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Abstract SHRIMP U-Pb zircon analyses from eight samples of metamorphosed intermediate to felsic volcanic rocks from the lower, middle and upper ‘subgroups’ of the Wutai sequence in the North China Craton define a weighted mean 207 Pb/ 206 Pb age of 2523 ± 3 Ma. Although individual rock ages range from 2533 ± 8 Ma to 2513 ± 8 Ma, all overlap within the error of the mean and do not support a stratigraphic interpretation for the sequence, since variations within individual previously assigned ‘formations’ in the sequence match the total age range. Contrary to previous interpretations, there is no correlation in age with metamorphic grade. These features highlight the need to reformulate stratigraphic schemes when defining the Precambrian geology of the North China Craton. The similarity in age between volcanic rocks of the Wutai Complex and higher-grade gneisses of the adjacent Fuping and Hengshan complexes supports the view that all three complexes represent portions of a Late Archaean arc complex that was tectonically dismembered and then re-assembled. There is no Fuping or Wutai orogeny in this, its type area: all three complexes were deformed and metamorphosed during collision of the eastern and western blocks of the North China Craton in the Lüliang orogeny c. 1.8 Ga ago.
Abstract The Hengshan–Wutai–Fuping mountain belt constitutes the middle segment of the Trans-North China Orogen, which separates the North China Craton into the Eastern and Western Blocks. The belt consists of the high-grade Hengshan and Fuping complexes, and the intervening low- to medium-grade Wutai Complex. Previous tectonic models assumed that the high-grade complexes were an older basement (Archaean to Palaeoproterozoic) to the low-grade Wutai Complex. However, new geochronological data show that the emplacement of granitoid rocks and eruption of volcanic rocks in the Wutai Complex occurred essentially coeval with or slightly earlier than intrusion of the tonalitic–trondhjemitic–granodioritic (TTG) suites in the Hengshan and Fuping complexes. New isotopic data also reveal the widespread presence of Palaeoproterozoic granitoid rocks in these complexes. Structural and metamorphic data demonstrate similar tectonothermal histories for the three complexes, which are characterized by peak medium- to high-pressure metamorphism accompanied by the development of thrusting, isoclinal folding (F 2 ) and penetrative foliations, followed by near-isothermal decompression and cooling and retrogression associated with the formation of large-scale ductile shear zones and asymmetrical folds (F 3 ) with nearly vertical axial planes. These geochronological, structural and metamorphic data suggest that the tectonic evolution of the Hengshan–Wutai–Fuping mountain belt may not be related to local interaction of the three complexes, as suggested in earlier models, either through closure of a Wutai rift or collision between a Wutai arc and the Hengshan and Fuping micro-continental blocks. Instead, they may represent elements of a single Late Archaean to Early Palaeoproterozoic magmatic arc that was subsequently incorporated into the Trans-North China Orogen along which the Eastern and Western blocks amalgamated to form the North China Craton at around 1.85 Ga.
Abstract The North China Craton (NCC) is a major Archaean craton, covering an area of c. 300 000 km 2 in north and northeast China. Almost all Archaean rocks on the craton experienced high-grade metamorphism and strong migmatization, so that the preserved greenstone belts underwent granulite-amphibolite-facies metamorphism, anatectic melting and strong deformation. This suggests that the NCC may have a more complicated early tectonic history than most other cratonic nuclei. The oldest NCC rocks are 3.8 Ga granitic gneisses in NE China and supracrustal rocks in eastern Hebei. Major continental growth occurred at 2.9–2.7 Ga. Two subsequent high-grade metamorphic events occurred at 2.6–2.45 Ga (‘2.5 Ga event’) and 1.9–1.75 Ga (‘1.8 Ga event’). The older episode is considered to mark an amalgamation event, whereas the 1.8 Ga event represents the final cratonization of the NCC. Some researchers have divided the 1.8 Ga event into a 1.9–1.8 Ga metamorphic event (interpreted as a continent-continent collision) followed by a 1.8–1.65 Ga rifting episode. Other workers have suggested that the metamorphism and rifting could be parts of a single tectonic event related to Palaeo-Mesoproterozoic mantle upwelling. The general consensus on the NCC for the period 2.5–1.8 Ga is that the craton was then in an inactive stage. However, in this paper it is proposed that several Palaeoproterozoic mobile belts existed (showing many of the characteristics of Phanerozoic orogens). During the Mesoproterozoic–Neoproterozoic, a set of sedimentary sequences (the Changcheng-Jixian-Qingbaikou systems) constituted a disconformable-pseudoconformable succession within an intra-cratonic aulacogen. The signature of a 1.4–0.9 Ga orogen and the Rodinia breakup is very weak, indicating that the NCC did not experience major deformation as it was amalgamated into the Rodinia supercontinent.
The Central Asian Orogenic Belt and growth of the continental crust in the Phanerozoic
Abstract Asia is the world’s largest composite continent, comprising numerous old cratonic blocks and young mobile belts. During the Phanerozoic it was enlarged by successive accretion of dispersed Gondwana-derived terranes. The opening and closing of palaeo-oceans would have inevitably produced a certain amount of fresh mantle-derived juvenile crust. The Central Asian Orogenic Belt (CAOB), otherwise known as the Altaid tectonic collage, is now celebrated for its accretionary tectonics and massive juvenile crustal production in the Phanerozoic. It is composed of a variety of tectonic units, including Precambrian microcontinental blocks, ancient island arcs, ocean island, accretionary complexes, ophiolites and passive continental margins. Yet, the most outstanding feature is the vast expanse of granitic intrusions and their volcanic equivalents. Since granitoids are generated in lower-to-middle crustal conditions, they are used to probe the nature of their crustal sources, and to evaluate the relative contribution of juvenile v. recycled crust in the orogenic belts. Using the Nd–Sr isotope tracer technique, the majority of granitoids from the CAOB can be shown to contain high proportions (60 to 100%) of the mantle component in their generation. This implies an important crustal growth in continental scale during the period of 500–100 Ma. The evolution of the CAOB undoubtedly involved both lateral and vertical accretion of juvenile material. The lateral accretion implies stacking of arc complexes, accompanied by amalgamation of old microcontinental blocks. Parts of the accreted arc assemblages were later converted into granitoids via underplating of basaltic magmas. The emplacement of large volumes of post-accretionary alkaline and peralkaline granites was most likely achieved by vertical accretion through a series of processes, including underplating of basaltic magma, mixing of basaltic liquid with lower-crustal rocks, partial melting of the mixed lithologies leading to generation of granitic liquids, and followed by fractional crystallization. The recognition of vast juvenile terranes in the Canadian Cordillera, the western US, the Appalachians and the Central Asian Orogenic Belt has considerably changed our view on the growth rate of the continental crust in the Phanerozoic.
Abstract Nine separate Cambrian to Carboniferous terranes are recognized in West Junggar, northwest China. They were amalgamated as part of the Central Asian Orogenic Belt which records accretion of continental, island-arc and oceanic terranes to Archaean-Proterozoic continental nuclei. Tangbale, Kekesayi, Ebinur and Mayila terranes (CambriaN–Silurian) evolved in intra-oceanic settings and docked, along a series of north-dipping subduction zones, on to the Laba terrane to their south. This southern continent was contiguous with lithosphere of the Kulumudi Ocean to the north. Devonian subduction on the northern edge of this ocean resulted in formation of a continental arc (Toli terrane) and accretionary complex (Kulumudi terrane). The Karamay terrane formed as an accretionary complex during the Carboniferous. The ophiolitic Sartuohai terrane was emplaced as mélange between Kulumudi and Karamay terranes during the Late Carboniferous. Subduction migrated southward, continuing beneath these terranes, resulting in the intrusion of I-type granites into the Toli, Kulumudi, Sartuohai and Karamay terranes. These granites are closely associated with epithermal and porphyry-style gold mineralization. Composite terranes either side of the Kulumudi Ocean collided in the Late Carboniferous, marking the final consolidation of Central Asia. Collision was accompanied by anorogenic granite and diabase dyke intrusion, followed by widespread latest Carboniferous to Permian extension, and subsequently the formation of the Junggar Basin. West Junggar has been further disrupted by Cenozoic strike-slip faulting along Junggar and Dalabute faults.
Abstract The Akaz metavolcanic rocks of the West Kunlun Mountains possess low to intermediate SiO 2 (42.3–64.7 wt%) and MgO (2.69–7.54 wt%) and high TiO 2 (0.94–3.05 wt%) and Fe 2 O 3 T (7.64–18.47 wt%), indicating a basaltic to andesitic protolith. These rocks have high contents of Zr (89.6–470 ppm), Nb (10.0–40.3 ppm), Y (19.7–52.7 ppm), Th (0.86–15.96 ppm) and total REE (67.7–407 ppm), and are characterized by relatively high Ti/Y (183–649), Th/Yb (0.5–3.9), and low Hf/Ta (3.0–8.6) ratios. They are LREE-enriched (La/Yb = 5.4–20) and most have small negative Nb anomalies (Nb/Nb* = 0.20–1.16). These characteristics are transitional between within-plate and subduction-related basalts. The relatively high Gd/Yb ratios (1.4–2.9) distinguish these rocks from island-arc tholeiites and the high Zr/Y (3–12), Ta/Yb (0.3–0.7) and low Zr/Nb (<12) ratios strongly support a continental affinity. The protoliths for the Akaz metavolcanic rocks are interpreted to be continental rift basalts formed during rifting of the Tarim Craton from Gondwana. Stratigraphic and palaeontological data indicate that the rifting occurred in Sinian to Cambrian times, roughly contemporaneously with rifting in the East Kunlun and North Qilian orogenic belts farther to the east.
Abstract Isotope signatures and T DM model ages in Hong Kong and neighbouring Guangdong Province have indicated that the basement of the Cathaysia Block is probably an amalgamation of narrow crustal slices, ranging in age from latest Archaean to Mesoproterozoic. Inheritance ages from zircons contained within Mesozoic volcanic and plutonic rocks also show Proterozoic and Archaean components. Regional gravity survey studies display NNE- to NE-trending Bouguer anomalies that are indicative of sharp changes in rock densities at middle and lower crustal levels. The anomalies displayed on the gravity profile from Guangdong to Hong Kong have been modelled as narrow slices of Archaean and Proterozoic crust. A substantial E-W-trending Bouguer anomaly, which largely parallels the trend of the foliation in the Proterozoic schists of the region, is present to the east of Guangzhou. It is proposed that the basement of the Cathaysia Block consists of an amalgamation of NE- to NNE-trending Palaeo- to Mesoproterozoic and Archaean crustal terranes, which in places have retained the pre-amalgamation E-W-trending tectonic fabric. The discontinuities between the basement terranes, and the E-W structures have strongly influenced the geological evolution of the Phanerozoic sequences and igneous complexes in southeast China. These are most obviously manifest in the regional NE-trending fault and shear zones that displace the cover sequences.
Abstract High-pressure metamorphism and ophiolite emplacement (Songshugou ophiolite) attended suturing of the Yangtze craton to Rodinia during the c. 1.0 Ga Grenvillian orogeny. The Qinling microcontinent then rifted from the Yangtze craton at c. 750 Ma. The Erlangping intraoceanic arc formed in the Early Ordovician, was emplaced onto the Qinling microcontinent in the OrdoviciaN–Silurian, and then both units were accreted to the Sino-Korea craton before being stitched together by the c. 400 Ma AndeaN–Style Qinling arc. Subsequent subduction beneath the Qinling-Sino-Korean plate created a Devonian-Triassic accretionary wedge that includes eclogites, and formed a coeval volcano-plutonic arc that stretches from the Longmen Shan to Korea. In the Late Permian-Early Triassic, the northern edge of the South China Block was subducted to >150 km depth, creating the diamond- and coesite-bearing eclogites of the Dabie and Sulu areas. Exhumation from the mantle by lithosphere-scale extension occurred between 245 and 195 Ma during clockwise rotation of the craton. The Yangtze-Sino-Korea suture locally lies tens of km north of the exhumed UHP–HP part of the South China Block, implying perhaps that the very tip of the South China Block was not subducted, or that the UHP–HP rocks rose as a wedge that peeled the upper crust of the unsubducted South China Block from the lower crust. The Tan–Lu fault is an Early Cretaceous to Cenozoic feature. The apparent offset of the Dabie and Sulu UHP terranes by the Tan–Lu fault is a result of this Cretaceous to Cenozoic faulting combined with post-collisional extension north of Dabie.
Abstract The Dabieshan Orogenic Belt, which contains ultra-high-pressure (UHP) metamorphic rocks, is the Mesozoic collision zone between the Sino-Korean and Yangtze cratons. With respect to the exhumation of the UHP rocks, the Dabieshan Orogenic Belt can be divided into four units, i.e. allochthonous, parautochthonous, autochthonous and reworked units. The allochthonous unit is composed of UHP rocks. The parautochthonous unit is represented by the non-UHP rocks of the Yangtze sedimentary cover and crystalline basement, as well as an accretionary wedge. The autochthonous unit includes Jurassic and Cretaceous sedimentary and igneous rocks. The reworked unit is characterized by migmatization. The deep structure of the Dabieshan Orogenic Belt is characterized by a Moho offset and dome structure in the middle and upper crust, as recording a compressional state. A northward subduction of the Yangtze craton is evidenced by geological, geophysical and geochemical data. In the formation of the Dabieshan orogenic belt, a precondition is the low density of the subducted continental materials. If the UHP unit is the piston to build up the orogenic belt, then the continuous compression between the Sino-Korean and Yangtze cratons is the motor to trigger the mountain-building processes.
Abstract The Mesozoic geology of SE China is characterized by intensive and widespread magmatism. However, the tectonic regime that accounted for the Mesozoic magmatism has been an issue with little consensus. A comprehensive study of 40 Ar– 39 Ar dating, geochemistry and Sr–Nd isotopes has been conducted on basalts from southern Hunan and syenite intrusions from eastern Guangxi. Three episodes of Jurassic magmatism, i.e. alkaline basalts of c .175 Ma in age, syenitic intrusions of c .160 Ma and high-Mg basalts of c .150 Ma, are identified. The older, c .175 Ma alkaline basalts are characterized by low Sr ( I Sr = 0.7035–0.7040) and high Nd ( ε Nd ( T ) = 5 to 6) isotopic compositions and OIB-like trace-element patterns (e.g. Nb/La > 1). In contrast, the younger, c .150 Ma high-Mg basalts have high Sr ( I Sr c .0.7054) and low Nd ( ε Nd ( T ) c .−2) isotopic compositions and incompatible trace-element patterns of arc affinity. The c .160 Ma syenitic intrusions display a relatively large range of Sr and Nd isotopic compositions ( I Sr = 0.7032–0.7082, ε Nd ( T ) = 5.5 to −4.1), with the Qinghu syenites having the lowest I Sr , highest ε Nd ( T ) and OIB-type incompatible trace-element patterns analogous to the c .175 Ma alkaline basalts. Such a secular variation in rock types and geochemical and isotopic characteristics reveals changes in melt segregation depth and mantle sources, which are inferred to have resulted from the post-Indosinian orogenic lithosphere extension and thinning. The c .175 Ma alkaline basalts are suggested to have formed by small degrees of decompression melting of the asthenosphere or an enriched lithospheric mantle source accreted by asthenosphere-derived melts during the initial extension. The c .160 Ma syenitic and c .150 Ma high-Mg basaltic rocks mainly originated from the enriched lithospheric mantle that melted owing to a raised geotherm caused by lithosphere thinning. This interpretation is at odds with the active continental margin related to the subduction of palaeo-Pacific plate, but consistent with continental rifting and extension for the Mesozoic of SE China.
Evidence for the multiphase nature of the India–Asia collision from the Yarlung Tsangpo suture zone, Tibet
Abstract Recent investigations in southern Tibet enable the testing and refinement of existing models for India–Asia collision. Presently available data indicate that marine deposition continued in the southern central portion of Tibet until at least the end of the Eocene. Sub-duction-related magmatism continued until the Mid-Oligocene, after which rapid uplift of the plateau was initiated. Mass-wasting of sediments into molasse basins did not commence until the latest Oligocene. The implications are that existing models, based on less-precise age constraints, invoking India–Asia collision at 55 Ma, are either flawed, or collision began at a different time. Recent work has produced sufficient data to allow the recognition of two different collisional events along the suture between India and Asia. Features related to each event require separate interpretation, and no collisional continuum should be assumed. In southern Tibet, a collision between the northern margin of India and a southfacing intra-oceanic island arc occurred at around 55 Ma, whereas continent–continent collision between India and Asia did not occur until at least 20 million years later.
Conglomerates record the tectonic evolution of the Yarlung–Tsangpo suture zone in southern Tibet
Abstract The histories of individual conglomeratic units along the Yarlung–Tsangpo (River) suture zone in southern Tibet reflect significant phases in the Mesozoic to Cenozoic tectonic evolution of this area. Several temporally distinct conglomerate units are recognized along the suture, and their detailed examination permits analysis of the collision between India and Asia. Upper Jurassic to Lower Cretaceous conglomerates crop out within the Sangri Group along the southern Lhasa terrane. They are dominated by limestone and andesitic volcanic cobbles derived entirely from the Lhasa terrane. These rocks have experienced amphibolite facies metamorphism, and exhibit a strong penetrative regional foliation. Thick successions of the Palaeocene Liuqu Conglomerate crop out within the suture from Xigaze to Lhaze. They contain detritus sourced from intra-oceanic terranes associated with the suture zone, as well as clasts of Indian affinity, while Lhasa and Xigaze terrane-derived material is notably absent. These conglomerates record an early suture zone event prior to India–Asia collision. Uppermost Oligocene to Lower Miocene ‘Gangrinboche facies’ conglomerates crop out on the southern edge of the Lhasa terrane along the length of the suture. Several correlative units within this facies exhibit broadly similar stratigraphic histories. A basal depositional contact upon an eroded Lhasa terrane surface is ubiquitous with initial clast derivation from the north. Up-section, the first arrival of coarse-grained, suture-zone and India-derived clasts, is abrupt. These southerly derived clasts predominate by the top of most sections. An areally restricted succession of gently dipping Late Neogene ultramafic breccias unconformably overlies folded Liuqu Conglomerate near Quanggong. Other Neogene sediments are extensive west of Mount Kailas. Deposition of coarse clastic sediments is presently continuing along the length of the Yarlung Tsangpo. Discrimination and detailed investigation of each of these units will improve our understanding of the evolution of the India–Asia collision.
Ultra-high pressure minerals in the Luobusa Ophiolite, Tibet, and their tectonic implications
Abstract Numerous ultra-high-pressure minerals have been recovered from podiform chromities in the Luobusa ophiolite, Tibet. Recovered minerals include diamond, moissanite, Fe-silicides, wüstite, Ni–Fe–Cr–C alloys, PGE alloys and octahedral Mg–Fe silicates. These are accompanied by a variety of native elements, including Si, Fe, Ni, Cr and graphite. All of the minerals were hand-picked from heavy-mineral separates of the chromitites and care was taken to prevent natural or anthropogenic contamination of the samples. Many of the minerals and alloys are either enclosed in, or attached to, chromite grains, leaving no doubt as to their provenance. The ophiolite formed originally at a mid-ocean ridge (MOR) spreading centre at 177±33 Ma, and was later modified by suprasubduction zone magmatism at about 126 Ma. The chromitites were formed in the suprasubduction zone environment from boninitic melts reacting with the host peridotites. The UHP minerals are believed to have been transported from the lower mantle by a plume and incorporated in the ophiolite during seafloor spreading at 176 Ma. Blocks of the mantle containing the UHP minerals were presumably picked up by the later boninitic melts, transported to shallow depth and incorporated in the chromitites during crystallization.
Cretaceous palaeomagnetism of Indochina and surrounding regions: Cenozoic tectonic implications
Abstract Results of a detailed palaeomagnetic study of Cretaceous-age volcanic, intrusive and sedimentary rock formations from southern Vietnam (24 sites, 163 core samples) are presented. The palaeomagnetic and supplementary rock magnetic studies indicate that magnetite and titanomagnetite are the predominant magnetic carriers in the volcanic and intrusive rock samples, whereas hematite is the principal carrier in the red-beds. The mean palaeomagnetic direction of twenty-one sites from southern Vietnam yields D = 14.5°, I = 33.3°, α 95 = 6.3°, k s / k g = 1.04, which corresponds with a VGP at λ = 74.2°N, φ = 171.1°E, A 95 = 5.9°. Comparison of the pole with the Eurasia mean Cretaceous palaeopole shows that relative to Eurasia southern Vietnam has experienced a southward displacement of 6.5° ± 5.1°, but with insignificant rotation since the Cretaceous. Previously reported Cretaceous palaeomagnetic data, combined with new palaeomagnetic data from this study and analysis of regional structural trends, indicate that Sundaland can be divided into several fault-bounded tectonic domains (Shan–Thai, Indochina, offshore Sundaland), each with a different rotation and/or translation history. Such differential motion might explain, for example, Oligocene transtension and basin formation in the Gulf of Thailand and central onshore Thailand (between the Shan–Thai and Indochina blocks). Our data combined with previously acquired palaeomagnetic data across Southeast Asia, also suggest that, during the Cenozoic, Indochina and parts of Sundaland underwent complex internal deformation and did not behave as a rigid block.
Geology of the Zamboanga Peninsula, Mindanao, Philippines: an enigmatic South China continental fragment?
Abstract Mindanao Island in the southern Philippines is made up of two blocks: the island-arc-related eastern-central Mindanao block and the continental Zamboanga Peninsula, which contains several ophiolitic bodies and mélanges. The Middle Miocene Siayan–Sindangan Suture Zone represents the tectonic boundary between the island-arc and continental blocks. A Middle Miocene age of collision is interpreted from the unconformity between the Late Miocene Motibot Formation and the underlying Middle Miocene Gunyan Mélange, which serves as basement to the suture zone. The Middle Miocene Siayan–Sindangan Suture Zone was formerly a subduction zone complex that was reactivated as a sinistral strikeslip fault following the collision of eastern-central Mindanao with the Zamboanga Peninsula. New 40 K- 40 Ar whole-rock dating of lava flows from the Zamboanga Peninsula has revealed Middle to Late Miocene ages, which is consistent with the possible existence of an Early Miocene Sulu Trench. The possibility that the Zamboanga Peninsula could be part of the Palawan microcontinental block has been forwarded by previous workers, due to their similarity in stratigraphy, geological structure and metamorphic rock suites. The Palawan microcontinental block separated from southern China during the opening of the South China Sea in Oligo-Miocene times. If indeed the Zamboanga Peninsula was once part of Palawan, it represents the southernmost part of the rifted southeastern China continental margin.
Abstract The continental margin to the east and south of China comprises an active margin in the East China Sea, a collision mountain belt in Taiwan, and a passive margin in the South China Sea. These three segments were generally regarded as separate tectonic entities and their interrelations have long been the subject of debate. Here we synthesize available information to outline the tectonic and geological background of the China margin, examine the link between Taiwan and the neighbouring China margins, and thereby establish a Cenozoic evolutionary model. The China margin is floored with a pre-Cenozoic continental basement covered with an up to 10-km-thick pile of Cenozoic sedimentary strata. The continental basement has been invariably stretched and moulded into a series of northeast-trending horsts and grabens. Except in the Okinawa Trough of the East China Sea, the Cenozoic sedimentary cover typically exhibits a two-tier tectonostratigraphic structure, with narrow Palaeogene rift basins draped by a blanket-like Neogene–Quaternary sequence. The two-tier structure prevails in the entire inner part of the China margin, including the Taiwan Strait off western Taiwan. In the outer China margin, however, the two-tier structure persists only in the South China Sea, and is in stark contrast with the collisional orogen of Taiwan and the Ryukyu arc of the East China Sea. By untangling the contractional deformation of the northern Taiwan mountain belt, it has been possible to reconstruct a precollisional tectonostratigraphic section with a distinctive two-tier structure shown by a Palaeogene half-graben covered with a Miocene drape sequence. When put together with Palaeogene rift basins of the Taiwan Strait, it becomes clear that the precollisional continental margin of Taiwan resembles that of the South China Sea, characterized by two lines of Palaeogene rift basins. Hence before the collision started in Late Miocene times, Taiwan was part of the passive South China margin that extended northward to the southern Ryukyu area. Ever since the end of the Cretaceous, the China continental margin has been dominated by extensional tectonics, regardless of the presence or absence of subduction zones. In the Early Cenozoic, extensive crustal attenuation resulted in region-wide subsidence and formation of rift basins. Extension in the South China Sea culminated in Late Oligocene times, when part of the outer margin was drifted away by the opening ocean basin. In the East China Sea, the margin remained intact and became separated from the South China Sea margin by a transform fault. From the Miocene onwards, the South China Sea margin has been passively subsiding, sporadically punctuated with basaltic volcanism. In the East China Sea margin, the Okinawa Trough has opened and the Ryukyu volcanic arc thrived. The NE edge of the South China Sea margin was deformed as the Taiwan orogen.
Abstract The 1999 Chi-Chi earthquake series occurred in Central Taiwan, where ongoing mountain building is most active. The pre- and post-Chi-Chi seismicity helps to clarify the internal orogenic activity. The 27 000 earthquakes from the 1993–2002 catalogues have been relocated with greater precision. By associating the seismicity with focal mechanisms, many structures inside the orogen have been mapped. Among them are a steeply dipping thrust fault in the deep crust; a 50-km-long left-lateral strike-slip fault in the south; and an Eastern Central Range NNE-striking normal fault. While the deep crustal thrust appears to contribute to the root-building, the southern strike-slip slip fault accommodates the mainshock fault motion, and the Eastern Central Range normal faulting probably occurs mainly after a major western Taiwan thrust type earthquake. Much of the Backbone Range and the Eastern Central Range were seismically quiescent before and after the Chi-Chi earthquake. The contrast in the seismicity of the Central Range and the surrounding regions implies different material behaviour in these different regimes of the orogen.
Abstract The subject of this Special Publication is one of the most interesting in global geoscience, the tectonic evolution of China. The assemblage of terranes that underlie this part of the world provides outstanding opportunities to elucidate global processes, and many of the factors that shape the Earth's lithosphere are best exemplified by the geology of China and its immediately adjacent areas In addition, there are geological features that are particular and unique to the region. Some have been the focus of recent attention and have attracted international interest because of their global importance. This volume provides accounts of up-to-date research by Chinese and international geological teams on key aspects of the tectonic evolution of China and its surrounding areas. The papers describe the formation of the geological terranes that make up this part of east Asia, place constraints on plate tectonic models for their assembly and provide accounts of unique geological feature of the subcontinent.