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Dynamic process of episodic rifting in continental marginal basin and tectonic events since 10 Ma in South China Sea
... The tectonic subsidence in the Zhongsha Trough was 0.15 m/ky in this phase for the sediment depositing all over the study area. This rapid subsidence was universal in the north margin of the South China Sea [10,31,34,48]. The inherited stretched and thinned lithosphere and crust were considered to be responsible for the rapid subsidence and the crust-stretching factors of the Qiongdongnan Basin. ...
... Theoretically, the tectonic subsidence caused by the heat loss of the deep mantle should be relatively slow. However, the rate was different from the recovery of tectonic subsidence in the study area, and this anomalous subsidence pervasively existed on the north margin of the Qiongdongnan Basin [9,10,48]. In former research, the interpretation usually focused on the rapid subsidence occurring in the Late Miocene, while little attention was given to its change during the Miocene. ...
... Theoretically, when the nature of the Red River Fault Zone changed from sinistral to dextral movement, the extrusive component could have disappeared and shifted to an extensive component according to stress-field analysis, as shown in Figure 10B, which would lead to regional stress to absolute release and further cause rapid tectonic subsidence. Indeed, this rapid tectonic subsidence took place and was accompanied by diapirs and high rate of sedimentation in the Yinggehai Basin, the Beibuwan Basin, and the northern Qiongdongnan Basin [8,17,38,48,53,54]. ...
The evolution and mechanisms of tectonic subsidence in the Xisha area are poorly investigated, especially the spatiotemporal distribution features and reasons for the variations in tectonic subsidence. In this study, multi-channel seismic data and stratigraphic and lithologic features of wells are used to examine tectonic subsidence in the Xisha area from the Paleogene to Quaternary. The largest tectonic subsidence in the Xisha area is located in the Changchang Depression, with a maximum subsidence of 5.4 km, while the smallest tectonic subsidence is located on the Guangle Uplift and Xisha Uplift, which are close to 1.0 km and 1.5 km, respectively. Two rapid tectonic subsidence phases were mainly in the Oligocene, and from Middle to Late Miocene, with maximum subsidence rates of 0.45 m/ky and 0.32 m/ky, respectively. Five phases for the tectonic subsidence are proposed since the Paleogene based on our data. (1) The slow subsidence phase during the Eocene (53.5–32 Ma) was due to the transchronicity of the basement in the pro-rifted stage. (2) The rapid subsidence phase was common in the south and north margins of Qiongdongnan Basin, because of the faults triggered by the inherited stretched and thinned of crust in the Oligocene from 32 to 23.3 Ma. (3) The interim phase followed the rapid subsidence phase was in the Early Miocene (23.3–15.5 Ma) and marked the end of the rifted stage. (4) The accelerated rise phase started from the Middle Miocene (15.5 Ma) to the Late Miocene (5.5 Ma), and the reversal of the Red River Fault Zone may be tied to the acceleration of the tectonic subsidence. (5) The transitional phase started in the Pliocene (5.5 Ma) and lasts to the present. As the Red River Fault Zone changed from sinistral to dextral movement, the stress field of the study area has changed. Our results are helpful to better understand the spatiotemporal coupling relationship between tectonic subsidence and regional geological evolution in the Xisha area, South China Sea.
... Toward Vietnam and Hainan Island, the basin overlaps with fault terraces or gentle slope deposition (Sun et al., 1995). In the Yinggehai Basin, the maximum thick strata (8000e10,000 m) probably developed in the basin's depocenter since the Neogene (Li et al., 1998). The evolution of the Yinggehai Basin which is an extensional basin is influenced by the mantle upheaval as well as dextral strike slip (Li et al., 1998). ...
... In the Yinggehai Basin, the maximum thick strata (8000e10,000 m) probably developed in the basin's depocenter since the Neogene (Li et al., 1998). The evolution of the Yinggehai Basin which is an extensional basin is influenced by the mantle upheaval as well as dextral strike slip (Li et al., 1998). The basin experienced three stages of evolution namely early rift extension, broad downwarping during thermal subsidence, and final repeated extension (Zhang and Hao, 1997;Gong et al., 2011Gong et al., , 2014Gong et al., , 2015. ...
... In the study area, the muddy sediments were quickly deposited due to the high sedimentation rates in Yinggehai Basin since the Neogene (Shan and Dong, 1996;Li et al., 1998;Xie et al., 2004). DF1-1 gas field is located in the transitional belt between lower shore face and offshore, where it is far from sediment provenance as discussed above. ...
... Located in the northwest margin of the SCS, the Qiongdongnan basin has been proved to host substantial post-rift igneous edifices. The post-rift magmatism has been directly evidenced by the volcanic rocks and mantle sourced CO 2 that were sampled in the post-rift sequence in different locations of the basin (Li et al., 1998;He and Liu, 2004;Guo et al., 2017). Interpretation from 2D seismic data (Mao et al., 2015;Zhao et al., 2016b;Guo et al., 2017) and in-situ measured heat flow (Shi et al., 2017) indicate that the distribution of post-rift magmatic bodies is preferentially confined to the eastern area of the Qiongdongnan basin, with very few occurrences in the west. ...
... Based on the chronology outlined by CNOOC (Xie et al., 2012) and the stratigraphic contact between igneous bodies and surrounding strata, it is found that massive magmatism began to occur since the end of early Miocene in the Qiongdongnan basin (Zhang et al., 2016;Zhao et al., 2016b), which also corresponds to the cessation of seafloor spreading of the SCS (Taylor and Hayes, 1983;Li et al., 2014). In addition, the middle Miocene magmatism in the Lingshui sag also coincides with Neogene long-term deep thermal upwelling (Shi et al., 2017), continuous fault activity (Li et al., 2016), and the stage of relatively slow post-rift subsidence of the northwestern margin of the SCS, especially east of the central depression of the Qiongdongnan basin (Li et al., 1998;Xie et al., 2006;Zhao et al., 2013). We conjecture that the magmatism began to be active in a broader zone after the seafloor spreading ceased in the SCS (ca. ...
... Deng et al. (1998) proposed that the Cenozoic magmatism and the opening of the SCS might be linked with a mantle plume. Li et al. (1998) further suggested that the mantle plume was located in the southern Indochina block, based on the characteristics of low velocity mantle anomalies revealed by seismic tomography. Seismic velocities from tomography (Lebedev and Nolet, 2003;Montelli et al., 2004;Lei et al., 2009;Xia et al., 2016) further suggested the existence of the Hainan Plume. ...
... Can a mantle plume be responsible for the post-spreading magmatism? If a mantle plume, e.g., the suggested Hainan plume, existed and triggered the opening of the SCS (Deng et al., 1998;Li et al., 1998;Lebedev and Nolet, 2003;Lei et al., 2009;Xia et al., 2016), and postspreading volcanism, it should have caused bursts of extensive and voluminous magmatism over a focused period of time (White and McKenzie, 1989;Menzies et al., 2002). However, there is no evidence of large igneous eruptions or magma intrusions within the Yinggehai Basin near the Hainan hotspot and along the SCS margins. ...
Timing, distribution, and intensity of magmatism are critical to understanding deep lithospheric processes in the opening of the South China Sea (SCS). Based primarily on multichannel seismic reflection data, and aided with gravity and magnetic anomalies, we identify various igneous features, such as sills, stocks, volcanic edifices, and volcanoes, which are often characterized by high positive seismic amplitudes, and/or by chaotic or blank reflections beneath them because of their seismic shielding effect. We estimate the timing of igneous activities and analyze their areal distribution in the SCS region based on seismic stratigraphy. We confirm that most igneous emplacements in the SCS margins occurred after the cessation of seafloor spreading, and are sparse and volumetrically small during the rifting and seafloor spreading phases, supporting magma-poor margins prior to the breakup of the continental lithosphere. By contrast, post-spreading magmatic activities are widespread in the continental slope areas and in the central SCS basin, and are most likely triggered by extension in relation to cooling and subsidence of the oceanic and attenuated continental lithosphere, which could accumulate a total thermal contractional displacement up to 24 km.
... Located to the southeast of Hainan Island, the Qiongdongnan Basin covers an area of 45,000 km 2 . It is a Cenozoic rifted continental margin oil and gas-bearing basin with a basement composed of pre-Paleogene strata (Li et al., 1998;Wang et al., 2004). The basin is structurally characterized by "north-south zonation". ...
Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary system analysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems.The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins.
... The SCS is located in the junction of the Pacific Plate, the Eurasian Plate and the Indo-Australian Plate. It is one of the largest marginal seas in the western Pacific (LaFond, 1966;Yao et al., 2005) Li et al., 1998;Zhu et al., 2016;Zou et al., 1995) (Figure 1a). The evolution and structural characteristics of the SCS are complex with numerous geological features and it is the best natural geological laboratory on Earth to many geologists (Briais et al., 1993;Hall, 1996;J. ...
The high‐velocity layer in the lower crust is widely distributed in the northern continental margin of the South China Sea. A detailed anatomy of the high‐velocity layer is crucial for understanding the continental rifting and crustal thinning. Based on three seismic reflection profiles across the Pearl River Mouth Basin (PRMB) and the global free‐air gravity anomaly data in this study, by the gravity modelling we construct the crustal structure along three seismic reflection profiles across the depression and uplift zones. The free‐air gravity anomaly data within the uplift and depression zones indicates the distinct zonation, and the high and low values of free‐air gravity anomalies in the basin show the northeastward trend. Based on the gravity modelling along the three seismic profiles, the crustal thickness is of 12–23 km beneath the basin and thickness of the crust is gradually thinning from the continental shelf to the continental slope. The high‐velocity layer extends eastward to the Dongsha Uplift and terminates westward beneath the Baiyun Sag. The average thickness of the high‐velocity layer is 4–6 km and the maximum thickness is about 8 km at the Dongsha Uplift. The thickness variation of the high‐velocity layer suggests the continuous distribution of mantle underplating and intense magma activity. According to the isolated distribution and the continuous distribution of the high‐velocity layer found by previous studies in the northern South China Sea, we use gravity modelling to test which models of the high‐velocity layer within the PRMB are reasonable. According to testing models and preferred models of the crustal structure by gravity modelling, we propose that the continuous distribution pattern of the high‐velocity layer is the best model to interpret the crustal thinning characteristics and the gravity anomaly responses of the high‐velocity layer in the basin. We propose that the high‐velocity layer in the Pearl River Mouth Basin was formed by the long‐term underplating of the high‐temperature melted mantle.
... A great number of postrift buried volcanic mounds and intrusive complexes emplaced in the sediments were identified by seismic reflection mapping and borehole data (Savva et al., 2013;Zhao et al., 2016a;Vu et al., 2017;Wang et al., 2019). These volcanoes are composed of tholeiite basalt, pyroclastic rock, and tuff, according to field outcrops and boreholes (Hoang and Flower, 1998;Li et al., 1998;Guo et al., 2017). ...
possible to investigate the size, age, and geographical distribution of the buried volcanoes from multi-beam, single-, and multi-channel seismic data collected beneath the South China Sea (SCS) Xisha massif, which we argue is a continental ribbon. These data made it evident that the Middle Miocene volcanoes frequently generated massive volcanic fields that erupted along the rift fault zones, in contrast to the Early Miocene volcanoes, which typically built clusters of small-volume volcanic cones in the half-graben. Details include the presence of numerous volcanoes above and to the side of the dome-shaped main edifice that constitutes the middle Miocene volcanic field. Intrusive sills beneath volcanoes are isolated and have a dispersed distribution pattern at different levels, whereas dykes beneath volcanoes are numerous and have vertical zones of disruption (VZD) that connect to underlying faults or extend through the sediments to the crust. The relationship between the volcanoes and intrusions suggests that shallow igneous plumbing systems within the Xisha massif are most likely dyke domains. The Xisha massif has favorable conditions, including a relatively thin sedimentary sequence over a slightly extended continental crust (2028 km) that might provide enough magma pressure for an igneous plumbing system that is primarily fed by dykes. Additionally, rifted faults in the upper crust and possibly sub-vertical foliations in the basement rock mass were thought to be viable routes for magma transport vertically. We emphasize the importance of crustal structure on the continental ribbon in controlling igneous plumbing styles and the distribution of post-rift volcanic systems along magma-poor continental margins, including crustal thickness, pre-existing faults, heterogeneous basement, and sediments.
... Ma for the augite peridotite in Gaojianshi Island, which is the only volcanic island in the Xisha Islands. The K -Ar dating of 115 m-thick tholeiitic basalts encountered in the Lingshui Depression of the QDNB indicated <10 Ma (Li et al., 1998). Seismic study of the QDNB also showed strong magmatic activity in the Pliocene (~5.5 Ma) from the characteristics of the stratigraphic uplift and unconformity interface . ...
... The Miocene in Yinggehai Basin has complex provenance systems, with sediment sources from western Hainan Island, Red River in the northwest, and Blue River F I G U R E 2 Schematic map summarizing the depositional evolution, sequence stratigraphic classification, tectonic evolution stage and sea level change of the Miocene in eastern slope of Yinggehai Basin (stratigraphic divisions are mainly from Xie et al., 2012; the tectonic evolution stage mainly from Li et al., 1998 andSun et al., 2007). in the west (Cao et al., 2015;Wang et al., 2015). The provenance of the Meishan and Huangliu Formation in the study area mainly belongs to the western Hainan Island , which can be subdivided into distal source in the northern and proximal source in the northeastern of Hainan Island . ...
Submarine channels act as the main conduits for the transport of sediment to deep-water basins by sediment gravity flows which possess enormous economic and geological significance worldwide. In this context, the interplay between fault-related deformation and the initiation and development of the channels is least understood. This paper presents the identification, formation and evolution of the Miocene slope-parallel channel by employing 3D seismic reflection, wireline-log and core data in the eastern slope of Yinggehai Basin, South China Sea. Based on the lengths and plan-view shapes, a total of three different types of fault-associated slope-parallel depressions have been identified. The depressions were formed in the fault zone and controlled by the reactivation of the underlying older faults. Among them, Type-1 depressions are short (> 20 km) oval or circle shaped possessing only one depocenter. Type-2 depressions are elongated (25-70 km), and usually have multiple depocenters. Type-3 depressions, which are usually connected by slope-perpendicular channels in the head and middle, are longer (< 190 km) and connect shallow and deep-water basins. The analysis of morphology, erosivity and material transport shows that Type-3 depressions are fully-fledged channels. Type-1 and Type-2 depressions are channel precursors representing the initial stage of channel evolution. With this motive, a model for the initiation and evolution of slope-parallel submarine channels controlled by strike-slip-extensional faults is presented. Unlike the previous investigations which suggest that erosion takes place at the inception of submarine channel formation, the fault-controlled slope-parallel channel is mainly controlled by faulting and has no initial erosive base and does not develop levees. The depressions are extended and elongated by fault growth. It is differed that the slope-parallel depression connected with large-scale slope-perpendicular channels transporting sediments into the depression via erosive turbidity currentsthat it evolved into a channel-levee system. This study is of global importance for understanding submarine channel generation and evolution since fault-controlled slope-parallel channels have been found in tectonic active basins worldwide.
... Deng JF et al. (1992) considered that three plumes under the East Asian continent led to the formation of the SCS, the Japan Sea, and the Okhotsk Sea, and large areas of Cenozoic rift basalts formed in the three marginal seas and on the continents to the west of these seas. Based on studies conducted on the tectonic-sedimentary filling, thermal structure, and deep background of the BBGB, the YGHB, the QDNB, and the PRMB since the Tertiary, Li ST et al. (1998) suggested that the SCS plume and lateral mantle flow are the most reasonable factors in explaining the formation and evolution of the SCS and its marginal basins in the future. ...
... Even though no boreholes have directly encountered these magmatic intrusions, the dating of magmatic rocks collected in adjacent areas indicates that the ages of the magmatic activity in the QDNB are very young. The dating of a 115-m-thick tholeiitic basalt encountered in the Lingshui Depression indicates~10 Ma (Li et al., 1998), and the dating of basalt on Gaojianshi Island (see Figure 1b for location) is 1.57-2.05 Ma (Zou, 1993). ...
The Qiongdongnan Basin (QDNB) is a rift basin located in the extension direction of the oceanic ridge of the Northwest Subbasin of the South China Sea. This basin is surrounded by Late Cenozoic Ocean Island Basalts (OIBs) magmatism associated with the putative Hainan mantle plume. However, how the Hainan mantle plume has affected the QDNB has not been studied in detail. To reveal the crustal structure of the QDNB and the possible influence of the Hainan mantle plume, we conducted a wide-angle seismic exploration from Hainan Island across the QDNB to the Xisha Block, and obtained the crustal structure by travel-time tomography. The results show that the crustal stretching factors of the Northern and Southern Rises of the QDNB are estimated to be 1.3–2.0, indicating slight or moderate crustal thinning. Whereas, the crustal stretching factor in the Central Depression of the QDNB is estimated to be more than 3.0, which means that the crust has been hyperextended. Controlled by two detachment faults (F2 and F11), the upper and lower crust show brittle and ductile thinning, respectively. Three anomalous low-velocity conduits penetrating the crystalline crust are developed in the Songnan Uplift and the Southern Rise of the QDNB. Their P-wave velocities are 5.5–6.0 km s−1, which are significantly lower than those of the surrounding crust (6.0–6.8 km s−1). The Late Cenozoic magmatic intrusions (e.g., sills and dikes) and hydrothermal activities can be observed in the sedimentary strata above these low-velocity conduits. We interpret that the low-velocity conduits might be the crustal magmatic footprints of the Hainan mantle plume, due to the correlated distributions of OIB-type magmatism, the magmatic intrusion patterns, the deep structure of the Hainan mantle plume and the high heat flow of 95 mW m−2. Thus, we propose that the crustal structure of the QDNB is the product of crustal hyperextension in the rifting stage and subsequently affected by the Hainan mantle plume magmatism. This study provides a typical case for understanding the influence of a mantle plume on the continental crust with pre-existing rift structures.
... However, post-rifting magmatism widely occurred in the northern SCS margin (e.g., Yan et al., 2006 ;Zhao et al., 2014 ;Deng et al., 2018 ;Fan et al., 2017 ;Li et al., 2019 ;Sun et al., 2020b ) and ocean basin (e.g., Li et al., 2014 ;Zhao et al., 2018 ;Larsen et al., 2018 ). Magmatism has also reported in the QDNB, which is proven by extrusive structures observed on the seismic data and mantle sourced CO 2 sampled in the post-rifting strata ( Li et al., 1998 ;He and Liu, 2004 ;Ying et al., 2012 ;Mao et al., 2015 ;Zhao et al., 2016 ;Guo et al., 2017 ;Wang et al., 2019 ). These magmatism may be related to the Hainan Plume ( Zhang et al., 2016 ), the detachment faults ( Lei and Ren, 2016 ) and/or the dyke and polygonal fault system . ...
Sills and hydrothermal vents are commonly observed in sedimentary basins. However, not all sills could generate overlying hydrothermal vents, and whether a sill generates a hydrothermal vent or not is still poorly constrained. In this study, a large number of sills and hydrothermal vents are observed, using high-resolution reflection seismic data in the Qiongdongnan Basin of northern South China Sea. These sills are characterized by saucer or linear shapes and present as isolated sills or sill swarms, roughly being larger with buried depth increase. More importantly, the hydrothermal vents are mainly related to the underlying sills intruding into the shallow strata (buried depth <1.4 km), which suggests that magma intrusion depth (from paleo-seabed to the tip of sill) plays an important role on the formation of hydrothermal vents. The duration of magmatism lasted for ∼5 Ma from ∼11.6 Ma to ∼5.7 Ma with peak occurring at ∼8.2 Ma, judging from the spans of hydrothermal vents in the sedimentary strata. This study reports the intense magmatism in the eastern Qiongdongnan Basin for the first time, which extends the distribution of post-rift magmatism in the South China Sea and benefits to explore the mysterious origin post-rift magmatism. The intense magmatism would also influence the maturity of source rock and hydrocarbon migration in such a petroliferous basin. Moreover, this study also highlights that shallow emplacement of sills is advantageous for the occurrence of hydrothermal vents due to the heating of unconsolidated/less consolidated strata by magmatic sills.
... Zhu1 depression is one of the secondary structural units in the north fault terrace, which was composed by 5 units, from east to west direction, they are the Enping sag, the Xijiang sag, the Huizhou sag, the Lufeng sag and the Hanjiang sag ( Figure 1). Existing studies show that Zhu 1 depression had experienced the development stages of rift and depression during Paleogene, and now characterized with faulted in deep and depressed in shallow, and for marine sediment in the early stage and for continental sediment in the late (Li et al., 1998) (Lüdmann and Wong, 1999) (Morley, 2002) (Zhou et al., 2002) (Sun et al., 2006) (Zhang et al., 2007) ) (Cullen et al., 2010) (Wang et al., 2011) (Dai, 2013) (Xu et al., 2014). The stratum developed the early-Middle Eocene Wen-chang group which bounded by Tg in the bottom firstly, and followed by the Late Eocene to early Oligocene En-ping group which bounded by T80 in the bottom, and sediment at last with the Late Oligocene Zhuhai group which bounded by T70 in the bottom (Cui et al., 2009). ...
... . Shortly after the cessation of seafloor spreading, widespread intraplate volcanism occurred in the SCS region, and the magmatic series of these volcanic activities gradually evolved from tholeiitic to alkalic [5,6]. The post-spreading volcanism has not only affected the SCS basin itself, but also Leiqiong Peninsula and Indochina Peninsula . ...
Shortly after the cessation of seafloor spreading, intraplate magmatism affected large areas in the South China Sea (SCS) region. The origin and geodynamic setting of the post-spreading volcanism is still in debate, for many previous studies have focused on petrogenesis and mantle source of the late Cenozoic basalts from the SCS region. In this study, we obtained in situ major element compositions (by using Electron microprobe analysis—EMPA) and trace element compositions (by using laser ablation inductively coupled plasma mass spectrometry— LA-ICP-MS) for minerals (clinopyroxenes (Cpx), plagioclases (Pl), and olivines (Ol)) hosted by late Cenozoic basaltic rocks from Thailand. The results showed that the olivines had forsterite contents between 60.12% and 84.74%. Clinopyroxene were diopside and augite, and they were enriched in light rare earth elements (LREEs) (LaN/YbN = 1.93–4.27) and depleted in large-ion lithophile elements (LILEs). Mineral compositions (mainly based on clinopyroxene) confirmed that these late Cenozoic basaltic rocks were of an intraplate affinity and were similar to contemporaneous basaltic fields in the SCS region (Southern Vietnam, Northern Hainan, and SCS seamounts). Plagioclases were predominantly labradorite, with a few andesine and bytownite, and they were enriched in LREEs and Ba, Sr, and Pb, and most of them exhibited strong positive Eu anomalies. The source lithology of Thailand basaltic rocks could be garnet pyroxenite. The mantle potential temperature beneath Thailand is in the range of 1448–1467 °C, which can be comparable to those beneath Southern Vietnam and Northern Hainan, indicating the Thailand basaltic rocks could be produced by the Hainan mantle plume. In addition, the crystallization temperature of clinopyroxenes (1145–1214 °C) and plagioclase (1067–1133 °C) and their composition characteristics indicate that the magmatic processes have a conspicuous characteristic of fast rate of magma upwelling. Thus, we proposed that the deep geodynamic setting of Thailand late Cenozoic basaltic rocks is similar to those of the whole SCS region, and Hainan mantle plume plays a significant role in the petrogenesis of these basaltic rocks.
... Characterized by frequent Cenozoic tectonic-magmatic activities, the northern continental margin developed three main suites of faults that are NE-trending (early Eocene), ENE-to EW-trending (middle Eocene-Oligocene), and NW-trending (late Miocene), respectively (Wu et al., 2001). Contrary to the largely stable passive continental margins, the northern continental margin has experienced strong tectonic-magmatic activities, and its tectonic characteristics are still not clear (Wu et al., 2001;Liang and Li, 1991;Feng and Miao, 1992;Li et al., 1998;Song et al., 1998). ...
Many marine Fe-Mn polymetallic nodules may contain high concentrations of Mn, Cu, Ni, Zn, Co and rare earth elements plus yttrium (REY). To determine the occurrence and enrichment processes of these metals in the Fe-Mn nodules, we conducted high resolution mineralogical and geochemical studies on the Fe-Mn nodules collected from the South China Sea. In-situ EPMA and LA-ICP-MS analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions.
The whole-rock mineralogical and chemical compositions of the Fe-Mn nodules indicate a hydrogenetic origin. The Mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 Å and 7 Å phyllomanganates, such as todorokite, birnessite, and buserite. Fe(-Ti) oxides/hydroxides are intergrown and essentially X-ray amorphous feroxyhyte and goethite. We recognize two main types of microlayers: Type-A layer (suboxic diagenetic precipitates) containing a high Mn/Fe ratio and high concentrations of Cu, Ni, Zn, Ba, Li and Mg, and Type-B layer (oxic hydrogenetic accretions) with low fractionation of Mn and Fe and high contents of Co, REY, Ti, Sr and Pb. Furthermore, elemental mapping indicates that the enrichments of Co and REY are mainly associated with Fe mineral phases rather than Mn ones, which are enriched in Mg, Cu, Ni, Zn, Li and Ba. Two mineralization processes and metal distributions in the individual microlayers are identified in the Fe or Mn mineral phases. The occurrence of 10 Å and 7 Å phyllomanganates in Type-A layers are commonly enriched in trace metals such as Ni, Cu, Zn, Li, Ba, and Mg, whereas the metals for the Type-B layers include Co, Ti, Pb, Sr, REY, which may be carried by the intergrowing Fe(-Ti) oxyhydroxides and vernadite. Thus, hydrogenesis and diagenesis facilitate the enrichment of Fe-Co-Ti-Sr-Pb-REY and Mn-Ni-Zn-Cu-Li-Ba-Mg, respectively, during the mineralization of the South China Sea nodules.
... In addition, with the great increase of water depth and cessation of the SCS spreading, the interpretation of anomalous sediment thickness in the depression has been explained by the domination of rapid post-rift thermal subsidence Xie, Li, Dong, & Hu, 2001;Zhu et al., 2009), and the continental shelf breaks present a diachronous north-westward recession. It is also related to the pattern of water mass circulation and deep mantle convection in or under the northern SCS margin that have been strongly influenced by the arc-continental collision of the Luzon Arc to the Eurasian continental margin since 5 Ma (Figure 1; Taylor & Hayes, 1980;Tapponnier, Peltzer, Dain, Armijo, & Cobbold, 1982;Ru & Pigott, 1986, Pigott & Ru, 1994Flower, Chung, Lo, & Lee, 1998;Li, Lin, & Zhang, 1998;Lüdmann & Wong, 1999;Lüdmann, Wong, & Wang, 2001;Hall, 2002). The recent depositional system on the northern SCS continental margin has abundant clastic sediments derived from the Pearl River and the Red River. ...
Submarine canyons are common features on the northern South China Sea (SCS) continental slope. Three main submarine canyon systems were observed by multi-beam investigation and evaluated by a pre-existing sedimentary dataset. They include the Xisha Canyon Zone, Shenhu Canyon Zone, and Taiwan Canyon Zone on the northern SCS continental slope which developed from the middle Miocene to the present-day. Previous analysis implied that an enriched oil-gas accumulation formed under this region with distinct gravity anomalies or active tectonic activity. Previous interpretation and geodynamics studies have revealed the detailed sedimentary records and the coupled tectonic-sedimentary processes. However, the timing and mechanism of formation of the canyons on the northern SCS slope are still poorly constrained and vigorously debated, especially the differences among three submarine canyons from west to east that requires allowances for a variety of conflicting datasets. Here, we adopt the high-resolution multi-beam relief map and seismic profiles from these three canyon systems to estimate if the SCS slope controlled geometric segmentation and differentiation of canyon formation mechanisms and times. For this purpose, we ascertained that these canyons were initially controlled by the NE-to NW-trending faults as a better constraint on the sediment flow direction. All the submarine canyons in the northern SCS slope extend in a range from NE-/N-S-to NW-and E-W-trending directions associated with the SCS oceanic spreading and the subsequent subduction-related deformation along the Manila Trench. Furthermore, the present-day morphology of these canyons implies a remarkable tectonic jump from west to east in the SCS continental slope and a north-westward recession of the continental slope. Apart from the neo-tectonic faults, the sea-level fluctuation, gas hydrate disas-sociation, sediment source, and transportation channel also yielded dynamic processes and preservation for the submarine canyons. We finally propose a coupling model of the sedimentary and tectonic processes and confirm the spatial and temporal evolution of mechanisms of these canyons.
... In addition, with the great increase of water depth and cessation of the SCS spreading, the interpretation of anomalous sediment thickness in the depression has been explained by the domination of rapid post-rift thermal subsidence Xie, Li, Dong, & Hu, 2001;Zhu et al., 2009), and the continental shelf breaks present a diachronous north-westward recession. It is also related to the pattern of water mass circulation and deep mantle convection in or under the northern SCS margin that have been strongly influenced by the arc-continental collision of the Luzon Arc to the Eurasian continental margin since 5 Ma (Figure 1; Taylor & Hayes, 1980;Tapponnier, Peltzer, Dain, Armijo, & Cobbold, 1982;Ru & Pigott, 1986, Pigott & Ru, 1994Flower, Chung, Lo, & Lee, 1998;Li, Lin, & Zhang, 1998;Lüdmann & Wong, 1999;Lüdmann, Wong, & Wang, 2001;Hall, 2002). The recent depositional system on the northern SCS continental margin has abundant clastic sediments derived from the Pearl River and the Red River. ...
... In addition, with the great increase of water depth and cessation of the SCS spreading, the interpretation of anomalous sediment thickness in the depression has been explained by the domination of rapid post-rift thermal subsidence Xie, Li, Dong, & Hu, 2001;Zhu et al., 2009), and the continental shelf breaks present a diachronous north-westward recession. It is also related to the pattern of water mass circulation and deep mantle convection in or under the northern SCS margin that have been strongly influenced by the arc-continental collision of the Luzon Arc to the Eurasian continental margin since 5 Ma (Figure 1; Taylor & Hayes, 1980;Tapponnier, Peltzer, Dain, Armijo, & Cobbold, 1982;Ru & Pigott, 1986, Pigott & Ru, 1994Flower, Chung, Lo, & Lee, 1998;Li, Lin, & Zhang, 1998;Lüdmann & Wong, 1999;Lüdmann, Wong, & Wang, 2001;Hall, 2002). The recent depositional system on the northern SCS continental margin has abundant clastic sediments derived from the Pearl River and the Red River. ...
Submarine canyons are common features on the northern South China Sea (SCS) continental slope. Three main submarine canyon systems were observed by multi‐beam investigation and evaluated by a pre‐existing sedimentary dataset. They include the Xisha Canyon Zone, Shenhu Canyon Zone, and Taiwan Canyon Zone on the northern SCS continental slope which developed from the middle Miocene to the present‐day. Previous analysis implied that an enriched oil‐gas accumulation formed under this region with distinct gravity anomalies or active tectonic activity. Previous interpretation and geodynamics studies have revealed the detailed sedimentary records and the coupled tectonic‐sedimentary processes. However, the timing and mechanism of formation of the canyons on the northern SCS slope are still poorly constrained and vigorously debated, especially the differences among three submarine canyons from west to east that requires allowances for a variety of conflicting datasets. Here, we adopt the high‐resolution multi‐beam relief map and seismic profiles from these three canyon systems to estimate if the SCS slope controlled geometric segmentation and differentiation of canyon formation mechanisms and times. For this purpose, we ascertained that these canyons were initially controlled by the NE‐ to NW‐trending faults as a better constraint on the sediment flow direction. All the submarine canyons in the northern SCS slope extend in a range from NE‐/N–S‐ to NW‐ and E–W‐trending directions associated with the SCS oceanic spreading and the subsequent subduction‐related deformation along the Manila Trench. Furthermore, the present‐day morphology of these canyons implies a remarkable tectonic jump from west to east in the SCS continental slope and a north‐westward recession of the continental slope. Apart from the neo‐tectonic faults, the sea‐level fluctuation, gas hydrate disassociation, sediment source, and transportation channel also yielded dynamic processes and preservation for the submarine canyons. We finally propose a coupling model of the sedimentary and tectonic processes and confirm the spatial and temporal evolution of mechanisms of these canyons.
... The main geological features that define the SCS include the East-Vietnam fault in the west, the Nansha Trough in the south, the Manila trench in the east, and the continent-ocean transition zone in the north. After the early Cenozoic breakup of the SCS, some micro-blocks (e.g., Zhongsha, Xisha, and Nansha blocks) began to rift and drifted from the South China block (e.g., Clift et al., 2008;Yan et al., 2010Yan et al., , 2014, while at the same time a series of Tertiary rifted basins formed by extension the northern region of the SCS (e.g., Li et al., 1998). Subsequently, the SCS experienced seafloor spreading (33-16 Ma) Hayes, 1980, 1983;Briais et al., 1993;Li et al., 2015) and post-spreading intraplate volcanism (e.g., Kudrass et al., 1986;Tu et al., 1992;Yan et al., 2014). ...
Post-spreading intraplate volcanism has widely affected the South China Sea (SCS) region including Indochina, the northern margin of the SCS, and the SCS basin itself. In the SCS basin, several off- and on-fossil spreading center seamounts formed between 3.8 and 7.9 Ma. Based on previously published geochemical and Sr-Nd-Pb isotopic data, the intraplate volcanism is widely related to the Hainan mantle plume, whose existence has been evidenced by recent geophysical studies. To test this petrogenetic model, new Hf isotope data have been obtained from volcanic rocks from a suite of compositionally representative seamounts in the SCS basin. Compared to published Nd isotope ratios (0.512675–0.512965, 5 εNd units), ¹⁷⁶Hf/¹⁷⁷Hf ratios span a much larger range (0.282876–0.283097, 8 εHf units), even within individual seamounts (e.g., Zhangzhong seamount). These features, combined with previous studies, clearly confirm mantle heterogeneity beneath the SCS region. Similar to the trends in Sr-Nd-Pb isotope space, Nd-Hf isotope ratio show a relatively narrow, elongate mixing trend between a depleted Indian MORB-type mantle endmember and an enriched EMII-type mantle end member. We propose that this narrow trend is inconsistent with the origin of the enriched end member from a heterogeneous sub-continental lithospheric mantle (SCLM) and instead suggests a plume-related origin. As a conceptual model for the post-spreading tectonic scenario of the Hainan plume affecting the SCS region, we propose that a plume ascends to the bottom of the lithosphere beneath Hainan and its northern Leizhou peninsula at the northern margin of SCS, from where it migrates along sloping rheologic boundary layers to lithospheric faults under an extensional setting towards the central SCS where the magmas erupt at the young spreading centers.
... (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Li et al., 1998;Xu et al., 2012). Despite of the fact that the formation mechanism of the SCS remains the topic of considerable debate, the geodynamic processes involved in its formation share a typical course, i.e., from continental extension through continental breakup to seafloor spreading. ...
We investigate the kinematics of continent breakup and seafloor spreading in response to the upwelling divergent mantle flow using the optimal nearly-analytical discrete method. Modeling results show that a larger upwelling rate (Vz) in the upwelling divergent flow system favors the earlier development of continent breakup and seafloor spreading and the formation of narrow continental rifted margins and mantle exhumation; while a larger half divergent rate (Vx) favors the diffusive lithospheric thinning and the formation of wide continental rifted margins and mantle exhumation. The upwelling divergent flow-driven continent extension is strongly depth-dependent at the proximal margins, but it behaves approximately in a depth-uniform manner at the distal margins. Application of this model to the South China Sea (SCS) demonstrates that: 1) an upwelling flow operation with Vz = 0.3cm/yr can explain the pre-spreading continent extension of the SCS between ca. 65 Ma and ca. 33 Ma; 2) the followed upwelling divergent flow with Vx = 2.5cm/yr and Vz = 0.3cm/yr can reproduce the seafloor spreading history at ca. 33-16 Ma in the SCS central oceanic basin; and 3) the post-16 Ma thermal cooling since the cessation of the SCS seafloor spreading contributed ∼1.2 km to the present-day bathymetry at the relict spreading ridge. The upwelling divergent flow with a high ratio of Vx/Vz was also likely responsible for the occurrence of the very wide rifted continental margins bounded the SCS. We suggest that an upwelling divergent mantle flow played a leading role in the opening of the SCS.
... Based on seismic reflection profiles, magnetic data, geomorphology and drill samples, magmatic injections during the post-spreading phase have also been identified in the Xisha Trough and Qiongdongnan Basin (Liu & Wu, 2006;Lu et al., 2011;Yang et al., 2011; (Fig. 1). For example, a tholeiitic basalt sill with a thickness of 115 m was found in the Pliocene of Drill Y32-1-1, offshore of SW Hainan (Li et al., 1998). Igneous injections could be identified on seismic profiles in the eastern Qiongdongnan Basin (e.g. ...
The Qiongdongnan Basin is one of the largest Cenozoic rifted basins on the northern passive margin
of the South China Sea. It is well known that since the Late Miocene, approximately 10 Ma after the
end of the syn-rift phase, this basin has exhibited rapid thermal subsidence. However, detailed analysis
reveals a two-stage anomalous subsidence feature of the syn-rift subsidence deficit and the wellknown
rapid post-rift subsidence after 10.5 Ma. Heat-flow data show that heat flow in the central
depression zone is 70–105 mW m
�2, considerably higher than the heat flow (<70 mW m
�2) on the
northern shelf. In particular, there is a NE-trending high heat-flow zone of >85 mW m
�2 in the
eastern basin. We used a numerical model of coupled geothermal processes, lithosphere thinning
and depositional processes to analyse the origin of the anomalous subsidence pattern. Numerical
analysis of different cases shows that the stretching factor bs based on syn-rift sequences is less than
the observed crustal stretching factor bc, and if the lithosphere is thinned with bc during the syn-rift
phase (before 21 Ma), the present basement depth can be predicted fairly accurately. Further analysis
does not support crustal thinning after 21 Ma, which indicates that the syn-rift subsidence is in
deficit compared with the predicted subsidence with the crustal stretching factor bc. The observed
high heat flow in the central depression zone is caused by the heating of magmatic injection equivalently
at approximately 3–5 Ma, which affected the eastern basin more than the western basin, and
the Neogene magmatism might be fed by the deep thermal anomaly. Our results suggest that the
causes of the syn-rift subsidence deficit and rapid post-rift subsidence might be related. The syn-rift
subsidence deficit might be caused by the dynamic support of the influx of warmer asthenosphere
material and a small-scale thermal upwelling beneath the study area, which might have been persisting
for about 10 Ma during the early post-rift phase, and the post-rift rapid subsidence might be the
result of losing the dynamic support with the decaying or moving away of the deep thermal source,
and the rapid cooling of the asthenosphere. We concluded that the excess post-rift subsidence occurs
to compensate for the syn-rift subsidence deficit, and the deep thermal anomaly might have affected
the eastern Qiongdongnan Basin since the Late Oligocene.
... The QDNB belongs to the northern passive margin of the SCS. It was formed by lithospheric stretching during the Palaeogene (rift stage), followed by thermal subsidence since the Miocene (post-rift stage) (Li et al., 1998). Faults mainly deform the rift succession and are rarely observed within the Neogene strata (Xie et al., 2006). ...
This study describes a previously unobserved reflection seismic configuration comprising a honeycomb planform and a repeated erosion/infill cross-section, based on high-resolution three-dimensional/two-dimensional seismic data and bathymetric data. The honeycomb structures cover an area of more than 5000 km2 and are developed within the Late Miocene to recent deep-water sediments of the north-western South China Sea. Linear erosional troughs up to 10 km long and 1 km wide are widely developed in this area, are intimately related to the particular seismic configuration, and interpreted to represent a new type of sediment drift that is caused by unsteady bottom current regimes operating since the Late Miocene. The unsteady bottom current regimes are suggested to be triggered by irregular seabed morphologies. Considerable sea-floor topography was generated as a direct result of tectonic movements in the area since the Late Miocene, and this topography then influenced the pathways of strong bottom currents. This study highlights that: (i) an unsteady bottom current regime can be laterally extensive and persist for millions of years; (ii) structurally controlled sea-floor relief plays an important role in controlling the depositional pattern; and (iii) the bottom currents were active since the Late Miocene, flowing from the south-east through the Xisha–Guangle Gateway and crossing the honeycomb structure zone. This study documents a new style of drift and will help to improve current knowledge of palaeoceanography and understanding of the South China Sea deep-water circulation which is at present still poorly understood. This article is protected by copyright. All rights reserved.
... This model was based on plasticine experiments, field investigations along the Ailao Shan-Red River fault zone (e.g., Wu et al., 1989;Tapponnier et al., 1990;Leloup et al., 1995) and magnetic anomaly lineations (e.g., Briais et al., 1993). (2) The opening of the SCS was due to extension caused by an upwelling mantle plume beneath the SCS during the Cenozoic after the closure of the Tethys Ocean (e.g., Fan and Menzies, 1992;Li et al., 1998;Zhu et al., 2004). This model was based on petrological and geochemical studies of the Cenozoic basalts and mantle xenoliths from the region. ...
... The SCS is a wedge-shaped basin; it is not consistent with the left-lateral pull-apart mechanism of the southeastern end of the NW-trending Red River Fault Zone (RRFZ) (Zhou et al., 2002; Fig. 1). Li et al. (1998) pointed out that the Yinggehai Basin was formed by the RRFZ extending at the SCS, and that the RRFZ had been not left-lateral but right-lateral since the Eocene. This indicates that the Ailaoshan-RRFZ did not affect the SCS. ...
... The SCS is a wedge-shaped basin; it is not consistent with the left-lateral pull-apart mechanism of the southeastern end of the NW-trending Red River Fault Zone (RRFZ) (Zhou et al., 2002; Fig. 1). Li et al. (1998) pointed out that the Yinggehai Basin was formed by the RRFZ extending at the SCS, and that the RRFZ had been not left-lateral but right-lateral since the Eocene. This indicates that the Ailaoshan-RRFZ did not affect the SCS. ...
Transform faults in back-arc basins are the key to revealing the evolution of marginal seas. Four marginal basins in the Western Pacific, i.e. the South China Sea (SCS), Okinawa Trough (OT), West Philippine Basin (WPB) and Shikoku-Parece Vela Basin (SPVB), were studied to redefine the strikes and spatial distribution of transform faults or fracture zones. Based on high-resolution tectonomorphology, gravity and magnetic anomalies, pattern of magnetic lineations, seismic profiles, geometry of basins and palaeomagnetic data, together with analyses of regional geological setting, plate reconstruction and geodynamic analysis, this paper suggests that all the transform faults in the four marginal basins are in general NNE-trending. Moreover, by comparing with the contemporary structural framework of the East Asian Continental Margin, we propose new models concerning marginal seas spreading and have revised the previous Cenozoic plate reconstruction models related to the East Asian Continental Margin and the Western Pacific marginal seas. There are three possible origins of these NNE-trending transform faults. 1. Inheriting the orientation of the strike-slip faults at the rifting continental margin (e.g. the SCS and OT). The real strike of transform faults should not be NW but NNE. The large-scale NNE-trending dextral strike-slip faults distributed in the continental shelf of the SCS control a series of pull-apart basins of the SCS. Due to a higher degree of pull-apart, oceanic crust began to open. Then they evolved into the NNE-trending transform faults in the SCS and could also be regarded as a natural extension of the NNE-trending strike-slip faults in the South China Block (SCB). The geodynamic mechanism of the OT is similar to that of the SCS. Consequently, transform faults of the OT should also be NNE-trending, which is not perpendicular to the spreading axis but instead displays oblique spreading. 2. Izu-Bonin-Mariana (IBM) Trench retreat to the NNE and NE. Subduction rollback to the NE and NNE produced the NE- and NNE-striking horizontal tensile stress, resulting in the rifting of the Kyushu-Palau Ridge (KPR), controlling the spreading of the SPVB and forming the NE- and NNE-trending transform faults. This also involves oblique spreading. 3. The later overall rotation of the Philippine Sea Plate (PSP). Since 25Ma, the WPB has rotated clockwise about 40°. Therefore the NW- and NNW-trending transform faults that formed at the later spreading stage have rotated to be the near-N-S- or NNE-striking faults. These transform faults are almost perpendicular to the spreading axis.
... The TXNB, TXB and ECSSB had similar rock assemblages and developed littoral-neritic, lacustrine delta and fluvial facies, respectively, which are associated with a southeastward retreat from the ECS (Fig. 5; Wang and Zhu, 1992). Li et al. (1998) and Zhu et al. (2008) concluded that the northern SCS experienced an evolution of terrigenous, transitional trending faults. Due to these faults with different characteristics, episodes and trends, their structural frameworks are featured by E-W-directed zonation and N-S-directed block faulting (Du, 1994). ...
The East China Sea Shelf Basin (ECSSB), the Pearl River Mouth Basin (PRMB) and the Taixinan Basin (TXNB) in the northern continental margin of the South China Sea (SCS) are important oil- and gas-bearing basins on the Western Pacific Continental Margin. During the Paleocene to Late Miocene, their strata can be compared, and the lithofacies were continuous from the TXNB, via the Taixi Basin (TXB) to the ECSSB. The lithologies mainly consist of interbedded shale, sandstone and mudstone layers. In addition, these basins have similar tectonic and sedimentation features. The three basins had similar marine-terrigenous facies in the Paleocene and marine-lacustrine-fluvial facies during the Eocene and Late Miocene. The basins experienced several coeval tectonic movements and episodes, and they developed a series of NE- and NNE-trending faults during the Paleocene and Eocene, which controlled the structure of the basins. During the Early Oligocene and Middle Miocene, they developed a series of NW- and WNW-trending strike-slip faults, reverse folds and flower-like strike-slip faults. However, there were obvious differences in sedimentary and tectonic evolution since the Late Miocene. The TXNB and TXB developed marine facies after the Late Miocene, while in the Quaternary, open marine facies replaced the Pliocene terrigenous facies in the ECSSB. Since the Late Miocene, the south of the ECSSB developed into a subsidence stage, and fault activity stopped. The TXB and TXNB developed some inverse structures and then developed into a thermal subsidence episode after the Dongsha Movement. Thus, this paper proposes that the ECSSB and the Cenozoic basins in the SCS were originally a unified basin and then subsequently separated into two basins as a result of the indentation of the Philippine Sea Plate (PSP) and the arc-continent collision between the Luzon Arc and the Eurasian Plate.
... The QDNB on the northwest slope of the SCS is bounded by the Yinggehai Basin (YGHB) to the west ( Fig. 37.1). The basins along the northern SCS margin were formed by lithospheric stretching during the Paleocene and Oligocene, followed by thermal subsidence (Li et al. 1998). In the QDNB the rift phase was associated with the initial opening of the SCS in the Eocene and Oligocene (Ru and Pigott 1986), and post-rift subsidence followed after Early Miocene ( 21 Ma). ...
Mass transport deposits (MTDs) were identified in Quaternary sedimentary sequences of the southern deep-water (water depth 1000 ~1500 m) region of the Qiongdongnan Basin, South China Sea. Based on high resolution 3D seismic data, seismic amplitude and coherence data are obtained and used to analyse MTDs. Through the seismic profile, two-way-travel time (TWT) time map, time thickness and time slice of target strata, profile characteristics and internal structure of MTDs are revealed. MTDs are characterized of mounded, hummocky, chaotic, low amplitude and discontinuous seismic reflection. MTD-internal thrusts and basal groove marks indicate mass-transport direction from WSW to ENE, suggesting MTD source in the shelf edge/upper slope system offshore central Vietnam, where mountainous rivers deliver high amount of terrigenous clastics. Since about 0.78-1.8 Ma, three depositional cycles characterized by basal MTDs overlain by turbidite channel levee systems have been emplaced in the study area. Timing and source of MTDs suggest a causal link between Quaternary high sedimentation rate to the shelf/upper slope in the Western South China Sea influenced by the eccentricity scale sea-level change and the emplacement of MTDs.
... The QDNB on the northwest slope of the SCS is bounded by the Yinggehai Basin (YGHB) to the west (Fig. 37.1). The basins along the northern SCS margin were formed by lithospheric stretching during the Paleocene and Oligocene, followed by thermal subsidence (Li et al. 1998). In the QDNB the rift phase was associated with the initial opening of the SCS in the Eocene and Oligocene (Ru and Pigott 1986), and post-rift subsidence followed after Early Miocene (21 Ma). ...
The Song Chay Dome in southeastern Yunnan Province, China, is intruded by the Late Cretaceous Laojunshan granites. New apatite and zircon fission-track data for the Laojunshan granites allow us to reconstruct the exhumation history of the Song Chay Dome. The fission-track dating indicates that the Laojunshan granites experienced four main stages of rapid cooling and exhumation at 75–63, 53–43, 31–20, and 12–4 Ma. The first stage was related to the thermal equilibration with surrounding rocks after magma emplacement. The rapid cooling and exhumation at 53–43 Ma were caused by normal faulting in the Late Mesozoic–Early Cenozoic extensional setting of southwestern South China, which resulted in the Laojunshan granites and Song Chay Dome being exhumed in the footwall of faults. The third stage (31–20 Ma) was the result of southeastward extrusion of the Tibetan Plateau and sinistral strike-slip movement on the NW-SE-trending Nanwenhe and Maguan-Dulong faults. The 31 Ma representing the beginning of the interaction between the Tethyan Himalayan tectonic domain and the South China Block. The final stage was mainly due to activity on the Nanwenhe Fault to the north of the Laojunshan granites, caused by lateral extrusion of the southeastern Tibetan Plateau since ca. 15 Ma. These cooling and exhumation events since the Late Cretaceous indicate that the Song Chay Dome and southwestern South China Block have been affected by the Himalayan Orogeny since the Oligocene.
Tsunamis are a series of giant waves with super-long wavelengths that occur and migrate through the ocean, most of which are caused by earthquakes (that occur below or near the ocean floor), underwater volcanic eruptions, landslides, and potentially coastal landslides.
Shallow gas is generally referred to in the seabed below 1000 m of gas accumulation in the sediments. The components of shallow gas have simple structures, including methane, carbon dioxide, hydrogen sulfide, ethane, etc. Shallow gas has the characteristics of small molecule, small density, high buoyancy, low viscosity, small adsorption capacity, strong diffusion, easy to dissolve, volatile, and so on.
As one of the most important forcing factors, relative sea‐level changes exert a major influence on the building of shelf‐margin clinothems. However, it is still not well understood how these changes control the growth of shelf edges and the condition of sediments transporting into deep water, especially over the individual‐clinothem scale of several 100 ky. On the late‐Quaternary Pearl River margin, there are two distinct shelf‐margin clinothems: SQ3 and SQ4. They have different shelf‐edge trajectories (slight rising vs. steep rising) and different styles of deep‐water deposition (fan lobes consisting mainly of MTDs vs. fan lobes consisting mainly of turbidites). This work takes those SQ3 and SQ4 as study objects and runs a total of 136 experiments from the Dionisos stratigraphic forward model to investigate how relative sea‐level changes control the trajectories of shelf edges and the volumes of MTDs in deep water over the individual‐clinothem scale. Our quantitative results suggest that under the geological background of high sediment supply on the late‐Quaternary Pearl River margin, the duration of highstand systems tracts (HST) relative to lowstand systems tracts (LST) or forced regressive systems tracts (FST) has a significant influence on the building of individual shelf‐margin clinothems. If the relative duration of HST is either very short or very long, slight‐rising shelf‐edge trajectories and large‐volume MTDs would be formed, whereas if the relative duration of HST is comparable with LST or FST, steep‐rising shelf‐edge trajectories and limited MTDs would be formed. Through the constrains of the model set to the real geological condition of the SQ3 and SQ4 clinothems, it is found that SQ3 was caused by the quite long relative duration of HST, which made highstand deltaic systems advance over the pre‐existing shelf‐slope break, leading to significant accretion and instability of the shelf edge and thus, giving rise to the formation of slight‐rising shelf‐edge trajectories and fan lobes with high MTDs contents. SQ4, however, formed as a result of the comparable durations of HST, LST, and FST, which made highstand deltaic systems advance to but not beyond the previous shelf‐slope break allowing the subsequent FST to be directly perched on the clinoform slope. Such building processes did not drive pronounced accretion and instability of the shelf edge and thus, caused the formation of steep‐rising shelf‐edge trajectories and fan lobes with low MTDs contents.
High-resolution seismic data and partial drilling data reveals that the evolution of the spatial distributions of reefs and carbonate platforms in the Dongsha area can be divided into four temporal stages, which are essential to our understanding of these geological structures and their potential for hydrocarbon exploration. First, in the early Early Miocene epoch, the carbonate platforms initially developed on a basement high, while the reefs were mainly point reefs. Second, in the early-middle Early Miocene, carbonate platforms flourished throughout the Dongsha area while organic reefs bloomed on its steep southwestern slopes. Third, in the middle-late Early Miocene, carbonate platforms decreased by approximately 50%, but the number and types of organic reefs continued to bloom on the southwestern margin of the platforms. Finally, in late Early Miocene, most of the reefs and carbonate platforms had been submerged, with only a small number of isolated platforms surviving around the Dongsha Islands. Tectonic movement and relative sea level change are the two major controlling factors in the area. The slow tectonic subsidence limits the vertical development of reefs, therefore leading to their rapid lateral growth. At the same time, short-term relative sea level fluctuation has led to this multi-stage development.
Rift-related normal faults generally have various geometries, and cause the syn-rift stratigraphy in their hanging wall to be characterized by different infilling patterns. Our understanding of the tectonic control on the syn-rift stratigraphy mainly stems from the analysis of fault kinematics, stratigraphic styles and depositional facies. However, questions remain about how fault geometry, kinematics and slip rate influence the style of a rift-related half-graben and the syn-rift stratigraphy, and what enlightenment that relationship has for the hydrocarbon exploration in rifts. Using the 2D MOVE Software, this study attempts to simulate the development of a fault-bounded half-graben, with the aim of investigating the aforementioned questions. The modeling results show that, a planar, listric and ramp-flat-ramp border fault controls a tabular, wedged-shaped, and composite wedge-shaped growth package, respectively, but exceptionally, the planar fault bounds a wedge-shaped package if the fault rotates with movement. In addition, rollover structure forms when the border fault has a listric or ramp-flat-ramp shape, indicating that the fault geometry and kinematics dominate the syn-tectonic stratigraphic pattern. Besides, fault slip rate relative to sediment supply affects the scale, dip and infilling pattern of the syn-tectonic stratigraphy. In details, reduction of fault slip rate or increment of sediment supply results in: i) the extent of the syn-tectonic stratigraphy enlarging, ii) the dip angle of the syn-tectonic stratigraphy decreasing, and iii) the water depth in the related half-graben getting shallower. This study provides insights into understanding the origin of the variable styles of rift-related half-graben and syn-rift stratigraphy. Also, our modeling results have an important implication for evaluating source rock quality in rifts. Finally, we give a preliminary example of using the MOVE Software to investigate the geometry and evolution of fault-bounded basin, which is well worth being further explored.
The East Asian continental margin straddles the boundary between the Pacific Plate subduction Domain to the east and the Indo-Eurasian collision Domain to the west. The spatial and temporal interaction between these two dynamic domains induced dextral trans-tensional stress field, which resulted in generating nearly 75% of the globe's marginal seas and continental margin rifts during the Cenozoic. Among these, the South China Sea (SCS) and its northern margin are located in the core of the Pacific Tectonic Domain and the Tethyan Tectonic Domain. The evolution of the SCS and its northern margin are of prime interest because of the spectacular magnetic lineation and strong rifting. In spite of the several investigations on the Cenozoic marginal seas and rift basins occurred, their mechanisms of formation remain equivocal. Here we perform a comprehensive analysis of seismic profiles and fault architecture data with a view to understanding the Cenozoic tectonic evolution of the northern margin of the SCS. Based on detailed structural analysis of the geometry and kinematics, we demonstrate that the NE- and ENE-striking faults assembled to horsetail- or feather-shaped structures in plan view, with flower-like structures on seismic profiles. Two stages of faulting with NE-trending are identified along the northern margin of the SCS. The earlier oblique extension developed during the Paleocene to the early Middle Eocene (~44–42 Ma), accompanied by strong rifting and some left-stepping en echelon-like faults. The later trans-tensional faulting developed during the late Middle Eocene to the Early Miocene (~21 Ma), resulting in the formation of the dextral right-stepping trans-tensional fault system. Two stages of faulting were linked to the joint effect among the collision domain of Indian-Eurasian plates to the west, the subduction domain of the Pacific Plate to the east and the slab-pull system of the proto-SCS to the south. Our study provides important insights into the dynamics and tectonics that controlled the opening of the South China Sea. During the Late Eocene to the Oligocene, the later trans-extensional faulting and right-stepping strike-slip fault system caused the opening of the Northwest Sub-basin, East Sub-basin and Northeast Sub-basin. However, during the Early Miocene, the left-lateral strike-slip of the Ailao Shan-Red River (ASRR) shear zone and the slab-pull force of the Proto-SCS resulted in the opening of the Southwest Sub-basin and the change in the spreading direction of the East Sub-basin.
Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.
In order to provide constraints on the interpretation of seismic data of the crust beneath the South China Sea (SCS) and its continental margins, we have measured P-wave velocities and anisotropy as a function of hydrostatic confining pressure, up to 650 MPa, for 31 representative samples (i.e., granite, diorite, felsic gneiss, mylonite and ultramylonite, amphibolite, schist, and marble) from the Yunkai Mts (Guangdong and Guangxi Provinces, China) that represent the crystalline basement beneath the continental margins of the SCS. The intrinsic velocity of each crack-free rock increases with increasing density (ρ) which is linearly dependent on the chemical composition: ρ increases with increasing MgO, CaO, FeO + Fe2O3, and Al2O3 contents, but decreases with increasing contents of SiO2 and Na2O + K2O. Most of the rocks have small (<4%) or moderate (4–8%) seismic anisotropy because (1) the contribution of quartz to the bulk anisotropy opposes that of feldspar, and (2) the rocks only contain small amounts of amphibole and/or mica. The interpretation of 12 seismic transects suggests that the crust of the Cathaysia block (the southern part of South China) has a mafic-to-felsic layer thickness ratio (Rm/f) of 41–43% and the ratio shows a general increase from the continental margin to the central basin. The high velocity (7.0–7.6 km/s) materials in the lower crust could be either the former lower crustal mafic rocks that were present before rifting, which have experienced less extensional thinning than the felsic upper crust, or the materials crystallized from mafic magma which underplated the lower crust from the partially molten upper mantle during rifting.
Based on the integrated analysis of the bathymetric data and high-resolution seismic data, the morphological features and internal structures of the Central Canyon System (CCS) in eastern Qiongdongnan basin (QDNB) have been described and dissected accurately. The result shows that the CCS in eastern QDNB was located in the central part of the Changchang depression with an NEE orientation, showing a narrow, straight course in the plan and symmetrical V-shaped morphology with steep flanks in seismic profiles. The infillings were considered as turbidite channel lag deposits, mass transport complex-sheet sands (MTC-sheet complex) with cake-layer geometry, turbidites, and collapse deposits. They showed a multiple evolutional processes. The distinct differences of the CCS between the western and eastern segments implied that the canyon in eastern QDNB was primarily controlled by the plaeo-morphological feature associated to the tectonic transformation around 11.6 Ma, which might form the axial sub-basin in the central part of Changchang depression seemed as the rudiment of the CCS, define the morphology, and influence the sediment transports and accumulation patterns. The canyon in eastern QDNB wasconsidered as a tectonic-dominated submarine canyon. During the Holocene period, the sufficient deposits could be discharged by the slope canyons at the lower slope, where the modern submarine fan developed. Then the deposits were captured by the head of modern central canyon, and further transported along the canyon from west to east. The three modern sediment transportation models in eastern QDNB, the vertical transportation along the slope from north to south, the veer motion transportation in the head area of modern central canyon dominated by the topography, and the axial transportation associated to the canyon orientation from west to east, would be helpful in understanding the deepwater sedimentary processes in QDNB and provide more evidence for the forming of the CCS.
Submarine gas hydrates are closely related to active tectonics. Recently submarine active tectonics in the northern South China Sea attract much attention because of exploration of submarine gashydrate in the past decades. We descript the features of faults, earthquakes, and volcanic activity and other active tectonics relating to gashydrate. There are three sets of active faults including NE-, NEE-EW-, NW-striking faults in the northern South China Sea, of which NW-trending faults cut the other two groups. Most of these active faults are inherited from pre-existing basement faults. NE- and ENE-trending faults are crustal or lithospheric faults. The earthquake distribution is focused on a NE-trending striped region of the northern South China Sea. However, the NW-trending earthquakes are controlled by the Red River strike-slipping fault. Gas chimneys are related to active structures that play an important role of the formation of the gashydrates, as same as the channel which provides the gas to vertically migrate up to the place under appropriate temperature and pressure for gas-hydrate formation. The distribution of volcanic rocks clockwise rotates from east to west. Based on seismic profile, the volcanic rocks are controlled by tensional fault. The distribution of gashydrates in the eastern part is affected by the NW-trending active faults, however, the west is inextricably linked with the submarine landslide.
The evolution of overpressure system and its coupling relationship with hydrocarbon accumulation in the deepwater area of Qiongdongnan basin were studied based on 2D basin modeling. The results show that overpressure system in the central depression has already developed during the Yacheng period and consisted of an eastern subsystem and a western subsystem during the initial rifting period. They gradually evolve into a big overpressure system in the west till 10.5 Ma and exhibit a trend transferring eastward. The current top overpressured surface (TOS) totally deepens eastward, similarly with the top migration surface (TMS). The eastern basin experiences three pressure cycles while the western basin experiences three and a half. It is recognized that tectonics, fault activity and sedimentation play important roles in the cyclicity of pressure evolution, while hydrocarbon generation cannot be a dominant factor. The critical period for petroleum migration and accumulation is from the late Miocene, and the predominant direction should be the northern slope of the central depression. The most favorable targets for future exploration should be the traps in the transitional pressure zone and normal pressure zone in the western basin and the traps near faults in the low scope or transitional pressure zone in the eastern basin.
Based on geological and geophysical data, the Paleogene syndepositional fault and its control on sequence architecture of Lingshui sag were studied by analyzing the combination features and faulting-activity rate of the fault. The results show that three kinds of frameworks, i.e., asymmetric graben, symmetric graben and half-graben, were developed individually in the east, middle, and west of Lingshui sag. Three kinds of structural paleogeomorphologies, i.e., up-dip foot slope break belt, down-dip foot slope break belt and gentle slope-break belt, were developed in response to the changes of faulting-activity, which influenced the sequence-infill patterns. Different sequence-infill patterns distributing within tectono-stratigraphic frameworks have characteristic sequence architectures, which will favorably contribute to exploration of potential reservoirs and subtle oil pools in deepwater area.
A geochemical analysis of rare-earth elements (REEs) in 97 samples collected from the core of deep-water Well LS-A located at the Lingnan Low Uplift Area of the Qiongdongnan Basin is conducted, with the purpose of revealing the changes of sedimentary source and environment in the study region since Oligocene and evaluating the response of geochemical characteristics of REEs to the tectonic evolution. In the core samples, both ΣREE and ΣLREE (LREE is short for light-group REEs) fluctuate in a relatively wide range, while ΣHREE (HREE is short for heavy-group REEs) maintains a relatively stable level. With the stratigraphic chronology becoming newer, both ΣREE and ΣLREE show a gradually rising trend overall. The ΣREE of the core is relatively high from the bottom of Yacheng Formation (at a well depth of 4 207 m) to the top of Ledong Formation, and the REEs show partitioning characteristics of the enrichment of LREE, the stable content of HREE, and the negative anomaly of Eu to varying degrees. Overall the geochemical characteristics of REEs are relatively approximate to those of China’s neritic sediments and loess, with significant “continental orientation”. The ΣREE of the core is relatively low in the lower part of Yacheng Formation (at a well depth of 4 207–4 330 m), as shown by the REEs partitioning characteristics of the depletion of LREE, the relative enrichment of HREE, and the positive anomaly of Eu; the geochemical characteristics of REEs are approximate to those of oceanic crust and basalt overall, indicating that the provenance is primarily composed of volcanic eruption matters. As shown by the analyses based on sequence stratigraphy and mineralogy, the provenance in study region in the early Oligocene mainly resulted from the volcanic materials of the peripheral uplift areas; the continental margin materials from the north contributed only insignificantly; the provenance developed to a certain extent in the late Oligocene. Since the Miocene, the provenance has ceaselessly expanded from proximal to distal realm, embodying a characteristic of multi-source sedimentation. In the core strata with 31.5, 28.4, 25.5, 23, and 16 Ma from today, the geochemical parameters of REEs and Th/Sc ratio have significant saltation, embodying the tectonic movement events in the evolution of the Qiongdongnan Basin. In the tectonic evolution history of the South China Sea, the South China Sea Movement (34-25 Ma BP, early expansion of the South China Sea), Baiyun Movement (23 Ma BP), late expansion movement (23.5-16.5 Ma BP), expansion-settlement transition, and other important events are all clearly recorded by the geochemical characteristics of REEs in the core.
The understanding of tectonic activity in the north basins of South China Sea has long been controversial. It is especially difficult for researchers to hold identical views in the problem of the determination of the Zhu-Qiong movement. Based on the research on the dynamic setting in the South China Sea and its surrounding basin, the authors believe that the Zhu-Qiong movement was a great extensional tectonic activity between Eocene and Oligocene, and it could be divided two episodes according to the dynamics in different stages. Fushan Sag is located in the southeast corner of Beibuwan Basin, which is one of the northern basins of the South China Sea. The sag's tectonic and sedimentary characteristics show that there existed two backgrounds of extensional structure during the Zhu-Qiong movement, corresponding respectively to two episodes of Zhu-Qiong movement. In addition, according to the characteristics of the change of sedimentary rate as well as the time of the formation of faults which controlled sedimentation and distribution of multi-phase faults, it is held that the activity of the first episode of Zhu-Qiong movement occurred in Early-Middle Eocene (54Ma-39.4Ma). Its dynamics mechanism was that the West Pacific plate drew back in subduction caused by SE-trending mantle flow under the subduction of Indian plate beneath Eurasian plate. And the activity of the second episode of Zhu-Qiong movement took place in Late Eocene to Oligocene (39.4Ma-25.5Ma). The dynamics mechanism of this stage was different from that of the previous phase, and the extensional effect of Hainan mantle plume action on the lithospheric bottom led to the tectonic activity in this episode.
Gas accumulation mechanisms of the Dongfang area and Ledong area are different to some extent although both are the key gas exploration areas located in the same central diapers in the Yinggehai Sag, Yinggehai Basin. We analyzed the control effect of tectonic evolution on source rock development and diapirism and further on the differences of gas accumulation mechanisms between these two blocks. (1) The tectonic evolution since the Miocene caused the migration of the subsidence center and depocenter from the Dongfang Block to the Ledong Block, which was a key factor controlling the Miocene source rock development and diapirism and the follow-up gas generation, accumulation and distribution. (2) Gas generation in the Dongfang Block initiated earlier and lasted for a rather long time. In contrast, gas generation in the Ledong Block began later and completed in a shorter period, thus favorable for gas accumulation. (3) The diapirism since the Late Miocene determined the gas migration, accumulation and distribution. (4) The number of diapirs is small and their intensity of activity was relatively weak in the Dongfang Block. In contrast, diapirs were highly developed and their activities were more complex in the Dongfang area. Despite these differences, they have some similarities, such as their locations in high temperature and high pressure zones as well as the control of diapirism on gas accumulation. It was finally pointed out that the diapir distribution areas in this basin, featured by relatively low energy, early gas accumulation in the middle and deep layers, good sealing conditions, and a low risk of CO2 occurrence, are thus favorable play fairways for gas exploration. ©, 2015, Natural Gas Industry Journal Agency. All right reserved.
Marine heat flow data are essential for study of marine geodynamics and reliable evaluation of hydrocarbon resources. Detailed temperature and well log data of commercial drills are invaluable for acquisition of surface heat flow data, thus to understanding the geothermal features of the Qiongdongnan Basin. Since heat flow values from various methods of calculating heat flow might be different, the present vertical variations of some main geothermal parameters were calculated to facilitate explanation of such differences. A numerical model coupling the heat transfer, sedimentation and lithospheric stretching was employed to predict the present vertical variations of some main geothermal parameters in a rifted basin, then well log data of sonic, density, neutron porosity, resistivity, and gamma ray were used to calculated average thermal conductivity following the method of Goutorbe et al.(2008), and GR (total gamma-ray logs) was used to calculate average heat generation rates with the relationship of Bucker & Rybach (1996). A total of 44 heat flow data were determined with the calculated thermal conductivity and average geothermal gradient. The results show that the thermal blanketing of the sedimentation could greatly reduce the heat flow value in the strata, and due to the opposite thermal contributions of sedimentary heat generation and thermal blanketing, the difference in the average heat flow between the seafloor and the deep drill hole temperature measured in a range of 3000~4000 m, and the seafloor heat flow is very small. Thus both of the heat flows could be put together for analyzing the heat flow distribution of the Qiongdongnan Basin. The thermal conductivity variation with depth of the Yinggehai and Ledong groups is much smaller than that of those older groups, with an average of about 1.7 W·(m·K)-1. The average Cenozoic heat generation is generally lower than 2.5 μW·m-3, with an average of 1.34 μW·m-3. The average geothermal gradient ranges from 30 to 45 ℃/km, and the heat flow ranges from 50 to 99 mW·m-2. The sedimentary contribution to surface heat flow is larger than 20 mW·m-2 in the western basin and about 10 mW·m-2 in the eastern basin, respectively. The heat flow in the shelf is mostly in the range of 60~70 mW·m-2, and the geothermal gradient and heat flow are generally much higher in the deep-water area. In conjunction with the seafloor heat flow data, heat flow in the shelf and upper slope area are generally lower than 70 mW·m-2, while in the deep-water area, heat flow values are generally in the range of 70~85 mW·m-2. There is a high heat flow zone with values higher than 85 mW·m-2 trending in northeast in the eastern part of the study area. In the study area, the difference between the average drill heat flow and the seafloor heat flow is very small, thus both can be adopted for analyzing the heat flow distribution of the Qiongdongnan Basin. The geothermal gradient and heat flow are generally much higher in the deep-water area than the northern shelf, and there is a high heat flow zone trending in northeast in the eastern part of the study area. Further analysis suggests that the present heat flow distribution features resulted from multiple factors such as thermal anomalies in the upper mantle, the cooling of the highly thinned lithosphere, recent extensive magmatism, the crustal and sedimentary heat generation, and the sedimentary thermal blanketing.
This chapter summarizes the tectonic framework and evolutionary history of the China Seas since the early Mesozoic. Mesozoic tectonics left many weak zones along collisional and subduction boundaries, which later reactivated to form regional faults that have largely controlled the formation of Cenozoic rifting basins and marine depositions. Widespread magmatism and neotectonics are also reviewed, with particular focuses on the multiphased opening of the South China Sea and Okinawa Trough.
To reveal the tectonic thermal evolution and influence factors on the present heat flow distribution, based on 154 heat flow data, the present heat flow distribution features of the main tectonic units are first analyzed in detail, then the tectonic thermal evolution histories of 20 profiles are reestablished crossing the main deep-water sags with a structural, thermal and sedimentary coupled numerical model. On the basis of the present geothermal features, the Qiongdongnan Basin could be divided into three regions: the northern shelf and upper slope region with a heat flow of 50–70 mW/m2, most of the central depression zone of 70–85 mW/m2, and a NE trending high heat flow zone of 85–105 mW/m2 lying in the eastern basin. Numerical modeling shows that during the syn-rift phase, the heat flow increases generally with time, and is higher in basement high area than in its adjacent sags. At the end of the syn-rift phase, the heat flow in the deepwater sags was in a range of 60–85 mW/m2, while in the basement high area, it was in a range of 75–100 mW/m2. During the post-rift phase, the heat flow decreased gradually, and tended to be more uniform in the basement highs and sags. However, an extensive magmatism, which equivalently happened at around 5 Ma, has greatly increased the heat flow values, and the relict heat still contributes about 10–25 mW/m2 to the present surface heat flow in the central depression zone and the southern uplift zone. Further analyses suggested that the present high heat flow in the deep-water Qiongdongnan Basin is a combined result of the thermal anomaly in the upper mantle, highly thinning of the lithosphere, and the recent extensive magmatism. Other secondary factors might have affected the heat flow distribution features in some local regions. These factors include basement and seafloor topography, sediment heat generation, thermal blanketing, local magmatic injecting and hydrothermal activities related to faulting and overpressure.
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