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1.
Abstract   Two groups of Quaternary faults occur in the southeastern Korean Peninsula. The first group is north-northeast-striking, high-angle dextral strike–slip faults. The second group is north-northeast-striking, low-angle reverse faults that represent the reactivation of the pre-existing normal faults. Optically stimulated luminescence dating of Quaternary sediments cut by one of the reverse faults constrains the faulting age to post-32 Ka. These faults seem to be capable of further slip under the current tectonic stress regime, as determined by recent earthquake events in northeast Asia. Therefore, the traditional concept that the southeastern Korean Peninsula is seismically stable should be reappraised.  相似文献   

2.
Thermal histories of Cretaceous sedimentary basins in the Korean peninsula have been assessed to understand the response of the East Asian continental margin to subduction of the Paleo‐Pacific (Izanagi) Plate. The Izanagi Plate subducted obliquely beneath the East Asian continent during the Early Cretaceous and orthogonally in the Late Cretaceous. First, the Jinan Basin, a pull‐apart basin, was studied by illite crystallinity and apatite fission‐track analyses. Analytical results indicate that Jinan Basin sediment was heated to a maximum temperature of approximately 287°C by burial. The sediment experienced two cooling episodes during ca 95–80 Ma and after ca 30 Ma, with a quiescent period between them. A similar cooling pattern is recognized in the Gyeongsang Basin, the largest Cretaceous basin in Korea. The Jinan and Gyeongsang Basins were cooled mainly by exhumation between ca 95 and 80 Ma, but the former was exhumed slightly earlier than the latter by transpressional force due to the subduction direction change of the Izanagi Plate. Comparison of thermal history of Korean Cretaceous basins with those of granitoids in northeastern China and the accretionary complexes in southwestern Japan reveals that the Upper Cretaceous regional exhumation of the East Asian continental margin including the Korean peninsula during ca 95–80 Ma was facilitated by the subduction of the Izanagi–Pacific ridge, which migrated northeastwards with time, resulting in the end of regional exhumation at ca 80 Ma in this region.  相似文献   

3.
The Andaman–Sumatra margin displays a unique set‐up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner‐arc volcanoes, and an extensional back‐arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction‐related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right‐lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer‐arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction‐related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south‐trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench‐slope sediments, were uplifted and emplaced by a series of east‐dipping thrusts to shape the outer‐arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back‐arc occurred in two phases: an early (～11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner‐arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.  相似文献   

4.
The Mazhan Basin, Shandong Province, China, is located between the main faults, F3 and F4, of the Tan-Lu Fault Zone. It is an elongated basin more than 60 km in length and 8 km in width and contains a series of typical continental sediments (the Upper Cretaceous Wangshi Group). This series was divided into three sedimentary facies associations: conglomerate facies association; sandstone facies association of alluvial fan to lake margin environment; and siltstone facies association of lacustrine origins. Their zonal distribution pattern may represent a contemporaneous heterotopic facies due to a lateral facies change from margins to axis of the basin. Their stratigraphic sequence becomes younger northward along the boundary faults. This suggests that the depocenter of the fan–lake system tends to migrate northward along F3. From the asymmetric features (i.e. basin shape, lithofacies distribution, facies change) the Mazhan Basin can be explained by progressive subsidence at the Tangwu releasing bend of F3 with sinistral strike–slip movement. Judging from the fission track (FT) ages from the Wangshi Group, it was concluded that a sinistral strike–slip movement along the main fault, F3 of the Tan-Lu Fault in Shandong, has lasted until the Late Cretaceous. Its displacement is estimated to be larger than the migrated distance, 60 km, of the depocenter of the Mazhan Basin.  相似文献   

5.
Southern Central America is a Late Mesozoic/Cenozoic island arc that evolved in response to the subduction of the Farallón Plate beneath the Caribbean Plate in the Late Cretaceous and, from the Oligocene, the Cocos and Nazca Plates. Southern Central America is one of the best studied convergent margins in the world. The aim of this paper is to review the sedimentary and structural evolution of arc‐related sedimentary basins in southern Central America, and to show how the arc developed from a pre‐extensional intra‐oceanic island arc into a doubly‐vergent, subduction orogen. The Cenozoic sedimentary history of southern Central America is placed into the plate tectonic context of existing Caribbean Plate models. From regional basin analysis, the evolution of the southern Central American island arc is subdivided into three phases: (i) non‐extensional stage during the Campanian; (ii) extensional phase during the Maastrichtian‐Oligocene with rapid basin subsidence and deposition of arc‐related, clastic sediments; and (iii) doubly‐vergent, compressional arc phase along the 280 km long southern Costa Rican arc segment related to either oblique subduction of the Nazca plate, west‐to‐east passage of the Nazca–Cocos–Caribbean triple junction, or the subduction of rough oceanic crust of the Cocos Plate. The Pleistocene subduction of the Cocos Ridge contributed to the contraction but was not the primary driver. The architecture of the arc‐related sedimentary basin‐fills has been controlled by four factors: (i) subsidence caused by tectonic mechanisms, linked to the angle and morphology of the incoming plate, as shown by the fact that subduction of aseismic ridges and slab segments with rough crust were important drivers for subduction erosion, controlling the shape of forearc and trench‐slope basins, the lifespan of sedimentary basins, and the subsidence and uplift patterns; (ii) subsidence caused by slab rollback and resulting trench retreat; (iii) eustatic sea‐level changes; and (iv) sediment dispersal systems.  相似文献   

6.
The relationship between the Yanshanian Movement, destruction of the North China Craton(NCC), and subduction of the western Pacific plate is crucial to reconstructing the middle-late Mesozoic tectonic evolution of the eastern Asian continent and margin. The Yanshanian Movement was a globally important change in crustal tectonics during the Middle-Late Jurassic.Previous research has systematically studied the formation and evolution of the Yanshanian Movement, focusing on the timing and location of tectonic movements, and the sedimentary and volcanic strata. However, the question of whether the tectonic activity occurred globally, and the characteristics of the Yanshanian Movement remain debated. The main argument is that if a tectonic movement can only be characterized by a regional or local disconformity, and if the tectonic movement occurred in an intracontinental setting, with extensive deformation but with no disconformity despite volcanic eruptions and magmatic intrusions, accompanied by changes in crustal structure and composition, should it be defined as a tectonic event or process? This question requires further analysis. The main aim of this study is to distinguish whether the Yanshanian Movement is a local feature of the eastern Asian continent, or a global tectonic event related to subduction of the Pacific Plate. In this paper, based on previous research, we discuss the spatial and temporal evolution of the Yanshanian Movement, the controlling tectonic mechanisms, and its relationship to the reactivation and destruction of the NCC and the subduction of the western Paleo-Pacific slab.We emphasize that the Yanshanian Movement in the Middle-Late Jurassic is distinct from the lithospheric thinning responsible for Early Cretaceous extension and magmatism related to the destruction of the NCC. The various tectonic stages were constrained by different dynamics and tectonic settings, or by different tectonic events and processes. Therefore, it is possible that the deformation and reactivation of the NCC contributed to its destruction, in addition to lithospheric thinning. Finally, we discuss whether the Yanshanian Movement was associated with the destruction of the NCC.  相似文献   

7.
Abstract   The development of voluminous granitic magmatism and widespread high-grade metamorphism in Mid-Cretaceous southwest Japan have been explained by the subduction of a spreading ridge (Kula–Pacific or Farallon–Izanagi plate boundaries) beneath the Eurasian continent and the formation of a slab window. In the present study, the thermal consequences of the formation of a slab window beneath a continental margin are evaluated through a 2-D numerical simulation. The model results are evaluated by comparison with the Mid-Cretaceous geology of southwest Japan. Of particular interest are the absence of an amphibolite- to granulite-facies metamorphic belt near the Wadati–Benioff plane, and significant melting of the lower crustal-mafic rocks sufficient to form a large amount of granitic magma. Because none of the model results simultaneously satisfied these two geological interpretations, it is suggested that subduction of plate boundaries in Mid-Cretaceous southwest Japan was not associated with the opening of a slab window. According to previous studies, and the results of the present study, two different tectonic scenarios could reasonably explain the geological interpretations for Mid-Cretaceous southwest Japan: (i) The spreading ridge did not subduct beneath the Eurasian continent, but was located off the continental margin, implying the continuous subduction of very young oceanic lithosphere; (ii) ridge subduction beneath the continental margin occurred after active spreading had ceased. Consequently, in both tectonic scenarios, the subduction of plate boundaries at the Mid-Cretaceous southwest Japan was not associated with a slab window, but very young (hot) oceanic lithosphere.  相似文献   

8.
Kenshiro  Otsuki 《Island Arc》1992,1(1):51-63
Abstract The 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 were reactivated.  相似文献   

9.
中国东北地区大兴安岭西侧盆地群包括漠河盆地、根河盆地、拉布达林盆地、海拉尔盆地和二连盆地等,蕴藏着丰富的中、新生代油气资源.为研究该盆地群域古生代、中新生代构造演化,综合建立盆地群域地球动力学模型,补充东北亚构造演化理论,本文综述该盆地群域受控的区域构造与深部构造背景、盆地群构造特征与性质、主要控盆断裂特征、盆地群油气条件比较以及盆地群域已完成并取得重要结果的地球物理工作.归纳已有主要认识和研究结果:(1)对大兴安岭西侧的盆地群起构造控制作用的构造带包括蒙古—鄂霍茨克洋缝合带、西拉木伦河缝合带、黑河—贺根山缝合带、塔原—喜桂图缝合带、西太平洋板块俯冲带,以及额尔古纳—呼伦断裂和得尔布干断裂.(2)二连盆地、海拉尔盆地和漠河盆地的盆地构造轴向与蒙古—鄂霍茨克洋缝合带走向相关;而且三个盆地内的一级构造单元走向(隆起、坳陷和推覆带)也具有这类特点.(3)几个地学断面的综合地球物理研究表明,大兴安岭西侧盆地群岩石圈地幔厚度自北向南变厚,南部盆地基底与华北地台基底表现类似;盆地群基底电性结构因受到软流圈热物质作用可能在继续演化.(4)在盆地沉积地层方面,漠河盆地的下部是侏罗系陆相煤系地层,上部是白垩系火山岩地层;海拉尔盆地由下侏罗统的铜钵庙组、南屯组,上侏罗统的大磨拐河组和下白垩统的伊敏组共同组成扎赉诺尔群,厚约3000m;二连盆地中生代地层中,中下侏罗统主要为含煤建造,上侏罗统为火山岩建造,下白垩统主要为含油建造和含煤建造,上白垩统为砂砾岩建造.(5)盆地群整体勘探程度较低.基于上述研究结果,需要进一步研究的科学问题包括:由本研究区的地球物理、构造地质、石油地质等多学科的综合研究,解决研究区受控的区域构造应力场所包括的因素及其作用,以及在岩石圈尺度上三维空间的地球物理场表征;深部构造对盆地群域构造的作用;从晚古生代到中新生代研究区构造演化特点及其依据;从北至南约1650km长的盆地群域构造差异与依据;盆地群(域)油气条件与毗邻的松辽盆地在构造成因上的差异.  相似文献   

10.
The North China Craton (NCC) witnessed Mesozoic vigorous tectono-thermal activities and transition in the nature of deep lithosphere. These processes took place in three periods: (1) Late Paleozoic to Early Jurassic (～170 Ma); (2) Middle Jurassic to Early Cretaceous (160–140 Ma); (3) Early Cretaceous to Cenozoic (140 Ma to present). The last two stages saw the lithospheric mantle replacement and coupled basin-mountain response within the North China Craton due to subduction and retreating of the Paleo-Pacific plate, and is the emphasis in this paper. In the first period, the subduction and closure of the Paleo- Asian Ocean triggered the back-arc extension, syn-collisional compression and then post-collisional extension accompanied by ubiquitous magmatism along the northern margin of the NCC. Similar processes happened in the southern margin of the craton as the subduction of the Paleo-Tethys ocean and collision with the South China Block. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenosphere upwelling and had the priority for magmatism and deformation. The second period saw the closure of the Mongol-Okhotsk ocean and the shear deformation and magmatism induced by the drifting of the Paleo-Pacific slab. The former led to two pulse of N-S trending compression (Episodes A and B of the Yanshan Movement) and thus the pre-existing continental marginal basins were disintegrated into sporadically basin and range province by the Mesozoic magmatic plutons and NE-SW trending faults. With the anticlockwise rotation of the Paleo-Pacific moving direction, the subduction-related magmatism migrated into the inner part of the craton and the Tanlu fault became normal fault from a sinistral one. The NCC thus turned into a back-arc extension setting at the end of this period. In the third period, the refractory subcontinental lithospheric mantle (SCLM) was firstly remarkably eroded and thinned by the subduction-induced asthenospheric upwelling, especially those beneath the weak zones (i.e., cratonic margins and the lithospheric Tanlu fault zone). Then a slightly lithospheric thickening occurred when the upwelled asthenosphere got cool and transformed to be lithospheric mantle accreted (～125 Ma) beneath the thinned SCLM. Besides, the magmatism continuously moved southeastward and the extensional deformations preferentially developed in weak zones, which include the Early Cenozoic normal fault transformed from the Jurassic thrust in the Trans-North Orogenic Belt, the crustal detachment and the subsidence of Bohai basin caused by the continuous normal strike slip of the Tanlu fault, the Cenozoic graben basins originated from the fault depression in the Trans-North Orogenic Belt, the Bohai Basin and the Sulu Orogenic belt. With small block size, inner lithospheric weak zones and the surrounding subductions/collisions, the Mesozoic NCC was characterized by (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating. Therefore, the subduction and retreating of the western Pacific plate is the outside dynamics which resulted in mantle replacement and coupled basin-mountain respond within the North China Craton. We consider that the Mesozoic decratonization of the North China Craton, or the Yanshan Movement, is a comprehensive consequence of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust.  相似文献   

11.
The Cretaceous tectonic and geodynamic settings of the southeastern Russian continental margin are discussed using data generated during several recent geological studies. The structural patterns of the East Asian Cretaceous continental margin are the result of the influence of global and regional processes. The interaction and reorganization of the Eurasian, Pacific and other related plates induced intraplate tectonic processes such as rifting, subduction, collision, transform faulting, and basin formation. Three major basin types are recognized in this area: (i) mainly marine active continental margins associated with shear components (Sangjian–Middle Amur Basin); (ii) passive continental margins (Bureya, Partizansk, and Razdolny basins); (iii) intracontinental basins (Amur–Zeya Basin). The evolution of the biota in this region allows the examination of Early and Late Cretaceous biostratigraphy, faunal and floral changes, and the phytogeography of the southeastern Russian continental margin.  相似文献   

12.
Abstract Mesozoic accretionary complexes of the southern Chichibu and the northern Shimanto Belts, widely exposed in the Kanto Mountains, consist of 15 tectonostratigraphic units according to radiolarian biochronologic data. The units show a zonal arrangement of imbricate structure and the age of the terrigenous clastics of each unit indicates successive and systematic southwestward younging. Although rocks in these complexes range in age from Carboniferous to Cretaceous, the trench-fill deposits corresponding to the Hauterivian, the Aptian to Middle Albian and the Turonian are missing. A close relationship between the missing accretionary complexes and the development of strike-slip basins is recognizable. The tectonic nature of the continental margin might have resulted from a change from a convergent into a transform or oblique-slip condition, so that strike-slip basins were formed along the mobile zones on the ancient accretionary complexes. Most terrigenous materials were probably trapped by the strike-slip basins. Then, the accretion of the clastic rock sequence occurred, probably as a result of the small supply of terrigenous materials in the trench. However, in the case of right-angle subduction, terrigenous materials might have been transported to the trench through submarine canyons and deposited there. Thus, the accretionary complexes grew rapidly and thickened. Changes both in oceanic plate motion and in the fluctuation of terrigenous supply due to the sedimentary trap caused pulses of accretionary complex growth during Jurassic and Cretaceous times. In the Kanto Mountains, three tectonic phases are recognized, reflecting the changes of the consuming direction of the oceanic plates along the eastern margin of the Asian continent. These are the Early Jurassic to early Early Cretaceous right-angle subduction of the Izanagi Plate, the Early to early Late Cretaceous strike-slip movement of the Izanagi and Kula Plates, and the late Late Cretaceous right-angle subduction of the Kula Plate.  相似文献   

13.
Abstract The Korean peninsula is widely regarded as being located at the relatively stable eastern margin of the Asian continent. However, more than 10 Quaternary faults have recently been discovered in and reported from the southeastern part of the Korean Peninsula. One of these, the Eupchon Fault, was discovered during the construction of a primary school, and it is located close to a nuclear power plant. To understand the nature and characteristics of the Quaternary Eupchon Fault, we carried out two trench surveys near the discovery site. The fault system includes one main reverse fault (N20°E/40°SE) with approximately 4 m displacement, and a series of branch faults, cutting unconsolidated Quaternary sediments. Structures in the fault system include synthetic and antithetic faults, hanging‐wall anticlines, drag folds, back thrusts, pop‐up structures, flat‐ramp geometries and duplexes, which are very similar to those seen in thrust systems in consolidated rocks. In the upper part of the fault system, several tip damage zones are observed, indicating that the fault system propagates upward and terminates in the upper part of the section. Pebbles along the main fault plane show a preferred orientation of long axes, indicating the fault trace. The unconformity surface between the Quaternary deposits and the underlying Tertiary andesites or Cretaceous sedimentary rocks is displaced by this fault with a reverse movement sense. The stratigraphic relationship shows normal slip sense at the lower part of the section, indicating that the fault had a normal slip movement and was reversely reactivated during the Quaternary. The inferred length of the Quaternary thrust fault, based on the relationship between fault length and displacement, is 200–2000 m. The current maximum horizontal compressive stress direction in this area is generally east‐northeast–west‐southwest, which would be expected to produce oblique slip on the Eupchon Fault, with reverse and right‐lateral strike‐slip components.  相似文献   

14.
One of the more prominent architectural elements of the Nankai subduction margin, offshore southwest Japan, is an out‐of‐sequence thrust fault (megasplay) that separates the inner accretionary prism from the outer prism. The inner prism (hanging wall of the megasplay) is dominated by mudstone, which is enigmatic when the sedimentary facies is compared to coeval deposits in the Shikoku Basin (i.e. inputs from the subducting Philippine Sea plate) and to coarser‐grained turbidite sequences from the Quaternary trench wedge. Clay mineral assemblages amplify the mismatches of sedimentary facies. Mudstones from the inner prism are uniformly depleted in smectite, with average bulk values of 23–24 wt%, whereas the Shikoku Basin deposits show progressive decreases in proportions of smectite over time, from averages of 46–48 wt% at 10 Ma to 17–21 wt% at 1 Ma. Plate‐boundary reconstructions for the Philippine Sea region provide one solution to the conundrum. Between 15 Ma and 10 Ma, the Pacific plate subducted near the NanTroSEIZE transect, and a trench‐trench‐trench triple junction migrated to the northeast. Accretion during that period involved sediments that had been deposited on the Pacific plate. Motion of the Philippine Sea plate changed from 10 Ma to 6 Ma, resulting in sinistral slip along the proto‐Nankai Trough. Sediments accreted during that period probably had been deposited near the triple junction, with a hybrid detrital provenance. Renewed subduction of the Philippine Sea plate at 6 Ma led to reorganization of watersheds near the Izu–Honshu collision zone and gradual incision of large submarine canyons on both sides of the colliding Izu arc. Accreted Pliocene mudstones share more of an affinity to the triple junction paleoenvironment than they do to Shikoku Basin. These differences between subducting Shikoku Basin strata and accreted Pacific plate sediments have important implications for interpretations of frictional properties, structural architecture, and diagenetic fluid production.  相似文献   

15.
It is essential to clarify the lithological, structural, and chronological relationships between the Sanbagawa Metamorphic Complex (MC) and the Cretaceous Shimanto Accretionary Complex (AC) for understanding the tectonic evolution of SW Japan. To this end, we carried out a detailed field survey of the Sanbagawa MC and the Cretaceous Shimanto AC on the central Kii Peninsula, where they are in direct contact with each other. We also conducted U–Pb dating of detrital zircons from these complexes. The field survey showed that the boundary between the Iro Complex of the Sanbagawa MC and the Mugitani Complex of the Shimanto AC, Narai Fault, shows a sinistral sense of shear with a reverse dip‐slip component, and there are significant differences in the strain intensity and the degree of recrystallization between the two complexes across this fault. Detrital zircon U–Pb dating indicates that the Iro Complex in the hanging wall of the Narai Fault shows a significantly younger maximum depositional age than the Mugitani Complex in the footwall of the fault, and an apparently large gap in the MDA of ca. 35 Myr exists across this fault. This large age gap across the Narai Fault suggests that this fault is an essential tectonic boundary fault within the Cretaceous accretionary–metamorphic complexes on the Kii Peninsula, and is considered to be an out‐of‐sequence thrust. In addition, a similar shear direction and a large age gap have been identified across the Ui Thrust, which marks the boundary between the Kouyasan and Hidakagawa belts of the Cretaceous Shimanto AC. The Cretaceous accretionary–metamorphic complexes record the large‐scale tectonic juxtapositions of complexes, and these juxtaposed structures had been caused by sinistral–reverse movements on the tectonic boundary faults such as the Narai Fault and the Ui Thrust.  相似文献   

16.
Paleozoic sedimentation and tectonics in Korea: A review   总被引：11，自引：1，他引：11  
Yong Il Lee  Jae Il Lee 《Island Arc》2003,12(2):162-179
Abstract The geological history of the Korean Paleozoic is recorded in lower and upper Paleozoic strata, mostly distributed in two relatively large sedimentary basins, the Taebaeksan and Pyeongnam basins. The lower Paleozoic sedimentary rocks are exclusively of marine origin, dominated by shallow platform carbonate rocks with minor interbedded siliciclastic rocks. The development of the lower Paleozoic sequence was mostly controlled by eustatic changes, having cyclic sedimentation of various temporal scales. During the early Paleozoic the Korean Peninsula was located in a low‐latitude tropical region and experienced frequent storm activities. The upper Paleozoic sequence comprises paralic to non‐marine rocks with minor limestone intercalations in the lower part of the sequence. Upsection changes in sandstone composition and mudrock geochemistry of the upper Paleozoic Pyeongan Supergroup in the Samcheok coalfield indicate that sediments may have been derived from the continued uplift and unroofing of a collisional orogen source. There exists a great unconformity between the lower and upper Paleozoic strata, which spans the geological time from the Late Ordovician to Early Carboniferous. The unconformity period is conventionally thought to be of non‐deposition, but a recent study suggests that it is characterized by continuous sedimentation and significant removal (>1 km thick) of sediments by erosion. No Paleozoic tectonic history has been addressed so far, and thus it needs further study to elucidate geological events during the middle–late Paleozoic in the Korean Peninsula. Tectonostratigraphic correlation of the Korean Peninsula with neighboring Chinese blocks has been a hot issue for a long time. Although the eastward extension of the Chinese collision belt has been recently suggested to be the Imjingang belt located in the middle of the peninsula, further studies are needed to test this hypothesis because results of recent paleontological, sedimentological and stratigraphic studies on Paleozoic sediments are not in agreement with this possibility.  相似文献   

17.
The Taebaeksan Basin comprises the lower Paleozoic Joseon Supergroup and the upper Paleozoic Pyeongan Supergroup, which are separated by a disconformity representing a 140 myr‐long hiatus. This paper deals mainly with the late Paleozoic paleogeographical and tectonic evolution of the Taebaeksan Basin on the basis of updated stratigraphy, sedimentation, and geochronology of the Pyeongan Supergroup. Late Paleozoic sedimentation in the Taebaeksan Basin recommenced at ~ 320 Ma and formed a thick siliciclastic succession of marginal marine and non‐marine alluvial deposits, the Pyeongan Supergroup. The Pyeongan Supergroup was deposited in a retroarc foreland basin formed by build‐up of a magmatic arc along the northern margin of the Sino‐Korean Craton. The formation of sedimentary deposits ceased at ~ 250 Ma due to the collision of the Sino‐Korean Craton and South China Craton that generated the Triassic Songnim orogeny in Korea. Diverse tectonic models have been proposed for assembly of the proto‐Korean Peninsula, but the indented wedge model is considered to best explain the geological features of the peninsula. The indented wedge model entails northward subduction of the central block of the Korean Peninsula (part of the South China Craton) beneath the northern block of the Korean Peninsula (part of the Sino‐Korean Craton) along the Sulu‐Imjingang Belt.  相似文献   

18.
Two grabens were developed in the Yi-Shu segment of the Tan-Lu fault zone (TLFZ) during its exten-sional activities, and are now confined by four major NNE-trending normal faults and filled with Creta-ceous sediments. These faults were developed due to their reactivities, containing gouge and cutting the graben sediments. Detailed fieldwork demonstrates that the faults experienced sinistral transten-sional moment related to regional NE-SW extension during the reactivity. X-ray diffraction (XRD) analysis of ...  相似文献   

19.
The Daeri Member, a Cretaceous volcanic–sedimentary succession, can be divided into lower, middle, and upper parts based on vertical changes in its lithologic characters. The lower Daeri Member is composed of siliciclastic deposits formed in a semi‐arid floodplain environment, which is overlain by the middle Daeri Member consisting mainly of andesite lava flow. After the emplacement of the andesite, activities of intrabasinal normal faults created accommodation on hanging wall blocks together with the development of intrabasinal topographic relief. The upper Daeri Member occurs only in hanging wall blocks and is composed of rhyolitic volcaniclastic sediments formed during an explosive volcanic eruption. Following the eruption, owing to semi‐arid climatic conditions and the destruction of vegetation, the eruptive materials were easily remobilized and deposited by episodic sediment gravity flows, resulting in deposition of the resedimented volcaniclastic deposits with sheet‐like geometry. Away from the intrabasinal normal faults, the resedimented volcaniclastic deposits show a decrease in grain size together with changes in inferred depositional processes from debris flows to hyperconcentrated flows and supercritical sheetfloods. This suggests that the resedimented volcaniclastic deposits were stacked on alluvial fan environments induced by intrabasinal topographic relief associated with normal fault activities. In addition, episodic movement of the faults gave rise to periodic fluctuation of the accommodation and an increase in gradient of the alluvial fan surface, resulting in the development of coarsening‐upward trends in the resedimented volcaniclastic deposits. The development of the alluvial fan and the coarsening‐upward trends indicate that dynamic tectonic subsidence and concomitant changes in the intrabasinal physiographic relief influenced the depositional processes and sizes of the transported volcaniclastic sediments of the upper Daeri Member. Thus, it is necessary to carefully observe tectonic signatures in volcaniclastic successions, particularly the syneruptive lithofacies, in order to reconstruct the tectonic and volcanic histories of receiving basins.  相似文献   

20.
When combined with the Miocene-Recent volcanic record of Baja California, a parallel drawn between the Chile and Mexico triple junction areas substantiates slab window development beneath northwestern Mexico during the past 12-10 Myr. The slab-free zone manifestations challenge the notion that ridge subduction has not occurred beneath the southern Baja California peninsula. The geochemically distinctive rocks from the Santa Clara volcanic field of west-central Baja California, including coeval adakites and niobium-enriched basalt, are commonly inferred to signal partial melting of the subducting plate at shallow depths and relatively high temperatures, before slab dehydration occurs. Such PT conditions for slab melting have only been observed in association with spreading-ridge subduction. We propose that slab window development beneath southern Baja California and mainland Mexico (30° to 18°N) resulted from subduction of the East Pacific rise.  相似文献   

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