ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractNortheast Japan is a typical island arc region and its topographic arrangement reflects the geophysical characteristics of the island arc system. However, the structural style of the arc is very complicated and varied due to the repeated superposing of faults and folds on to earlier structures.Geotectonic events that involved creation of the fundamental framework of the island arc crust occurred in east Asia in the Late Jurassic to Early Cretaceous and were probably induced by accretion and collision tectonics. The fragmentation and subsequent displacement of the crust took place during the Early Neogene in response to the terrane collision and the change in oceanic plate motion, leading to the opening of the Japan Sea. Huge amounts of volcano‐sedimentary rocks buried the tilted fault blocks of pre‐Tertiary basement with the development of the island

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMulti‐ and single‐channel seismic profiles are used to investigate the structural evolution of back‐arc rifting in the intra‐oceanic Izu‐Bonin Arc. Hachijo and Aoga Shima Rifts, located west of the Izu‐Bonin frontal arc, are bounded along‐strike by structural and volcanic highs west of Kurose Hole, North Aoga Shima Caldera and Myojin Sho arc volcanoes. Zig‐zag and curvilinear faults subdivide the rifts longitudinally into an arc margin (AM), inner rift, outer rift and proto‐remnant arc margin (PRA). Hachijo Rift is 65 km long and 20–40 km wide. Aoga Shima Rift is 70 km long and up to 45 km wide. Large‐offset border fault zones, with convex and concave dip slopes and uplifted rift flanks, occur along the east (AM) side of the Hachijo Rift and along the west (PRA) side of the Aoga Shima Rift. No cross‐rift structures are observed at the transfer zone between these two regions; differential strain may be accommodated by interdigitating rift‐parallel faults rather than by strike‐ or oblique‐slip faults. In the Aoga Shima Rift, a 12 km long flank uplift, facing the flank uplift of the PRA, extends northeast from beneath the Myojin Knoll Caldera. Fore‐arc sedimentary sequences onlap this uplift creating an unconformity that constrains rift onset to ∼1‐2Ma. Estimates of extension (∼3km) and inferred age suggest that these rifts are in the early syn‐rift stage of back‐arc formation. A two‐stage evolution of early back‐arc structural evolution is proposed: initially, half‐graben form with synthetically faulted, structural rollovers (ramping side of the half‐graben) dipping towards zig‐zagging large‐offset border fault zones. The half‐graben asymmetry alternates sides along‐strike. The present ‘full‐graben’ stage is dominated by rift‐parallel hanging wall collapse and by antithetic faulting that concentrates subsidence in an inner rift. Structurally controlled back‐arc magmatism occurs within the rift and PRA during both stages. Significant complications to this simple model occur in the Aoga Shima Rift where the east‐dipping half‐graben dips away from the flank uplift along the PRA. A linear zone of weakness caused by the greater temperatures and crustal thickness along the arc volcanic line controls the initial locus of rifting. Rifts are better developed between the arc edifices; intrusions may be accommodating extensional strain adjacent to the arc volcanoes. Pre‐existing structures have little influence on rift evolution; the rifts cut across large structural and volcanic highs west of the North Aoga Shima Caldera and Aoga Shima. Large, rift‐elongate volcanic ridges, usually extruded within the most extended inner rift between arc volcanoes, may be the precursors of sea floor spreading. As extension continues, the fissure ridges may become spreading cells and propagate toward the ends of the rifts (adjacent to the arc volcanoes), eventually coalescing with those in adjacent rift basins to form a continuous spreading centre. Analysis of the rift fault patterns suggests an extension direction of N80°E ± 10° that is orthogonal to the trend of the active volcanic arc (N10°W). The zig‐zag pattern of border faults may indicate orthorhombic fault formation in response to this extension. Elongation of arc volcanic constructs may also be developed along one set of the possible orthorhombic orientations. Border fault formation may modify the regional stress field locally within the rift basin resulting in the formation of rift‐parallel faults and emplacement of rift‐parallel volcanic ridges. The border faults dip 45–55° near the surface and the majority of the basin subsidence is accommodated by only a few of these faults. Distinct border fault reflections decreases dips to only 30° at 2.5 km below the sea floor (possibly flattening to near horizontal at 2.8 km although the overlying rollover geometry shows a deeper detachment) sug

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMultichannel seismic reflection profiling in the Ulleung back‐arc Basin reveals that the acoustic basement largely comprises volcanic materials. The volcanics are interlayered with sediment sequences, forming an anomalously thick layer. The volcanic activities resulted in a zonation of the acoustic basement, trending northeast‐southwest. In the southeastern part, the acoustic basement is deep and obscure, whereas in the northwestern part it is shallow and forms mounds and seamounts. The volcanic activities were probably initiated in the Early Miocene (ca20Ma). The volcanism was time‐transgressive northward, associated with the possible southward drift of the Japanese is

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractExtensive subduction‐related and intraplate volcanism characterize Cenozoic magmatism in the North Is., New Zealand. Volcanics in the central North Is., predominantly intermediate to felsic, form above the dipping seismic zone and show tectonic/geochemical features common to magmatism in most subduction zones. Basaltic volcanism in Northland, the northern part of the North Is., has chemical characteristics typical of intraplate magmatism and may be caused by the upwelling of asthenospheric materials from deeper parts of the mantle. The rifting just behind the present volcanic front (the Taupo‐Rotorua Depression), which follows the trench ward migration of the volcanic front and the gradual steepening of the subducted slab, is also a feature of the North Is. A possible mechanism for the back‐arc rifting in the area is injection of asthenospheric materials into the mantle wedge; this asthenospheric flow results from the mantle upwelling beneath Northland and pushes both the rigid fore‐arc mantle wedge and the subducted slab trenchwards. This mechanism is also consistent with the stress fields in the North Is.: dilatation in Northland, northwest‐southeast tension in the Taupo‐Rotorua Depression, and the northeast‐southwest compression in the fo

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00056.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe Izanagi plate subducted rapidly and obliquely under the accretionary terrane of Japan in the Cretaceous before 85 Ma. A chain of microcontinents collided with it at about 140 Ma. In southwest Japan the major part of it subducted thereafter, but in northeast Japan it accreted and the trench jumped oceanward, resulting in a curved volcanic front. The oblique subduction and the underplated microcon‐tinent caused uplifting of high‐pressure (high‐P) metamorphic rocks and large scale crustal shortening in southwest Japan. The oblique subduction caused left‐lateral faulting and ductile shearing in northeast Japan. The arc sliver crossed over the high‐temperature (high‐T) zone of arc magmatism, resulting in a wide high‐T metamorphosed belt. At about 85 Ma, the subduction mode changed from oblique to normal and the tectonic mode changed drastically. Just after this the Kula/Pacific ridge subducted and the subduction rate of the Pacific plate decreased gradually, causing the intrusion of huge amounts of granite magma and the eruption of acidic volcanics from large cauldrons. The oblique subduction of the Pacific plate resumed at 53 Ma and the left‐lateral faults w

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00057.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractEvidence for South Korean Palaeozoic geodynamic evolution is restricted to the Ogcheon Belt, which is a complex polycyclic domain forming the boundary between the Precambrian Gyeonggi Block to the northwest and the Ryeongnam Block to the southeast. Two independent sub‐zones can be distinguished: the Taebaeksan Zone to the northeast and the Ogcheon Zonesensu stricto.The Taebaeksan Zone and Ryeongnam Block display characteristic features of the North China palaeocontinent. This domain remained relatively stable during the Palaeozoic.In contrast, the Ogcheon Belt s. s. is a highly mobile zone that belongs to the South China palaeocontinent and corresponds to a rift that opened during the Early Palaeozoic. In lowermost Devonian times, the rift basin was closed and the Ogcheon Belt was structured in a pile of nappes. From the lack of suture in the Ogcheon Belt it can be inferred that the Gyeonggi Block belongs to the South China palaeocontinent. Thus, the boundary between the North China and South China blocks should be located to the north of Gyeonggi Block, that is, in the Palaeozoic Imjingang Belt. From the Middle Carboniferous, sedimentation started again on a weakly subsiding paralic platform located in the hinterland of the Late Palaeozoic orogen of southwest Japan. In the Late Carboniferous, increasing subsidence recorded extensional tectonics related to the opening of the Yakuno Oceanic Basin (southwest Japan). In the Middle Permian, the end of marine influences in the platform and emplacement of terrestrial coal measures, may be correlated with the closure of the oceanic area and subsequent ophiolite obduction. In Late Permian to Early Triassic times, the Honshu Block (the eastern palaeomargin of the Yakuno Basin) collided with Sino‐Korea.Post‐collisional intracontinental tectonics reached the Ogcheon Belt in the Middle Triassic (Songnim tectonism). Ductile dextral shear zones associated with synkinematic granitoids were emplaced in the southwest of the belt. In the Upper Triassic, the late stages of the intracontinental transcurrent tectonics generated narrow intramontane troughs (Daedong Supergroup). The Daedong basins were deformed during two tectonic events, in the Middle (?) and Late Jurassic. The Upper Jurassic to Lower Cretaceous basins (Gyeongsang Supergroup), that are controlled by left‐lateral faults, may have resulted from the same tectoni

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00058.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractLarge petroliferous basins in the continental interior are characterized by very thick sedimentary sequences. It is suggested that these are not intracratonic basins, but areas underlain by oceanic crust. These include the Western Siberian, Pre‐Caspian, South Caspian, North and South Kara Basins of the Commonwealth of Independent States, and Tarim, junggar and Qaidam Basins of China. The relict ocean basins are distinguished by their basement topography, by their magnetic signatures and by their elevated Moho. Their sedimentary history is distinguished by an abrupt subsidence, followed by isostastic subsidence under sedimentary load. Two circumstances have contributed to the genesis of giant hydrocarbon deposits in these basins: (1) the geochemical environment in those basins was at one time oxygen‐deficient as they evolved from the open marine, through restricted marine to become inland alluvial basins; and (2) the sedimentary in‐fill provide thick reservoir beds. Oil has accumulated in older structures, folds, faults, unconformities etc. on the margin of the basins, trapping early migrated hydroca

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00059.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe Palaeo‐Tethyan suture separates regions characterized by two fundamentally different tectonic styles in the structure of the Tethysides. North of the suture in Iran, Turkmenistan, Afghanistan, Tadjikistan, Kirgizstan, Uzbekistan, Kazakhstan and large parts of the Russian Federation and China, orogenic development is characterized by very large subduction‐accretion complexes developed since the late Proterozoic. Magmatic arc axes migrated radially outwards from the ‘Old Vertex of Eurasia’ and consolidated the accretionary prisms into a ‘basement complex’ dominated by a pelitic composition. In such orogens, called the ‘Turkic‐type’ after the dominant ethnic population of Central Asia, ophiolites are unreliable indicators of sutures, because they are present throughout the ‘basement’ as in‐faulted shreds and rarely as nappes. By contrast, south of the Palaeo‐Tethyan suture, orogeny was commonly characterized by a Sumatra‐ or Andean‐type continental margin arc (e.g. the Transhimalaya arc) that in places became an island arc by back‐arc basin rifting (e.g. the Black Sea behind the Rhodope‐Pontide fragment) and later collided with an Atlantic‐ (as in the Himalaya) or California‐type (as in the Alps) continental margin to create Alpine‐ or Himalayan‐type orogenic belts. Turkic‐type orogenic belts result from the exaggeration of the Himalayan‐type as a result of the subduction of very large oceanic areas that contain great amounts of sediment. They contribute to the enlargement and also possibly the growth of the continental crust which has a composition more silicic than basalt. The Palaeo‐Tethyan suture is thus a line across which the rate of continental enlargeme

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00060.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMylonites along the Median Tectonic Line, southwest Japan commonly contain shear bands comprising S(‐C)‐Ss fabrics. This paper stresses the lithologic control on the orientation, dimension and development of shear bands by comparing the microstructure of the shear bands in different rock types (P mylonites, F mylonites, micaceous phyllonite and quartzose phyllonite). There is no significant change of the α angles (average 21–24°) between Ss and S toward the centre of the shear zone (viz. increasing the intensity of mylonitization) and it is different from the S‐C relationship in a narrow sense.The generation of the composite planar fabric can be classified into four different strain partitioning models: S only type without any slip surface (model A); S‐C type (model B); S‐Ss type with Ss‐slip precedence (model C), and S‐Ss type with S‐slip precedence (model D). Model C is proposed in this paper and is similar to the model for the generation of Riedel shears in brittle shear zones. An unstable slip between porphyroclasts and the matrix during ductile flow can easily initiate shear bands. Formation of a composite planar fabric is initiated according to model A, followed by model C in conditions of increasing strain, and then model D when the angle between S and the shear zone boundary becomes small enough (α/2 = 10°) to produce S‐slip. Thus the generation of the shear bands probably begins in the early stages of shear deformation and continues

ISSN:1038-4871    

DOI:10.1111/j.1440-1738.1992.tb00061.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY