifting stage. However, the tectonic subsidence amounts of center (L2) and western part (L3) of the Dangerous Grounds increase rapidly with an average subsidence rate of 66.69 and 39.87 m/Ma, respectively. The average subsidence rate of seismic profile L2 is relatively higher than that of profile L3, suggesting a westward migration of extension from Reed Bank to the Center-Dangerous Grounds, and focusing on the area near the Zhenghe Massif during the E-Drift stage.
4.1.3
SW-Drift stage
After the ridge jump and the initiation of seafloor spreading in the Southwest Subbasin, the tectonic subsidence in the Center-Dangerous Grounds referred from seismic profile L2 starts to attenuate. In contrast, that of seismic profiles L1 and L3 become intensive. Rapid subsidence is observed in the western part of the Dangerous Grounds with a subsidence rate of > 90 m/Ma, while the average subsidence rate of L2 reduces to 46.21 m/Ma. This phenomenon indicates the continuous southwestward migration of extension during the SW-Drift stage.
4.1.4
Post-drift stage
The tectonic subsidence curves of the center and eastern areas show a similar increasing trend after the cessation of seafloor spreading. The average subsidence rate ranges from 61 to 66 m/Ma. However, the average tectonic subsidence rate of seismic profile L3 decreases sharply, from 90.28 to 42.89 m/Ma. It shows the accelerated subsidence mainly focuses on the center and eastern segment of the Dangerous Grounds.
4.2
Cenozoic Brittle Extension
Quantification of the brittle extension, represented by the stretching amount and rate (Fig. 8), is derived from the restoration of the three seismic profiles. Results show a NE-SW propagation of brittle stretching during Cenozoic. Details are as following.
Figure
8.
Extension ratio (bars) and extension rate (red lines marked with numbers, unit: km/Ma) of Reed Bank (L1), Center-Dangerous Grounds (L2) and West-Dangerous Grounds (L3) in each structural evolution period. Extension ratio shows an apparent migration from NE (L1) to SW (L3) along the southern margin of the Southwest Subbasin. Extension rate increased in both L2 and L3 while decreased in L1 from the syn-rift to E-Drift stage. From E-Drift to SW-Drift stage, an accelerated extension occurred in L3 while the extension in L1 and L2 slow down. DG. Dangerous Grounds.
During this stage the stretching amounts of seismic profiles L1, L2 and L3 are 11.91, 41.18 and 4.46 km, accounting for 81.4%, 59.5% and 17% of total extension amount in each profile during the Cenozoic, respectively. The maximum extensional proportion is found in seismic profile L1 across the Reed Bank area, which indicates that the brittle stretching was concentrated on the Reed Bank area during syn-rift stage.
4.2.2
E-Drift stage
As shown in Fig. 8, seismic profile L2 has the largest extension amount of 17.31 km with 25% of total extension during the Cenozoic. Meanwhile, profiles L1 and L3 show a relatively small extension value, which is 2 km (accounting for 13.6% of total Cenozoic extension) and 4.15 km (accounting for 15.7% of total extension), respectively. From the syn-rift to E-Drift stage, both the extension rates of profiles L2 and L3 increase while profile L1 decreases. This change suggests that the stretching deformation had generally migrated southwestwards and focused on the center part of the Dangerous Grounds with the opening of the East Subbasin, SCS.
4.2.3
SW-Drift stage
As the seafloor spreading of the Southwest Subbasin initiated, an intensive stretching is observed in the southwestern part of the Dangerous Grounds with 10.79 km extension amount (accounting for 40.9% of total extension; Fig. 8, profile L3). In contrast, the extension amount of profile L2 in the Center-Dangerous Grounds reduces to 6.57 km (accounting for 9.5% of total extension), and that of profile L1 in the Reed Bank area drops to 0.39 km (accounting for 2.7% of total extension; Fig. 8, profile L1). From E-Drift to SW-Drift, the extension rates of seismic profiles L1 and L2 decrease while an accelerated extension occurred in profile L3, indicating a localized extension in the West-Dangerous Grounds.
4.2.4
Post-drift stage
With the cessation of the seafloor spreading, brittle extension continually shows an increasing trend from NE to SW. Generally, the West-Dangerous Grounds presents the highest extension proportion (26.4%; Fig. 8, profile L3), while in the east, the Reed Bank has the lowest extension amount (0.33 km; Fig. 8, profile L1), accounting for 2.3% of total extension. Result illustrates that an intense stretching deformation persists at the tip of the oceanic basin even after the cessation of seafloor spreading.
4.3
Correlation between the Crustal Extension and Tectonic Subsidence
A spatial change of the whole crustal stretching is demonstrated by the thinning factor γ which shows good agreement with the subsidence (Fig. 9).
Figure
9.
Tectonic subsidence amount since the Cenozoic and the crustal thinning factor (γ) in seismic profile L1 (a), L2 (b) and L3 (c). The crustal extension along each profile shows good agreement with the tectonic subsidence.
For the SE part of seismic profile L1 (Fig. 9a), the crustal thinning factor γ ranges from 0.29 to 0.36 with a tectonic subsidence amount between 1 500 and 2 200 m, suggesting the crust was not stretched a lot. The larger fault-blocks accommodating more intense crustal stretching have relatively higher basin subsidence amount. For seismic profile L2 across the center part of Dangerous Grounds (Fig. 9b), the thinning factor remains stable with a range of 0.25 to 0.45 in the middle and SE part. The corresponding subsidence amount ranges from 700 to 2 500 m. Towards the NW part of this profile, the thinning factor changes abruptly to 0.95 and the subsidence amount increases from 700 to > 4 000 m over a horizontal distance of 80 km. This high thinning factor near the COT typically indicates the highly attenuated continental crust. In comparison, for seismic profile L3 (Fig. 9c), the crustal thinning factor γ becomes more constant along the whole profile with a range between 0.2 and 0.5 and the subsidence amount ranges between 1 200 and 2 200 m. These relatively low thinning factors are typical of intra-continental rift basins. Close to the COT, the thinning factor along this profile reaches 0.5, which still implies significant stretching in this area, but obviously a lower value. Correspondingly the subsidence amount increases from 1 200 to 2 000 m within a distance of 150 km.
Bringing these observations together, it is clear that the crustal thinning factors along each profile are in good agreement with the subsidence estimated by flexural back-stripping. The range of the value changing agrees with the width of the Dangerous Grounds, where the continental margin becomes wider from NE to SW. Noting that the positive correlation between the tectonic subsidence and crustal extension is not appropriate in the southeastern part of profile L3, which may be related to the compression resulted from the collision of the Dangerous Grounds and Borneo.
5.
DISCUSSION
5.1
NE-SW Propagated Rifting History in the Dangerous Grounds Related with Seafloor Spreading
Previous studies on the oceanic basin of the SCS have indicated a NE-SW rifting propagation (Ding et al., 2016; Savva et al., 2014; Li et al., 2012), which might result in the so-called breakup propagation corresponding to the strain localization within a stretched continental lithosphere (Franke et al., 2014; Huchon et al., 2001). Integrating the calculation of tectonic subsidence, brittle extension and the whole crustal thinning factor from three typical seismic profiles across the Dangerous Grounds, we provide quantitative evidences on the NE-SW rift propagation along the Dangerous Grounds, which is closely related to the opening of the oceanic basin.
During the Eocene, the entire Dangerous Grounds was dominated by intensive rifting, and the extension mainly focused on the Reed Bank or the eastern part of the Dangerous Grounds with a maximum subsidence rate and the highest extension ratio.
Since the Oligocene, rifting migrated to the center part of the Dangerous Grounds with intense extension and rapid subsidence. The variation in the West-Dangerous Grounds is similar. While the Reed Bank area was featured with decreased extension amount and low subsidence rate. These observations indicate that after the initiation of seafloor spreading in the East Subbasin, the continental rifting migrated southwestwards and concentrated on the Center-Dangerous Grounds. The continental rifting continued until the occurrence of the southward ridge jump and subsequent seafloor spreading in the Southwest Subbasin. After that, the rifting propagated southwestwards and focused on the West-Dangerous Grounds area featured with the highest subsidence rate and extension rate during this stage. Meanwhile, the extension in the Center-Dangerous Grounds weakened with decreasing subsidence rate.
After the end of seafloor spreading since the Middle Miocene, accelerated subsidence with limited extension was found in the Reed Bank and Center-Dangerous Grounds area, which is related to the rapid thermal subsidence and a sharp change of sedimentary environment (Fang et al., 2017; Ding et al., 2014). In comparison, the West-Dangerous Grounds area was featured with relatively slow subsidence but high extension amount. Combined with an analysis of three transects across the entire SCS, Hayes and Nissen (2005) reported that the amount of crustal extension along the eastern and central segments of the margin is much less than that along the western segment. Moreover, rifting in the west continued longer than that in the east, which has been further evidenced by other works (e.g., Franke et al., 2014; Pichot et al., 2014; Savva et al., 2014). These previous observations agree with the continuous continental extension found out in the West-Dangerous Grounds even after the cessation of seafloor spreading. We propose that a possible mechanism might be the dextral strike-slip activity of the Lizhun-Tinjia fault zone related to the collision of the Dangerous Grounds and Borneo (Zheng et al., 2016; Xiong et al., 2012; Liu et al., 2004).
5.2
Implication for the Syn-Rift Subsidence Delay
Subsidence of rifted continental margins can be explained by the mechanical and isostatic response to lithospheric stretching (McKenzie, 1978). The continental breakup is expected to result in rapid subsidence when an initial seafloor spreading is driven by cooling and thickening of the asthenosphere (Ding et al., 2014). However, we observe a temporary subsidence delay during the drifting stage in the study area. Results show that slow subsidence occurred between 32–23.8 Ma in the Reed Bank area and 21–16 Ma in the Center-Dangerous Grounds (Fig. 7), which is synchronized with the spreading of the adjacent East Subbasin and Southwest Subbasin, respectively. In fact, such appearance has been widely reported from the mama-poor passive continental margins (Péron-Pinvidic and Manatschal, 2009; Kusznir and Karner, 2007).
The deficit of the subsidence after the continental breakup can be explained by thermal and dynamic uplift or mineralogical and density changes in the mantle during rifting (Reston, 2009). Franke et al. (2011) suggested that the ongoing rifting to the southwest may delay the subsidence until the cessation of seafloor spreading. Ding et al. (2014) and Fang et al. (2017) have proposed an explanation that a secondary mantle convection (first or major mantle convection happened in the oceanic basin) caused by lateral temperature gradients beneath the passive rifts in the continental margin may induce the decrease of the tectonic subsidence. This opinion can be proved in our results. The subsidence curves demonstrate that the subsidence delay in the Reed Bank area fit well with the opening of the East Subbasin, while that in the Dangerous Grounds was coincident with the spreading stage of the Southwest Subbasin. The ongoing southwestward rifting on the Center-Dangerous Grounds may have prevented the Reed Bank region from subsiding, and the rifting on the West-Dangerous Grounds also would have postponed the subsidence on the Center-Dangerous Grounds. Rapid subsidence occurred after the cessation of seafloor spreading in the whole SCS.
6.
CONCLUSIONS
Three multi-channel seismic profiles across different part of the Dangerous Grounds have been investigated to reconstruct the tectono-sedimentary evolution history, as well as the quantification of Cenozoic tectonic subsidence and crustal thinning. Results provide evidences for the propagated continental rifting during the Cenozoic in response with the NE-SW propagation of the oceanic basin, SCS.
Before the seafloor spreading, the continental rifting focused in the eastern part of the Dangerous Grounds first. With the opening of the East Subbasin, the extension migrated southwestwards and focused on the middle part of the Dangerous Grounds, indicated by both the increased brittle stretching and tectonic subsidence from NE to SW with geological timing along the southern continental margin of the SCS. Subsequently, the propagation of the seafloor spreading in the Southwest Subbasin resulted in a continuous rifting in the West-Dangerous Grounds and a further extension near the tip of the oceanic basin.
Besides, the West-Dangerous Grounds experienced longer stretch than the eastern area. The dextral strike-slip motion of the Lizhun-Tinjia fault zone during the post-drifting stage probably strengthened the extension at the tip of the Southwest Subbasin. A temporary subsidence delay during the drift period is observed in the Dangerous Grounds, which is related to the propagating rift and the secondary mantle convection during the seafloor spreading.
ACKNOWLEDGMENTS:
This work was financially supported by the Open Fund of Hubei Key Laboratory of Marine Geological Resources (No. MGR202004), and the National Natural Science Foundation of China (Nos. 41890811, 41676027, 41906070). We gratefully thank Prof. Zhen Sun from the South China Sea Institute, CAS for granting permission to use the seismic data. We also thank Dr. Licheng Cao and another anonymous reviewer for their helpful reviews to improve the manuscript. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1064-9.
Barckhausen, U., Engels, M., Franke, D., et al., 2014. Evolution of the South China Sea: Revised Ages for Breakup and Seafloor Spreading. Marine and Petroleum Geology, 58: 599–611. https://doi.org/10.1016/j.marpetgeo.2014.02.022
Barckhausen, U., Roeser, H., 2013. Seafloor Spreading Anomalies in the South China Sea Revisited. Geophysical Monograph, 149: 121–125. https://doi.org/10.1029/149gm07
Benes, V., Scott, S. D., Binns, R. A., 1994. Tectonics of Rift Propagation into a Continental Margin: Western Woodlark Basin, Papua New Guinea. Journal of Geophysical Research: Solid Earth, 99(B3): 4439–4455. https://doi.org/10.1029/93jb02878
Briais, A., Patriat, P., Tapponnier, P., 1993. Updated Interpretation of Magnetic Anomalies and Seafloor Spreading Stages in the South China Sea: Implications for the Tertiary Tectonics of Southeast Asia. Journal of Geophysical Research: Solid Earth, 98(B4): 6299–6328. https://doi.org/10.1029/92JB02280
Bulois, C., Pubellier, M., Chamot-Rooke, N., et al., 2018. Successive Rifting Events in Marginal Basins: The Example of the Coral Sea Region (Papua New Guinea). Tectonics, 37(1): 3–29. https://doi.org/10.1002/2017tc004783
Chang, J. H., Hsu, H. H., Liu, C. S., et al., 2017a. Seismic Sequence Stratigraphic Analysis of the Carbonate Platform, North Offshore Taiping Island, Dangerous Grounds, South China Sea. Tectonophysics, 702: 70–81. https://doi.org/10.1016/j.tecto.2015.12.010
Chang, J. H., Hsieh, H. H., Mirza, A., et al., 2017b. Crustal Structure North of the Taiping Island (Itu Aba Island), Southern Margin of the South China Sea. Journal of Asian Earth Sciences, 142: 119–133. https://doi.org/10.1016/j.jseaes.2016.08.005
Clift, P., Lee, G. H., Anh Duc, N., et al., 2008. Seismic Reflection Evidence for a Dangerous Grounds Miniplate: No Extrusion Origin for the South China Sea. Tectonics, 27(3): TC3008. https://doi.org/10.1029/2007tc002216
Cullen, A. B., 2010. Transverse Segmentation of the Baram-Balabac Basin, NW Borneo: Refining the Model of Borneo's Tectonic Evolution. Petroleum Geoscience, 16(1): 3–29. https://doi.org/10.1144/1354-079309-828
Daesslé, L. W., Cronan, D. S., Marchig, V., et al., 2000. Hydrothermal Sedimentation Adjacent to the Propagating Valu Fa Ridge, Lau Basin, SW Pacific. Marine Geology, 162(2/3/4): 479–500. https://doi.org/10.1016/S0025-3227(99)00065-1
Ding, W. W, 2021. Continental Margin Dynamics of South China Sea: From Continental Break-up to Seafloor Spreading. Earth Science, 46(3): 790–800. https://doi.org/10.3799/dqkx.2020.303 (in Chinese with English Abstract)
Ding, W. W., Franke, D., Li, J. B., et al., 2013. Seismic Stratigraphy and Tectonic Structure from a Composite Multi-Channel Seismic Profile across the Entire Dangerous Grounds, South China Sea. Tectonophysics, 582: 162–176. https://doi.org/10.1016/j.tecto.2012.09.026
Ding, W. W., Li, J. B., Clift, P. D., et al., 2016. Spreading Dynamics and Sedimentary Process of the Southwest Sub-Basin, South China Sea: Constraints from Multi-Channel Seismic Data and IODP Expedition 349. Journal of Asian Earth Sciences, 115: 97–113. https://doi.org/10.1016/j.jseaes.2015.09.013
Ding, W. W., Li, J. B., Dong, C. Z., et al., 2014. Carbonate Platforms in the Reed Bank Area, South China Sea: Seismic Characteristics, Development and Controlling Factors. Energy Exploration & Exploitation, 32(1): 243–261. https://doi.org/10.1260/0144-5987. 32.1.243 doi: 10.1260/0144-5987.32.1.243
Ding, W. W., Sun, Z., Dadd, K., et al., 2018. Structures within the Oceanic Crust of the Central South China Sea Basin and Their Implications for Oceanic Accretionary Processes. Earth and Planetary Science Letters, 488: 115–125. https://doi.org/10.1016/j.epsl.2018.02.011
Ding, W. W., Sun, Z., Mohn, G., et al., 2020. Lateral Evolution of the Rift-to-Drift Transition in the South China Sea: Evidence from Multi-Channel Seismic Data and IODP Expeditions 367 & 368 Drilling Results. Earth and Planetary Science Letters, 531: 115932. https://doi.org/10.1016/j.epsl.2019.115932
Falvey, D. A., 1974. The Development of Continental Margins in Plate Tectonic Theory. The APPEA Journal, 14(1): 95. https://doi.org/10.1071/aj73012
Fang, P. G., Ding, W. W., Fang, Y. X., et al., 2017. Cenozoic Tectonic Subsidence in the Southern Continental Margin, South China Sea. Frontiers of Earth Science, 11(2): 427–441. https://doi.org/10.1007/s11707-016-0594-z
Franke, D., Barckhausen, U., Baristeas, N., et al., 2011. The Continent-Ocean Transition at the Southeastern Margin of the South China Sea. Marine and Petroleum Geology, 28(6): 1187–1204. https://doi.org/10.1016/j.marpetgeo.2011.01.004
Franke, D., Savva, D., Pubellier, M., et al., 2014. The Final Rifting Evolution in the South China Sea. Marine and Petroleum Geology, 58: 704–720. https://doi.org/10.1016/j.marpetgeo.2013.11.020
Galindo-Zaldívar, J., Bohoyo, F., Maldonado, A., et al., 2006. Propagating Rift during the Opening of a Small Oceanic Basin: The Protector Basin (Scotia Arc, Antarctica). Earth and Planetary Science Letters, 241(3/4): 398–412. https://doi.org/10.1016/j.epsl.2005.11.056
Gozzard, S., Kusznir, N., Franke, D., et al., 2019. South China Sea Crustal Thickness and Oceanic Lithosphere Distribution from Satellite Gravity Inversion. Petroleum Geoscience, 25(1): 112–128. https://doi.org/10.1144/petgeo2016-162
Hall, R., 2002. Cenozoic Geological and Plate Tectonic Evolution of SE Asia and the SW Pacific: Computer-Based Reconstructions, Model and Animations. Journal of Asian Earth Sciences, 20(4): 353–431. https://doi.org/10.1016/S1367-9120(01)00069-4
Hayes, D. E., Nissen, S. S., 2005. The South China Sea Margins: Implications for Rifting Contrasts. Earth and Planetary Science Letters, 237(3/4): 601–616. https://doi.org/10.1016/j.epsl.2005.06.017
Huchon, P., Nguyen, T. N. H., Chamot-Rooke, N., 2001. Propagation of Continental Break-up in the Southwestern South China Sea. Geological Society, London, Special Publications, 187(1): 31–50. https://doi.org/10.1144/gsl.sp.2001.187.01.03
Hutchison, C. S., Bergman, S. C., Swauger, D. A., et al., 2000. A Miocene Collisional Belt in North Borneo: Uplift Mechanism and Isostatic Adjustment Quantified by Thermochronology. Journal of the Geological Society, 157(4): 783–793. https://doi.org/10.1144/jgs.157.4.783
Jamaludin, S. N. F., Pubellier, M., Menier, D., 2018. Structural Restoration of Carbonate Platform in the Southern Part of Central Luconia, Malaysia. Journal of Earth Science, 29(1): 155–168. https://doi.org/10.1007/s12583-017-0812-y
Korenaga, J., Hey, R. N., 1996. Recent Dueling Propagation History at the Fastest Spreading Center, the East Pacific Rise, 26°-32°S. Journal of Geophysical Research: Solid Earth, 101(B8): 18023–18041. https://doi.org/10.1029/96jb00176
Kudrass, H. R., Wiedicke, M., Cepek, P., et al., 1986. Mesozoic and Cainozoic Rocks Dredged from the South China Sea (Reed Bank Area) and Sulu Sea and Their Significance for Plate-Tectonic Reconstructions. Marine and Petroleum Geology, 3(1): 19–30. https://doi.org/10.1016/0264-8172(86)90053-x
Kusznir, N. J., Karner, G. D., 2007. Continental Lithospheric Thinning and Breakup in Response to Upwelling Divergent Mantle Flow: Application to the Woodlark, Newfoundland and Iberia Margins. Geological Society, London, Special Publications, 282(1): 389–419. https://doi.org/10.1144/sp282.16
LaFemina, P. C., Dixon, T. H., Malservisi, R., et al., 2005. Geodetic GPS Measurements in South Iceland: Strain Accumulation and Partitioning in a Propagating Ridge System. Journal of Geophysical Research: Solid Earth, 110(B11): B11405. https://doi.org/10.1029/2005jb003675
Larsen, H. C., Mohn, G., Nirrengarten, M., et al., 2018. Rapid Transition from Continental Breakup to Igneous Oceanic Crust in the South China Sea. Nature Geoscience, 11(10): 782–789. https://doi.org/10.1038/s41561-018-0198-1
le Pourhiet, L., Chamot-Rooke, N., Delescluse, M., et al., 2018. Continental Break-up of the South China Sea Stalled by Far-Field Compression. Nature Geoscience, 11(8): 605–609. https://doi.org/10.1038/s41561-018-0178-5
Leyla, B. H., Zhang, J. X., Yang, L. L., 2018. Quantitative Analysis of Faults in Huizhou Sub-Basin, Pearl River Mouth Basin. Journal of Earth Science, 29(1): 169–181. https://doi.org/10.1007/s12583-018-0823-3
Li, C. F., Lin, J., Kulhanek, D. K., et al., 2015. South China Sea Tectonics. International Ocean Discovery Program, College Station, Texas. https://doi.org/10.14379/iodp.proc.349.2015
Li, C. F., Xu, X., Lin, J., et al., 2014. Ages and Magnetic Structures of the South China Sea Constrained by Deep Tow Magnetic Surveys and IODP Expedition 349. Geochemistry, Geophysics, Geosystems, 15(12): 4958–4983. https://doi.org/10.1002/2014GC005567
Li, J. B., Ding, W. W., Wu, Z. Y., et al., 2012. The Propagation of Seafloor Spreading in the Southwestern Subbasin, South China Sea. Chinese Science Bulletin, 57(24): 3182–3191. https://doi.org/10.1007/s11434-012-5329-2
Li, L., Clift, P. D., Nguyen, H. T., 2013. The Sedimentary, Magmatic and Tectonic Evolution of the Southwestern South China Sea Revealed by Seismic Stratigraphic Analysis. Marine Geophysical Research, 34(3/4): 341–365. https://doi.org/10.1007/s11001-013-9171-y
Li, L., Clift, P. D., Stephenson, R., et al., 2014. Non-Uniform Hyper-Extension in Advance of Seafloor Spreading on the Vietnam Continental Margin and the SW South China Sea. Basin Research, 26(1): 106–134. https://doi.org/10.1111/bre.12045
Liu, H. L., Yan, P., Zhang, B. Y., et al., 2004. Role of the Wan-Na Fault System in the Western Nansha Islands (Southern South China Sea). Journal of Asian Earth Sciences, 23(2): 221–233. https://doi.org/10.1016/S1367-9120(03)00121-4
Manighetti, I., Tapponnier, P., Courtillot, V., et al., 1997. Propagation of Rifting along the Arabia-Somalia Plate Boundary: The Gulfs of Aden and Tadjoura. Journal of Geophysical Research: Solid Earth, 102(B2): 2681–2710. https://doi.org/10.1029/96JB01185
Morley, C. K., 2016. Major Unconformities/Termination of Extension Events and Associated Surfaces in the South China Seas: Review and Implications for Tectonic Development. Journal of Asian Earth Sciences, 120: 62–86. https://doi.org/10.1016/j.jseaes.2016.01.013
Peng, X., Shen, C. B., Mei, L. F., et al., 2019. Rift-Drift Transition in the Dangerous Grounds, South China Sea. Marine Geophysical Research, 40(2): 163–183. https://doi.org/10.1007/s11001-018-9353-8
Péron-Pinvidic, G., Manatschal, G., 2009. The Final Rifting Evolution at Deep Magma-Poor Passive Margins from Iberia-Newfoundland: A New Point of View. International Journal of Earth Sciences, 98(7): 1581–1597. https://doi.org/10.1007/s00531-008-0337-9
Pichot, T., Delescluse, M., Chamot-Rooke, N., et al., 2014. Deep Crustal Structure of the Conjugate Margins of the SW South China Sea from Wide-Angle Refraction Seismic Data. Marine and Petroleum Geology, 58: 627–643. https://doi.org/10.1016/j.marpetgeo.2013.10.008
Qiu, X., Zhao, M., Ao, W., et al., 2011. OBS Survey and Crustal Structure of the SW Sub-Basin and Nansha Block, South China Sea. Chinese Journal of Geophysics, 54(12): 3117–3128. https://doi.org/10.1002/cjg2.1680 (in Chinese with English Abstract)
Reston, T. J., 2009. The Extension Discrepancy and Syn-Rift Subsidence Deficit at Rifted Margins. Petroleum Geoscience, 15(3): 217–237. https://doi.org/10.1144/1354-079309-845
Roberts, A. M., Kusznir, N. J., Corfield, R. I., et al., 2013. Integrated Tectonic Basin Modelling as an Aid to Understanding Deep-Water Rifted Continental Margin Structure and Location. Petroleum Geoscience, 19(1): 65–88. https://doi.org/10.1144/petgeo2011-046
Ruan, A. G., Niu, X. W., Qiu, X. L., et al., 2011. A Wide Angle Ocean Bottom Seismometer Profile across Liyue Bank, the Southern Margin of South China Sea. Chinese Journal of Geophysics, 54(12): 3139–3149 (in Chinese with English Abstract)
Savva, D., Pubellier, M., Franke, D., et al., 2014. Different Expressions of Rifting on the South China Sea Margins. Marine and Petroleum Geology, 58: 579–598. https://doi.org/10.1016/j.marpetgeo.2014.05.023
Schlüter, H. U., Hinz, K., Block, M., 1996. Tectono-Stratigraphic Terranes and Detachment Faulting of the South China Sea and Sulu Sea. Marine Geology, 130(1/2): 39–78. https://doi.org/10.1016/0025-3227(95)00137-9
Shi, H. S., Li, C. F., 2012. Mesozoic and Early Cenozoic Tectonic Convergence-to-Rifting Transition Prior to Opening of the South China Sea. International Geology Review, 54(15): 1801–1828. https://doi.org/10.1080/00206814.2012.677136
Shipboard Scientific Party, 2000. Leg 184 Summary: Exploring the Asian Monsoon through Drilling in the South China Sea. In: Wang, P., Prell, W., Blum, P., eds., Proc. ODP, Initial results. IODP, College Station, Texas. 1–77
Song, T. R., Li, C. F., 2015. Rifting to Drifting Transition of the Southwest Subbasin of the South China Sea. Marine Geophysical Research, 36(2/3): 167–185. https://doi.org/10.1007/s11001-015-9253-0
Steckler, M. S., Watts, A. B., 1978. Subsidence of the Atlantic-Type Continental Margin off New York. Earth and Planetary Science Letters, 41(1): 1–13. https://doi.org/10.1016/0012-821x(78)90036-5
Steuer, S., Franke, D., Meresse, F., et al., 2013. Time Constraints on the Evolution of Southern Palawan Island, Philippines from Onshore and Offshore Correlation of Miocene Limestones. Journal of Asian Earth Sciences, 76: 412–427. https://doi.org/10.1016/j.jseaes.2013.01.007
Steuer, S., Franke, D., Meresse, F., et al., 2014. Oligocene–Miocene Carbonates and Their Role for Constraining the Rifting and Collision History of the Dangerous Grounds, South China Sea. Marine and Petroleum Geology, 58: 644–657. https://doi.org/10.1016/j.marpetgeo.2013.12.010
Sun, Z., Ding, W. W., Zhao, X. X., et al., 2019. The Latest Spreading Periods of the South China Sea: New Constraints from Macrostructure Analysis of IODP Expedition 349 Cores and Geophysical Data. Journal of Geophysical Research: Solid Earth, 124(10): 9980–9998. https://doi.org/10.1029/2019jb017584
Sun, Z., Jian, Z., Stock, J. M., et al, 2018. South China Sea Rifted Margin. International Ocean Discovery Program, College Station, Texas
Sun, Z., Li, F. C., Lin, J., et al., 2021. The Rifting-Breakup Process of the Passive Continental Margin and Its Relationship with Magmatism: The Attribution of the South China Sea. Earth Science, 46(3): 770–789. https://doi.org/10.3799/dqkx.2020.371 (in Chinese with English Abstract)
Sun, Z., Zhao, Z. X., Li, J. B., et al., 2011. Tectonic Analysis of the Breakup and Collision Unconformities in the Nansha. Chinese Journal of Geophysics, 54(12): 3196–3209. https://doi.org/10.3969/j.issn.0001-5733.2011.12.019 (in Chinese with English Abstract)
Sun, Z., Zhong, Z. H., Keep, M., et al., 2009. 3D Analogue Modeling of the South China Sea: A Discussion on Breakup Pattern. Journal of Asian Earth Sciences, 34(4): 544–556. https://doi.org/10.1016/j.jseaes.2008.09.002
Sutra, E., Manatschal, G., Mohn, G., et al., 2013. Quantification and Restoration of Extensional Deformation along the Western Iberia and Newfoundland Rifted Margins. Geochemistry, Geophysics, Geosystems, 14(8): 2575–2597. https://doi.org/10.1002/ggge.20135
Taylor, B., Hayes, D., 1983. Origin and History of the South China Sea Basin. Washington DC American Geophysical Union Geophysical Monograph Series, 27: 23–56. https://doi.org/10.1029/gm027p0023
Taylor, B., Zellmer, K., Martinez, F., et al., 1996. Sea-Floor Spreading in the Lau Back-Arc Basin. Earth and Planetary Science Letters, 144(1/2): 35–40. https://doi.org/10.1016/0012-821X(96)00148-3
Tong, D. J., Ren, J. Y., Liao, Y. T., et al., 2019. Cenozoic Tectonic Events and Their Implications for Constraining the Structure and Stratigraphic Styles from Rifting to Collision at the Southeastern Margin of the South China Sea. Marine Geophysical Research, 40(2): 145–161. https://doi.org/10.1007/s11001-018-09376-0
Wei, D., Jia, L. Q., 2011. Seismic Stratigraphy, Tectonic Structure and Extension Factors across the Southern Margin of the South China Sea: Evidence from Two Regional Multi-Channel Seismic Profiles. Chinese Journal of Geophysics, 54 (12): 3038–3056 (in Chinese with English Abstract)
Xie, H., Zhou, D., Li, Y. P., et al., 2014. Cenozoic Tectonic Subsidence in Deepwater Sags in the Pearl River Mouth Basin, Northern South China Sea. Tectonophysics, 615/616: 182–198. https://doi.org/10.1016/j.tecto.2014.01.010
Xiong, L. J., Li, S. Z., Suo, Y. H., et al., 2012. Cenozoic Basin-Controlling Faults and Their Bearing on Basin Groups Formation in the Southern South China Sea. Marine Geology & Quaternary Geology, 32(6): 113–127. https://doi.org/10.3724/sp.j.1140.2012.06113 (in Chinese with English Abstract)
Yan, P., Liu, H. L., 2004. Tectonic-Stratigraphic Division and Blind Fold Structures in Nansha Waters, South China Sea. Journal of Asian Earth Sciences, 24(3): 337–348. https://doi.org/10.1016/j.jseaes.2003.12.005
Yan, P., Zhou, D., Liu, Z. S., 2001. A Crustal Structure Profile across the Northern Continental Margin of the South China Sea. Tectonophysics, 338(1): 1–21. https://doi.org/10.1016/S0040-1951(01)00062-2
Yao, Y. J., Liu, H. L., Yang, C. P., et al., 2012. Characteristics and Evolution of Cenozoic Sediments in the Liyue Basin, SE South China Sea. Journal of Asian Earth Sciences, 60: 114–129. https://doi.org/10.1016/j.jseaes.2012.08.003
Yumul, G. P. Jr., Dimalanta, C. B., Tamayo, R. A. Jr., et al., 2003. Collision, Subduction and Accretion Events in the Philippines: a Synthesis. Island Arc, 12(2): 77–91. https://doi.org/10.1046/j.1440-1738.2003.00382.x
Zhang, Y. X., Xia, S. H., Cao, J. H., et al., 2020. Extensional Tectonics and Post-Rift Magmatism in the Southern South China Sea: New Constraints from Multi-Channel Seismic Data. Marine and Petroleum Geology, 117: 104396. https://doi.org/10.1016/j.marpetgeo. 2020.104396 doi: 10.1016/j.marpetgeo.2020.104396
Zhao, Y. H., Ren, J. Y., Pang, X., et al., 2018. Structural Style, Formation of Low Angle Normal Fault and Its Controls on the Evolution of Baiyun Rift, Northern Margin of the South China Sea. Marine and Petroleum Geology, 89: 687–700. https://doi.org/10.1016/j.marpetgeo.2017.11.001
Zhao, Z. X., Sun, Z., Chen, G. H., et al., 2011. Cenozoic Structural Characteristics and Subsidence Evolution in Nansha. Earth Science, 36(5): 815–822. https://doi.org/10.3799/dqkx.2011.084 (in Chinese with English Abstract)
Zheng, Q. L., Li, S. Z., Suo, Y. H., et al., 2016. Structures around the Tinjar-West Baram Line in Northern Kalimantan and Seafloor Spreading in the Proto-South China Sea. Geological Journal, 51: 513–523. https://doi.org/10.1002/gj.2806
Zhou, D., Wu, S. M., Chen, H. Z., 2005. Some Remarks on the Tectonic Evolution of Nansha and Its Adjacent Regions in Southern South China Sea. Geotectonica et Metallogenia, 29(3): 339–345. https://doi.org/10.16539/j.ddgzyckx.2005.03.008 (in Chinese with English Abstract)
Zhou, Z. C., Mei, L. F., Shi, H. S., et al., 2019. Evolution of Low-Angle Normal Faults in the Enping Sag, the Northern South China Sea: Lateral Growth and Vertical Rotation. Journal of Earth Science, 30(6): 1326–1340. https://doi.org/10.1007/s12583-019-0899-4
Zhu, J. J., Qiu, X. L., Kopp, H., et al., 2012. Shallow Anatomy of a Continent-Ocean Transition Zone in the Northern South China Sea from Multichannel Seismic Data. Tectonophysics, 554/555/556/557: 18–29. https://doi.org/10.1016/j.tecto.2012.05.027
Shihao Hao, Lianfu Mei, César R. Ranero, et al. 3D Crustal Architecture and Along‐Strike Variation in the Mid‐Northern South China Sea Rifted Margin. Journal of Geophysical Research: Solid Earth, 2024, 129(1) doi:10.1029/2023JB026876
2.
Qing He, Zongdong Pan, Shaoping Lu, et al. Origin of a high-velocity layer: Insights from seismic reflection imaging (South China Sea). Marine and Petroleum Geology, 2024, 163: 106798. doi:10.1016/j.marpetgeo.2024.106798
3.
Wei Duan, Cheng-Fei Luo, Lin Shi, et al. Formation Mechanism and Petroleum Geological Significance of (Ferro) Dolomite Veins from Fractured Reservoirs in Granite Buried Hills: Insights from Qiongdongnan Basin, South China Sea. Journal of Marine Science and Engineering, 2024, 12(11): 1970. doi:10.3390/jmse12111970
4.
Wenbin Jiang, Heng Zhang, Fuyuan Li, et al. Imaging the shallow velocity structure of the slow‐spreading ridge of the South China Sea with downward continued multichannel seismic data. Geophysical Prospecting, 2024. doi:10.1111/1365-2478.13490
5.
Yunliu Yang, Xinong Xie, Yunlong He, et al. Opening and Closure of the Sulu Sea: Revealed by Its Peripheral Subduction and Collision Processes. Journal of Marine Science and Engineering, 2024, 12(8): 1456. doi:10.3390/jmse12081456
6.
Feng Wu, Xinong Xie, Wen Yan, et al. Quaternary evolution of the Meiji Atoll (Mischief Reef) in the southern South China Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 2024, 634: 111912. doi:10.1016/j.palaeo.2023.111912
7.
Chufeng Guo, Yong Tang, Yinxia Fang, et al. Magmatism along the Nansha Trough on the southern continental margin of the South China Sea: Recent evidence from along-strike seismic profile. Marine Geology, 2024, 475: 107344. doi:10.1016/j.margeo.2024.107344
8.
Ismailalwali Babikir, Mohamed Elsaadany. Machine learning-based seismic characterization of deepwater turbidites in the Dangerous Grounds area, Northwest Sabah, offshore Malaysia. Acta Geophysica, 2024. doi:10.1007/s11600-024-01396-2
9.
Entao Liu, Wei Luo, Detian Yan, et al. Depositional evolution in response to long-term marine transgression in the northern South China Sea. Frontiers in Marine Science, 2023, 10 doi:10.3389/fmars.2023.1329338
10.
Caiwei Fan, Kongyou Wu, Jun Li. A New Methodology Combining Geophysical Calculations and Geological Analysis to Identify and Characterize Carrier Systems for Vertical Hydrocarbon Migration in the Central Diapir Zone of the Yinggehai Basin, China. Energies, 2023, 16(4): 1774. doi:10.3390/en16041774
11.
Entao Liu, Yong Deng, Xudong Lin, et al. Cenozoic Depositional Evolution and Stratal Patterns in the Western Pearl River Mouth Basin, South China Sea: Implications for Hydrocarbon Exploration. Energies, 2022, 15(21): 8050. doi:10.3390/en15218050
Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
Yuanyuan Wang, Yanghui Zhao, Weiwei Ding, Penggao Fang, Jiabiao Li. Cenozoic Propagated Rifting in the Dangerous Grounds in Response to the Episodic Seafloor Spreading of the South China Sea. Journal of Earth Science, 2022, 33(4): 1031-1046. doi: 10.1007/s12583-020-1064-9
Figure 1. Morphological features and major tectonic units in the Dangerous Grounds, southern continental margin of the South China Sea. Three seismic profiles, L1 (Ding et al., 2014) across Reed Bank area, L2 (Ding et al., 2013) across the Center-Dangerous Grounds and L3 (Sun et al., 2011) across the West-Dangerous Grounds have been selected to demonstrate the structural changes along the southern margin. The yellow solid line shows the location of previous Ocean bottom seismometers profile OBS-PR2 (Pichot et al., 2014). Drilling holes are after ODP Shipboard Scientific Party (2000) and Schlüter et al. (1996).
Figure 2. Stratigraphy, lithology, eustatic sea level curve and major tectonic events of the study area (summarized from Peng et al., 2019; Ding et al., 2016; Savva et al., 2014; Franke et al., 2011; Yan and Liu, 2004). DG. Dangerous Grounds; BRU-E. breakup unconformity of the East Subbasin; BRU-SW. breakup unconformity of the Southwest Subbasin; MMU. Middle Miocene unconformity.
Figure 3. Seismic profile L1 across the Reed Bank (a), geological interpretation of L1 modified from Ding et al. (2014) (b), and the depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~23.8 Ma; T40. ~16 Ma; T0. seabed. The dash line marks the area for tectonic subsidence modelling.
Figure 4. Seismic profile L2 across the Center-Dangerous Grounds (a), the geological interpretation of seismic profile L2 modified from Ding et al. (2013) (b), and its depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~21 Ma; T40. ~16 Ma; T0. seabed. The dash line marks the continental-ocean transition (COT) area.
Figure 5. Seismic profile L3 across the West-Dangerous Grounds (a), geological interpretation of seismic profile L3 modified from Sun et al. (2011) (b) and its depth-converted profile (c). TWT. Two way time; Tg. basement of Cenozoic (~65 Ma); T70. ~32 Ma; T60. ~18.5 Ma; T40. ~16 Ma; T0. seabed.
Figure 6. Structural evolution of seismic profiles L1, L2 and L3. During continental rifting, faults were widely developed in all three profiles. Syn-rift sequence (marked by blue) in Reed Bank with the largest thickness suggests the basin subsidence and deposition were focused on the northeastern Dangerous Grounds area. After the formation of the seafloor spreading sequence (marked by green and orange), the tectonics related to the extension and subsidence apparently migrated and focused on L3, southwest of the southern continental margin.
Figure 7. An overview of the back-stripping tectonic subsidence curves. (a) The tectonic subsidence rate of Reed Bank area (L1), Center-Dangerous Grounds (L2) and West-Dangerous Grounds (L3). (b) The average subsidence rate curves in the Dangerous Grounds. (c) Ten equally-distributed artificial wells are extracted from profiles L1, L2 and L3, respectively to show the tectonic subsidence change.
Figure 8. Extension ratio (bars) and extension rate (red lines marked with numbers, unit: km/Ma) of Reed Bank (L1), Center-Dangerous Grounds (L2) and West-Dangerous Grounds (L3) in each structural evolution period. Extension ratio shows an apparent migration from NE (L1) to SW (L3) along the southern margin of the Southwest Subbasin. Extension rate increased in both L2 and L3 while decreased in L1 from the syn-rift to E-Drift stage. From E-Drift to SW-Drift stage, an accelerated extension occurred in L3 while the extension in L1 and L2 slow down. DG. Dangerous Grounds.
Figure 9. Tectonic subsidence amount since the Cenozoic and the crustal thinning factor (γ) in seismic profile L1 (a), L2 (b) and L3 (c). The crustal extension along each profile shows good agreement with the tectonic subsidence.
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