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1.
Neoproterozoic rocks in the Saxo-Thuringian part of Armorica formed in an active margin setting and were overprinted during Cadomian orogenic processes at the northern margin of Gondwana. The Early Palaeozoic overstep sequence in Saxo-Thuringia was deposited in a Cambro-Ordovician rift setting that reflects the separation of Avalonia and other terranes from the Gondwana mainland. Upper Ordovician and Silurian to Early Carboniferous shelf sediments of Saxo-Thuringia were deposited at the southern passive margin of the Rheic Ocean. SHRIMP U/Pb geochronology on detrital and inherited zircon grains from pre-Variscan basement rocks of the northern part of the Bohemian Massif (Saxo-Thuringia, Germany) demonstrates a distinct West African provenance for sediments and magmatic rocks in this part of peri-Gondwana. Nd-isotope data of Late Neoproterozoic to Early Carboniferous sedimentary rocks show no change in sediment provenance from the Neoproterozoic to the Lower Carboniferous, which implies that Saxo-Thuringia did not leave its West African source before the Variscan Orogeny leading to the Lower Carboniferous configuration of Pangea. Hence, large parts of the pre-Variscan basement of Western and Central Europe often referred to as Armorica or Armorican Terrane Assemblage may have remained with Africa in pre-Pangean time, which makes Armorica a remnant of a Greater Africa in Gondwanan Europe. The separation of Armorica from the Gondwana mainland and a long drift during the Palaeozoic is not supported by the presented data. 相似文献
2.
Melanges play a key role in the interpretation of orogenic belts, including those that have experienced deformation and metamorphism during continental collision. This is exemplified by a Palaeozoic tectonic-sedimentary melange (part of the Konya complex) that is exposed beneath a regionally metamorphosed carbonate platform near the city of Konya in central Anatolia. The Konya complex as a whole comprises three units: a dismembered, latest Silurian–Early Carboniferous carbonate platform, a Carboniferous melange made up of sedimentary and igneous blocks in a sedimentary matrix (also known as the Hal?c? Group or S?zma Group), and an overlying Volcanic-sedimentary Unit (earliest Permian?). The Palaeozoic carbonates accumulated on a subsiding carbonate platform that bordered the northern margin of Gondwana, perhaps as an off-margin unit. The matrix of the melange was mainly deposited as turbidites, debris flows and background terrigenous muds. Petrographic evidence shows that the clastic sediments were mostly derived from granitic and psammitic/pelitic metamorphic rocks, typical of upper continental crust. Both extension- and contraction-related origins of the melange can be considered. However, we interpret the melange as a Carboniferous subduction complex that formed along the northern margin of Gondwana, related to partial closure of Palaeotethys. Blocks and slices of Upper Palaeozoic radiolarian chert, basic igneous rocks and shallow-water carbonates were accreted and locally reworked by gravity processes. Large (up to km-sized) blocks and slices of shallow-water limestone were emplaced in response to collision of the Palaeozoic Carbonate Platform with the subduction zone. The overlying Volcanic-sedimentary Unit (earliest Permian?) comprises alkaline lava flows, interbedded with volcaniclastic debris flows and turbidites, volcanogenic shales and tuff. The complex as a whole is overlain by shallow-water, mixed carbonate–siliciclastic sediments of mainly Late Permian age that accumulated on a regional-scale shelf adjacent to Gondwana. Successions pass transitionally into Lower Triassic rift-related shallow-water carbonates and terrigenous sandstones in the southwest of the area. In contrast, Triassic sediments in the southeast overlie the melange unconformably and pass upwards from non-marine clastic sediments into shallow-marine calcareous sediments of Mid-Triassic age, marking the base of a regional Mesozoic carbonate platform. During the latest Cretaceous–Early Cenozoic the entire assemblage subducted northwards and underwent high pressure/low temperature metamorphism and polyphase folding as a part of the regional Anatolide unit. 相似文献
3.
《International Geology Review》2012,54(15):1914-1939
ABSTRACTGlobal-scale Palaeozoic plate tectonic reconstructions have suggested that Laurentia was obliquely approaching against the northwestern margin of Gondwana until the final agglutination of Pangea. In this contribution integrated petrographic analysis, heavy mineral analysis, and tourmaline geochemistry were done, and U–Pb detrital zircon geochronology was obtained, in late Palaeozoic sedimentary and meta-sedimentary units from the Floresta and Santander Massifs in the Eastern Colombian Andes in order to constrain their provenance and related it with the magmatic, sedimentary, and deformational record of the Gondwana–Laurentia convergence until the late Carboniferous to Permian formation of Pangea. Late Devonian to early Carboniferous sandstones from the Floresta Massif changed from sublithoarenites to lithoarenites, tracking the progressive uplift and unroofing of sedimentary and metamorphic rocks, with associated volcanic activity. The U–Pb detrital zircon geochronology from the sedimentary and metasedimentary of Floresta and Santander documents Mesoproterozoic and Palaeoproterozoic sources, and younger Ordovician to Silurian age populations, that can be related to the early to middle Palaeozoic plutonic rocks and the Amazon Craton. The limited Silurian to Early Devonian detrital ages that contrast with the more significant Middle to Late Devonian zircons that document the erosion of contemporaneous magmatic sources formed after a late Silurian to Early Devonian reduction on the magmatic activity along the proto-Andean margin. These rocks were apparently deformed and metamorphosed between the late Carboniferous and the early Permian. It is suggested that the filling and deformation record of these rocks documented the changes in plate convergence obliquity at the western margin of Gondwana associated with the migration of Laurentia until its final position in Pangea. Between the late Carboniferous and the early Permian, peri-Gondwanan continental terranes also collided with the continental margin. Over-imposed Mesozoic tectonics have contributed to the final redistribution of these terranes to their current position.Abbreviations:LA: laser ablation inductively couple mass spectrometer; CL: cathodoluminiscence 相似文献
4.
During Late Palaeozoic time a wide ocean, known as Palaeotethys, separated the future Eurasian and African continents. This ocean closed in Europe in the west during the Variscan orogeny, whereas in Asia further east it remained open and evolved into the Mesozoic Tethys, only finally closing during Late Cretaceous–Early Cenozoic.Three Upper Palaeozoic lithological assemblages, the Chios Melange (on the Aegean Greek island), the Karaburun Melange (westernmost Aegean Turkey) and the Teke Dere Unit (Lycian Nappes, SW Turkey) provide critical information concerning sedimentary and tectonic processes during closure of Palaeotethys. The Chios and Karaburun melanges in the west are mainly terrigenous turbidites with blocks and dismembered sheets of Silurian–Upper Carboniferous platform carbonate rocks (shallow-water and slope facies) and poorly dated volcanic rocks. The Teke Dere Unit to the southeast begins with alkaline, within-plate-type volcanics, depositionally overlain by Upper Carboniferous shallow-water carbonates. This intact succession is overlain by a tectonic slice complex comprising sandstone turbidites that are intersliced with shallow-water, slope and deep-sea sediments (locally dated as Early Carboniferous). Sandstone petrography and published detrital mineral dating imply derivation from units affected by the Panafrican (Cadomian) and Variscan orogenies.All three units are interpreted as parts of subduction complexes in which pervasive shear zones separate component parts. Silurian–Lower Carboniferous black cherts (lydites) and slope carbonates accreted in a subduction trench where sandstone turbidites accumulated. Some blocks retain primary depositional contacts, showing that gravitational processes contributed to formation of the melange. Detached blocks of Upper Palaeozoic shallow-water carbonates (e.g. Chios) are commonly mantled by conglomerates, which include water-worn clasts of black chert. The carbonate blocks are restored as one, or several, carbonate platforms that collided with an active margin, fragmenting into elongate blocks that slid into a subduction trench. This material was tectonically accreted at shallow levels within a subduction complex, resulting in layer-parallel extension, shearing and slicing. The accretion mainly took place during Late Carboniferous time.Alternative sedimentary-tectonic models are considered in which the timing and extent of closure of Palaeotethys differ, and in which subduction was either northwards towards Eurasia, or southwards towards Gondwana (or both). Terrane displacement is also an option. A similar (but metamorphosed) accretionary unit, the Konya Complex, occurs hundreds of kilometres further east. All of these units appear to have been assembled along the northern margin of Gondwana by Permian time, followed by deposition of overlying Tauride-type carbonate platforms. Northward subduction of Palaeotethys beneath Eurasia is commonly proposed. However, the accretionary units studied here are more easily explained by southward subduction towards Gondwana. Palaeotethys was possibly consumed by long-lived (Late Palaeozoic) northward subduction beneath Eurasia, coupled with more short-lived (Late Carboniferous) southward subduction near Gondwana, during or soon after closure of Palaeotethys in the Balkan region to the west. 相似文献
5.
6.
Ming Wang Xiao-wen Zeng Chao-Ming Xie Awang Danzeng Cai Li Jian-Jun Fan 《International Geology Review》2020,62(4):465-478
ABSTRACTTo determine the Late Palaeozoic evolution of the Lhasa terrane, we report the results of field mapping, petrological and fossil investigations, and U–Pb dating of detrital zircon grains (n = 474) from lower-greenschist-facies clastic rocks of the Lagar Formation in the Baruo area, Tibet. Our results indicate that the Lagar Formation was deposited during the Late Carboniferous to Early Permian in a shallow-marine environment on the northern margin of Gondwana. Glacial marine diamictites are common within the Lagar Formation and record glaciation of Gondwana during the Late Palaeozoic. Moreover, the detrital materials of the Lagar formation originated mostly from the collision orogenic belt. The ages of detrital zircon grains from the Lagar Formation make up five main groups with ages of 410–540 Ma, 550–650 Ma, 800–1100 Ma, 1600–1800 Ma, and 2300–2500 Ma, which display three characteristic age peaks at ~1150, 2390 and 2648 Ma. We tentatively suggest that the Lhasa terrane was a shallow-marine basin under the influence of the Gondwanan glaciation during the Late Carboniferous–Early Permian. 相似文献
7.
造山带中远洋深水沉积物是恢复古大洋的重要依据之一,昌宁-孟连古特提斯结合带存在大量海相沉积物,但是否存在大洋盆地相的远洋沉积还不清楚.对弄巴地区被认为最可能是洋盆相沉积的石炭系岩片和海相泥盆系岩片进行了岩石学、放射虫时代、碎屑锆石U-Pb年龄和Hf同位素研究.石炭系岩片放射虫硅质岩中鉴定出放射虫6属8种,时代为早石炭世早-中期.LA-ICP-MS锆石U-Pb定年结果显示,泥盆系岩片岩屑石英杂砂岩碎屑锆石年龄范围为387~3 266 Ma,最年轻一组年龄为387~413 Ma;石炭系岩片中与放射虫硅质岩共生的基性凝灰岩碎屑锆石年龄为341~3 403 Ma,最年轻一组年龄为341~354 Ma.综合锆石年龄和化石资料,限定泥盆系岩片原始沉积时代为早-中泥盆世,石炭系岩片时代为早石炭世早-中期.碎屑锆石U-Pb年龄谱特征和Hf同位素组成指示泥盆系岩片和石炭系岩片具有相似的物质源区,主要来源于亲冈瓦纳的陆壳,少量来自于古生代特提斯域新生岛弧.早-中泥盆世地层岩片原始沉积于亲冈瓦纳的大陆斜坡环境;早石炭世地层岩片原始沉积于亲冈瓦纳的大陆斜坡至古特提斯洋盆边缘环境,不是远洋深水的大洋盆地环境.寻找以远洋深水沉积物为代表的大洋盆地相沉积并开展研究是当前昌宁-孟连古特提斯研究的重要方向之一. 相似文献
8.
The Palaeozoic to Mesozoic igneous and metamorphic basement rocks exposed in the Mérida Andes of Venezuela and the Santander Massif of Colombia are generally considered to define allochthonous terranes that accreted to the margin of Gondwana during the Ordovician and the Carboniferous. However, terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains. A general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of Gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the Mérida Andes and the Santander Massif. We present new zircon U–Pb (ICP-MS) data from 52 igneous and metamorphic rocks, which we combine with whole rock geochemical and Pb isotopic data to constrain the tectonic history of the Precambrian to Mesozoic basement of the Mérida Andes and the Santander Massif. These data show that the basement rocks of these massifs are autochthonous to Gondwana and share a similar tectono-magmatic history with the Gondwanan margin of Peru, Chile and Argentina, which evolved during the subduction of oceanic lithosphere of the Iapetus Ocean. The oldest Palaeozoic arc magmatism is recorded at ~ 500 Ma, and was followed shortly by Barrovian metamorphism. Peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at ~ 477 Ma and the intrusion of synkinematic granitoids until ~ 472 Ma. Subsequent retrogression resulted from localised back-arc or intra-arc extension at ~ 453 Ma, when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement. Continental arc magmatism dwindled after ~ 430 Ma and terminated at ~ 415 Ma, coevally with most of the western margin of Gondwana. After Pangaea amalgamation in the Late Carboniferous to Early Permian, a magmatic arc developed on its western margin at ~ 294 Ma as a result of subduction of oceanic crust of the palaeo-Pacific ocean. Intermittent arc magmatism recorded between ~ 294 and ~ 225 Ma was followed by the onset of the Andean subduction cycle at ~ 213 Ma, in an extensional regime. Extension was accompanied by slab roll-back which led to the migration of the arc axis into the Central Cordillera of Colombia in the Early Jurassic. 相似文献
9.
河南商城—固始地区石炭系沉积环境及其构造意义 总被引：13，自引：0，他引：13
根据沉积相分析,同时综合分析区域地质资料,笔者提出河南商城－固始地区石炭系及安徽金寨地区梅山群为典型前陆磨拉石含煤建造,其沉积相主要为滨海、潮坪、泻湖、局限台地及砾质辫状河－冲积扇相,代表了统一的石炭纪一二叠纪合肥弧后前陆盆地的南部边缘相,说明大别地块（北大别弧）于早古生代晚期－晚古生代早期即与华北板块碰扪结成一体。 相似文献
10.
Henning Lorenz Peep Männik David Gee Vasilij Proskurnin 《International Journal of Earth Sciences》2008,97(3):519-547
The Severnaya Zemlya Archipelago is located at 80°N near the continental shelf break, between the Kara and Laptev seas. Sedimentary
successions of Neoproterozoic and Palaeozoic age dominate the bedrock geology. Together with Northern Tajmyr, Severnaya Zemlya
constitutes the main land areas of the North Kara Terrane (NKT), which is inferred here to have been a part of the Timanide
margin of Baltica, i.e. an integral part of Baltica at least since the Vendian. Vendian turbidites derived from the Timanide
Orogen are inferred to have been deposited on Neoproterozoic greenschist facies, granite-intruded basement. Shallow-water
siliclastic deposition in the Early to Mid-Cambrian was followed by highly organic-rich shales in the Late Cambrian and influx
of more turbidites. An episode of folding, the Kan’on River deformation, separates these formations from the overlying Tremadocian
conglomerates and sandstones. In the Early Ordovician, rift-related magmatic rocks accompanied the deposition of variegated
marls, sandstones, carbonates and evaporites. Dark shales and gypsiferous limestones characterise the Mid-Ordovician. Late
Ordovician quartz-sandstones mark a hiatus, followed by carbonate rocks that extend up into and through most of the Silurian.
The latter give way upwards into Old Red Sandstones, which are inferred to have been deposited in a Caledonian foreland basin.
Deformation, reaching the area in the latest Devonian or earliest Carboniferous and referred to as the Severnaya Zemlya episode,
is thought to be Caledonian-related. The dominating E-vergent structure was controlled by décollement zones in Ordovician
evaporite-bearing strata; detachment folds and thrusts developed in the west and were apparently impeded by a barrier of Ordovician
igneous rocks in the east. Below the décollement zones, the Neoproterozoic to Early Ordovician succession was deformed into
open to close folds. The exposed strata in the lower structural level have been juxtaposed with those in the upper structural
level along the major N-trending Fiordovoe Lake Fault Zone, which involved several kilometres of dextral strike-slip movement
and downthrow to the west. A major Early Carboniferous unconformity separates the folded Mid-Palaeozoic and older rocks from
overlying Carboniferous formations, as on Franz Joseph Land and Svalbard. Subsequent latest Palaeozoic to Early Mesozoic orogeny,
as on Taimyr, apparently had little influence on the Severnaya Zemlya successions. 相似文献
11.
华北陆台晚古生代岩相古地理 总被引：1，自引：0，他引：1
位于天山-阴山、昆仑山-秦岭两大纬向构造带之间的华北陆台。在稳定地壳基底上逐渐发展形成晚古生代多旋回克拉通大型含煤盆地。加里东运动使陆台缺失O3-C1沉积，晚石炭世至晚二叠世陆台为海陆交互相滨海、湖泊、三角洲沉积，随着古地理环境演变,陆台各沉积古地理环境在时、表现为由老至新、自北向南迁移。 相似文献
12.
胜利油区早古生代沉积相 总被引：3，自引：0，他引：3
早古生代，胜利油区作为华北地台的一部分，接受了一套以海相碳酸盐岩为主的沉积，其沉积相与其他地区既有相似性，又有特殊性。文中首先按沉积岩类型，将沉积相划分为碎屑沉积相系和碳酸盐岩沉积相系。根据岩石的沉积构造、指相矿物、生物化石等，将下古生界沉积相进一步划分为４个相９种亚相，并对各种相的特征进行了简要说明。在单井相分析的基础上，利用单因素和三端元作图法编制了基础图件，结合相序的变化规律和区域地质背景，对区内早古生代不同时期的沉积相展布特征进行了探讨：馒头期—徐庄期，基本为潮上到潮间带；张夏期—崮山期，发育有潮下浅滩和开阔海两种主要沉积相；长山期—早奥陶世，以潮间—潮下带为主；中奥陶世，以浅水的潮上、潮间带与较深水的潮下带间互出现。研究早古生代沉积相，对于评价碳酸盐岩储层和烃源岩有重要意义。 相似文献
13.
云南思茅地区上石炭统沉积特征及其构造背景 总被引：2，自引：0，他引：2
思茅地区位于东特提斯构造域的东段,晚古生代时期属扬子地台西缘的一部分。晚石炭世具有台盆相间的沉积格局,形成了三类不同的沉积：滨岸沉积、浅海台地沉积和深水浊流沉积。其中深水浊流沉积以火山源浊流沉积为特征,是在平缓的碳酸盐台地或陆棚之上通过断陷事件发展起来的,包括了５个沉积旋回,表现出强烈的火山活动期与火山休眠期交递进行的沉积旋回特征。自晚石炭世早期到晚期,火山活动期逐渐增长,休眠期逐渐缩短,反映出盆地性质自稳定向活动的转化过程。火山岩具有岛弧型火山岩特征,说明晚石炭世,思茅地区具有活动型大陆边缘沉积特征 相似文献
14.
P. V. Crowhurst R. Maas K. C. Hill D. A. Foster C. M. Fanning 《Australian Journal of Earth Sciences》2013,60(1):107-122
New U–Pb zircon ages and Sr–Nd isotopic data for Triassic igneous and metamorphic rocks from northern New Guinea help constrain models of the evolution of Australia's northern and eastern margin. These data provide further evidence for an Early to Late Triassic volcanic arc in northern New Guinea, interpreted to have been part of a continuous magmatic belt along the Gondwana margin, through South America, Antarctica, New Zealand, the New England Fold Belt, New Guinea and into southeast Asia. The Early to Late Triassic volcanic arc in northern New Guinea intrudes high‐grade metamorphic rocks probably resulting from Late Permian to Early Triassic (ca 260–240 Ma) orogenesis, as recorded in the New England Fold Belt. Late Triassic magmatism in New Guinea (ca 220 Ma) is related to coeval extension and rifting as a precursor to Jurassic breakup of the Gondwana margin. In general, mantle‐like Sr–Nd isotopic compositions of mafic Palaeozoic to Tertiary granitoids appear to rule out the presence of a North Australian‐type Proterozoic basement under the New Guinea Mobile Belt. Parts of northern New Guinea may have a continental or transitional basement whereas adjacent areas are underlain by oceanic crust. It is proposed that the post‐breakup margin comprised promontories of extended Proterozoic‐Palaeozoic continental crust separated by embayments of oceanic crust, analogous to Australia's North West Shelf. Inferred movement to the south of an accretionary prism through the Triassic is consistent with subduction to the south‐southwest beneath northeast Australia generating arc‐related magmatism in New Guinea and the New England Fold Belt. 相似文献
15.
Basins within the African sector of Gondwana contain a Late Palaeozoic to Early Mesozoic Gondwana sequence unconformably
overlying Precambrian basement in the interior and mid-Palaeozoic strata along the palaeo-Pacific margin. Small sea-board
Pacific basins form an exception in having a Carboniferous to Early Permian fill overlying Devonian metasediments and intrusives.
The Late Palaeozoic geographic and tectonic changes in the region followed four well-defined consecutive events which can
also be traced outside the study area. During the Late Devonian to Early Carboniferous period (up to 330 Ma) accretion of
microplates along the Patagonian margin of Gondwana resulted in the evolution of the Pacific basins. Thermal uplift of the
Gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and
330 Ma. At the end of this period the Gondwana Ice Sheet was well established over the uplands. The period 260–300 Ma evidenced
the release of the Gondwana heat and thermal subsidence caused widespread basin formation. Late Carboniferous transpressive
strike-slip basins (e.g. Sierra Australes/Colorado, Karoo-Falklands, Ellsworth-Central Transantarctic Mountains) in which
thick glacial deposits accumulated, formed inboard of the palaeo-Pacific margin. In the continental interior the formation
of Zambesi-type rift and extensional strike-slip basins were controlled by large mega-shear systems, whereas rare intracratonic
thermal subsidence basins formed locally. In the Late Permian the tectonic regime changed to compressional largely due to
northwest-directed subduction along the palaeo-Pacific margin. The orogenic cycle between 240 and 260 Ma resulted in the formation
of the Gondwana fold belt and overall north–south crustal shortening with strike-slip motions and regional uplift within the
interior. The Gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened
marginal crustal belt subject to dextral transpressive motions. Associated with the orogenic cycle was the formation of mega-shear
systems one of which (Falklands-East Africa-Tethys shear) split the supercontinent in the Permo-Triassic into a West and an
East Gondwana. By a slight clockwise rotation of East Gondwana a supradetachment basin formed along the Tethyan margin and
northward displacement of Madagascar, West Falkland and the Gondwana fold belt occurred relative to a southward motion of
Africa.
Received: 2 October 1995 / Accepted: 28 May 1996 相似文献
16.
The Thomson Orogen forms the northwestern segment of the Tasman Orogenic Zone. It was a tectonically active area with several episodes of deposition, deformation and plutonism from Cambrian to Carboniferous time.Only the northeastern part of the orogen is exposed; the remainder is covered by gently folded Permian and Mesozoic sediments of the Galilee, Cooper and Great Artesian Basins. Information on the concealed Thomson Orogen is available from geophysical surveys and petroleum exploration wells which have penetrated the Permian and Mesozoic cover.The boundaries of the Thomson Orogen with other tectonic units are concealed, but discordant trends suggest that they are abrupt. To the west, the orogen is bordered by Proterozoic structural blocks which form basement west of the northeast-trending Diamantina River Lineament. The most appropriate boundary with the Lachlan and Kanmantoo Orogens to the south is an arcuate line marking a distinct change in the direction of gravity trends. The north-northwest orientation of the northern part of the New England Orogen to the east cuts strongly across the dominant northeast trend of the Thomson Orogen.The Thomson Orogen developed as a tectonic entity in latest Proterozoic or Early Cambrian time when the former northern extension of the Adelaide Orogen * was truncated along the Muloorinna Ridge. Early Palaeozoic deposition was dominated by finegrained, quartz-rich clastic sediments. Cambrian carbonates accumulated in the southwest and a Cambro-Ordovician island arc was active in the north. Along the western margin of the orogen, sediments were probably laid down on downfaulted blocks of deformed Proterozoic rocks, with oceanic crust further to the east.A mid- to Late Ordovician orogeny which affected the whole of the Thomson Orogen marked the climax of its precratonic (orogenic) stage. The northeast structural trend of the orogen (parallel to its western boundary with the Precambrian craton) was imposed at this time and has controlled the orientation of later folding and faulting. Up to three generations of folding have been recognized and fine-grained metasediments exhibit a prominent slaty cleavage. Metamorphism was to the greenschist and amphibolite facies, the highest grade rocks being associated with synorogenic granodiorite batholiths in the north. Following deposition of Late Ordovician marine sediments at the eastern margin, emplacement of post-tectonic Late Silurian or Early Devonian batholiths ended the precratonic history of the Thomson Orogen.The subsequent transitional tectonic regime was characterized by deposition of Devonian to Early Carboniferous shallow marine and continental sediments including widespread red-beds and andesitic volcanics. The maximum marine transgression occurred in the early Middle Devonian. Localized folding affected the easternmost part of the Thomson Orogen at the end of Middle Devonian time and was followed by intrusion of Devono-Carboniferous granitic plutons. However, the terminal orogeny which deformed all Devonian to Early Carboniferous rocks of the orogen was of mid-Carboniferous age. It produced northeast-trending open folds and normal and high-angle reverse faults which are considered to reflect basement structures. The cratonization of the Thomson Orogen was completed with the emplacement of Late Carboniferous granites and the eruption of comagmatic volcanics in the northeast, permian and Mesozoic sediments accumulated in broad, relatively shallow down warps which covered most of the former orogen. 相似文献
17.
Geodynamic models for the Antarctic sector of the active Early Palaeozoic Palaeo-Pacific margin of Gondwana are based on the nature and age of the deep crust of the Robertson Bay terrane, the outermost lithotectonic unit of the margin. As this crustal block is covered with thick turbidite deposits, the only way to probe the deep crust is through the analysis of granulite xenoliths from Cenozoic scoria cones. Low-K felsic xenoliths yield the oldest (Middle Cambrian) laser-probe U–Pb ages on zircon areas with igneous growth zoning. This finding, along with the positive whole-rock εNd(500Ma) , suggests that these felsic rocks derived from a juvenile magma formed during the Early Palaeozoic Ross orogenic cycle. Mafic xenoliths have geochemical-isotopic compositions similar to those of modern primitive island arcs, suggesting the involvement of subducted oceanic crust in their magma genesis and accretion of juvenile crust at the Antarctic margin of Gondwana. 相似文献
18.
柳忠泉 《沉积与特提斯地质》2009,29(1):37-45
在大别造山带内发现的可燃天然气和发生燃烧的隧道具有明显的区域性,集中分布于磨子潭-晓天断裂以南的北大别杂岩带和信阳-舒城断裂附近的早石炭世变质石英片岩中,磨子潭-晓天断裂和信阳。舒城断裂是连通深部的气源通道断裂;推覆体之下的下寒武统凤台组和北淮阳型石炭系两套海相烃源岩是隧道可燃天然气的主力气源岩,其中下寒武统凤台组属大陆边缘沉积,其发育的海相泥质烃源岩具有高碳,高“R。”,高T…和低氯仿“A”的特点,已进入热演化的过成熟阶段;北淮阳型石炭系处于前陆盆地的沉积中心,地层序列齐全,其煤系源岩有机质丰度高,以Ⅲ型干酪根为主,热演化程度很高,大量的油气已经生成,最重要的是研究其成烃过程与圈闭配套史的关系。大别造山带隧道可燃天然气的发现展示了合肥盆地区深部海相层系可能潜在良好的勘探前景。因此,进一步勘探重心应从“中新生代盆地系统”转移到“深部海相层系”,以寻找“古生古储”或“古生新储”类型油气藏为主。 相似文献
19.
Bimodal metavolcanic rocks, granitic gneisses and metasediments are associated in the Frankenberg massif, Germany. These rocks are faulted against underlying very low-grade Palaeozoic sequences and adjacent metamorphic complexes of the Variscan basement. The granitic gneisses record an Rb–Sr whole-rock isochron age of 461±20 Ma that is taken as at least a minimum protolith age. The bimodal meta-igneous suites are interpreted to have formed during rifting of the Gondwana continental margin in the Cambro-Ordovician. The various metamorphic units have all experienced a common P–T history. The peak-pressure stage is constrained to around 490–520 °C and 10–14 kbar (10–12 kbar being most realistic). The metamorphism proceeded along a clockwise P–T path towards conditions of around 580–610 °C and 7–8.5 kbar at the thermal peak followed by a final low-pressure overprint which spanned amphibolite facies to prehnite–actinolite facies temperatures. Owing to a secondary Rb–Sr whole-rock isochron age of 381±24 Ma, interpreted to date the retrograde stage, the whole metamorphic cycle in the Frankenberg massif is ascribed to the late Silurian–early Devonian high-pressure event widely recorded in the European Variscides. The antiformal complexes bordering the Frankenberg massif underwent a well-documented early Carboniferous metamorphism, suggesting that the Frankenberg massif constitutes a klippe which was overthrust towards the end of this second metamorphic cycle. 相似文献
20.
I. Metcalfe 《Journal of Asian Earth Sciences》2000,18(6)
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