West Pacific Margin Research Articles

Crust and Upper Mantle of the South China Sea (probabilistic-deterministic gravity model)

Rheological layering of a tectonosphere of the South China Sea (SCS) on the crust rigid (the depth interval of 5–30 km), viscous subcrustal (the depth interval of 30–70 km), rigid lower lithospheric (50–90 km), astenospheric (80–150 km) and rigid subastenospheric (the depth interval is more than 150 km) is established. Distributions of the density inhomogeneities connecting with the main tectonic events in SCS are caused by the Paleo-Pacific’s convergence, and later — the Philippine’a oceanic plate with the Philippine archipelago and further — with the Asian margin. In this zone by distributions of density contrast in a tectonosphere are tracing Cenozoic processes of a subduction, stretching, transformic shift and structure of the central type of the probable plume nature which form an evolutionary sequence: back arc, or paleo-oceanic spreading → the Philippine subduction → NE-stretching with shift → formation of the structure of the central type of a probable plume origin. The structures caused by convergence of the Asian continent with the Indo-Australian plate are isolated from the West Pacific margin, and the underthrsting of rigid lithospheric plates from the South under a lithosphere of the margin sea reflects traces of more ancient collision of fragments of the Gondwana with Asian continent.

Tectono-magmatic evolution of the Philippine Sea Plate: A review

• Geological and geophysical characteristics of the PSP. • Tectonic evolution of the PSP as a key to the west Pacific trench-arc-basin system. • Subduction initiation, origin of basins and intraplate magmatism. • Relationship between subduction input and arc/back-arc output. The West Pacific Margin incorporates 75% of global marginal basins/back-arc basins. These basins and their adjacent trenches and island arcs constitute a huge trench-arc-basin system created by the interactions among three tectonic plates (the Pacific, Eurasian, and Indian plates) since about 50 Ma. Located among these three plates, the Philippine Sea Plate (PSP) is surrounded by a series of subduction zones, e.g., the Philippine Trench to the west, the Ryukyu Trench and the Nankai Trough to the north, the Izu-Bonin-Mariana (IBM) Trench to the east, and the Yap and Palau trenches to the south. Plate reconstruction shows that the PSP was originally located near the equator, and it has gradually moved northward since the Early Cenozoic. In addition, due to multiple subducted slab rollback events and the related multiple rifting of the proto-IBM Arc, several important tectonic units have been formed, including back-arc basins and relic/active arcs. The back-arc basins include the West Philippine Basin (WPB, spreading at 65-35 Ma), the Shikoku Basin (SKB, spreading at 27-15 Ma), the Parece Vela Basin (PVB, spreading at 29-15 Ma), and the Mariana Trough (MT, spreading from 5 Ma to present), and the main arcs include the Relic Kyushu-Palau Arc (ridge) (KPR, termination at 29 Ma), the Relic West Mariana Arc (ridge) (WMR, termination at 6Ma), the Active IBM Arc (since 11 Ma), and the Yap Arc (since 24 Ma). The geochemistry of these main tectonic units is as follows. The WPB has undergone back-arc spreading and intraplate magmatism, producing many rock types such as back-arc basin basalts (BABBs) similar to normal mid-oceanic ridge basalt (NMORB) and/or enriched mid-oceanic ridge basalt (EMORB) in the central basin, and oceanic island basalts (OIBs) in the Benham Rise and the Urdaneta. In addition, several Late Mesozoic arc terranes (e.g., the Amami Plateau, the Daito Ridge, and the Huatun Basin) developed in the WPB. The SKB mainly contains back-arc basin basalts (BABBs). After termination of the spreading in the SKB, two groups of seamounts with ages of 15-7 Ma formed. One group has undergone subduction. The other group (the Kinan Seamount Chain) is characterized by an OIB and mixed mantle source (Indian Ocean MORB and enriched mantle type one (EM1) geochemical signatures. The PVB basement rock is composed of back-arc basin basalts (BABBs). However, the southern PSP basin is very complex. The Mariana Trough mainly contains BABBs, with island arc basalts (IABs) occurring in the spreading center near the island arc. The IBM Arc mainly contains 52-51 Ma fore-arc basalts, 49-45 Ma boninites, and <45 Ma mature island-arc magmatic rocks. The two relic arcs (the KPR and the WMR) mainly contain IABs. The basement rocks in these back-arc/arc tectonic units are isotopically similar to Indian Ocean MORB. Thus, the West Pacific Ocean, e.g., the PSP, is an ideal place for studying several important geological processes, including interactions between large-scale tectonic plates, subduction initiation, back-arc spreading, intra-oceanic subduction, intraplate magmatism in a back-arc basin, and the geochemical cycle of a subduction zone.

Construction of the Continental Asia in Phanerozoic: A Review

AbstractThis is a review of the formation and tectonic evolution of the continental Asia in Phanerozoic. The continental Asia has formed on the bases of some pre‐Cambrian cratons, such as the Siberia, India, Arabia, North China, Tarim, South China, and Indochina, through multi‐stage plate convergence and collisional collages in Phanerozoic. The north‐central Asia had experienced the expansion and subduction of the Paleo‐Asian Ocean (PAO) in the early Paleozoic and the closure of the PAO in the late Paleozoic and early Mesozoic, forming the PAO regime and Central Asian orogenic belt (CAOB). In the core of the CAOB, the Mongol‐Okhotsk Ocean (MOO) opened with limited expansion in the Early Permian and finally closed in the Late Jurassic–Early Cretaceous. The south‐central Asia had experienced mainly multi‐stage oceanic opening, subduction and collision evolution in the Tethys Ocean, forming the Tethys regime and Himalaya‐Tibetan orogenic belt. In eastern Asia, the plate subduction and continental margin orogeny on western margin of the Pacific Ocean, forms the West Pacific regime and West Pacific orogenic belt. The PAO, Tethys, and West Pacific regimes, together with Precambrian cratons among or surrounding them, made up the major tectonic and dynamic systems of the continental Asia in Phanerozoic. Major tectonic events, such as the Early Paleozoic Qilian, Uralian, and Dunhuang orogeneses, the late Paleozoic East Junggar, Tianshan and West Junggar orogeneses, the Middle to Late Permian Ailaoshan orogeny and North‐South Lhasa collision, the early Mesozoic Indochina‐South China and North‐South China collisions, the late Mesozoic Mongolia‐Okhotsk orogeny, Lhasa‐Qiangtang collision, and intra‐continental Yanshanian orogeny, and the Cenozoic Indo‐Asian, Arab‐Asian, and West Pacific margin collisions, constrained the formation and evolution of the continental Asia. The complex dynamic systems have left large number of deformation features, such as large‐scale strike‐slip faults, thrust‐fold systems and extensional detachments on the continental Asia. Based on past tectonics, a future supercontinent, the Ameurasia, is prospected for the development of the Asia in ca. 250 Myr.

Microfossil as proxy for palaeoclimate and palaeoceanography

Recent global warming has been addressed due to human activity that causes increased greenhouse gases. However, there are inherent uncertainties in the statement, one of them is the level of natural variability inherent in the climate system. Climate data from measuring instruments are not long enough to evaluate climate variability and current climate evolution. Therefore, we need climate data that has a long back span. To get adequate past climate data, we need natural phenomena which are climate dependent. This natural phenomenon provides a proxy record of the climate. This study of proxy data is the foundation of palaeoclimatology and paleoceanography. Microfossils (i.e., foraminifera, palynomorphs, nannofossils) which in geology are used as a standard tool in biostratigraphy for both age determination and paleoenvironment and correlation, can also be used as a proxy for obtaining paleoclimate and paleoceanography data. Using microfossil as a proxy to study past climate and paleoceanography, we need an understanding of the type of proxy data available and methods used in their analysis.In addition to the dating method (biostratigraphy), there are many climate and oceanography parameters that can be obtained from microfossil proxies such as: sea surface temperature (SST), sea surface salinity, (SST) climate (warm, cold, dry, wet), precipitation, productivity, oxygen content and organic carbon level, deep sea current and ventilation/upwelling, thermocline and mixed layer, variability deep water properties, CCD, bathymetry, sea level change and dissolution. The methods to obtain data fall into some categories e.g., faunal/floral displacement, morphology changes, transfer function/modern analog and isotopic content. Another method that can be used is observing microfossil assemblages and link them to ecological changes associated with climate change and its paleoceanography.A paleoclimate and paleoceanography study using microfossil proxies has been conducted in the Cendrawasih bay, Papua, Indonesia. The study shows that climate in the tropical west Pacific margin (Cendrawasih bay) during Late Pleistocene to Holocene shows high variability. There are nineteen climate changes occurred during Holocene. Early Holocene dated as ca. 11,800-year BP marked by rapid warming with SST differences to last glacial is about 4oC. Early to Middle Holocene (ca. 5960-year BP) marked by increasing temperature up to 2oC, interrupted by cooling at ca. 11230-, 8310- and 7120-years BP. At Middle Holocene temperature decreased rapidly and reached its peak at around ca. 3150-year BP. After cooling at ca. 3150-year BP, temperature increased and then decreased with its peak at ca. 1710-year BP. Since ca. 1710-year BP to Recent, temperature shows warming trend. SST from MAT indicates warming environment near to 1.5oC. The warming trend was interrupted by rapid cooling and warming at ca. 300-year BP. This last warming trend indicates that global warming had started before industrial era and rapid cooling, or warming can occur without anthropogenic gases influence. The typical Holocene climate of warm-wet, dry-cold reverse and become warm-dry, cold-wet during ca. 790-370-year BP and then reversed back to preceding state.Semi-restricted basin occurred since last glacial with anaerobic condition and estuarine circulation system. Warming during interstadial 1e-1a, causing reverse water circulation and basin become sub-aerobic with anti-estuarine circulation. A lot of terrestrial organic matter flow to the bay and increase acidity and carbonate dissolution. High sedimentation found occurred during glacial period especially at the end of glacial period. Rapid warming during late glacial to middle Holocene, rising relative sea level and the bay become more open marine with well oxygenated bottom water and high marine productivity. Warm temperature and deeper thermocline depth (~ 250 m) in west Pacific occurred up to ca. 5960-year BP. Decreasing Sea surface temperature at ca. 5960-year BP and drop of relative sea level causing sub-aerobic condition inside bay. The semi-restricted state with sub-aerobic condition occurred up to Recent.Distribution of Sphaeroidinella group in the tropical west Pacific shows strong correlation with thermocline depth and reflect El Niño frequency event. Early middle Holocene dominated by La Niña-like condition and since Middle Holocene (ca. 5960-year BP) frequent El Niño event began to occur.

Chronostratigraphic framework of the East China Sea since MIS 6 from geomagnetic paleointensity and environmental magnetic records

Abstract Continental shelf is a globally important reservoir for terrigenous sediments, and provides sediment transportation pathways that extend from the shoreline to abyssal basins. Due to the strong land-sea interaction in response to frequent sea level change during the late Quaternary and methods' constraint, it is a big challenge to establish a reliable chronostratigraphy on the continental margin with terrigenous sediments dominance. Relative geomagnetic paleointensity (RPI) is quite useful for high-resolution chronostratigraphy in Brunhes epoch. In this study, relative paleointensity record for a sediment core (SFK-1, 82.9 m) from the outer East China Sea (ECS) shelf was studied. Rock magnetic results show that coarse vortex state magnetite is the dominant magnetic carrier throughout the core and that these sediments generally meet the accepted criteria for constructing relative paleointensity (RPI) record. RPI was established by normalizing the natural remanent magnetization (NRM) with isothermal remanent magnetization (IRM), both after 30 mT alternating demagnetization. Further, our RPI record was correlated with PISO-1500 and 7 age tie points were obtained. An age model is established for SFK-1 core with a basal age of 165 ka by combining the radiocarbon dates, relative geomagnetic paleointensity, and tandem correlation of environmental magnetic parameters to foraminiferal stable oxygen isotopes, which provides a reliable chronological framework for the later paleoenvironmental studies of ECS. The consistency of RPI record of SFK-1 and other worldwide observations suggest that global-scale pattern of geomagnetic paleointensity behavior is also documented in the sediments of the East China Sea, and the RPI of SFK-1 can be used as a reference curve for the RPI studies of other cores of ECS area, and even the whole west Pacific margin seas.

Erratum to: A new resource of single nucleotide polymorphisms in the Japanese eel Anguilla japonica derived from restriction site-associated DNA

We present a new resource of single nucleotide polymorphisms (SNPs) in the Japanese eel Anguilla japonica, a catadromous eel species distributed along the west Pacific margin. We used the restriction site-associated DNA (RAD) sequencing for the detection of SNPs. On the basis of glass eel samples collected from two Japanese coastal areas, 33,976 SNP sites that occurred among 18,353 RAD loci were identified. Using the RAD loci, we preliminarily tested genetic differentiation between the two geographical samples. No evidence of genetic population heterogeneity was obtained (F ST = 0.0015, P = 0.073), although a small portion of loci (0.8 %) exhibited an elevated level of genetic differentiation (F ST ≥ 0.100). A catalogue of SNPs constructed in the present study, in which we provide the positions of SNP sites within RAD loci and the scaffolds in the reference genome, and, if available, the position of RAD loci on genetic linkage groups, will be of great use for advancing ecological and breeding studies in A. japonica.

Seawater Nd isotope variation in the Western Pacific Ocean since 80 Ma (ODP 807, Ontong Java Plateau)

This study reports neodymium isotopic (εNd) variability at a time resolution of 0.5 to 3Ma since the Late Cretaceous as recorded in a marine sedimentary core from the Western Pacific (ODP 807; 3°36′N, 156°3′E; Ontong Java Plateau). Our core is mainly fine-grained and composed of continuous sequences of nannofossil oozes. The εNd measured in the carbonate fraction was used as a proxy of εNd of seawater of the Western Pacific. On a long term, our results indicate a general increase in εNd of seawater by 4.5εNdunits from the Late Cretaceous (εNd=−6) to modern times (εNd=−1.7). This pattern was related to the emergence of the West Pacific margin and the progressive isolation of the Pacific Ocean from the other oceanic basins, resulting in its progressive shift to more radiogenic values through the Cenozoic. This long-term pattern is in accordance with previously published FeMn crusts data from the same study area. Nonetheless, by being at higher time resolution, our data records additional sharp and pseudo-cyclic variations (~7–11Ma periods) superimposed on this long-term pattern from ~40Ma to modern times. These oscillations might reflect the alternating dominance of the two main deep water masses (NPDW and UCDW) bathing our study area. In the same core, we also measured the εNd in the detrital fraction in order to trace back the local terrigenous inputs. The terrigenous record shows a significant variability up to +12εNdunits. This was linked to the emergence of the west Pacific subduction zone ~50Ma ago causing a higher input of radiogenic isotopes. In conclusion, the large variability observed in both seawater and detrital εNd records most probably result from a major tectonic and oceanic circulation reorganization of the Pacific Ocean.

Late Mesozoic–Early Cenozoic deformation history of the Yuanma Basin, central South China

The Yuanma Basin, situated in central South China with more than 800km far away from the active plate boundaries, is a key region in deciphering the Late Mesozoic–Early Cenozoic tectonic evolution of South China. Based on a field analysis of fault–slip data collected from different rock units, we document polyphase tectonic stress fields and address the changes in the orientation of the principal stresses, and finally establish a five-phase stress evolution of the basin during the Late Mesozoic–Early Cenozoic. The earliest one with E–W compression and N–S extension occurred in the Mid–Late Jurassic and resulted in regional folding and west-directed thrusting along the eastern margin of the basin. This deformational event constrains the timing of the significant intracontinental orogeny in South China to be Mid–Late Jurassic. The subsequent NW–SE extensional regime was responsible for the initial opening and sedimentary infill of the basin during the earliest Cretaceous, which occurred coevally with the extensive Early Cretaceous magmatism, volcanism and extensional doming in South China. The tectonic regime then changed, in the late Early Cretaceous, to a compressional one with NW–SE compression and NE–SW extension, causing the inversion of this extensional basin. This compression affected the whole South China, leading to an apparent magmatic quiescence at ~108–117Ma and sinistral strike–slip faulting on the NNE-trending faults. The N–S extension prevailed in the Late Cretaceous, and activated the east-trending normal faults that controlled the Late Cretaceous subsidence. This extensional phase seems to have lasted through the Early Paleogene and ended in the Late Paleogene by a compressional regime with NE–SW compression and NW–SE extension, as attested by the stratigraphic unconformity at the base of the Neogene in the Jianghan Basin. The temporary evolution of these tectonic stress fields documented in the Yuanma Basin provides a new insight into the influences of different plate tectonics exerting on the South China Block over the Late Mesozoic to Early Cenozoic time. We infer that the Yuanma Basin was influenced, in the Middle Jurassic–Early Cretaceous, by the process of westward subduction of paleo-Pacific plate; and in the Late Cretaceous–Early Paleogene by a combined effect of the subduction along the west pacific margin and in the Tethyan domain; and finally in the Late Paleogene by the far-field effects of India–Asia collision.

Ridge subduction and porphyry copper-gold mineralization: An overview

Many large porphyry Cu-Au deposits are connected to adakitic rocks known to be closely associated with ridge subduction. For example, there are several subducting ridges along the east Pacific margin, e.g., in Chile, Peru, and South America, most of which are associated with large porphyry Cu-Au deposits. In contrast, there are much fewer ridge subductions on the west Pacific margin and porphyry Cu-Au deposits are much less there, both in terms of tonnage and the number of deposits. Given that Cu and Au are moderately incompatible elements, oceanic crust has much higher Cu-Au concentrations than the mantle and the continental crust, and thus slab melts with their diagnostic adakitic chemistry have systematically higher Cu and Au, which is favorable for mineralization. Considering the geotherm of subducting slabs in the Phanerozoic, ridge subduction is the most favorable tectonic setting for this. Therefore, slab melting is the likely link in the spatial association between ridge subduction and Cu-Au deposits. Geochemical signatures of slab melting and hence maybe ridge subduction in less eroded regions in eastern China, the central Asian orogenic belt etc. may indicate important exploration targets for large porphyry Cu-Au deposits.

Back-arc zones of the active West Pacific margin: An analog of Atlantic-type passive margins and their petroleum potential

Back-arc zones of the active West Pacific margin: An analog of Atlantic-type passive margins and their petroleum potential

Present-day heat flow, thermal history and tectonic subsidence of the East China Sea Basin

The East China Sea Basin is located in the convergence area between the Eurasian plate, the Pacific plate and the Philippine Sea plate, and consists of two depressions, the Taibei Depression in the west and the Xihu Depression in the east. Heat flow measurements show that the East China Sea Basin is characterized by present-day heat flow around 70.6 mW/m 2, varying between 55 and 88 mW/m 2. No significant difference in heat flow is observed between the Xihu and the Taibei Depressions. Thermal history reconstruction using vitrinite reflectance suggests that the thermal history was, however, different in the Taibei and the Xihu Depressions. Paleo-heat flow values when the pre-Tertiary formations experienced their maximum temperature at the end of the Paleocene reached a mean of 82 mW/m 2 in the Taibei Depression, much higher than the present-day value. The lower Tertiary sediments in the Xihu Depression experienced maximum temperatures at the end of Oligocene (35.4–23.3 Ma) and reached a mean paleo-heat flow value of 83 mW/m 2. Tectonic subsidence analysis shows that the timing of the major rifting episode was different across the East China Sea Basin. The rifting occurred from the Late Cretaceous (∼65 Ma) to the early Eocene (∼55 Ma) in the Taibei Depression, followed by thermal subsidence from the late Eocene to the end of Miocene (23.3-5.2 Ma). In contrast, in the Xihu Depression the initial subsidence lasted until the early Miocene and thermal subsidence to the end of Miocene. From Pliocene to the present, an accelerated subsidence took place all along the West Pacific margin of Asia. Significant thicknesses of strata were removed from the unconformities in the basin: the mean amount of erosion was 1147 m from the Paleocene and 1208 m above the Oligocene in the Taibei Depression, and 1409 m from the Oligocene in the Xihu Depression.

Westward Pacific drift and the tectonics of eastern Asia

The tectonics of southeast Asia is attributed to the flow of mantle material away from a region of accumulation in the mantle at the west Pacific margin. The accumulation is dynamically maintained by the continuous introduction of material from the east, in the form of the westward-drifting Pacific plate. The region bounded on the north by southern Siberia and on the south by southern Indonesia is experiencing westward displacement as a result of slow flow in the mantle. The displacement is fastest in low latitudes, resulting in the westward embayment of the Equatorial west Pacific margin. Besides the westward displacement of Sundaland in the fashion described by Powell and Johnson (1980), the model calls for the encroachment of southeast Asia upon northern Burma and India. The geoidal features upon which the model is based are attributed to mantle mass anomalies, rather than to core-mantle topography. The pressure gradient associated with the western slope of the west Pacific geoidal high results in the flow of mantle material in that direction.