NE South China Research Articles

Numerical study on biogeochemical processes induced by methane leakage and its application in estimating the time of cold seeps formation

In shallow marine sediments, cold seeps of methane fluid is a widely observed phenomenon, which will lead to a series of biogeochemical reactions. These processes will change the pore water environment and trigger the formation of authigenic minerals. In this study, based on the data from the site GC10 in the NE South China Sea, numerical simulation studies were conducted to investigate the relative biogeochemical processes induced by methane leakage. The results of simulations show that anaerobic methane oxidation is the dominant sulfate consuming process in methane leakage environment, and the typical sulfate-methane interface is indicative of methane leakage. The pore water chemistry conditions are closely related to methane flux. Methane flux was calibrated from GC10 site data, when methane leaks upwards at flux of 2.42 × 10−3 mmol cm−2 a−1, the simulation results fit well with measured data. Some kinetic parameters of related reaction were calibrated during the fitting process. The microbially-mediated reactions in methane leakage environment trigger the precipitation of authigenic minerals, such as calcite and pyrite, which can sometimes be used as indicators of the occurrence of hydrate reservoirs. Through simulating the change of sulfate concentrations along the vertical column, the model was also used to estimate duration of active cold seeps at the study site. The results showed that the methane leakage in GC10 has been going on at least 5600 years. This study provided a new method to the study of cold seeps activities, and was significant for future investigations on the biogeochemical processes above the hydrate reservoirs.

Geological records of South China Sea tsunamis on Penghu Islands, Taiwan

The coasts around the South China Sea are highly populated and threatened by the ubiquitous tsunamigenic structures of the Manila trench-arc system. However, owing to limited historical records and rare geological findings of tsunamis, our comprehension of and preparation for regional tsunami risks are far from sufficient. Located in the NE South China Sea, the Penghu Islands in Taiwan’s western offshore area are selected for a geological tsunami survey because of their advantages of lengthy coastlines and abundant upper Holocene deposits.Three gravel layers of marine incursion events were identified and correlated between three far-separated coastal sections based on the constraints of radiocarbon dating. Intercalated with talus, soil, and dune sand, the gravel layers are poorly sorted, matrix-supported, up to boulder in size, and dominated by marine bioclastics and rounded basalts, which are identical to modern beach gravels. The deposits are located 3–4 m above present sea level, which is significantly higher than the local high tide levels and maximal typhoon surges of 2–3 m high. Furthermore, the deposits are distributed extensively on south-facing shores, indicating relatively large and abnormal inundation events from the South China Sea.Based on the radiocarbon dating results of the event deposits, three tsunamis likely occurred in the periods from the 4th to 6th, 11th to 12th, and 15th to 16th centuries. A recurrence interval of 400–500 years is accordingly associated with these event deposits. These findings demonstrate great tsunami risks exist in the South China Sea basin and call for more attestations and future studies. The major contribution of this study is also supported by the AD 1076 Guangzhou tsunami, which is comparable in age to the middle event deposit.

Paleoclimatic evolution of the SW and NE South China Sea and its relationship with spectral reflectance data over various age scales

Spectral analysis of sediment from International Ocean Discovery Program (IODP) Site U1433 in the South China Sea can be used to constrain humidity and temperature through time by constructing hematite/goethite records spanning the last 10 million years. Records in the southwest and northern parts of this basin show long-term contrasting trends, despite the fact that geochemical evidence for alteration is similar in both parts of the basin, i.e. towards less alteration since 10 Ma. However, contrasting clay mineral assemblages in the northern and southwestern areas do suggest long-term changes in the relative climate of Indochina and southern China. We interpret this to reflect the northward migration of the ITCZ since the Miocene resulting in a progressive drying of Indochina and increasingly wet conditions in South China. Sediment believed to be supplied from the Mekong River (IODP Site U1433) shows increasing chemical weathering at a time of long-term drying of the climate. This probably reflects increasing chemical weathering driven by slower transport and despite reduced rates of chemical alteration in the context of a colder, drier climate since the Miocene. In general hematite/goethite data are consistent with pollen constraints from the same drill site that show colder conditions with increasing hematite/goethite since 3 Ma and with a transition to apparently wetter conditions since the mid-Pleistocene transition (MPT). This implies that most of the sediment in the southwestern basin is weathered and eroded during warmer, wetter interglacial phases, at least since the MPT.

End of Capitanian (Middle Permian) Patch Reef on a Shallow Marine Shelf in NE South China: Lithostrategraphy of Uppermost Iwaizaki Limestone in the South Kitakami Belt, NE Japan

End of Capitanian (Middle Permian) Patch Reef on a Shallow Marine Shelf in NE South China: Lithostrategraphy of Uppermost Iwaizaki Limestone in the South Kitakami Belt, NE Japan

Petrogenesis of Early Cretaceous granitoids from southwest Zhejiang, NE South China Block and its geodynamic implication

In situ zircon U–Pb ages, whole-rock major and trace elements, and Sr–Nd isotopic compositions of the Sucun, Yunfeng, and Jingning intrusions from southwest Zhejiang, NE South China Block, are presented to trace their petrogenesis and shed light on its lithosphere evolution. LA–ICP–MS U–Pb zircon dating shows that the Sucun quartz monzonite and Jingning monzogranite were emplaced at ~135 Ma, and the Yunfeng quartz monzonite and Jingning granite were emplaced at 104 and 112 Ma, respectively. All these intrusions are metaluminous to weakly peraluminous and lie within high-K calc-alkaline to shoshonite series field (SiO2 = 66–76 wt%, A/CNK = 0.95–1.09, K2O/Na2O = 0.78–1.77). The Yunfeng quartz monzonite clearly have lower K2O and total REE contents, and higher CaO, Na2O, Al2O3, P2O5, MgO, and TiO2 contents, and relatively less enriched Sr–Nd isotopic compositions than those of the Sucun quartz monzonite, indicating that the Yunfeng quartz monzonite were derived from partial melting of a more juvenile lower crust sources compared with the magma source of the Sucun quartz monzonite. The Jingning monzogranite exhibit similar major elements covariations and Nd isotopic compositions, but higher Ba, Sr, and Eu contents and lower Rb, Th, and U contents than those of the Jingning granite. The geochemical features imply that the Jingning monzogranite and granite were fluid-present and fluid-absent anatexis products of the same Paleoproterozoic crustal source, respectively. Whole-rock Sr–Nd isotopic data imply that the estimated amounts of juvenile mantle-derived melts input into the mature crust show southeastward decreasing trend away from the Jiangshan–Shaoxing fault. We propose that roll-back and retreat of the Paleo-Pacific subducting plate might cause extensive asthenosphere mantle upwelling in East China, and the mantle-derived melts tend to rise through the regional main fault zones and preferentially modify the lithosphere nearby these faults.

Tracing an Early Jurassic magmatic arc from South to East China Seas

Drilling has revealed suites of magnesian granite and diorite emplaced in Early Jurassic time (198-195 Ma) and an arc-related low-temperature (678 to 696 °C) magmatism in NE South China Sea. These rocks have 87Sr/86Sri (0.705494 to 0.706623) and eNdt (−0.9 to +2.2) as evidence of evolved mantle-derived magmas, coupled with enriched fluid-mobile elements Cs to K and Pb implying involvement of subduction-zone fluids. Another Early Jurassic granodiorite (zircon U-Pb 187 Ma) drilled from the SW East China Sea, is a magnesian high-K calc-alkaline, is comparably confined to a range of low-temperature (~675 °C) arc-related granite, characterized by enrichment of fluid-mobile elements and Nb-Ta depletion. Its Sr-Nd isotopes (87Sr/86Sri = 0.705200, eNdt = 1.1) suggest a product of evolved mantle-derived melts. Together with detrital igneous zircons from Paleocene sequences, these observations reveal an Early Jurassic arc-related low-temperature (600 to 740 °C) magmatism in the SW East China Sea. These arc-related granitoids, along with those from SE Taiwan, could define an Early Jurassic NE-SW-trending Dongsha-Talun-Yandang magmatic arc zone along the East Asian continental margin paired with Jurassic accretionary complexes from SW Japan, E Taiwan to the W Philippines. This arc-subduction complex assembly was associated with oblique subduction of the paleo-Pacific slab beneath Eurasia, presumably responsible for early Jurassic lithospheric extension in South China block.

A foraminiferal study on Middle Eocene-Oligocene break-up unconformity in northern Taiwan and its correlation with IODP Site U1435 to constrain the onset event of South China Sea opening

Taiwan is situated in the SE Asian continental margin where lower Cenozoic strata are well exposed. Its geological and tectonic setting provides a unique opportunity to study the time constraint of the break-up unconformity relevant to the opening of the South China Sea. A detailed foraminiferal study on four land sections and a deep core across the boundary between the Upper and Lower Wulai Groups in the Hsüehshan Range, northern Taiwan, was conducted. Results show remarkable changes of depositional environment and lithology from the amalgamated fluvial dominant sandstones (>2000m) of Middle Eocene in the Lower Wulai Group to the overlying inner neritic shales and siltstones (>2000m) of Oligocene in the Upper Wulai Group. Integrated sedimentological and foraminiferal data further suggest an occurrence of a depositional hiatus between 32 ∼33 and 40Ma across the boundary between the Kankou Formation of the Upper Wulai Group and the Szeleng Sandstone of the Lower Wulai Group in the northern Hsüehshan Range, as same as the scenario seen in the Western Foothills (25–39Ma) of central Taiwan and the Penghu Basin (25–40Ma) in the Taiwan Strait.This stratigraphic hiatus in the Taiwan mountain belt marks a regional break-up unconformity between the Middle Eocene syn-rift strata and the overlying Oligocene post-rift sequences in the NE South China Sea. The break-up unconformity can be correlated with those commonly recognized in the seismic profiles of the Pearl River Mouth Basin and drilling of the IODP site U1435 (Expedition 349) in the northern shelf-slope of the South China Sea. The upper time limit of the breakup unconformity 32Ma could mark the tectonic change from rifting to depression in the Paleogene Asian continental margin which eventually led to opening of the deep South China Sea in the Early Oligocene (∼33Ma).

Provenance of Cretaceous trench slope sediments from the Mesozoic Wandashan Orogen, NE China: Implications for determining ancient drainage systems and tectonics of the Paleo-Pacific

The Wandashan Orogen of NE China is a typical accretionary orogen related to Paleo-Pacific subduction. The Raohe Complex, as a major part of the orogen, consists of mid-Triassic to mid-Jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial-sourced clastic trench slope sediments. Sensitive high-resolution ion microprobe U-Pb dating and LA-MC-ICPMS Hf isotopic analysis of detrital zircons from the terrestrial-sourced Yongfuqiao Formation sandstone show that most zircons are Phanerozoic (90%): 140–150 Ma (10%), 180–220 Ma (25%), 240–270 Ma (15%), 300–360 Ma (15%), 391–395 Ma (3%), and 450–540 Ma (20%), whereas 10% are Precambrian in age. About 90% of the zircons have eHf(t) values ranging from +11.1 to −12.8. This suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the Central Asian Orogenic Belt and the Jiamusi Block. The age of the Yongfuqiao Formation is constrained to the earliest Cretaceous, which represents the accretion time of the mid-Triassic to mid-Jurassic oceanic complexes. When compared with the Mino Complex in Japan and the Tananao Complex in Taiwan, three different provenances are identified suggesting three ancient drainage systems which transported sediments from NE China, North China, and South China to the Paleo-Pacific subduction-accretion system.

Sedimentation in remnant ocean basin off SW Taiwan with implication for closing northeastern South China Sea

Taiwan is one of the most cited examples of modern mountain building in an oblique arc–continent collision. However, the recognition and significance of the Taiwan remnant ocean basin in the final stages of the collision of Luzon with the Chinese margin have long been ignored. This paper emphasizes the Taiwan remnant ocean basin as the main sink for sediments from the uplifted Taiwan suture zone and as a record of clues to the suturing history of the Taiwan collision zone. A part of the palaeo South China Sea has been closed by oblique collision of the Luzon Arc with the Chinese margin in the Taiwan region since about 4 Ma. As collision continued southward along the Taiwan–Luzon convergent zone the remaining South China Sea off SW Taiwan became the Taiwan remnant ocean basin. Beginning about 1.6 Ma much sediment from the longitudinal drainage of the Taiwan orogen was fed into this remaining basin and trapped in the intra-slope basins of the Kaoping slope, with some sediment bypassing via the Kaoping Canyon to the lower reach of the Penghu Canyon. This basin is characteristic of an axial canyon–deep-sea channel–oceanic trench system without significant sediment accumulation in submarine fans. Excess sediments from the Penghu Canyon mainly spill over out of the closing basin to the South China Sea and Manila Trench via the deep-sea Penghu Channel. The Taiwan–Luzon convergent zone continues along the NE South China Sea where the Taiwan remnant ocean basin exists. The implication of the convergence is that the Taiwan remnant ocean basin will keep shrinking in the next few million years southward to the northern end of the Manila Trench at around 20°N, where collision is replaced by subduction. The remnant ocean basin would be closed and deformed, and sediments would be accreted to uplifted collisional terranes north of the Manila Trench.

Seismic, satellite, and site observations of internal solitary waves in the NE South China Sea.

Internal solitary waves (ISWs) in the NE South China Sea (SCS) are tidally generated at the Luzon Strait. Their propagation, evolution, and dissipation processes involve numerous issues still poorly understood. Here, a novel method of seismic oceanography capable of capturing oceanic finescale structures is used to study ISWs in the slope region of the NE SCS. Near-simultaneous observations of two ISWs were acquired using seismic and satellite imaging, and water column measurements. The vertical and horizontal length scales of the seismic observed ISWs are around 50 m and 1–2 km, respectively. Wave phase speeds calculated from seismic observations, satellite images, and water column data are consistent with each other. Observed waveforms and vertical velocities also correspond well with those estimated using KdV theory. These results suggest that the seismic method, a new option to oceanographers, can be further applied to resolve other important issues related to ISWs.

Morphology and formation mechanism of pyrite induced by the anaerobic oxidation of methane from the continental slope of the NE South China Sea

In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate–methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate.

Geochronology and isotope analysis of the Late Paleozoic to Mesozoic granitoids from northeastern Vietnam and implications for the evolution of the South China block

In northeastern Vietnam, Late Paleozoic and Permo-Triassic granitic plutons are widespread, but their tectonic significance is controversial. In order to understand the regional magmatism and crustal evolution processes of the South China block (SCB), this study reports integrated in situ U–Pb, Hf–O and Sr–Nd isotope analyses of granitic rocks from five plutons in northeastern Vietnam. Zircon SIMS U–Pb ages of six granitic samples cluster around in two groups 255–228Ma and 90Ma. Bulk-rock εNd (t) ranges from −11 to −9.7, suggesting that continental crust materials were involved in their granitic genesis. In situ zircon Hf–O isotopic measurements for the granitic samples yield a mixing trend between the mantle- and supracrustal-derived melts. It is suggested that the granitic rocks were formed by re-melting of the continental crust. These new data are compared with the Paleozoic and Mesozoic granitic rocks of South China. We argue that northeastern Vietnam belongs to the South China block. Though still speculated, an ophiolitic suture between NE Vietnam and South China, so-called Babu ophiolite, appears unlikely. The Late Paleozoic to Mesozoic magmatism in the research area provides new insights for the magmatic evolution of the South China block.

The first record of Eocene tuff in a Paleogene rift basin near Nantou, Western Foothills, central Taiwan

Microfossils and a U–Pb age dating on zircon grains in the tuff beds exposed in the axial part of the Tsukeng anticline along the Pinglin River in the Western Foothills near Nantou, central Taiwan, show an occurrence of the Eocene volcanics unconformably beneath the uppermost part of the Latest Oligocene Wuchihshan Formation. This is the first discovery of the Eocene tuff exposed in the Western Foothills.The proposed Miocene “Tsukeng Formation” and “Takeng Formation” of Ho et al. (1956) named for sequences exposed in the Nantou area, Western Foothills, have to be abandoned and the standard Oligocene–Miocene lithostratigraphy used commonly in the Western Foothills of northern Taiwan is properly applicable in central Taiwan. The thick pink–brown–green colored volcanics unconformably beneath the uppermost Wuchihshan Formation is named for the first time as the Pinglin Tuff which contains Late Middle Eocene calcareous nannofossils (Zone NP16) consistent with a U–Pb age dating (38.8±1Ma) on zircon grains in the tuff. The Pinglin Tuff is overlying the Middle Eocene Chungliao Formation which contains indigenous larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannofossils of Zones NP14–15. The Middle Eocene Pinglin Tuff and Chungliao Formation represent the Paleogene syn-rift sequence unconformably overlain by the Latest Oligocene–Miocene post-rift sequence. This is the first document with conclusive paleontological data and age dating showing an occurrence of Paleogene marine rift basin exposed in the Western Foothills. This study also confirms similar Tertiary basin architecture between the Taiwan Strait–Pearl River Mouth Basin in the NE South China Sea and the Western Foothills onland central Taiwan.

A Cenozoic tectono-sedimentary model of the Tainan Basin, the South China Sea: evidence from a multi-channel seismic profile

The Tainan Basin is one of the set of Cenozoic extensional basins along northern margin of the South China Sea that experienced extension and subsequently thermal subsidence. The Tainan Basin is close to the Taiwan Arc-Trench System and straddles a transition zone between oceanic and continental crust. A new regional multi-channel seismic profile (973-01) across the region of NE South China Sea is introduced in this paper. In seismic stratigraphy and structural geology, a model of Cenozoic tectono-sedimentation of the Tainan Basin is established. The results show that three stages can be suggested in Tainan Basin; In Stage A (Oligocene (?)-Lower Miocene) the stratigraphy shows restricted rifting, indicating crustal extension. Terrestrial sedi- ments mostly filled the faulted sags of the North Depression on the continental shelf. Structural highs, including the Central Uplift, blocked material transportation to the South Depression in abyssal basin. In Stage B the Tainan Basin (Middle-Upper Miocene) exhibits a broad subsidence resulting from the post-rifting thermal cooling. The faulted-sags in North Depression had been filled up. Terrestrial materials were transported over the structural highs and deposited directly in the South Depression through sub- marine gullies or canyons. This sedimentation resulted in a crucial change in the slope to a modern shape. In Stage C (Latest Miocene-Recent) a phase change from extension to compression took place due to the orogeny caused by the overthrusting of the Luzon volcanic arc. Many inverse structures, such as thrusts, fault bend folds, and a regional unconformity were formed. Forland basin began developing.

Mesozoic subduction-accretion zone in northeastern south china sea inferred from geophysical interpretations

A segment of Mesozoic subduction-accretion zone was inferred across the northeastern South China Sea at approximately NE45° orientation. Basic evidence includes the following: A belt of peek gross horizontal Bouguer gravity gradient (PGHGBA) is comparable in size and intensity to that of the Manila subduction-accretion zone. A belt of high positive magnetic anomalies appears to the north and sub-parallel to the PGHGBA, representing the volcanic arc associated to the subduction zone. The PGHGBA crosses obliquely both Cenozoic structures and present seafloor topography, indicating a pre-Cenozoic age. The segment is offset left-laterally by NW-running strike-slip faults, in concord with the Mesozoic stress field of South China. In addition, the existence of the subduction zone is supported by wide-angle seismic data obtained in different years by different institutions. At approximate localities, a north-dipping ramp of Moho surface is indicated by records of ocean-bottom seismometers, and a strong reflector about 8 km beneath the Moho reflector is indicated by both OBS and long-cable seismic records. The identification of a segment of Mesozoic subduction zone in NE South China Sea fills nicely the gap of the Great Late Mesozoic Circum SE Asia Subduction-acrretion Zone, which extended from Sumatra, Java, SE Kalimantan to N Palawan, and from Taiwan, Ryukyu to SW Japan.

The Geological Structure and Prospect of Gas Hydrate over the Dongsha Slope, South China Sea

The area around the Dongsha Island in the northeastern South China Sea was generally known for the occurrence of gas hydrate related features, like BSR, cold seep carbonates and chemoautotrophic bacteria. To precisely evaluate the potential of gas hydrate occurrence in the NE South China Sea, marine geology of the large Dongsha slope region is studied based on more geophysical and geological data including multiple-channel seismic and high resolution sub-bottom topographic images. The east Dongsha slope area represents the largest slumping zone in the northern slope of the South China Sea, and might exhibit the highest potential of gas hydrate occurrences. The central Dongsha slope area, with very thin Cenozoic sediments, was tectonically disturbed by the latest Cenozoic uplifting and magmatism events, therefore is unfavorable for gas hydrate occurrence. The west Dongsha slope area with the deepest Cenozoic depression and moderate to minor slumping bodies might be favorable for gas hydrate occurrence.

Measurement and analysis of acoustic intensity fluctuations induced by South China Sea internal solitons

In May 2001, a suite of acoustic and oceanographic sensors was deployed by a team of US, Taiwan, and Singapore scientists in the NE South China Sea to study the effects of ocean variability on low-frequency sound propagation in a shelfbreak environment. The primary acoustic receiver was an L-shaped hydrophone array moored on the continental shelf that monitored a variety of signals transmitted parallel to and across the shelfbreak by fixed and towed sources. This talk discusses and contrasts the amplitude fluctuations in the signals measured by the vertical segment of the listening array in two different days, one with the passage of several huge solitons that depressed the shallow isotherms to the sea bottom, and one with a much less energetic soliton field. In addition to exhibiting large temporal changes, the acoustic data also show a much more vertically diffused sound intensity field as the huge solitons occupied and passed through the transmission path. Using a space-time continuous empirical sound speed model based on the moored temperature records and geoacoustic parameters estimated using the close-range towed source signals, the observed acoustic intensity fluctuations are explained using coupled-mode physics. [Work supported by ONR under the ASIAEX program.]

Structural evolution from Paleogene extension to Latest Miocene-Recent arc-continent collision offshore Taiwan: comparison with on land geology

Marine structures observed in seismic profiles across the NE South China Sea–Taiwan Strait–Luzon Arc region show that they are comparable to those observed onshore Taiwan. The Hanjiang Depression and Dongsha Uplift off the SE China coast extend to the Penghu Basin and Penghu Platform, respectively, in the Taiwan Strait, while the Tainan Basin in the south of Penghu Platform is connected to the Chaoshan Depression south of the Dongsha Uplift. The Hanjiang Depression and the Penghu Basin are composed of Paleogene syn-rift sequences on the Mesozoic basement and are unconformably overlain by Neogene post-rift strata. Similar successions are found underneath the coastal plain or have been thrust up as a fold-and-thrust belt bordering the Peikang Basement High onshore central Taiwan.East of the Manila Trench, off southwestern Taiwan, parts of the Tainan Basin are thrust into the submarine syn-collision accretionary wedge (the fold-and-thrust Kaoping Slope) in the initial arc-continent collision zone. They have also been exposed in the fold-and-thrust Western Foothills south of the Peikang Basement High in southern Taiwan during an advanced stage of arc-continent collision since the Late Pliocene. Further east, the pre-collision accretionary wedge (the Hengchun Ridge) shoals northward to the Hengchun Peninsula, with Late Miocene turbidites unconformably overlain by Plio–Pleistocene shallow-marine slope basin sequences. In the arc domain, east of the arc-prism boundary fault, the western forearc sequences in the North Luzon Trough are deformed. Two normal-faulted intra-arc basins occur on the eastern part of the Lanhsu Island in the Luzon Arc. The scenario of the deformed forearc sequences and the development of the two intra-arc basins in the initial arc-continent collision zone are analogous to the Lichi Mélange–Taiyuan Basin and the intra-arc basins in the southern Coastal Range, eastern Taiwan.Additionally, the lateral change in the marine structure from the passive Asian continental margin to the Manila subduction system is comparable to the temporal evolution from Paleogene normal faulting, through Neogene subduction, to Latest Miocene-Recent arc-continent collision observed onshore Taiwan.

Tectono-sedimentary controls on the likelihood of gas hydrate occurrence near Taiwan

Marine sediments on the continental slope of the NE South China Sea have appropriate thickness, methane-generating potential, and occur in a suitable pressure–temperature regime to host gas hydrate. Evidence for gas hydrate, the bottom simulating reflector (BSR), is observed to the south of Taiwan on reflection seismic records, and can be used to suggest that gas hydrates are widely distributed. The tectono-sedimentary framework south of Taiwan bears directly upon methane generation and the likelihood of the presence of significant gas hydrate deposits. Three zones of probable hydrate occurrence have been delineated along the margins of the NE South China Sea: (1) in a thick accumulation of sediment along the northern passive margin; (2) along a more thinly sedimented eastern active collisional margin, and especially; (3) in a zone of thick originally passive margin sedimentation into which the collisional margin has encroached obliquely.