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1.
After Rodinia supercontinent was disintegrated in Late Proterozoic, an ocean, namely, Tethys Ocean, occurred between Gondwana continental group and Pan-Cathaysian continental group from Late Proterozoic to Mesozoic. From Early Paleozoic to Mesozoic, Tethys Ocean was subducted toward Pan-Cathaysian block group, which results in backarc expansion, arc-land collision and forearc accretion. When the backarc basin expands and reaches the small oceanic basin, ophiolite melange will be generated. As accretion had already occurred in the south of the continental margin in the earlier stage, the succeeding backarc expansion and the frontal arc position were migrated toward south correspondingly. Therefore, multiple ophiolite belts and magmatic rock belts occurred, and show a trend of decreasing age from north toward south. As the continental margin was split and migrated toward south and reached a high latitude position, i.e., with the shortening and subduction of oceanic crust, the sedimentary bodies at high latitude was accreted continuously toward low latitude area together with the formation of oceanic island, mixing of cold-type and warm-type organism was generated. Moreover, blocks split and separated from Pan-Cathaysian or Gondwana continental group cannot traverse the oceanic median ridge and joins with another continental block. As a result, the Kunlun belt on the SW margin of the Pan-Cathaysian land was resulted from the multi-arc orogenesis such as the backarc seabed expansion, arc-arc collision, arc-land collision oceanic bed, and the continuous southward accretion process.  相似文献   

2.
The Late Caledonian to Early Hercynian North Qilian orogenic belt in northwestern China is an elongate tectonic unit situated between the North China plate in the north and the Qaidam plate in the south. North Qiilan started in the latest Proterozoic to Cambrian as a rift basin an the southern mar-gin of North China, and evolved later to an archipelagic ocean and active continental margin during the Ordovician and a fardand basin from Silurian to the Early and Middle Devonian. The Early Silurian fly-sch and sulmmrine alluvial fan, the Middle to Late Silurian shallow marine to tidal flat deposits and the Early and Middle Devonian terrestrial.molasse are developed along the corridor Nansimn. The shallo-wing-upward succession from subabyssal flysch, shallow marine, tidal flat to terrestrial molasse and its gradually narrowed regional distribution demonstrate that the foreland basin experienced the transition from flysch stake to molasse stake during the Silurian and Devonian time.  相似文献   

3.
Based on studies of palaeogeography, palaeobiogeography, palaeomagnetism, geochemistry and volcanism, this paper proposes that the Zhen'an-Xichuan area was a small Early Palaeozoic block rifted away from South Qinling and suturing onto North Qinling earlier than the other parts of South Qinling. In the Early Palaeozoic Qinling was a small archipelagic ocean basin with 5 rows of islands including the Zhen'an-Xichuan block. The drifting of the Yangtze and North China plates and the islands between them in the same direction at different speeds caused their suturing process to be different from the classic plate collision, which is the major feature of the suturing of the multi-island Tethys ocean basin. This also explains the problem that the Caledonian collision did not result in orogeny in eastern Qinling.  相似文献   

4.
Identification and anatomy of oceanic arcs within ancient orogenic belt are significant for better understanding the tectonic framework and closure process of paleo-ocean basin. This article summarizes the geological, geochemical, and geochronological characteristics of upper crust of Proto-Tethyan Lajishan intra-oceanic arc and provides new data to constrain the subduction evolution of the South Qilian Ocean. The intra-oceanic arc volcanic rocks, including intermediate–mafic lava, breccia, tuff, and minor felsic rocks, are distributed along southern part of the Lajishan ophiolite belt. Geochemical and isotopic compositions indicate that the intermediate–mafic lava were originated from depleted mantle contaminated by sediment melts or hydrous fluids, whereas the felsic rocks were likely generated by partial melting of juvenile mafic crust in intra-oceanic arc setting. Zircons from felsic rocks yield consistent and concordant ages ranging from 506 to 523 Ma, suggesting these volcanic rocks represent the relicts of upper crust of the Cambrian intra-oceanic arc. Combined with the Cambrian forearc ophiolite and accretionary complex, we suggest that the Cambrian intra-oceanic arc in the Lajishan ophiolite belt is belonging to the intra-oceanic arc system which was generated by south-directed subduction in the South Qilian Ocean at a relatively short interval between approximately 530 and 480 Ma.  相似文献   

5.
http://www.sciencedirect.com/science/article/pii/S1674987111001113   总被引：1，自引：0，他引：1  
The Rheic Ocean was one of the most important oceans of the Paleozoic Era.It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita-Alleghanian -Variscan orogen during the assembly of Pangea.Rifting began in the Cambrian as a continuation of Neoproterozoic orogenic activity and the ocean opened in the Early Ordovician with the separation of several Neoproterozoic arc terranes from the continental margin of northern Gondwana along the line of a former suture.The rapid rate of ocean opening suggests it was driven by slab pull in the outboard lapetus Ocean.The ocean reached its greatest width with the closure of lapetus and the accretion of the periGondwanan arc terranes to Laurentia in the Silurian.Ocean closure began in the Devonian and continued through the Mississippian as Gondwana sutured to Laurussia to form Pangea.The ocean consequently plays a dominant role in the Appalachian-Ouachita orogeny of North America,in the basement geology of southern Europe,and in the Paleozoic sedimentary,structural and tectonothermal record from Middle America to the Middle East.Its closure brought the Paleozoic Era to an end.  相似文献   

6.
This is a review of the formation and tectonic evolution of the continental Asia in Phanerozoic.The continental Asia has formed on the bases of some pre-Cambrian cratons,such as the Siberia,India,Arabia,North China,Tarim,South China,and Indochina,through multi-stage plate convergence and collisional collages in Phanerozoic.The north-central Asia had experienced the expansion and subduction of the Paleo-Asian Ocean(PAO)in the early Paleozoic and the closure of the PAO in the late Paleozoic and early Mesozoic,forming the PAO regime and Central Asian orogenic belt(CAOB).In the core of the CAOB,the Mongol-Okhotsk Ocean(MOO)opened with limited expansion in the Early Permian and finally closed in the Late Jurassic–Early Cretaceous.The south-central Asia had experienced mainly multi-stage oceanic opening,subduction and collision evolution in the Tethys Ocean,forming the Tethys regime and Himalaya-Tibetan orogenic belt.In eastern Asia,the plate subduction and continental margin orogeny on western margin of the Pacific Ocean,forms the West Pacific regime and West Pacific orogenic belt.The PAO,Tethys,and West Pacific regimes,together with Precambrian cratons among or surrounding them,made up the major tectonic and dynamic systems of the continental Asia in Phanerozoic.Major tectonic events,such as the Early Paleozoic Qilian,Uralian,and Dunhuang orogeneses,the late Paleozoic East Junggar,Tianshan and West Junggar orogeneses,the Middle to Late Permian Ailaoshan orogeny and NorthSouth Lhasa collision,the early Mesozoic Indochina-South China and North-South China collisions,the late Mesozoic Mongolia-Okhotsk orogeny,Lhasa-Qiangtang collision,and intra-continental Yanshanian orogeny,and the Cenozoic IndoAsian,Arab-Asian,and West Pacific margin collisions,constrained the formation and evolution of the continental Asia.The complex dynamic systems have left large number of deformation features,such as large-scale strike-slip faults,thrustfold systems and extensional detachments on the continental Asia.Based on past tectonics,a future supercontinent,the Ameurasia,is prospected for the development of the Asia in ca.250 Myr.  相似文献   

7.
The Solonker suture zone has long been considered to mark the location of the final disappearance of the PaleoAsian Ocean in the eastern Central Asian Orogenic Belt(CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated wholerock geochemistry and LA-ICP-MS zircon U-Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan-Xilinhot-Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian-Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady-state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back-arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo-Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back-arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo-Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.  相似文献   

8.
The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline base- ment. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite 40Ar/39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Cale- donian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin is determined. This pro- vides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.  相似文献   

9.
The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well-enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Paleozoic deposits. From the Cambrian to the middle Ordovician, this region was characterized by geographically extensive, flat-bedded siliceous mudstone, indicating the existence of a large ocean basin. The oceanic plate entered the convergence phase in terms of the Wilson Circle during the Middle Ordovician, when numerous magmatic arcs formed along two opposite sides of the ocean. The magmatic arcs became the widest during the Silurian, suggesting that the Hongliuhe-Niujuanzi-Xichangjing Ocean(HNX; a southern branch of the Paleo Asian Ocean) was reduced to a small residual ocean in the central Beishan region by that time, and probably lasted till the Carboniferous or later by newly published data.  相似文献   

10.
Muscovite 40Ar-39Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220–240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.  相似文献   

11.
The South Tianshan Orogen and adjacent regions of Central Asia are located in the southwestern part of the Central Asian Orogenic Belt.The formation of South Tianshan Orogen was a diachronous,scissors-like process,which took place during the Palaeozoic,and its western segment was accepted as a site of the fnal collision between the Tarim Craton and the North Asian continent,which occurred in the late Palaeozoic.However,the post-collisional tectonic evolution of the South Tianshan Orogen and adjacent regions remains debatable.Based on previous studies and recent geochronogical data,we suggest that the fnal collision between the Tarim Craton and the North Asian continent occurred during the late Carboniferous.Therefore,the Permian was a period of intracontinental environment in the southern Tianshan and adjacent regions.We propose that an earlier,small-scale intraplate orogenic stage occurred in late Permian to Triassic time,which was the frst intraplate process in the South Tianshan Orogen and adjacent regions.The later largescale and well-known Neogene to Quaternary intraplate orogeny was induced by the collision between the India subcontinent and the Eurasian plate.The paper presents a new evolutionary model for the South Tianshan Orogen and adjacent regions,which includes seven stages:(I)late Ordovicianeearly Silurian opening of the South Tianshan Ocean;(II)middle Silurianemiddle Devonian subduction of the South Tianshan Ocean beneath an active margin of the North Asian continent;(III)late Devonianelate Carboniferous closure of the South Tianshan Ocean and collision between the Kazakhstan-Yili and Tarim continental blocks;(IV)early Permian post-collisional magmatism and rifting;(V)late PermianeTriassic the frst intraplate orogeny;(VI)JurassicePalaeogene tectonic stagnation and(VII)NeoceneeQuaternary intraplate orogeny.  相似文献   

12.
REVIEWS     
Genesis of the so-called Bentong–Raub Suture of Malay Peninsula does not fit to the model of subduction-related collision. It has evolved from transpression tectonics resulting closure and exhumation of the inland basin which underwent extensive back-arc extension during Triassic. Crust having similar thickness (average ~35 km) below entire Malay Peninsula nagate collision of two separate continental blocks rather supports single continental block that collided with South China continental block during Permo-Triassic. Westward subduction of intervening sea (Proto South China Sea) below Malay Peninsula resulted in widespread I- and S-Type granitization and volcanism in the back-arc basins during Triassic. Extensive occurrence of Permo-Triassic Pahang volcanics of predominantly rhyolitic tuff suggest its derivation from back-arc extension. Back-arc extension, basin development and sedimentation of the central belt of the peninsula continued until Cretaceous. A-Type granite of metaluminous to peraluminous character indicates their emplacement in an intraplate tectonic setting. Malay Peninsula suffered an anticlockwise rotation due to the rifting of Luconia–Dangerous Grounds from the east Asia in the Late Cretaceous–Early Tertiary. Extensive ductile and brittle deformation including crustal segmentation, pull-apart fracturing and faulting occurred during the closure and exhumation of the basins developed in the peninsula during Late Cretaceous–Early Tertiary. Crustal shortening in the central belt of the peninsula has been accomodated through strike-slip displacement, shearing and uplift.  相似文献   

13.
The Tianshan range could have been built by both late Early Paleozoic accretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture is marked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphic relics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanic arc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along with unconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation. The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductile shearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductile deformation, and the later deformation, a dextral strike-slip tectonic process, occurred during the Late Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably on pre-Carboniferous metamorphic and ductilely sheared rocks, implying t  相似文献   

14.
This work carried out systematic geological field investigation, petrography observation, zircon geochronology and whole rock geochemistry on Late Paleozoic intrusions in the Xingxingxia region near the Xinjiang-Gansu provincial boundary, western China, aiming to constrain the Late Paleozoic tectonic framework of the Xingxingxia region and the final closure time of South Tianshan Ocean in the East Tianshan. The Xingxingxia area is located in the east part of the Tianshan orogen, and adjacent to the north of the Tarim Basin. The Late Paleozoic magma activities in the Xingxingxia region can be mainly divided into three stages. The first stage includes intrusive magma activities under a collision setting between Late Ordovician to the Late Devonian. The second stage is intrusive magma activities under a subduction setting during(304±3)–(278±3) Ma, and the third stage involves intrusive magma activities under a collision and post-collision setting during(268±5)–(259.9±2.6) Ma. The final suture zone of South Tianshan Ocean should be between the Central Tianshan Block and South Tianshan accretionary complex. Based on previous work, both the first stage magma activities(i.e., intrusive magmatic activities between the Late Ordovician to Late Devonian) and the Hongliuhe ophiolitic complex indicate a close event between Central Tianshan Block and South Tianshan Accretionary Complex. The 304±3 Ma dioritic metamorphic gneiss of the XingX ingxia complex and the 278±3 Ma diorite are all island arc calc-alkaline rocks, the 289±3 Ma gabbro is island arc tholeiitic gabbro formed by magma from metasomatic enrichment mantle. All these results indicate that the second stage of magmatic activities is under a subduction setting. The third stage magma activities i.e. the granitic magma activities of(268±5)–(259.9±2.6) Ma occurred at a transitional setting from compressional to post-collision extensional tectonic setting. Thus, around(268±5)–(260±3) Ma, the final closure of the South Tianshan Ocean occurred and the Tianshan orogen shifted into the intracontinental evolution stage. During and after the closure process, a wide range of metamorphism and large dextral strike-slip faults developed.  相似文献   

15.
The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements; it is in the eastern Alxa Block, adjacent to the North China Craton(NCC) and the North Qilian Orogenic Belt(NQOB).There are well-developed Paleozoic–Cenozoic strata in this basin, and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the Alxa Block and surrounding tectonic units.However, due to intensive post-depositional modification, and lack of subsurface data,several fundamental issues—including the distribution and evolution of the depositional systems, provenance supplies and source-to-sink relationships during the Carboniferous– Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin.Employing integrated outcrop surveys, new drilling data, and detrital zircon dating, this study examines the paleogeographic distribution and evolution, and provenance characteristics of the Carboniferous–Permian strata in the Bayanhot Basin.Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous–late Permian.The transgression extent could reach the central basin in the early Carboniferous.The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other.Subsequently, a gradual regression followed until the end of the Permian.The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the Alxa Block at that time.The NCC, Bayanwula Mountain, and NQOB jointly served as major provenances during the Carboniferous–Permian.There was no ocean separation, nor was there an orogenic belt between the Alxa Block and the NCC that provided sediments for both sides during the Carboniferous–Permian.The accretion of the Alxa and North China blocks should have been completed before the Carboniferous period.  相似文献   

16.
The early stage of Sichuan Basin formation was controlled by the convergence of three major Chinese continental blocks during the Indosinian orogeny that include South China,North China,and Qiangtang blocks.Although the Late Triassic Xujiahe Formation is assumed to represent the commencement of continental deposition in the Sichuan Basin,little research is available on the details of this particular stratum.Sequence stratigraphic analysis reveals that the Xujiahe Formation comprises four third-order depositional sequences.Moreover,two tectono-sedimentary evolution stages,deposition and denudation,have been identified.Typical wedge-shaped geometry revealed in a cross section of the southern Sichuan Basin normal to the Longmen Shan fold-thrust belt is displayed for the entire Xujiahe Formation.The depositional extent did not cover the Luzhou paleohigh during the LST1 to LST2 （LST,TST and HST mean Iowstand,transgressive and highstand systems tracts,1,2,3 and 4 represent depositional sequence 1,2,3 and 4）,deltaic and fluvial systems fed sediments from the Longmen Shan belt,Luzhou paleohigh,Hannan dome,and Daba Shan paleohigh into a foreland basin with a centrally located lake.The forebulge of the western Sichuan foreland basin was located southeast of the Luzhou paleohigh after LST2.According to the principle of nonmarine sequence stratigraphy and the lithology of the Xujiahe Formation,four thrusting events in the Longmen Shan fold-thrust belt were distinguished,corresponding to the basal boundaries of sequences 1,2,3,and 4.The northern Sichuan Basin was tilted after the deposition of sequence 3,inducing intensive erosion of sequences 3 and 4,and formation of wedge-shaped deposition geometry in sequence 4 from south to north.The tilting probably resulted from small-scale subduction and exhumation of the western South China block during the South and North China block collision.  相似文献   

17.
The Songpan-Aba area, similar to those basins on the Yangtze block, following the rifting and separation of the Yangtze block, gradually developed into a passive marginal basin on a passive continent margin in Early Paleozoic, and later, with the Qinling-Qilian oceanic crust subduction and ocean closure, the Caledonides were formed and the foreland basin was superimposed upon. Being influenced by the Paleo-Tethyan extension, intra-continental rifting-margin basins were formed in Late Paleozoic. Following the formation of peripheral orogenic belt, the Upper Triassic again superimposed the foreland basin. The Mesozoic and Cenozoic overprinted the faulted basin, forming the Qinghai-Tibet Plateau domes. Hydrocarbon source rock in the Early Paleozoic passive basin, the Upper Paleozoic platform carbonates and the Triassic mudstones comprise the main source-reservoircap combination. Each layer of this area is at the advanced stage of diagenetic evolution, being entered the middle and late diagenetic stages, and anadiagenetic stage. Besides the highly matured Triassic and Permian in Zoige and Hongyuan, almost all the area is at the early stage of over maturatation, generating much methane. This area has the potential for oil and gas.  相似文献   

18.
A group of alluvial fans formed in the early Paleogene represent marginal sedimentary facies at the foot of the South Tianshan Mountain, Kuqa Depression, Tarim Basin, Xinjiang province. Two types of fans occurred in the middle–late Paleogene Kumugeliemu and Suweiyi formations: one alluvial, and the other fan delta deposited in a lacustrine setting. Within the early Neogene Jidike Formation, coastal subaqueous fans developed, probably in a deeper water lacustrine setting. The three types of fans are stacked vertically in outcrop with the sequence in ascending order: bottom alluvial, middle fan-delta, and top subaqueous. The subaqueous is a typical coarse-fan deposit occurring in the glutinite member of the Jidike Formation in some wells. Laterally, from the foreland to the lacustrine settings, the distribution pattern of sedimentary facies represents the same three fan types sequentially. The spatial distribution of these fans was controlled by the Paleogene–Neogene Basin transformation, and evolution with different types of fans developed in the Kuqa Depression in response. In the Paleogene, the Kuqa Depression was a rift basin where an alluvial fan was deposited in the foreland setting, which, by early Neogene, became a foreland basin when the lake level changed. With any rise in lake level, fan-deltas migrated from lacustrine to foreland settings, whereas when the lake level fell, fan migration was reversed. In the early Neogene, with increasing slope and rising lake level, fans progressed and covered the previous fan-delta and lacustrine mudstone. Eventually, subaqueous fans developed, forming the present spatial configuration of these three fan types.  相似文献   

19.
：Yumushan block on the north margin of Qilian mountain, with Jiudong basin and Minle basin to the west and east respectively, belongs to the fore-land depression in NNW direction at the north margin of the Qilian mountain fold belt. The Yumushan block has been thought of as a fault-uplift, which separates the two basins formed during late Yanshanian orogeny. However, the recognition of fault zones at the western margin of the Yumushan block, and the tectonic and sedimentary analyses of the Yumushan block and the basins, cast doubts to the tectonic property of the block. It is suggested that the two basins be derived from an united large basin at least during Mesozoic and the Yumushan block be nappe sheet formed due to NE imbricate thrusting on the north margin fault zone of the Qilian mountain. This proposal would provide valuable clues to further exploration of oil-gas and water resources in Hexi corridor basin belt.  相似文献   

20.
Studies show that the Tianshan orogenic belt was built in the late stage of the Paleozoic, as evidenced by the Permian red molasses and foreland basins, which are distributed in parallel with the Tianshan belt, indicating that an intense folding and uplifting event took place. During the Triassic, this orogenic belt was strongly eroded, and basins were further developed. Starting from the Jurassic, a within-plate regional extension occurred, forming a series of Jurassic-Paleogene extensional basins in the peneplaned Tianshan region. Since the Neogene, a collision event between the Indian and the Eurasian plates that took place on the southern side of the Tianshan belt has caused a strong intra-continental orogeny, which is characterized by thrusting and folding. Extremely thick coarse conglomerate and sandy conglomerate of the Xiyu Formation of Neogene System were accumulated unconformably on the Tianshan piedmont. Studies have revealed that the strong compression caused by the Indian-Eurasian collision  相似文献   

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