Yanhui Suo

TECTONIC TRANSITION AND PLATE RECONSTRUCTIONS OF THE EAST ASIAN CONTINENTAL MAGIN

It is a hot debate on the Meso-Cenozoic dynamics of the East Asian continental margins,since the nature,type and evolution of its continental margins are not well-known..This paper systematically summarizes the results of plate reconstructions on the East Asian continental margin since Permian over the past 40 years with emphasis on the new research results in the past 10 years.The paper mainly focuses on the variation in types of the East Asian continental margin since Late Triassic,the transitions among different tectonic domains.Our data suggests that the East Asian continental margins as a whole experienced a pre-Triassic passive continental margin,a Late Triassic-Early Cretaceous continental magmatic arc of the Andean-type active continental margin,a Late Cretaceous-Eocene strike-slipping Andean-type active continental margin with of pull-apart basins,and a post-Oligocene Japanese-type active continental margin successively.Tectonic trasition is important for understanding of the formation of the Bohaisx Bay,the Yellow Sea,the East China Sea and the South China Sea basins in East China.The changes of the continent-ocean distribution,plate configuration and dynamics at the various stages are also discussed.

BASIN DYNAMICS AND BASIN GROUPS OF THE SOUTH CHINA SEA: BASIN DYNAMICS AND BASIN GROUPS OF THE SOUTH CHINA SEA

The South China Sea was formed in Cenozoic.Basins in the South China Sea could be divided into different types,such as continental shelf basins,continental slope basins and deep sea basins,which are closely related with the rifting and transition of the continental margins,and thus could be grouped into strike-slip-related pull-apart and extensional basins,extrusion-escape-related rifting basins,extension-and subduction-related buckling basins.They developed further into some ridge-spreading-related oceanic sub-basins in different stages.These basins were formed not under a single dynamics but under a very complex and changeable dynamics.These basins have suffered from a series of Cenozoic tectonic movements,such as the Shenhu,the South China Sea,the Dongsha,resulting in the formation and spatial-temperal migration of complex angular unconformities in these basins.Accompanying with the tectonic migrations and evolutions in these basins,faulting,magmatism,shifting of sedimentary subsidence centers and depocenters,oil accumulation and geohazards show a significant feature of jumping.The complex dynamic settings of the South China Sea have caused many controversies on their origin.The plate dynamic factors include the Pacific Plate subduction and the indentation of the Philippine Sea Plate along the Taiwan Orogen to the east side of the South China Sea,and the Indian Plate oblique subduction and mid-ocean ridge subduction to the west side.They may also be responsible for the uplifting of the Tibetan Plateau and the related extrusions of continental blocks to the north side.At the same time,the mantle dynamics of deep-seated magma underplating,delamination,mantle plume and mantle-hydrated process should not be ignored.At last,this paper proposes one strike-slipping pull-apart model to explain the onset of the South China Sea Basin which is closely related to the tectonic evolution of the Pacific Tectonic Domain.

BASIC STRCUTURAL PATTERN AND TECTONIC MODELS OF THE SOUTH CHINA SEA: PROBLEMS, ADVANCES AND CONTROVERSIES: BASIC STRCUTURAL PATTERN AND TECTONIC MODELS OF THE SOUTH CHINA SEA: PROBLEMS, ADVANCES AND CONTROVERSIES

The South China Sea is located at a juncture among the Eurasian,the Indian-Australian and the Pacific plates,being the largest continental marginal sea along the East Asian continental margin.It has experienced a complex transition of continental marginal types.The northern margin was an Andean-type continental margin before 80 Ma,then gradually transferred into a rifted continental margin in the Eocene and a typical passive continental margin since the middle Miocene.The eastern margin was an open water before 17 Ma and gradually became a subduction zone of the trench-arc-basin system by one-way subduction to double-way subduction,when the South China Sea became semi-closed basin since 6 Ma.The western boundary gradually transformed into a continental margin with strike-slipping faulting or transform faulting since 34 Ma.The southern margin was an asymmetric rift-type continental margin corresponding to the northern margin before 34 Ma,and became a passive continental margin during 34~16 Ma and gradually a thrusting-type continental margin after 16 Ma.Complex dynamic settings of the South China Sea have caused many controversies on their origin.The plate dynamic factors include either the Pacific Plate subduction and the indentation of the Philippine Sea Plate along the Taiwan Orogen to the east side the South China Sea,or the Indian Plate oblique subduction and mid-ocean ridge subduction to the west side.They may also be responsible for the uplifting of the Tibetan Plateau and the related extrusions of continental blocks to the north side.At the same time,the mantle dynamics of deep-seated magma underplating,delamination,mantle plume and mantle-hydrated process should not be ignored.

CENOZOIC TECTONICS AND DYNAMICS OF BASIN GROUPS OF THE NORTHERN SOUTH CHINA SEA: CENOZOIC TECTONICS AND DYNAMICS OF BASIN GROUPS OF THE NORTHERN SOUTH CHINA SEA

There are a lot of Cenozoic basins from west to east in the northern margin of the South China Sea,including the Beibu Gulf,the Qiongdongnan,the Pearl River Mouth and the Taixinan basins.Previous studies suggested that these basins are derived gradually during the rifting of the southeast continental margin of the South China Block and the formation of the northern passive margin of the South China Sea.However,a large number of seismic profiles revealed that some major basin-controlling faults in the northern margin of the South China Sea are landward-dipping,which are clearly inconsistent with the major seaward dipping faults of a typical passive continental margin basin.Thus,the Mckenzies extension model of passive continental margin remains controversial for the formation mechanism of the northern marginal basins of the South China Sea.This article,based on the comparison between a large number of field observation and marine seismic data,reveals that the northern continental margin of the South China Sea is not a passive continental margin before 34Ma.The early faults were well developed in NE—NNE-striking,corresponding to the strike-slipping faults in the southeast South China.These dextral,right-step strike-slipping faults are NE—NNE striking,controlling the secondary faults with near-EW or NEE strikes and the distribution of tectonic units in the pull-apart basins.Therefore,a series of Cenozoic basins in the northern margin of the South China Sea is dextral,right-step pull-apart basin group,having close relation in dynamics.This pull-apart model is consistent with the migration of sedimentary-subsidence centers and depocenters,tectonic jumping and magmatic migration within Cenozoic basins.The northern continental margin of the South China Sea actually became a typical passive continental margin since 15 Ma,when the South China Sea oceanic crust terminated spreading.At last,all structures in the northern continental margin of the South China Sea are offset by the late,diffusive NWW-striking faults resulting from the gradual indentation of the Philippines Plate to the Eurasian Plate along the Luzon Arc and the Taiwan Orogenic Belt between 10 Ma and about 5 Ma.Basin dynamics in northern continental margin of the South China Sea is mainly related to the dynamics of the Pacific Plate.

CENOZOIC BASIN-CONTROLLING FAULTS AND THEIR BEARING ON BASIN GROUPS FORMAION IN THE SOUTHERN SOUTH CHINA SEA: CENOZOIC BASIN-CONTROLLING FAULTS AND THEIR BEARING ON BASIN GROUPS FORMAION IN THE SOUTHERN SOUTH CHINA SEA

There are many small and medium-sized Cenozoic sedimentary basins in the southern South China Sea,such as the Nanweixi Basin,the Beikang Basin,the Liyue Basin,the Zengmu Basin,the Nansha Trough,the Brunei-Sabah Basin,the Northwest Palawan Basin and other basins from north to south.In general,NE-trending faults control the formation of the half grabens with faulting in the north and overlapping in the south.However,single grabens are mainly developed in the northern continental slope,while two-layered basins developed in the south of the region,of which the lower layer is the graben and the upper layer the imbricated nappes.According to the nature of main controlling faults and the transition of the basins at different evolutionary stages,these basins can be divided into three groups: the rift basin group(the Nanweixi,Beikang and Liyue basins),the rift-pull-apart-foreland superimposed basin group(the Zengmu basin) and the rift-foreland basin group(the Nansha Trough,Brunei-Sabah,the Northwest Palawan basins).The formation of these basin groups is closely related to major marginal faults of the basins and secondary faults in the sub-basins.Based on the nature of the faults,the basin-controlling fault belts can be subdivided into three types: tensile,shear and compressional,including the extensional fault belt in the northern edge of the Nansha Trough,the strike-slip fault belts at the west edge of the Wanan Basin and the Lupar and the Tingjia-Lee Jun Fault belts,and the thrust fault belt in the southern edge of the Nansha Trough.Tectonic events which happened in southern South China Sea,such as the South China Sea Movement in Oligocene and the Nansha Movement in the Middle Miocene,affected the basins to various degrees.As the result,there was the inversion from a rift basin/pull-apart basin to a marine foreland basin,as well as the inversion of fault belts from normal faults to reverse faults or strike-slip faults.The kinetic mechanism of the basin groups varies in different stages.In the early stage,it may be related to the continental rifting of the southeast edge of the Eurasia continent,and the subduction and dragging of the Paleo-South China Sea slab resulted in the splitting of southern South China Sea from the South China continent,and then,half garbens formed with faulting in the north and overlapping in the south.In the later period(about 16 Ma),the north-directed imbricated thrust nappes propagated forward in the southern South China Sea due to the collision of the southern Australian Plate to the northern Eurasian Plate,which resulted in the transition of basin types and the counterclockwise rotation of the Borneo Block.

Structural Geology and Tectonics in Marine Science: Perspectives in the Research of Deep Sea and Deep Interior

The fields of structural geology and tectonics have witnessed great progress over the last decade and are poised for further expansion in the future. One of the significant breakthroughs is the establishment of the ‘Beyond Plate Tectonics Theory’ where a combination of conceptual models and numerical modeling on plume tectonics and plate tectonics has enabled new insights into the structural and tectonic architecture and processes in the deep interior and deep sea. This paper synthesizes developments of structural geology and tectonics from a macroscopic perspective in deep interior and deep sea. Four key techniques are also reviewed: satellite altimetry for surface structures in deep-sea multi-beam sea-floor mapping; tomography for tectonics of the deep interior; diverse modeling approaches and software for unfolding dynamic evolution; and techniques for HT/HP experiments on material rheology and in situ component measurements.

Late Cretaceous basalts and rhyolites from Shimaoshan Group in eastern Fujian Province, SE China: age, petrogenesis, and tectonic implications

ABSTRACT Southeastern China is characterized by an extensive Late Mesozoic (Yanshanian) tectono-magmatic-metallogenic event. Although Late Cretaceous volcanism gradually weakened during the epilogue of the Yanshanian event, its petrogenesis and geodynamic processes remain unclear. In this study, we present new zircon U–Pb–Hf isotopic, whole-rock elemental, and Sr–Nd isotopic compositions data, for volcanic rocks from the Zhaixia Formation of the Shimaoshan Group in Fujian Province. The lower member of the Zhaixia Formation consists of basalts and rhyolites, and the upper member is only rhyolites. These volcanic rocks erupted in the early stage of Late Cretaceous, with basalts erupting earlier (ca. 99–98 Ma) than rhyolites (ca. 98–94 Ma). These basalts record high-K calc-alkaline to shoshonitic, light rare earth element (LREE)- and LILE-enrichment, high field strength element (HFSE)depletion with negligible Eu anomalies, and uniform whole-rock εNd(t) (–3 to –6) and zircon εHf(t) (–3.3 to –14.1) values. The overlying rhyolites record peraluminous and high-K calc-alkaline characteristics, LREE- and LILE-enrichment with negative Eu anomalies, and Nb–Ta depletion. The whole-rock εNd(t) and zircon εHf(t) values of these rhyolites both increase from the lower member (εNd(t), –1.5 to –4.7; εHf(t), –5.1 to –16.1) to the upper member (εNd(t), –0.5 to 0.1; εHf(t), –0.3 to –4.3). The features imply that these basalts were derived from the partial melting of the enriched lithospheric mantle and the overlying rhyolites from the melting of the crustal components, respectively. Data from the rhyolites in the upper member indicate that more juvenile, Nd–Hf isotopically depleted materials were injected into their source. During the Late Cretaceous, the new, fast rollback of the subducting slab triggered lithospheric extension and asthenospheric upwelling beneath the coastal regions, which induced the melting of lithospheric mantle and crustal components. As continued, the new round of basaltic underplating provided necessary heat to cause partial melting of the deep crust, including the younger, juvenile, and isotopically depleted crustal components.

The potential hydrothermal systems unexplored in the Southwest Indian Ocean

Deep-sea hydrothermal vents possess complex ecosystems and abundant metallic mineral deposits valuable to human being. On-axial vents along tectonic plate boundaries have achieved prominent results and obtained huge resources, while nearly 90% of the global mid-ocean ridge and the majority of the off-axial vents buried by thick oceanic sediments within plates remain as relatively undiscovered domains. Based on previous detailed investigations, hydrothermal vents have been mapped along five sections along the Southwest Indian Ridge (SWIR) with different bathymetry, spreading rates, and gravity features, two at the western end (10°–16°E Section B and 16°–25°E Section C) and three at the eastern end (49°–52°E Section D, 52°–61°E Section E and 61°–70°E Section F). Hydrothermal vents along the Sections B, C, E and F with thin oceanic crust are hosted by ultramafic rocks under tectonic-controlled magmatic-starved settings, and hydrothermal vents along the Section D are associated with exceed magmatism. Limited coverage of investigations is provided along the 35°–47°E SWIR (between Marion and Indomed fracture zones) and a lot of research has been done around the Bouvet Island, while no hydrothermal vents has been reported. Analyzing bathymetry, gravity and geochemical data, magmatism settings are favourable for the occurrence of hydrothermal systems along these two sections. An off-axial hydrothermal system in the southern flank of the SWIR that exhibits ultra-thin oceanic crust associated with an oceanic continental transition is postulated to exist along the 100-Ma slow-spreading isochron in the Enderby Basin. A discrete, denser enriched or less depleted mantle beneath the Antarctic Plate is an alternative explanation for the large scale thin oceanic crust concentrated on the southern flank of the SWIR.

Meso-Cenozoic Evolution of Earth Surface System under the East Asian Tectonic Superconvergence

The East Asian geological setting has a long duration related to the superconvergence of the Paleo-Asian, Tethyan and Paleo-Pacific tectonic domains. The Triassic Indosinian Movement contributed to an unified passive continental margin in East Asia. The later ophiolites and I-type granites associated with subduction of the Paleo-Pacific Plate in the Late Triassic, suggest a transition from passive to active continental margins. With the presence of the ongoing westward migration of the Paleo-Pacific Subduction Zone, the sinistral transpressional stress field could play an important role in the intraplate deformation in East Asia during the Late Triassic to Middle Jurassic, being characterized by the transition from the E-W-trending structural system controlled by the Tethys and Paleo-Asian oceans to the NE-trending structural system caused by the Paleo-Pacific Ocean subduction. The continuously westward migration of the subduction zones resulted in the transpressional stress field in East Asia marked by the emergence of the Eastern North China Plateau and the formation of the Andean-type active continental margin from late Late Jurassic to Early Cretaceous (160-135 Ma), accompanied by the development of a small amount of adakites. In the Late Cretaceous (135-90 Ma), due to the eastward retreat of the Paleo-Pacific Subduction Zone, the regional stress field was replaced from sinistral transpression to transtension. Since a large amount of late-stage adakites and metamorphic core complexes developed, the Andean-type active continental margin was destroyed and the Eastern North China Plateau started to collapse. In the Late Cretaceous, the extension in East Asia gradually decreased the eastward retreat of the Paleo-Pacific subduction zones. Futhermore, a significant topographic inversion had taken place during the Cenozoic that resulted from a rapid uplift of the Tibet Plateau resulting from the India-Eurasian collision and the formation of the Bohai Bay Basin and other basins in the East Asian continental margin. The inversion caused a remarkable eastward migration of deformation, basin formation and magmatism. Meanwhile, the basins that mainly developed in the Paleogene resulted in a three-step topography which typically appears to drop eastward in altitude. In the Neogene, the basins underwent a rapid subsidence in some depressions after basin-controlled faulting, as well as the intracontinental extensional events in East Asia, and are likely to be a contribution to the uplift of the Tibetan Plateau.

Origin and model of transform faults in the Okinawa Trough

Transform faults in back-arc basins are the key to revealing the opening and development of marginal seas. The Okinawa Trough (OT) represents an incipient and active back-arc or marginal sea basin oriented in a general NE-SW direction. To determine the strikes and spatial distribution of transform faults in the OT, this paper dissects the NW- and NNE-SN-trending fault patterns on the basis of seismic profiles, gravity anomalies and region geological data. There are three main NW-trending transpressional faults in the OT, which are the seaward propagation of NW-trending faults in the East China Continent. The NNE-SN-trending faults with right-stepping distribution behave as right-lateral shearing. The strike-slip pull-apart process or transtensional faulting triggered the back-arc rifting or extension, and these faults evolved into transform faults with the emergence of oceanic crust. Thus, the transform fault patterns are inherited from pre-existing oblique transtensional faults at the offsets between rifting segments. Therefore, the OT performs the oblique spreading mechanism similar to nascent oceans such as the Red Sea and Gulf of Aden.