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1.
Victor A. Ramos 《Journal of South American Earth Sciences》2010,29(1):77-91
The analysis of the basement of the Andes shows the strong Grenville affinities of most of the inliers exposed in the different terranes from Colombia to Patagonia. The terranes have different histories, but most of them participated in the Rodinia supercontinent amalgamation during the Mesoproterozoic between 1200 and 1000 Ma. After Rodinia break-up some terranes were left in the Laurentian side such as Cuyania and Chilenia, while others stayed in the Gondwanan side. Some of the terranes once collided with the Amazon craton remained attached, experiencing diverse rifting episodes all along the Phanerozoic, as the Arequipa and Pampia terranes. Some other basement inliers were detached in the Neoproterozoic and amalgamated again to Gondwana in the Early Cambrian, Middle Ordovician or Permian times. A few basement inliers with Permian metamorphic ages were transferred to Gondwana after Pangea break-up from the Laurentian side. Some of them were part of the present Middle America terrane. An exceptional case is the Oaxaquia terrane that was detached from the Gondwana margin after the Early Ordovician and is now one of the main Mexican terranes that collided with Laurentia. These displacements, detachments, and amalgamations indicate a complex terrane transfer between Laurentia and Gondwana during Paleozoic times, following plate reorganizations and changes in the absolute motion of Gondwana. 相似文献
2.
Critical assessment of Paleozoic paleomagnetic results from Australia shows that paleopoles from locations on the main craton and in the various terranes of the Tasman Fold Belt of eastern Australia follow the same path since 400 Ma for the Lachlan and Thomson superterranes, but not until 250 Ma or younger for the New England superterrane. Most of the paleopoles from the Tasman Fold Belt are derived from the Lolworth-Ravenswood terrane of the Thomson superterrane and the Molong-Monaro terrane of the Lachlan superterrane. Consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic Australia by the late Early Devonian. The Lolworth-Ravenswood terrane is interpreted to have undergone a 90° clockwise rotation between 425 and 380 Ma. Although the Tamworth terrane of the western New England superterrane is thought to have amalgamated with the Lachlan superterrane by the Late Carboniferous, geological syntheses suggest that movements between these regions may have persisted until the Middle Triassic. This view is supported by the available paleomagnetic data. With these constraints, an apparent polar wander path for Gondwana during the Paleozoic has been constructed after review of the Gondwana paleomagnetic data. The drift history of Gondwana with respect to Laurentia and Baltica during the Paleozoic is shown in a series of paleogeographic maps. 相似文献
3.
The Argentine Precordillera, a rifted fragment of Laurentian crust and sedimentary cover, collided with Gondwana in Middle Ordovician time; the time of collision (Ocloyic orogeny) is similar to that of the Taconic orogeny of eastern Laurentia. Three hypotheses have been proposed to explain Ordovician docking of the Precordillera with western Gondwana: (A) the Precordillera microcontinent was rifted from Laurentia in Cambrian time and, following solitary drift, collided with Gondwana, independent of the Laurentian Taconic orogeny; (B) a continent–continent collision of Laurentia with Gondwana, producing a continuous Taconic–Ocloyic orogenic belt, was followed by rifting that left the Precordillera attached to Gondwana; and (C) the Precordillera at the tip of a distal plateau on greatly stretched Laurentian crust collided with Gondwana and subsequently separated from Laurentia.Contrasts in several aspects of Taconic and Ocloyic orogenic history provide for discrimination between the microcontinent and continent–continent-collision hypotheses. Stratigraphic gradients and lithologic assemblages within the synorogenic clastic wedges are incompatible with a single continuous orogenic belt, which, in palinspastic location, places the thin, fine-grained southern fringe of the Taconic clastic wedge adjacent to the thickest and coarsest part of the Ocloyic clastic wedge. Separate temporal and spatial distribution patterns of volcanic ash (bentonite) beds in Laurentia and the Precordillera indicate originally separate dispersal systems. Late Ordovician Hirnantian Gondwanan glacial deposits in the Precordillera indicate substantial latitudinal separation from Laurentia. Post-collision faults with large vertical separation in the Precordillera have no coeval counterparts on the Laurentian foreland. These contrasts indicate originally separate (not initially continuous, and subsequently dismembered) orogenic belts, favoring the microcontinent hypothesis and eliminating the continent–continent-collision hypothesis.Initial Taconic tectonic loading near the southern corner of the Alabama promontory of Laurentia and the lack of post-Taconic extension there are inconsistent with the tectonic history required by the plateau hypothesis, but are consistent with the tectonic history required by the microcontinent hypothesis. Paleobiogeography, distribution of bentonite beds, and the Hirnantian glacial deposits, all indicate wide separation (Iapetus Ocean) between the Precordillera and southern Laurentia at the time of the Ocloyic and Taconic orogenies, further favoring the microcontinent hypothesis. 相似文献
4.
Neoproterozoic tectonics is dominated by the amalgamation of the supercontinent Rodinia at ca. 1.0 Ga, its breakup at ca. 0.75 Ga, and the collision between East and West Gondwana between 0.6 and 0.5 Ga. The principal stages in this evolution are recorded by terranes along the northern margin of West Gondwana (Amazonia and West Africa), which continuously faced open oceans during the Neoproterozoic. Two types of these so-called peri-Gondwanan terranes were distributed along this margin in the late Neoproterozoic: (1) Avalonian-type terranes (e.g. West Avalonia, East Avalonia, Carolina, Moravia-Silesia, Oaxaquia, Chortis block that originated from ca. 1.3 to 1.0 Ga juvenile crust within the Panthalassa-type ocean surrounding Rodinia and were accreted to the northern Gondwanan margin by 650 Ma, and (2) Cadomian-type terranes (North Armorica, Saxo-Thuringia, Moldanubia, and fringing terranes South Armorica, Ossa Morena and Tepla-Barrandian) formed along the West African margin by recycling ancient (2–3 Ga) West African crust. Subsequently detached from Gondwana, these terranes are now located within the Appalachian, Caledonide and Variscan orogens of North America and western Europe. Inferred relationships between these peri-Gondwanan terranes and the northern Gondwanan margin can be compared with paleomagnetically constrained movements interpreted for the Amazonian and West African cratons for the interval ca. 800–500 Ma. Since Amazonia is paleomagnetically unconstrained during this interval, in most tectonic syntheses its location is inferred from an interpreted connection with Laurentia. Hence, such an analysis has implications for Laurentia-Gondwana connections and for high latitude versus low latitude models for Laurentia in the interval ca. 615–570 Ma. In the high latitude model, Laurentia-Amazonia would have drifted rapidly south during this interval, and subduction along its leading edge would provide a geodynamic explanation for the voluminous magmatism evident in Neoproterozoic terranes, in a manner analogous to the Mesozoic-Cenozoic westward drift of North America and South America and subduction-related magmatism along the eastern margin of the Pacific ocean. On the other hand, if Laurentia-Amazonia remained at low latitudes during this interval, the most likely explanation for late Neoproterozoic peri-Gondwanan magmatism is the re-establishment of subduction zones following terrane accretion at ca. 650 Ma. Available paleomagnetic data for both West and East Avalonia show systematically lower paleolatitudes than predicted by these analyses, implying that more paleomagnetic data are required to document the movement histories of Laurentia, West Gondwana and the peri-Gondwanan terranes, and test the connections between them. 相似文献
5.
Ordovician K-bentonites in the upper-plate active margin of Western Gondwana, (Famatina Ranges): Stratigraphic and palaeogeographic significance 总被引：1，自引：0，他引：1
Numerous, thin-bedded, tabular pale-yellowish clay bands are interlayered with black shales in a biostratigraphically constrained Early Ordovician volcano-sedimentary succession at Famatina, western Argentina. This region was part of a fairly continuous upper-plate, convergent volcanic chain that fringed western Gondwana. Mineralogy on both clay and non-clay fractions, whole rock chemistry and field observations on these distinctive event-beds indicate that they originated as relatively coarse fallout tephras, altered first into bentonites and later, through burial metamorphism, into K-bentonites (metabentonites). These tephras were deposited as single crystals and glassy dust or pumiceous fragments in a restricted subtidal environment. The region of Famatina has previously been inferred as the source of abundant distal K-bentonites recorded in the adjacent lower-plate allochthonous Precordillera terrane. However, these K-bentonites within the proximal arc site were unknown and rather unexpected since they are generally better preserved like distal deposits, associated either with central vent plinian–ultraplinian eruptions or with accompanying co-ignimbrite ash clouds. Their chemistry and comparison with those K-bentonites in the Precordillera allow tracing an evolution from volcanic arcs into continental crust. K-bentonites described in this paper are much older than those recorded in the adjacent Precordillera terrane and seem to be associated with a first eruptive period along western Gondwana that has no counterpart in the Argentine Precordillera, suggesting a significant longitudinal separation between these two regions by the Early Ordovician. 相似文献
6.
7.
G. Gutirrez-Alonso J. Fernndez-Surez T.E. Jeffries G.A. Jenner M.N. Tubrett R. Cox S.E. Jackson 《Tectonophysics》2003,365(1-4):221
If reconstruction of major events in ancient orogenic belts is achieved in sufficient detail, the tectonic evolution of these belts can offer valuable information to widen our perspective of processes currently at work in modern orogens. Here, we illustrate this possibility taking the western European Cadomian–Avalonian belt as an example. This research is based mainly on the study and interpretation of U–Pb ages of more than 300 detrital zircons from Neoproterozoic and Early Paleozoic sedimentary rocks from Iberia and Brittany. Analyses have been performed using the laser ablation–ICP–MS technique. The U–Pb data record contrasting detrital zircon age spectra for various terranes of western Europe. The differences provide information on the processes involved in the genesis of the western European Precambrian terranes along the northern margin of Neoproterozoic Gondwana during arc construction and subduction, and their dispersal and re-amalgamation along the margin to form the Avalonia and Armorica microcontinents. The U–Pb ages reported here also support the alleged change from subduction to transform activity that led to the final break-up of the margin, the birth of the Rheic Ocean and the drift of Avalonia. We contend that the active northern margin of Gondwana evolved through several stages that match the different types of active margins recognised in modern settings. 相似文献
8.
A Cordilleran model for the evolution of Avalonia 总被引：2，自引：0，他引：2
Striking similarities between the late Mesoproterozoic–Early Paleozoic record of Avalonia and the Late Paleozoic–Cenozoic history of western North America suggest that the North American Cordillera provides a modern analogue for the evolution of Avalonia and other peri-Gondwanan terranes during the late Precambrian. Thus: (1) The evolution of primitive Avalonian arcs (proto-Avalonia) at 1.2–1.0 Ga coincides with the amalgamation of Rodinia, just as the evolution of primitive Cordilleran arcs in Panthalassa coincided with the Late Paleozoic amalgamation of Pangea. (2) The development of mature oceanic arcs at 750–650 Ma (early Avalonian magmatism), their accretion to Gondwana at ca. 650 Ma, and continental margin arc development at 635–570 Ma (main Avalonian magmatism) followed the breakup of Rodinia at ca. 755 Ma in the same way that the accretion of mature Cordilleran arcs to western North America and the development of the main phase of Cordilleran arc magmatism followed the Early Mesozoic breakup of Pangea. (3) In the absence of evidence for continental collision, the diachronous termination of subduction and its transition to an intracontinental wrench regime at 590–540 Ma is interpreted to record ridge–trench collision in the same way that North America's collision with the East Pacific Rise in the Oligocene led to the diachronous initiation of a transform margin. (4) The separation of Avalonia from Gondwana in the Early Ordovician resembles that brought about in Baja California by the Pliocene propagation of the East Pacific Rise into the continental margin. (5) The Late Ordovician–Early Silurian sinistral accretion of Avalonia to eastern Laurentia emulates the Cenozoic dispersal of Cordilleran terranes and may mimic the paths of future terranes transferred to the Pacific plate.This close similarity in tectonothermal histories suggests that a geodynamic coupling like that linking the evolution of the Cordillera with the assembly and breakup of Pangea, may have existed between Avalonia and the late Precambrian supercontinent Rodinia. Hence, the North American Cordillera is considered to provide an actualistic model for the evolution of Avalonia and other peri-Gondwanan terranes, the histories of which afford a proxy record of supercontinent assembly and breakup in the late Precambrian. 相似文献
9.
R. Damian Nance Gabriel Guti errez-Alonso J. Duncan Keppie Ulf Linnemann J. Brendan Murphy Cecilio Quesa Rob A. Strachan Nigel H. Woodcock 《地学前缘(英文版)》2012,3(2):125-135
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
10.
The Guarguardz Complex, basement of the Cordillera Frontal, included in the proposed Chilenia Terrane, consists of metasedimentary rocks deposited in clastic and carbonatic platforms. Turbiditic sequences point out to slope or external platform environments. According to geochemical data, the sedimentary protoliths derived through erosion of a mature cratonic continental basement. Volcanic and subvolcanic rocks with N and E-MORB signature were interbeded in the metasedimentary rocks during basin development. A compressional stage, starting with progressive deformation and metamorphism, followed this extensional stage. Continuing deformation led to the emplacement of slices of oceanic crust, conforming an accretionary prism during Late Devonian. The Guarguardz Complex and equivalent units in western Precordillera and also in the Chilean Coastal Cordillera share common evolutional stages, widely represented along the western Gondwana margin. These evidences imply that Chilenia is not an allochthonous terrane to Gondwana, but a portion of its Early Paleozoic margin. Regional configuration indicates that the Guarguardz Complex and equivalent units represent the accretionary prism of the Famatinian arc (Middle Ordovician-Late Devonian). 相似文献
11.
The magnetic anomaly map of North America serves as a useful base from which to attempt palinspastic reconstruction of terranes accreted during the Elzevirian orogeny (1250–1200 Ma); the Shawinigan (1200–1150 Ma), Ottawan (1080–1020 Ma), and Rigolet (1020–1000 Ma) phases of the Grenvillian orogeny; and post-Grenvillian magmatism (760–600 Ma) and deformation prior to Iapetan rifting at 565 Ma. Accreted terranes had unique histories prior to amalgamation and share common tectonic events afterwards. Comparisons with magnetic signatures of the Paleozoic craton–craton suture, sutures of accreted terranes, and the Jurassic rifted-margin for the southern-central Appalachians provide a basis for discriminating among alternative Grenvillian sutures beneath the Appalachian orogen.The Elzevirian suture is partially preserved beneath the Appalachians where it separates the Reading Prong terrane from Laurentia (i.e., Adirondacks and composite-arc terrane and Canadian Grenville Province). The Shawinigan suture is partially preserved in the Llano area (Texas), but separated the now-fragmented and allochthonous Amazonian (as indicated from Pb-isotope data) blocks of the outboard Blue Ridge terrane from the Reading Prong terrane in the Appalachians. Isolated blocks of the Sauratown Mountains terrane are interpreted as outboard of the Blue Ridge terrane, but were also accreted during the Shawinigan phase. Within present-day Laurentia, the only fragment of a terrane believed to have been accreted during the main Ottawan phase is the Mars Hill terrane (North Carolina–Tennessee). This suggests that the outboard Ottawan suture may have served as the locus of Iapetan rifting along much of Laurentia. The Rigolet phase (1020–1000 Ma) is characterized by widespread “Basin and Range” type extension (NW–SE) associated with sinistral or dextral movement on the NY-AL lineament, mobilization of core-complexes (Adirondack Highlands), and AMCG magmatism along the outboard flank of the extensional region. Following the Rigolet phase, the Appalachian region continued to be characterized by NW–SE extension during the passage of a possible hotspot along a NE-track (760–600 Ma) across the Blue Ridge and other terranes, and during initial Iapetan rifting (565 Ma). The palinspastic rifted-margin of Laurentia crosses many of these terranes and sutures as well as the possible region of Rigolet extension and the possible hotspot track, thus providing many potential piercing points within the Grenville orogen for comparison with Paleozoic terranes like the Precordillera in South America. 相似文献
12.
Cecilia M. Spagnuolo Augusto E. Rapalini Ricardo A. Astini 《International Journal of Earth Sciences》2011,100(2-3):603-618
Early Paleozoic paleomagnetic data from NW Argentina and Northern Chile have shown large systematic rotations within two domains: one composed of the Western Puna that yields very large (up to 80°) counter-clockwise rotations, and the other formed by the Famatina Ranges and the Eastern Puna that shows (~40°) clockwise rotations around vertical axes. In several locations, lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the Paleozoic. Previous tectonic models have explained these rotations as indicative of rigid-body rotations of large para-autochthonous crustal blocks or terranes. A different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of Precordillera in the Late Ordovician. This collision should have generated dextral shear zones in the back arc region of the convergent SW Gondwana margin, where systematic domino-like clockwise rotations of small crustal blocks accommodate crustal shortening. The Western Puna block, bordering the Precordillera terrane to the north, might have rotated counterclockwise as an independent microplate due to tectonic escape processes, in a fashion similar to the present-day relationship between the Anatolia block and the Arabian microplate. 相似文献
13.
The Precordillera terrane (Cuyania) in western Argentina is commonly accepted as an exotic fragment derived from Laurentia in the Early Paleozoic. Evidence supporting such an interpretation is manly based on similarities in the sedimentary cover successions and their paleontological content. Little is known about the basement of the Precordillera terrane. Its isotopic characterization is essential to better constrain the present areal distribution of the terrane and it may provide more insight into the pre-rifting evolution of the Precordillera terrane along the Iapetan margin of Laurentia. We present new Sr and Nd isotope data of pre-Late Ordovician meta-igneous rocks from the Río Bonete region in NW Argentina, interpreted as the northernmost extent of the Precordillera. The Nd systematics of the Río Bonete basement rocks including greenschists and metagabbros (εNd(470) = +2.14–−0.19; TDM = 0.99–1.2 Ga), a garnet-amphibolite (εNd(470) = −0.53; TDM = 1.32 Ga) and a quartz-phyllite (εNd(470) = −3.83; TDM = 1.55 Ga), are similar to other pre-Ordovician meta-igneous rocks from Sierra de Umango, Pie de Palo and the Ullum xenoliths, usually interpreted as the basement of the Precordillera terrane. Nd model ages around 1.2 Ga are also typical from the Mesoproterozoic Grenvillian basement of southern North America, currently exposed in the Llano region. In addition, the greenschists and metagabbros show a robust correlation with the Late Neoproterozoic Catoctin volcanics in the central Appalachians. The Sr isotope data (when not disturbed) also supports this novel interpretation and suggests the presence of the Blue Ridge rifting event in Precordillera. According to our interpretation, some lithotypes included within the basement complex of the Río Bonete area belonged to the basement of the Precordillera terrane supporting previous correlation between both regions. 相似文献
14.
Palaeozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: The Korean Peninsula in context 总被引：38，自引：2，他引：38
I. Metcalfe 《Gondwana Research》2006,9(1-2):24
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
15.
仲巴地体是雅鲁藏布江缝合带西段南北蛇绿岩带之间的重要构造单元,目前对其是否存在早古生代构造-热事件记录及构造属性判别尚不明确.通过野外观测、岩石地球化学研究和年代学分析,在仲巴地体中段的公珠错一带识别出一套侵入到黑云斜长片麻岩中的片麻状二长花岗岩,其锆石U-Pb年龄为~478 Ma,表明岩石形成时代为早奥陶世;该套花岗岩具有高Si、富Al和总碱含量较高的特点,铝饱和指数A/CNK=1.13~1.20,富集大离子亲石元素Rb、K,相对亏损Ba、Sr、Nb、Ti等,属于钙碱性强过铝质花岗岩.这是首次在雅鲁藏布江缝合带西段仲巴地体内部识别出代表早奥陶世构造-热事件的地质记录,该套花岗岩形成过程与原特提斯洋向冈瓦纳大陆北缘俯冲结束后的上地壳熔融相关,证明仲巴地体在早古生代应为东冈瓦纳大陆北缘的组成部分. 相似文献
16.
Cuyania, an Exotic Block to Gondwana: Review of a Historical Success and the Present Problems 总被引：3，自引：0，他引：3
A review of the early history of the Cuyania terrane and the numerous pioneering works of the past century provides the present robust framework of evidence supporting a derivation from Laurentia, travel towards Gondwana as an isolated microcontinent, and final amalgamation to the protomargin of western Gondwana in Middle to Late Ordovician times. The major remaining uncertainties and inconsistencies, such as the time of deformation and collision with Gondwana, the lack of evidence of Famatinian-derived zircons, the effects of strike-slip displacements proposed along the suture, as well as the potential sutures defined by ophiolite assemblages, are discussed. The precise boundary along the northern and southern limits is not yet well defined.
The most suitable hypothesis based on present data is that Cuyania originated as a conjugate margin of the Ouachita embayment, south of the Appalachian platform during Early Cambrian times. The subsequent travel toward the Gondwana protomargin is clearly depicted by the changing faunal assemblages in the carbonate platform. New geochemical and age data on K-bentonites presented by several authors reinforce the strong connection between Cuyania ash-fall tuffs and Famatina volcanics by 468–470 Ma, indicating Cuyania and Gondwana were in close proximity at that time.
Extension related to flexural subsidence, preceded by the drowning of the carbonate platform in early Llanvirnian times, is recorded by abrupt facies changes in the sedimentary cover during late Llanvirnian and early Caradocian times. This episode marked the beginning of contact between Cuyania and Gondwana. The subsequent evolution of the foreland basin indicates that deformation lasted until latest Silurian-Early Devonian times.
The time of collision is tracked by the cessation of arc-related magmatic activity in the upper plate (Gondwana protomargin), at about 465 Ma in western Sierras Pampeanas, and ages around 454 Ma corresponding to syncollisional and postcollisional magmatism. The age of the collision is also preserved in the lower plate (Cuyania), where both angular unconformities in the sedimentary cover and the ages of peak of regional metamorphism in the basement rocks point to 460 Ma as the most probable age for the beginning of the collision. Evidence from the upper plate is essentially identical with an age of 463 Ma. Thermal gradients along this suture vary from 13°C/km in the lower plate, to 18°C/km in the fore arc upper plate, reaching more than 30°C/km along the Famatinian arc. Based on these data, a Llandelian-Caradocian age for the collision can be postulated on firm grounds. Deformation continued through most of the early Paleozoic until amalgamation of the Chilenia terrane by the Late Devonian. 相似文献
17.
青藏高原南部拉萨地体的变质作用与动力学 总被引：3，自引：0，他引：3
拉萨地体位于欧亚板块的最南缘,它在新生代与印度大陆的碰撞形成了青藏高原和喜马拉雅造山带。因此,拉萨地体是揭示青藏高原形成与演化历史的关键之一。拉萨地体中的中、高级变质岩以前被认为是拉萨地体的前寒武纪变质基底。但新近的研究表明,拉萨地体经历了多期和不同类型的变质作用,包括在洋壳俯冲构造体制下发生的新元古代和晚古生代高压变质作用,在陆-陆碰撞环境下发生的早古生代和早中生代中压型变质作用,在洋中脊俯冲过程中发生的晚白垩纪高温/中压变质作用,以及在大陆俯冲带上盘加厚大陆地壳深部发生的两期新生代中压型变质作用。这些变质作用和伴生的岩浆作用表明,拉萨地体经历了从新元古代至新生代的复杂演化过程。(1)北拉萨地体的结晶基底包括新元古代的洋壳岩石,它们很可能是在Rodinia超大陆裂解过程中形成的莫桑比克洋的残余。(2)随着莫桑比克洋的俯冲和东、西冈瓦纳大陆的汇聚,拉萨地体洋壳基底经历了晚新元古代的(～650Ma)的高压变质作用和早古代的(～485Ma)中压型变质作用。这很可能表明北拉萨地体起源于东非造山带的北端。(3)在古特提斯洋向冈瓦纳大陆北缘的俯冲过程中,拉萨地体和羌塘地体经历了中古生代的(～360Ma)岩浆作用。(4)古特提斯洋盆的闭合和南、北拉萨地体的碰撞,导致了晚二叠纪(～260Ma)高压变质带和三叠纪(～220Ma)中压变质带的形成。(5)在新特提斯洋中脊向北的俯冲过程中,拉萨地体经历了晚白垩纪(～90Ma)安第斯型造山作用,形成了高温/中压型变质带和高温的紫苏花岗岩。(6)在早新生代(55～45Ma),印度与欧亚板块的碰撞,导致拉萨地体地壳加厚,形成了中压角闪岩相变质作用和同碰撞岩浆作用。(7)在晚始新世(40～30Ma),随着大陆的继续汇聚,南拉萨地体经历了另一期角闪岩相至麻粒岩相变质作用和深熔作用。拉萨地体的构造演化过程是研究汇聚板块边缘变质作用与动力学的最佳实例。 相似文献
18.
Alexander P. Gubanov 《Tectonophysics》2002,352(1-2)
The end of the Proterozoic–beginning of the Cambrian is marked by some of the most dramatic events in the history of Earth. The fall of the Ediacaran biota, followed by the Cambrian Explosion of skeletonised bilaterians, a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from ‘snowball earth’ to ‘greenhouse’ conditions all happened within a rather geologically short period of time. These events took place against a background of the rearrangement of the prevailing supercontinent; some authors view this as a sequence of individual supercontinents such as Mesoproterozoic Midgardia, Neoproterozoic Rodinia and Early Cambrian Pannotia. Assembled in the Mesoproterozoic, this supercontinent appears to have existed through the Neoproterozoic into the Early Cambrian with periodic changes in configuration. The final rearrangement took place during the Precambrian–Cambrian transition with the Cadomian and related phases of the Pan-African orogeny. The distribution of Early Cambrian molluscs and other small shelly fossils (SSF) across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time. Subsequently, Rodinia experienced breakup that led to the amalgamation of Gondwana, separation of Laurentia, Baltica, Siberia and some small terranes and the emergence of oceanic basins between them. Spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the Vendian–Early Cambrian. 相似文献
19.
Modern Tethyan, Mediterranean, and Pacific analogues are considered for several Appalachian, Caledonian, and Variscan terranes (Carolina, West and East Avalonia, Oaxaquia, Chortis, Maya, Suwannee, and Cadomia) that originated along the northern margin of Neoproterozoic Gondwana. These terranes record a protracted geological history that includes: (1) 1 Ga (Carolina, Avalonia, Oaxaquia, Chortis, and Suwannee) or 2 Ga (Cadomia) basement; (2) 750–600 Ma arc magmatism that diachronously switched to rift magmatism between 590 and 540 Ma, accompanied by development of rift basins and core complexes, in the absence of collisional orogenesis; (3) latest Neoproterozoic–Cambrian separation of Avalonia and Carolina from Gondwana leading to faunal endemism and the development of bordering passive margins; (4) Ordovician transport of Avalonia and Carolina across Iapetus terminating in Late Ordovician–Early Silurian accretion to the eastern Laurentian margin followed by dispersion along this margin; (5) Siluro-Devonian transfer of Cadomia across the Rheic Ocean; and (6) Permo-Carboniferous transfer of Oaxaquia, Chortis, Maya, and Suwannee during the amalgamation of Pangea. Three potential models are provided by more recent tectonic analogues: (1) an “accordion” model based on the orthogonal opening and closing of Alpine Tethys and the Mediterranean; (2) a “bulldozer” model based on forward-modelling of Australia during which oceanic plateaus are dispersed along the Australian plate margin; and (3) a “Baja” model based on the Pacific margin of North America where the diachronous replacement of subduction by transform faulting as a result of ridge–trench collision has been followed by rifting and the transfer of Baja California to the Pacific Plate. Future transport and accretion along the western Laurentian margin may mimic that of Baja British Columbia. Present geological data for Avalonia and Carolina favour a transition from a “Baja” model to a “bulldozer” model. By analogy with the eastern Pacific, we name the oceanic plates off northern Gondwana: Merlin (≡Farallon), Morgana (≡Pacific), and Mordred (≡Kula). If Neoproterozoic subduction was towards Gondwana, application of this combined model requires a total rotation of East Avalonia and Carolina through 180° either during separation (using a western Transverse Ranges model), during accretion (using a Baja British Columbia “train wreck” model), or during dispersion (using an Australia “bulldozer” model). On the other hand, Siluro-Devonian orthogonal transfer (“accordion” model) from northern Africa to southern Laurussia followed by a Carboniferous “Baja” model appears to best fit the existing data for Cadomia. Finally, Oaxaquia, Chortis, Maya, and Suwannee appear to have been transported along the margin of Gondwana until it collided with southern Laurentia on whose margin they were stranded following the breakup of Pangea. Forward modeling of a closing Mediterranean followed by breakup on the African margin may provide a modern analogue. These actualistic models differ in their dictates on the initial distribution of the peri-Gondwanan terranes and can be tested by comparing features of the modern analogues with their ancient tectonic counterparts. 相似文献
20.
We present a synopsis of detrital zircon U–Pb ages of sandstones from North Africa and neighboring Israel and Jordan, which allows us to identify zones with characteristic sediment provenance along the northern Gondwana margin (in present-day coordinates) in Cambrian–Ordovician times, and helps us to unravel the peri-Gondwana jigsaw puzzle. A special feature of the early Paleozoic cover sequence of North Africa is the eastward increase of 1.1–0.95 Ga detrital zircons, which become ubiquitous in the early Paleozoic sandstones of the Saharan Metacraton. Detrital zircons aged about 2.7–2.5, 2.15–1.75 and 0.75–0.53 Ga are also present. Early Paleozoic sandstones with similar provenance are known from peri-Gondwana terranes in the Eastern and Western Mediterranean and from NW Iberia. These terranes need not be transported from western Gondwana (Amazonia) as suggested previously. They were likely located to the north of the Saharan Metacraton during the early Paleozoic before they rifted off from Gondwana. Furthermore, we recognize an increase, as stratigraphic ages get younger, of ca. 1.0 Ga detrital zircons at some point between the Late Cambrian and late Middle Ordovician. We speculate that this might be linked to far-field tectonics and regional uplift in central Gondwana related to plate-tectonic reorganization along the Gondwana margin, leading to erosion of ca. 1.0 Ga basement and country rocks of the Transgondwanan supermountain and fluvial dispersal of detritus toward the Gondwana margin. 相似文献