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1.
Iran is a mosaic of Ediacaran–Cambrian (Cadomian; 520–600 Ma) blocks, stitched together by Paleozoic and Mesozoic ophiolites. In this paper we summarize the Paleozoic ophiolites of Iran for the international geoscientific audience including field, chemical and geochronological data from the literature and our own unpublished data. We focus on the five best known examples of Middle to Late Paleozoic ophiolites which are remnants of Paleotethys, aligned in two main zones in northern Iran: Aghdarband, Mashhad and Rasht in the north and Jandagh–Anarak and Takab ophiolites to the south. Paleozoic ophiolites were emplaced when N-directed subduction resulted in collision of Gondwana fragment “Cimmeria” with Eurasia in Permo-Triassic time. Paleozoic ophiolites show both SSZ- and MORB-type mineralogical and geochemical signatures, perhaps reflecting formation in a marginal basin. Paleozoic ophiolites of Iran suggest a progression from oceanic crust formation above a subduction zone in Devonian time to accretionary convergence in Permian time. The Iranian Paleozoic ophiolites along with those of the Caucausus and Turkey in the west and Afghanistan, Turkmenistan and Tibet to the east, define a series of diachronous subduction-related marginal basins active from at least Early Devonian to Late Permian time.  相似文献   

2.
Present-day Asia comprises a heterogeneous collage of continental blocks, derived from the Indian–west Australian margin of eastern Gondwana, and subduction related volcanic arcs assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones containing ophiolites, accretionary complexes and remnants of ocean island arcs. The Phanerozoic evolution of the region is the result of more than 400 million years of continental dispersion from Gondwana and plate tectonic convergence, collision and accretion. This involved successive dispersion of continental blocks, the northwards translation of these, and their amalgamation and accretion to form present-day Asia. Separation and northwards migration of the various continental terranes/blocks from Gondwana occurred in three phases linked with the successive opening and closure of three intervening Tethyan oceans, the Palaeo-Tethys (Devonian–Triassic), Meso-Tethys (late Early Permian–Late Cretaceous) and Ceno-Tethys (Late Triassic–Late Cretaceous). The first group of continental blocks dispersed from Gondwana in the Devonian, opening the Palaeo-Tethys behind them, and included the North China, Tarim, South China and Indochina blocks (including West Sumatra and West Burma). Remnants of the main Palaeo-Tethys ocean are now preserved within the Longmu Co-Shuanghu, Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub Suture Zones. During northwards subduction of the Palaeo-Tethys, the Sukhothai Arc was constructed on the margin of South China–Indochina and separated from those terranes by a short-lived back-arc basin now represented by the Jinghong, Nan–Uttaradit and Sra Kaeo Sutures. Concurrently, a second continental sliver or collage of blocks (Cimmerian continent) rifted and separated from northern Gondwana and the Meso-Tethys opened in the late Early Permian between these separating blocks and Gondwana. The eastern Cimmerian continent, including the South Qiangtang block and Sibumasu Terrane (including the Baoshan and Tengchong blocks of Yunnan) collided with the Sukhothai Arc and South China/Indochina in the Triassic, closing the Palaeo-Tethys. A third collage of continental blocks, including the Lhasa block, South West Borneo and East Java–West Sulawesi (now identified as the missing “Banda” and “Argoland” blocks) separated from NW Australia in the Late Triassic–Late Jurassic by opening of the Ceno-Tethys and accreted to SE Sundaland by subduction of the Meso-Tethys in the Cretaceous.  相似文献   

3.
The Lachlan Fold Belt of southeastern Australia developed along the Panthalassan margin of East Gondwana. Major silicic igneous activity and active tectonics with extensional, strike-slip and contractional deformation have been related to a continental backarc setting with a convergent margin to the east. In the Early Silurian (Benambran Orogeny), tectonic development was controlled by one or more subduction zones involved in collision and accretion of the Ordovician Macquarie Arc. Thermal instability in the Late Silurian to Middle Devonian interval was promoted by the presence of one or more shallow subducted slabs in the upper mantle and resulted in widespread silicic igneous activity. Extension dominated the Late Silurian in New South Wales and parts of eastern Victoria and led to formation of several sedimentary basins. Alternating episodes of contraction and extension, along with dispersed strike-slip faulting particularly in eastern Victoria, occurred in the Early Devonian culminating in the Middle Devonian contractional Tabberabberan Orogeny. Contractional deformation in modern systems, such as the central Andes, is driven by advance of the overriding plate, with highest strain developed at locations distant from plate edges. In the Ordovician to Early Devonian, it is inferred that East Gondwana was advancing towards Panthalassa. Extensional activity in the Lachlan backarc, although minor in comparison with backarc basins in the western Pacific Ocean, was driven by limited but continuous rollback of the subduction hinge. Alternation of contraction and extension reflects the delicate balance between plate motions with rollback being overtaken by advance of the upper plate intermittently in the Early to Middle Devonian resulting in contractional deformation in an otherwise dominantly extensional regime. A modern system that shows comparable behaviour is East Asia where rollback is considered responsible for widespread sedimentary basin development and basin inversion reflects advance of blocks driven by compression related to the Indian collision.  相似文献   

4.
The Antarctic Ross Orogen was built up during the early Paleozoic in the framework of the convergence between the Paleo-Pacific oceanic plate and the Gondwana continental margin. Models for the Ross Orogen in northern Victoria Land are based on terranes having a variable provenance with respect to the margin. However, recent studies provide evidence for the occurrence of different pieces of the lithospheric puzzle: (i) the Wilson continental magmatic arc, representing the main part of the active Gondwana margin, (ii) the Bowers arc–backarc system, (iii) the Admiralty crustal ribbon including continental material of the Wilson forearc, and (iv) the newly discovered, Cambrian oceanic magmatic Tiger arc, along the Ross Sea coast. An updated model is presented in which, after the Early Cambrian magmatic activity of the Wilson arc, a retreat of the subduction zone in the Early–Middle Cambrian gave way to boudinage of the Wilson forearc, trenchward arc migration, opening of the Bowers backarc basin and inception of the outboard Tiger subduction zone. Renewed convergence resulted in the development of the Middle Cambrian Bowers arc, closure of the backarc and deep underthrusting of portions of it at the Middle–Late Cambrian. Finally, in the latest Cambrian to earliest Ordovician, fast exhumation was coupled in the north with erosion and sediment shed to the northeast, and with extension and potassic magmatism in central and southern Victoria Land.  相似文献   

5.
通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。  相似文献   

6.
East and Southeast Asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments (terranes) together with volcanic arcs, and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the Eurasian, Indo-Australian and Pacific Plates. The former wide separation of Asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation, different palaeoclimates, and biogeographic isolation. The boundaries between Asian terranes are marked by major geological discontinuities (suture zones) that represent former ocean basins that once separated them. In some cases, the ocean basins have been completely destroyed, and terrane boundaries are marked by major fault zones. In other cases, remnants of the ocean basins and of subduction/accretion complexes remain and provide valuable information on the tectonic history of the terranes, the oceans that once separated them, and timings of amalgamation and accretion. The various allochthonous crustal fragments of East Asia have been brought into close juxtaposition by geological convergent plate tectonic processes. The Gondwana-derived East Asia crustal fragments successively rifted and separated from the margin of eastern Gondwana as three elongate continental slivers in the Devonian, Early Permian and Late Triassic–Late Jurassic. As these three continental slivers separated from Gondwana, three successive ocean basins, the Palaeo-Tethys,. Meso-Tethys and Ceno-Tethys, opened between these and Gondwana. Asian terranes progressively sutured to one another during the Palaeozoic to Cenozoic. South China and Indochina probably amalgamated in the Early Carboniferous but alternative scenarios with collision in the Permo–Triassic have been suggested. The Tarim terrane accreted to Eurasia in the Early Permian. The Sibumasu and Qiangtang terranes collided and sutured with Simao/Indochina/East Malaya in the Early–Middle Triassic and the West Sumatra terrane was transported westwards to a position outboard of Sibumasu during this collisional process. The Permo–Triassic also saw the progressive collision between South and North China (with possible extension of this collision being recognised in the Korean Peninsula) culminating in the Late Triassic. North China did not finally weld to Asia until the Late Jurassic. The Lhasa and West Burma terranes accreted to Eurasia in the Late Jurassic–Early Cretaceous and proto East and Southeast Asia had formed. Palaeogeographic reconstructions illustrating the evolution and assembly of Asian crustal fragments during the Phanerozoic are presented.  相似文献   

7.
The Paleo‐Tethys Ocean was a Paleozoic ocean located between the Gondwana and Laurasia supercontinents. It was usually consider to opening in the early Paleozoic with the rifting of the Hun superterrane from Gondwana following the subduction of the Rheic Ocean/proto‐Tethys Ocean. However, the opening time and detailed evolutionary history of the Paleo‐Tethys Ocean are still unclear. The Paleozoic ophiolites have recently been documented in the middle of the Qiangtang terrane, northern Tibetan Plateau, and they mainly occur in the Gangma Co area. These ophiolites are composed of serpentinite, pyroxenite, isotropic and cumulate gabbros, basalt, hornblendite and plagiogranite. Whole‐rock geochemical data suggest that all mafic rocks were formed in an oceanic‐ridge setting. Furthermore, positive whole‐rock εNd(t) and zircon εHf(t) values suggest that these rocks were derived from a long‐term depleted mantle source. The data allow us to conform that these rocks represent an ophiolite suite. Zircon U‐Pb dating of gabbros and plagiogranites yielded weighted mean ages of 437‐501 Ma. The occurrence of the ophiolite suite suggests that a Paleozoic Ocean basin (Paleo‐Tethys) existed in middle of the Qiangtang terrane. We hypothesize that the ophiolite in the middle of the Qiangtang terrane represents the western extension of the Sanjiang Paleo‐Tethys ophiolite in the east margin of the Tibetan Plateau, and they mark the main Paleo‐Tethys Ocean. This is the oldest ophiolite from the Paleo‐Tethyan suture zones and the Paleo‐Tethys Ocean basin probably opened in the Middle Cambrian, and continued to grow throughout the Paleozoic. The ocean was finally closed in the Middle to Late Triassic as inferred from the metamorphic ages of eclogite and blueschist that occur nearby. The Paleo‐Tethys Ocean was probably formed by the breakup of the northern margin of Gondwana, with southward subduction of the proto‐Tethys oceanic lithosphere along the northern margin of the supercontinent.  相似文献   

8.
The External Crystalline Massifs (ECMs) of the Alps record, during the Paleozoic, the progressive closure of oceanic domains between Gondwana, Armorica and Avalonia in three contrasting tectonic domains. The eastern one shows the Early Devonian closure of the Central-European Ocean between Armorica and Gondwana along a northwest dipping subduction zone. The western domain is marked by Lower Ordovician rifting followed by Mid-Devonian obduction of the back-arc Chamrousse ophiolite. The central domain underwent Late Devonian to Dinantian extension in a back arc setting associated with southeast dipping subduction of the Saxo-Thuringian Ocean. Based on tectonostratigraphic correlations, we propose that the western domain shows an affinity to the Barrandian domain while the eastern and central domains correspond to the north-eastward extension of the Moldanubian zone, to the south of the present-day Bohemian Massif. From Mid-Carboniferous to Permian, the eastern and central domains of the ECMs, including the internal parts of the Maures Massif, Sardinia and Corsica were stretched towards the south-west along the ca. 1500 km long dextral ECMs shear zone preceding the opening of the Palaeo-Tethys ocean.  相似文献   

9.
It is proposed that the Bentong–Raub Suture Zone represents a segment of the main Devonian to Middle Triassic Palaeo-Tethys ocean, and forms the boundary between the Gondwana-derived Sibumasu and Indochina terranes. Palaeo-Tethyan oceanic ribbon-bedded cherts preserved in the suture zone range in age from Middle Devonian to Middle Permian, and mélange includes chert and limestone clasts that range in age from Lower Carboniferous to Lower Permian. This indicates that the Palaeo-Tethys opened in the Devonian, when Indochina and other Chinese blocks separated from Gondwana, and closed in the Late Triassic (Peninsular Malaysia segment). The suture zone is the result of northwards subduction of the Palaeo-Tethys ocean beneath Indochina in the Late Palaeozoic and the Triassic collision of the Sibumasu terrane with, and the underthrusting of, Indochina. Tectonostratigraphic, palaeobiogeographic and palaeomagnetic data indicate that the Sibumasu Terrane separated from Gondwana in the late Sakmarian, and then drifted rapidly northwards during the Permian–Triassic. During the Permian subduction phase, the East Malaya volcano-plutonic arc, with I-Type granitoids and intermediate to acidic volcanism, was developed on the margin of Indochina. The main structural discontinuity in Peninsular Malaysia occurs between Palaeozoic and Triassic rocks, and orogenic deformation appears to have been initiated in the Upper Permian to Lower Triassic, when Sibumasu began to collide with Indochina. During the Early to Middle Triassic, A-Type subduction and crustal thickening generated the Main Range syn- to post-orogenic granites, which were emplaced in the Late Triassic–Early Jurassic. A foredeep basin developed on the depressed margin of Sibumasu in front of the uplifted accretionary complex in which the Semanggol “Formation” rocks accumulated. The suture zone is covered by a latest Triassic, Jurassic and Cretaceous, mainly continental, red bed overlap sequence.  相似文献   

10.
Regional geological evidence appears to be incompatible with the hypothesis that the alpine-type ophiolites, which are found at numerous localities on the northern margins of the Arabian and Indian continental blocks, represent oceanic lithosphere emplaced by obduction. All of them were emplaced during the same brief period in the Late Cretaceous, at which time these Gondwana continents were at varying distances from Eurasia and were drifting passively northwards towards a north-dipping subduction zone at the opposing, northern side of the closing Tethys ocean: they were apparently emplaced on inactive continental margins which show no evidence of underlying subduction or, necessarily, of compression. As a possible solution to the problem of their origin, it is suggested that they reached their present positions above the miogeosynclines on the continental margins by means of gravitational gliding from an uplift, caused by the intrusion/extrusion of mantle material at a locus of weakness along those margins. Although some material from the former Tethys floor may be included, the ophiolites are thought to consist primarily of mantle material that has broken through the earth's surface under conditions of tension. The necessary identification of ophiolites as fragments of oceanic lithosphere, as marking former plate boundaries, and as indicative of a compressive environment, should be regarded with caution.  相似文献   

11.
《地学前缘(英文版)》2019,10(3):1101-1111
Different final closing ages have been proposed for the evolution of the Paleo-Asian Ocean (PAO), including Late Silurian, pre-Late Devonian, Early Permian, Late-Permian and Late Permian–Early Triassic. Ophiolites represent fragments of ancient oceanic crust and play an important role in identifying the suture zone and unveiling the evolutionary history of fossil oceans. Our detailed geological, geochemical and geochronological investigations argue for the existence of Early Permian (297 Ma) SSZ type ophiolites in the Sunidyouqi area of central Inner Mongolia, China. The gabbros and basalts show LREE depleted REE patterns and left-leaning primitive mantle-normalized spider diagrams with variable negative Nb-Ta anomalies (Nb* = 0.24–1.28 and 0.29–0.55, respectively). The Sunidyouqi ophiolites were generated in a mature back-arc basin. The Sunidyouqi ophiolites share the same petrological, geochemical and geochronological characteristics with the other ophiolites along the Solonker suture zone, delineating a Late Paleozoic ocean and arc-trench system. This Late Paleozoic ocean and arc-trench system coincides with a Permian paleobiogeographical boundary, i.e. the boundary between the northern cold climate (Boreal faunal–Angaraland floral realm), and a southern warm climate (Tethys faunal–Cathaysian floral realm). A tectonic scenario was proposed at last for the closure of the SE PAO involving (1) Late Ordovician to Middle Permian continuous southward subduction beneath the northern margin of North China; (2) Carboniferous to Middle Permian continuous northward subduction the forming the Northern Accretionary Orogen; (3) Late Permian final closure of the SE PAO.  相似文献   

12.
《Gondwana Research》2014,25(2):756-763
The Variscan suture exposed in NW Iberia contains a stack of terranes including two allochthonous units with continental affinity and Gondwanan provenance (Upper and Basal Units), separated by an ophiolite belt where the most common units show protolith ages at c. 395 Ma. Recent Lu–Hf zircon data obtained from these ophiolites indicate interaction between the gabbroic magmas and old continental crust. Hence, the ophiolites could not have originated in a deep ocean basin associated with a mature mid-ocean-ridge or intraoceanic subduction. The tectonothermal evolution of the continental terranes bounding the suture zone records two consecutive events of deep subduction. The Upper Units record an initial high-P/ultra-high-P metamorphic event that occurred before 400–390 Ma, while the Basal Units were affected by a second high-P/low-to-intermediate-T metamorphic event dated at c. 370 Ma. Continental subduction affected the most external margin of Gondwana and developed in a setting of dextral convergence with Laurussia. Development of the two high-P events alternated with the opening of an ephemeral oceanic basin, probably of pull-apart type, in Early Devonian times. This ephemeral oceanic domain is suggested as the setting for the protoliths of the most common ophiolites involved in the Variscan suture. Current ideas for the assembly of Pangea advocate a single collisional event between Gondwana and Laurussia in the Carboniferous. However, the new evidence from the allochthonous terranes of the Variscan belt suggests a more complex scenario for the assembly of the supercontinent, with an interaction between the colliding continental margins that started earlier and lasted longer than previously considered. Based on modern analogs of continental interaction, the development of complex collisions, as here suggested for Gondwana and Laurussia during the assembly of Pangea, could have been the norm rather than the exception throughout Earth history.  相似文献   

13.
古亚洲洋不是西伯利亚陆台和华北地台间的一个简单洋盆,而是在不同时间、不同地区打开和封闭的多个大小不一的洋盆复杂活动(包括远距离运移)的综合体.其北部洋盆起始于新元古代末-寒武纪初(573~522Ma)冈瓦纳古陆裂解形成的寒武纪洋盆.寒武纪末-奥陶纪初(510~480Ma),冈瓦纳古陆裂解的碎块、寒武纪洋壳碎块和陆缘过渡壳碎块相互碰撞、联合形成原中亚-蒙古古陆.奥陶纪时,原中亚-蒙古古陆南边形成活动陆缘,志留纪形成稳定大陆.泥盆纪初原中亚-蒙古古陆裂解,裂解的碎块在新形成的泥盆纪洋内沿左旋断裂向北运动,于晚泥盆世末到达西伯利亚陆台南缘,重新联合形成现在的中亚-蒙古古陆.晚古生代时,在现在的中亚-蒙古古陆内发生晚石炭世(318~316Ma)和早二叠世(295~285Ma)裂谷岩浆活动,形成双峰式火山岩和碱性花岗岩类.蒙古-鄂霍次克带是西伯利亚古陆和中亚-蒙古古陆之间的泥盆纪洋盆,向东与古太平洋连通,洋盆发展到中晚侏罗世,与古太平洋同时结束,其洋壳移动到西伯利亚陆台边缘受阻而向陆台下俯冲,在陆台南缘形成广泛的陆缘岩浆岩带,从中泥盆世到晚侏罗世都非常活跃.古亚洲洋的南部洋盆始于晚寒武世.此时,华北古陆从冈瓦纳古陆裂解出来,在其北缘形成晚寒武世-早奥陶世的被动陆缘和中奥陶世-早志留世的沟弧盆系.志留纪腕足类生物群的分布表明,华北地台北缘洋盆与塔里木地台北缘、以及川西、云南、东澳大利亚有联系,而与上述的古亚洲洋北部洋盆没有关连,两洋盆之间有松嫩-图兰地块间隔.晚志留世-早泥盆世,华北地台北部发生弧-陆碰撞运动,泥盆纪时,在松嫩地块南缘形成陆缘火山岩带,晚二叠世-早三叠世华北地台与松嫩地块碰撞,至此古亚洲洋盆封闭.古亚洲洋的南、北洋盆最后的褶皱构造,以及与塔里木地台之间发生的直接关系,很可能是后期的构造运动所造成的.  相似文献   

14.
The Malay Peninsula is characterised by three north–south belts, the Western, Central, and Eastern belts based on distinct differences in stratigraphy, structure, magmatism, geophysical signatures and geological evolution. The Western Belt forms part of the Sibumasu Terrane, derived from the NW Australian Gondwana margin in the late Early Permian. The Central and Eastern Belts represent the Sukhothai Arc constructed in the Late Carboniferous–Early Permian on the margin of the Indochina Block (derived from the Gondwana margin in the Early Devonian). This arc was then separated from Indochina by back-arc spreading in the Permian. The Bentong-Raub suture zone forms the boundary between the Sibumasu Terrane (Western Belt) and Sukhothai Arc (Central and Eastern Belts) and preserves remnants of the Devonian–Permian main Palaeo-Tethys ocean basin destroyed by subduction beneath the Indochina Block/Sukhothai Arc, which produced the Permian–Triassic andesitic volcanism and I-Type granitoids observed in the Central and Eastern Belts of the Malay Peninsula. The collision between Sibumasu and the Sukhothai Arc began in Early Triassic times and was completed by the Late Triassic. Triassic cherts, turbidites and conglomerates of the Semanggol “Formation” were deposited in a fore-deep basin constructed on the leading edge of Sibumasu and the uplifted accretionary complex. Collisional crustal thickening, coupled with slab break off and rising hot asthenosphere produced the Main Range Late Triassic-earliest Jurassic S-Type granitoids that intrude the Western Belt and Bentong-Raub suture zone. The Sukhothai back-arc basin opened in the Early Permian and collapsed and closed in the Middle–Late Triassic. Marine sedimentation ceased in the Late Triassic in the Malay Peninsula due to tectonic and isostatic uplift, and Jurassic–Cretaceous continental red beds form a cover sequence. A significant Late Cretaceous tectono-thermal event affected the Peninsula with major faulting, granitoid intrusion and re-setting of palaeomagnetic signatures.  相似文献   

15.
研究表明,阿尔泰南缘和准噶尔北缘晚古生代大地构造演化及成矿作用均受古亚洲洋形成与演化的控制。晚古生代该地区经历了3个不同性质的构造演化阶段,同时伴有不同的多金属成矿作用。早泥盆世,由于古亚洲洋板块的俯冲,在阿尔泰南缘形成了一系列陆缘断陷盆地,并伴随以铅、锌、铜、铁多金属为主的矿化;同时,俯冲的古亚洲洋板块发生部分熔融,形成了埃达克岩及与其有关的铜矿床。随着板块俯冲的继续,中泥盆世出现了前弧盆地,并形成了铜-铅-锌多金属矿床。至石炭纪,西伯利亚板块与哈萨克斯坦-准噶尔板块发生碰撞,在额尔齐斯缝合带附近出现了由于挤压作用而形成的金矿床,同时,在缝合带北侧(阿尔泰地区),由于壳型花岗岩的广泛发育,形成了稀有金属矿床。早二叠世,在额尔齐斯缝合带附近又发生了碰撞后的板内拉张作用,从而诱发了一系列与地幔作用有关的岩浆活动,形成了以喀拉通克为代表的铜-镍矿化。因此,阿尔泰南缘和准噶尔北缘晚古生代多金属找矿远景区包括:阿勒泰南缘早泥盆世火山-沉积盆地内铅、锌、铜及铁多金属矿床和准噶尔北缘早泥盆世与埃达克岩有关的铜矿床;中泥盆世前弧盆地内的铜多金属矿床;石炭纪额尔齐斯缝合带内与碰撞有关的金矿床及稀有金属矿床;早二叠世与板内拉张有关的铜-镍多金属矿床。  相似文献   

16.
古亚洲洋与古特提斯洋关系初探   总被引：1，自引：0，他引：1  
李文渊 《岩石学报》2018,34(8):2201-2210
从板块构造研究中国古生代洋陆关系和构造-岩浆-成矿作用,离不开对古亚洲洋和古特提斯洋的关系判断,特别是对于中国西北部的研究,两个古生代大洋形成演化和关系是理清重要地质构造和成矿事件的关键。本文认为早古生代的原特提斯洋与古亚洲洋应连为一体,合称古亚洲-原特提斯洋,简称古亚洲洋。古亚洲洋是发育于早古生代劳亚大陆与冈瓦纳大陆之间的大洋,金川超大型铜镍矿床的形成是元古宙罗迪尼亚超大陆裂解三叉裂谷开启大洋的开始,塔里木陆块作为古亚洲洋南岸的一个陆块,早古生代的昆仑洋、祁连洋和秦岭洋只是古亚洲洋的分支或次生洋盆,这些次生洋盆于志留纪末闭合,古亚洲洋主洋则直到晚古生代泥盆纪末才闭合。石炭纪天山及邻区是古亚洲洋闭合后板块构造后碰撞机制与地幔柱作用提供热动力的两种地球动力学机制并存的构造背景,为大规模壳幔混合(染)岩浆作用和成矿爆发提供了可能。古特提斯洋是古亚洲洋在晚古生代的发展和继承,东昆仑夏日哈木超大型铜镍矿床的产生是冈瓦纳大陆北侧志留纪末破裂三叉裂谷开启大洋的开始,塔里木和华北等泛华夏陆块群构成了古特提斯洋北岸陆缘,石炭纪大洋形成,西昆仑玛尔坎苏大型优质锰矿可能就形成于大洋北侧被动大陆边缘的浅海或陆表海,成矿物质则很可能来自于同时代的大洋中脊。德尔尼大型铜钴矿为晚石炭世大洋中脊塞浦路斯型块状硫化物矿床。而铜峪沟大型铜矿和大场大型金矿等则分别为古特提斯洋消减俯冲岛弧岩浆作用矽卡岩-斑岩矿床和浅成低温热液矿床。中三叠世末古特提斯洋闭合。  相似文献   

17.
The Late Cretaceous Chagai arc outcrops in western Pakistan, southern Afghanistan and eastern Iran. It is in the Tethyan convergence zone, formed by northward subduction of the Arabian oceanic plate beneath the Afghan block. The oldest unit of the Chagai arc is the Late Cretaceous Sinjrani Volcanic Group. This is composed of porphyritic lava flows and volcaniclastic rocks, and subordinate shale, sandstone, limestone and chert. The flows are fractionated low-K tholeiitic basalts, basaltic-andesites, and andesites. Relative enrichment in their LILE and depletion in HFSE, and negative Nb and Ta and positive K, Ba and Sr anomalies point to a subduction-related origin. Compared to MORB, the least fractionated Chagai basalts have low Na2O, Fe2O3T, CaO, Ti, Zr, Y and 87Sr/86Sr. Rather than an Andean setting, these results suggest derivation from a highly depleted mantle in an intraoceanic arc formed by Late Cretaceous convergence in the Ceno-Tethys. The segmented subduction zone formed between Gondwana and a collage of small continental blocks (Iran, Afghan, Karakoram, Lhasa and Burma) was accompanied by a chain of oceanic island arcs and suprasubduction ophiolites including Semail, Zagros, Chagai-Raskoh, Kandahar, Muslim Bagh, Waziristan and Kohistan-Ladakh, Nidar, Nagaland and Manipur. These complexes accreted to the southern margin of Eurasia in the Late Cretaceous.  相似文献   

18.
柴达木盆地构造古地理分析   总被引：17，自引：2，他引：15  
魏斌 《地学前缘》2000,7(4):421-429
研究的目的是分析柴达木盆地显生宙构造古地理特征和盆地叠合过程。在寒武纪—泥盆纪 ,柴达木板块处于低纬度区 ,从寒武纪时的南纬 4 1°往北漂移到泥盆纪时的北纬 10 6° ,与塔里木、华北、扬子等块体有较大的纬度差 ,表明柴达木板块在该时期是一个并不隶属于其它任何板块的独立的块体 :与华北板块之间以北祁连洋相隔 ,与塔里木板块之间以阿尔金洋相隔 ,与中昆仑地块之间以东昆仑洋相隔 ,柴达木板块内部也被赛什腾—锡铁山洋所分隔。这些洋盆经历了寒武纪—早、中奥陶世张裂阶段和晚奥陶世—早、中泥盆世聚敛阶段 ,最终于中泥盆世末期闭合。该时期在柴达木盆地内部 ,叠合在震旦纪大陆裂谷盆地之上的是寒武—奥陶纪台地—陆棚相碳酸盐岩和碎屑岩建造 ,生物发育 ;志留纪—早、中泥盆世柴达木盆地以隆起为特征。石炭纪—三叠纪柴达木板块继续北移 ,石炭纪时位于北纬 11 9° ,二叠纪时位于北纬 12 7° ,三叠纪时位于北纬 2 2 2° ,该时期柴达木板块已与华北板块、塔里木板块拼合 ,但与羌塘板块之间以南昆仑洋相隔 ,柴达木处于南昆仑洋的弧后部位 ,叠加在早期盆地之上的是石炭纪—早二叠世滨岸—台地—陆棚相碳酸盐岩、碎屑岩夹煤线。晚二叠世—三叠纪柴达木盆地再度隆升。侏罗纪以来 ,柴达木板块缓慢北  相似文献   

19.
The Princhester Serpentinite of the Marlborough terrane of the northern New England Orogen is a remnant of upper mantle peridotite that was partially melted at an oceanic spreading centre at 562 Ma, and subsequently interacted with Late Devonian island arc basalts in an intra-oceanic supra-subduction zone (SSZ) setting. The full range of rare-earth element (REE) contents, including U-shaped patterns, can be explained by a single process of reaction of partially melted, depleted peridotite with Late Devonian calc-alkaline and island arc tholeiite magmas by equilibrium porous flow, fractionating the REE by a chromatographic column effect. The Northumberland Serpentinite on South Island of the Percy Group has similar REE and high field strength element (HFSE) contents to the most depleted samples of the Princhester Serpentinite, supporting a common origin. However, spinel compositions suggest that the Northumberland Serpentinite interacted with boninitic magmas. The REE and mineral geochemistry indicates that the Princhester and Northumberland Serpentinites both represent part of the mantle component of a disrupted SSZ ophiolite. The ophiolite is considered to have formed above an east-dipping subduction zone, based on the geochemistry of Devonian island arc basalts between Mt Morgan and Monto, which include compositions identical to dykes and gabbroic blocks within the Princhester Serpentinite. Blockage of the subduction zone by collision with the Australian continent during the Late Devonian led to slab breakoff and the reversal of subduction direction, trapping the Late Devonian ophiolite in a forearc position. Its location, in a forearc setting above a growing accretionary wedge, conforms to the definition of a Cordilleran-type ophiolite. This interpretation is consistent with current views that most ophiolites are formed from young, hot and thin oceanic lithosphere at forearc, intra-arc and backarc spreading centres in a SSZ setting, and that emplacement follows genesis by 10 million years or less. Late Devonian crustal growth may have been widespread in the New England Orogen, because the disrupted ophiolite assemblage of the Yarras complex in the southern New England Orogen is probably of this age. Extensional tectonism at the end of the Carboniferous dismembered the Princhester – Northumberland ophiolite, removed the crustal section, and produced windows of accretionary wedge rocks within the fragmented ophiolite. The Princhester Serpentinite, together with fault slices of metasedimentary rocks, was thrust westward as a flat sheet over folded strata of the Yarrol Forearc Basin by a Late Permian out-of-sequence thrust during the Hunter – Bowen Orogeny, completing the emplacement of the Marlborough terrane. The Princhester and Northumberland Serpentinites could have been displaced by strike-slip movement along the Stanage Fault Zone or an equivalent structure. There is no record in the northern New England Orogen of SSZ ophiolites and volcanic arc deposits of Cambrian age, as exposed along the Peel Fault. Partial melting of the Princhester Serpentinite at an oceanic spreading centre at 562 Ma, recorded by mafic intrusives displaying N-MORB chemistry, was an earlier event that was outboard of any Early Paleozoic subduction zone along the margin of the Australian continent, and cannot be regarded as representing the early history of the New England Orogen. It is possible that the formation of intra-oceanic arcs in latest Silurian and Devonian time was the first tectonic event common to both the southern and northern New England Orogen.  相似文献   

20.
Ophiolites exposed across the western Tauride Belt in SW Turkey represent tectonically emplaced fragments of oceanic lithosphere incorporated into continental margin following the closure of the Neotethys Ocean during the Late Cretaceous. The mantle sections of the ophiolites contain peridotites with diverse suites of geochemical signatures indicative of residual origin by melt depletion in both mid‐ocean ridge (MOR) and supra‐subduction zone (SSZ) settings. This study uses a laser‐ablation inductively‐coupled plasma‐mass spectrometry (LA‐ICP‐MS) for in situ measurements of trace elements in primary mantle phases in order to identify the upper mantle petrogenetic processes effective during variable stage of melt extraction in these discrete tectonic settings and to discriminate between the effects of reaction with chemically distinct mantle melts migrating through the solid residues. Trace element signatures in pyroxenes suggest small‐length scales of compositional variations which may be interpreted to be a result of post‐melting petrogenetic processes. Relative distribution of rare earth elements and Li between coexisting orthopyroxene‐clinopyroxene pairs in the peridotites suggests compositional disequilibrium in sub‐solidus conditions, which possibly reflects differential effects of diffusive exchange during melting and melt transport or interaction with subduction melts/fluids. On the basis of Ga abundances and Ga–Ti–Fe+3# [Fe+3/(Fe+3 + Cr + Al)] relationships of chrome‐spinels it is documented that the peridotites have experienced the combined effects of partial melting and variable extent of melt‐solid interaction. The MOR peridotites have spinels with geochemical signatures indicative of melt‐depleted residual origin with subsequent incompatible element enrichment through melt impregnation, while the Ga–Ti–Fe+3# relationships of chrome‐spinels in SSZ peridotites indicate that these highly depleted peridotites are not simple melt residues, but have been subject to significant compositional modification by interaction with subduction related melts/fluids. The observed compositional variations, which are related to long‐term tectonic reorganisation of oceanic lithosphere, provide evidence for a time integrated evolution from a mid‐ocean ridge to a supra‐subduction zone setting and may be a possible analogue to explain the coexistence of geochemically diverse MOR–SSZ suites in other Tethyan ophiolites. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

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