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1.
原定为青白口纪的龙潭河组时代应属早南华世;在志留系顶部发现一套岩层,认为存在中泥盆统云台观组;万县与通江两地层小区的下—中侏罗统存在相变过渡关系;城巴断裂以北分布较小型侵入岩体。重点调查研究了具重要控矿作用的城巴断裂和直接影响三峡库区稳定性的七曜山断裂带新构造运动。  相似文献   

2.
The Palaeozoic sediments from the Mauges Unit (Armorican Massif, France) are the best-preserved pre-orogenic sequences belonging to the Upper Allochthon. Two coherent sequences are identified. The southern unit (Chateaupanne Unit) represents the cover of the Proterozoic basement and consists of Ordovician sediments unconformably overlain by Emsian carbonates followed by Emsian to earliest Eifelian immature sandstones. The northern unit (Tombeau Leclerc Unit) consists of an Hirnantian to Emsian condensed sequence, in reverse position, that has been thrust over the southern unit. The Devonian unconformity is interpreted as evidence for an Early Devonian extension, recorded by normal faults affecting both the Early Devonian limestones and the underlying Ordovician series. This crustal extension, recorded here for the first time, is possibly related to the opening of a back-arc basin (Saint-Georges-sur-Loire) associated with the subduction of an ocean located further south (Galicia-Brittany-Massif Central Ocean).  相似文献   

3.
The first results of U–Pb dating of detrital zircons from Upper Ordovician sandstones of the Bashkir uplift in the Southern Urals and U–Pb isotopic ages available for detrital zircons from six stratigraphic levels of the Riphean–Paleozoic section of this region are discussed. It is established that the long (approximately 1.5 Ga) depositional history of sedimentary sequences of the Bashkir uplift includes a peculiar period lasting from the Late Vendian to the Emsian Age of the Early Devonian (0.55–0.41 Ga). This period is characterized by the following features: (1) prevalence of material from eroded Mesoproterozoic and Early Neoproterozoic crystalline complexes among clastics with ages atypical of the Volga–Urals segment of the East European Platform basement; (2) similarity of age spectra obtained for detrital zircons from different rocks of the period: Upper Vendian–Lower Cambrian lithic sandstones and Middle Ordovician substantially quartzose sandstones.  相似文献   

4.
A Paleozoic subduction complex dominates the Mossman Orogen developed at the northern extremity of the Tasmanides, eastern Australia. Its southern part, displayed in the Broken River Province, is characterised by dismembered ocean-plate stratigraphy in which turbidite-dominated packages and widespread tectonic mélange development are characteristic. The Broken River complex is characterised by formations with quartzose sandstone alternating with those largely formed of sandstone of more labile character. The two compositional groups are considered to reflect separate, age-significant sedimentary regimes, but their ages have hitherto been poorly constrained. With the use of 1082 concordant detrital zircon ages from 13 samples we provide age control for the complex and track its sedimentary provenance. Of quartzose units, the Tribute Hills Arenite and Pelican Range Formation are late Cambrian–Early Ordovician, and the Wairuna Formation is Middle to Late Ordovician, in age. The more labile units (Greenvale, Perry Creek and Kangaroo Hills formations) are collectively of late Silurian–mid-Devonian age. Development of the complex spanned some 130 Myr. Continent-derived sediment involved in accretion of much the complex, from mid-Ordovician to mid-Devonian, was largely sourced from a nearby magmatic arc of late Cambrian–Devonian age, now represented by granitoid plutons of the Macrossan and Pama igneous associations. An older far-field Pacific-Gondwana sediment source is characteristic of early-phase (late Cambrian–Early Ordovician) accretion, in common with sedimentary units of this age generally developed in the Tasmanides. We consider the complex to have grown largely by underplating that positioned younger components beneath those that are older, with out-of-sequence thrust interleaving of these components occurring late in the accretionary history. A Late Devonian contractional folding and cleavage development (Tabberabberan orogenesis) is uniformly expressed across the entire complex and reflects an abrupt change in plate engagement with imposition of a compressional stress regime.  相似文献   

5.
塔里木板块西北缘沉积地层的研究,对于恢复南天山洋的演化过程有重要意义。文中利用岩石地球化学的手段,对新疆阿合奇地区志留系砂岩进行物源和构造背景分析。研究表明,阿合奇地区志留系砂岩样品的SiO2含量范围变化较大,为61.97%~93.91%,平均含量为76.76%;稀土元素球粒陨石标准化配分型式为右倾型,(La/Yb)N值较高,δEu值较低,Ce异常不明显。中-顶志留统塔塔埃尔塔格组砂岩的成熟度高于下志留统柯坪塔格组。地球化学物源分析图解和大地构造背景判别表明: 研究区沉积物源区逐渐由活动型向稳定型转换,下志留统部分沉积物来自于火成岩物源区,具有主动大陆边缘和大陆岛弧性质;中-顶志留统沉积物全部来自于成熟大陆的石英岩沉积物源区。结合广泛分布的奥陶系-志留系平行不整合,认为晚奥陶世研究区为活动大陆边缘,南天山洋盆向南俯冲到塔里木板块之下;早志留世,向南俯冲结束,研究区大地构造背景开始由活动大陆边缘向稳定的被动大陆边缘转换,来自活动型物源区的沉积物逐渐减少,稳定型物源区的碎屑物质逐渐增多;中-末志留世,研究区构造背景完全转变为被动大陆边缘,碎屑物质全部来自于稳定型物源区。上述成果表明,南天山洋的演化过程中确实存在双向俯冲。  相似文献   

6.
The Hill End Trough of central‐western New South Wales was an elongate deep marine basin that existed in the Lachlan Fold Belt from the early Late Silurian to late Early Devonian. It is represented by a regionally extensive, unfossiliferous sequence of interbedded turbidites and hemipelagites of substantially silicic volcanic derivation, which passes laterally into contemporaneous shallow‐water sedimentary rocks. The Turondale and Merrions Formations of the Lower Devonian Crudine Group are two prominent volcanogenic formations in the predominantly sedimentary trough sequence. They contain a range of primary and resedimented volcanic facies suitable for U–Pb dating. These include widespread subaqueous silicic lavas and/or lava cryptodomes, and thick sequences of crystal‐rich volcaniclastic sandstone emplaced by a succession of mass‐flows that were generated by interaction between contemporaneous subaerial pyroclastic flows and the sea. Ion microprobe dating of the two volcanogenic formations by means of the commonly used SL 13 zircon standard yields ages ranging between 411.3 ± 5.1 and 404.8 ± 4.8 Ma. Normalising the data against a different zircon standard (QGNG) yields preferred slightly older mean ages that range between 413.4 ± 6.6 and 407.1 ± 6.9 Ma. These ages broadly approximate the Early Devonian age that has been historically associated with the Crudine Group. However, the biostratigraphically inferred late Lochkovian ‐ early Emsian (mid‐Early Devonian) age for the Merrions Formation is inconsistent with the current Australian Phanerozoic Timescale, which assigns an age of 410 Ma to the Silurian‐Devonian boundary, and ages of 404.5 Ma and 395.5 Ma to the base and top of the Pragian, respectively. There is, however, good agreement if the new ages are compared with the most recently published revision of the Devonian time‐scale. This suggests that the Early Devonian stage boundaries of the Australian Phanerozoic Timescale need to be revised downward. The new ages for the Merrions Formation could also provide a time point on this time‐scale for the Pragian to early Emsian, for which no data are presently available.  相似文献   

7.
One of the most significant, but poorly understood, tectonic events in the east Lachlan Fold Belt is that which caused the shift from mafic, mantle‐derived calc‐alkaline/shoshonitic volcanism in the Late Ordovician to silicic (S‐type) plutonism and volcanism in the late Early Silurian. We suggest that this chemical/isotopic shift required major changes in crustal architecture, but not tectonic setting, and simply involved ongoing subduction‐related magmatism following burial of the pre‐existing, active intraoceanic arc by overthrusting Ordovician sediments during Late Ordovician — Early Silurian (pre‐Benambran) deformation, associated with regional northeast‐southwest shortening. A review of ‘type’ Benambran deformation from the type area (central Lachlan Fold Belt) shows that it is constrained to a north‐northwest‐trending belt at ca 430 Ma (late Early Silurian), associated with high‐grade metamorphism and S‐type granite generation. Similar features were associated with ca 430 Ma deformation in east Lachlan Fold Belt, highlighted by the Cooma Complex, and formed within a separate north‐trending belt that included the S‐type Kosciuszko, Murrumbidgee, Young and Wyangala Batholiths. As Ordovician turbidites were partially melted at ca 430 Ma, they must have been buried already to ～20 km before the ‘type’ Benambran deformation. We suggest that this burial occurred during earlier northeast‐southwest shortening associated with regional oblique folds and thrusts, loosely referred to previously as latitudinal or east‐west structures. This event also caused the earliest Silurian uplift in the central Lachlan Fold Belt (Benambran highlands), which pre‐dated the ‘type’ Benambran deformation and is constrained as latest Ordovician — earliest Silurian (ca 450–440 Ma) in age. The south‐ to southwest‐verging, earliest Silurian folds and thrusts in the Tabberabbera Zone are considered to be associated with these early oblique structures, although similar deformation in that zone probably continued into the Devonian. We term these ‘pre’‐ and ‘type’‐Benambran events as ‘early’ and ‘late’ for historical reasons, although we do not consider that they are necessarily related. Heat‐flow modelling suggests that burial of ‘average’ Ordovician turbidites during early Benambran deformation at 450–440 Ma, to form a 30 km‐thick crustal pile, cannot provide sufficient heat to induce mid‐crustal melting at ca 430 Ma by internal heat generation alone. An external, mantle heat source is required, best illustrated by the mafic ca 430 Ma, Micalong Swamp Igneous Complex in the S‐type Young Batholith. Modern heat‐flow constraints also indicate that the lower crust cannot be felsic and, along with petrological evidence, appears to preclude older continental ‘basement terranes’ as sources for the S‐type granites. Restriction of the S‐type batholiths into two discrete, oblique, linear belts in the central and east Lachlan Fold Belt supports a model of separate magmatic arc/subduction zone complexes, consistent with the existence of adjacent, structurally imbricated turbidite zones with opposite tectonic vergence, inferred by other workers to be independent accretionary prisms. Arc magmas associated with this ‘double convergent’ subduction system in the east Lachlan Fold Belt were heavily contaminated by Ordovician sediment, recently buried during the early Benambran deformation, causing the shift from mafic to silicic (S‐type) magmatism. In contrast, the central Lachlan Fold Belt magmatic arc, represented by the Wagga‐Omeo Zone, only began in the Early Silurian in response to subduction associated with the early Benambran northeast‐southwest shortening. The model requires that the S‐type and subsequent I‐type (Late Silurian — Devonian) granites of the Lachlan Fold Belt were associated with ongoing, subduction‐related tectonic activity.  相似文献   

8.
The northwestern corner of New South Wales consists of the paratectonic Late Proterozoic to Early Cambrian Adelaide Fold Belt and older rocks, which represent basement inliers in this fold belt. The rest of the state is built by the composite Late Proterozoic to Triassic Tasman Fold Belt System or Tasmanides.In New South Wales the Tasman Fold Belt System includes three fold belts: (1) the Late Proterozoic to Early Palaeozoic Kanmantoo Fold Belt; (2) the Early to Middle Palaeozoic Lachlan Fold Belt; and (3) the Early Palaeozoic to Triassic New England Fold Belt. The Late Palaeozoic to Triassic Sydney—Bowen Basin represents the foredeep of the New England Fold Belt.The Tasmanides developed in an active plate margin setting through the interaction of East Gondwanaland with the Ur-(Precambrian) and Palaeo-Pacific plates. The Tasmanides are characterized by a polyphase terrane accretion history: during the Late Proterozoic to Triassic the Tasmanides experienced three major episodes of terrane dispersal (Late Proterozoic—Cambrian, Silurian—Devonian, and Late Carboniferous—Permian) and six terrane accretionary events (Cambrian—Ordovician, Late Ordovician—Early Silurian, Middle Devonian, Carboniferous, Middle-Late Permian, and Triassic). The individual fold belts resulted from one or more accretionary events.The Kanmantoo Fold Belt has a very restricted range of mineralization and is characterized by stratabound copper deposits, whereas the Lachlan and New England Fold Belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes.The earliest deposits in the Lachlan Fold Belt are stratabound Cu and Mn deposits of Cambro-Ordovician age. In the Ordovician Cu deposits were formed in a volcanic are. In the Silurian porphyry Cu---Au deposits were formed during the late stages of development of the same volcanic are. Post-accretionary porphyry Cu---Au deposits were emplaced in the Early Devonian on the sites of the accreted volcanic arc. In the Middle to Late Silurian and Early Devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism. In the Silurian and Early Devonian numerous Sn---W, Mo and base metal—Au granitoid related deposits were formed. A younger group of Mo---W and Sn deposits resulted from Early—Middle Carboniferous granitic plutonism in the eastern part of the Lachlan Fold Belt. In the Middle Devonian epithermal Au was associated with rifting and bimodal volcanism in the extreme eastern part of the Lachlan Fold Belt.In the New England Fold Belt pre-accretionary deposits comprise stratabound Cu and Mn deposits (pre-Early Devonian): stratabound Cu and Mn and ?exhalite Au deposits (Late Devonian to Early Carboniferous); and stratabound Cu, exhalite Au, and quartz—magnetite (?Late Carboniferous). S-type magmatism in the Late Carboniferous—Early Permian was responsible for vein Sn and possibly Au---As---Ag---Sb deposits. Volcanogenic base metals, when compared with the Lachlan Fold Belt, are only poorly represented, and were formed in the Early Permian. The metallogenesis of the New England Fold Belt is dominated by granitoid-related mineralization of Middle Permian to Triassic age, including Sn---W, Mo---W, and Au---Ag---As Sb deposits. Also in the Middle Permian epithermal Au---Ag mineralization was developed. During the above period of post-orogenic magmatism sizeable metahydrothermal Sb---Au(---W) and Au deposits were emplaced in major fracture and shear zones in central and eastern New England. The occurrence of antimony provides an additional distinguishing factor between the New England and Lachlan Fold Belts. In the New England Fold Belt antimony deposits are abundant whereas they are rare in the Lachlan Fold Belt. This may suggest fundamental crustal differences.  相似文献   

9.
早奥陶世和早志留世是北祁连加里东造山带构造演化和盆地转变的关键时期。在造山带东段景泰地区,下奥陶统阴沟组和下志留统肮脏沟组两套砂岩的微量元素和稀土元素特征显示,阴沟组杂砂岩样品（Cj1和Cj3）具有最小的Eu/Eu*及最大的Th/Sc和REE,肮脏沟组杂砂岩具有较小的Eu/Eu*和较大的Th/Sc及REE;阴沟组岩屑砂岩样品（Cj13、Cj15和Cj18）具有最大的Eu/Eu*及最小的Th/Sc、REE和La/Yb。多个物源、构造背景判别图解和多元素蛛网图分析表明,阴沟组杂砂岩样品具大陆边缘的构造背景,主要物源为大陆上地壳再旋回沉积物和长英质岩石;岩屑砂岩样品为岛弧构造背景,以中基性安山质岩石为主要物源,可能受陆源物质的微弱影响。肮脏沟组杂砂岩构造背景复杂,表现出大陆岛弧、活动陆缘和被动陆缘三种环境共存的特点,受中基性火山弧物质、长英质岩石和再旋回沉积岩的混合物源的影响。两套砂岩的元素特征表明二者可能具有相似的源区。阴沟组杂砂岩源区可能为阿拉善地块南缘海原群变沉积岩或其他相似的陆源再旋回沉积物,砂岩碎屑以来自初始火山弧物质为主,以石灰沟岛弧型中基性火山岩作为其源岩最合适。阴沟组形成于初始弧后盆地环境,是岛弧活动的直接记录。肮脏沟组可能的源岩为阿拉善地块南缘海原群变沉积岩和中高等成熟度的石灰沟岛弧型火山岩及海原群岛弧型变火山岩,沉积于弧后前陆盆地,对构造环境的反映存在滞后性。  相似文献   

10.
Tectonostratigraphy of the exposed Silurian deposits in Arabia   总被引：1，自引：1，他引：0  
Exposed Silurian deposits in Arabia are represented by the Qalibah Group, the Qusaiba and Sharawra formations. The Qusaiba Formation is composed of dark-gray claystones and siltstones. It is disconformably underlain by the Late Ordovician–Early Silurian? Uqlah Formation or unconformably underlain by the Late Ordovician Zarqa or Sarah formations. It is disconformably overlain by the Sharawra Formation. The Early Rhuddanian basal “hot shale” of the Qusaiba Formation represents the early stage of the early Silurian marine transgression over the Gondwana broad shelf. It is a regional marker used to outline the structural configuration of the area prior to the Silurian time. The Sharawra Formation is composed of siltstone and sandstone. It is unconformably overlain by the Late Silurian?–Early Devonian Tawil Formation. Silurian deposits show a pronounced thinning from 992 m in the Tabuk area in the west and are completely missing in the northern part of the Qusayba depression in the east. The thinning of the Qusaiba shale and Sharawra sandstone is interpreted as due to depositional and erosional features, respectively. Thinning and distribution of the Early Rhuddanian shale “hot shale” is depositional which is affected by preexisting Late Ordovician paleo-highs in central Arabia. Thinning of the Sharawra sandstones is erosional which is attributed to Late Silurian tectonic movements synchronous with the Acadian uplift phase of the Caledonian tectonic movements. The main structural elements in central Arabia are represented by the north–south trending and northerly plunging Hail arch and to a much lesser extent the northwest–southeast trending and southerly plunging Qusayba high.  相似文献   

11.
沉积物中重矿物分布受物源区、构造抬升与剥蚀作用、古地貌以及沉积古气候、古环境等多种因素影响,因此沉积重砂矿物的研究可应用于物源区、沉积环境的分析,阐明构造旋回与沉积作用的响应关系。本文通过对塔中地区中1井等6口探井上泥盆统东河砂岩和志留系柯坪塔格组砂岩中重砂矿物分析,提出了塔中东河砂岩重砂矿物主要来自稳定的基底再沉积及花岗岩来源,但受近源的基性火山岩及岩浆期后热液作用影响较大;志留系下砂岩重砂矿物主要来自下覆碳酸盐岩、花岗岩和搬运再沉积物,总体形成于稳定的、多物源的构造-沉积环境,物源方向可能是东南至西北方向。  相似文献   

12.
The structures across the Lambian Unconformity near Taralga show evidence of two, and possibly three, significant episodes of folding. The first, Early to Middle Silurian folding is poorly defined, but may be responsible for initial dips that are reflected in the more complex deformation patterns in the Late Ordovician than in the overlying younger rocks. The second, mid‐Devonian folding produced upright folds trending 10° west of north, and the last, latest Devonian to Early Carboniferous folding produced the meridional Cookbundoon Synclinorium and the regional cleavage. No cleavage was associated with the first two episodes of folding in the area studied. The angular discordance across the Lambian Unconformity caused by mid‐Devonian folding is much greater than in the northeastern Lachlan Fold Belt, and reflects the increasing intensity of mid‐Devonian folding southward. The tight, slightly overturned profile of the Cookbundoon Synclinorium reflects an intensity of latest Devonian to Early Carboniferous folding similar to that found in the northeastern Lachlan Fold Belt, but the intensity of this folding decreases further south.  相似文献   

13.
UPb dating of detrital zircons from metamorphic and unmetamorphosed siliciclastic units in northern, central, and southern parts of the late Paleozoic South Tianshan (STS) orogen allows us to elucidate depositional ages and provenances of studied deposits and provide important insights into Paleozoic tectonics and evolution of the southwest Central Asian Orogenic Belt (CAOB). In the northern flank of the orogen, the depositional age of metasandstones of the Kembel Complex has been constrained to 446–417 Ma. Greenschist-facies metasandstones of the Kan Complex, associated with the Turkestan suture and previously related to Proterozoic, yielded maximum depositional ages of 438–428 Ma based on the youngest clusters of detrital zircons, although the occurrence of a few younger grains implies, that these rocks may be late Silurian to Devonian in age. Greenschists of the Kan Complex were likely metamorphosed during the Mississippian (>330 Ma), based on the early Serpukhovian age of overlying strata. A similar depositional age has been proven for sandstones of the Balykty Formation, east of the Talas-Ferghana Fault. Detrital zircons ages for these metasediments suggest clastic provenances within Northern and Middle Tianshan. In the axial parts of the STS, coarse-grained turbidite sandstones yielded Silurian to Early Devonian maximum ages. The axial part of the STS was separated from continental domains in the north and south by deep-marine basins; therefore, these turbidite sandstones must have been derived from a local provenance in the STS. This local provenance is comprised of Precambrian crustal fragments, as indicated by high concentration of Precambrian magmatic zircons in detrital populations, along with Silurian and Devonian arc magmatic rocks. Precambrian crust can be inferred in the basement of the Alai microcontinent and Baubashata carbonate platform, which represented the likely provenance areas. Detrital zircons with Ediacaran 650–550 Ma ages in turbidites suggest that during the Neoproterozoic, these crustal fragments may have comprised a single continental domain with the Karakum-Tajik (Garm massif) and Tarim microcontinents, where magmatic rocks and detrital zircons with such ages have been also previously dated. Devonian slope turbidite facies of the Tarim Craton in the south Ferghana Range contain Precambrian detrital zircons with ages matching those of the Tarim, and numerous Paleozoic zircons clustering at 446 and 441 Ma. Paleozoic zircon ages indicate the occurrence of unidentified Ordovician and early Silurian magmatic rocks in northern and western Tarim. New data provide further evidence that Paleozoic evolution of CAOB was controlled by northward motion of the Precambrian terranes rifted off the Gondwana and colliding with the continental masses of Kazakhstan and Siberia in the north.  相似文献   

14.
下扬子地区从晚奥陶世开始沉积特征发生了明显转变,从浅海相转变为三角洲相沉积.这一沉积特征转变与早古生代晚期经历的强烈造山事件密切相关.通过下扬子地区晚奥陶世到志留纪沉积序列的沉积学和碎屑锆石年代学研究,揭示沉积盆地的性质及其时空演化过程,探讨沉积盆地发育与造山带隆升剥蚀之间的关系.下扬子地区早古生代晚期沉积学特征从东南向西北岩性由岩屑砂岩变为石英砂岩,粒度由粗粒变为细粒;沉积厚度等值线具有明显的不对称性,靠近东南等值线密,且沉积厚度大;往西北等值线稀疏,且沉积厚度小;沉积中心呈狭长带状分布,并从东南向西北方向迁移;具有前陆盆地的沉积特征.上奥陶统到中志留统的碎屑锆石以900～720Ma的年龄为主,指示物源以下伏新元古代晚期裂谷层序为主;从早志留世高家边组开始,450～420Ma碎屑锆石年龄出现并逐渐增多,表明同造山岩浆岩被剥露地表并开始提供物源;碎屑锆石中没有出现明显的代表华夏地块基底1.9～1.7Ga的特征年龄峰值,表明华夏地块不是下扬子地区早古生代晚期前陆盆地的主要物源区.下扬子地区前陆盆地从晚奥陶世开始沉降,晚奥陶世的构造沉降速率超过了沉积物的供给速率,前渊沉积了巨厚的浅海相泥岩夹粉砂岩和砂岩;晚奥陶世末造山带持续隆升并向西北方向扩展,沉积速率加快,沉积物粒度明显变粗,沉积相也由浅海相转变成三角洲前缘相;早志留世开始埋深较大的同造山岩浆岩开始遭受剥蚀,导致前陆盆地中450～420 Ma的碎屑锆石含量明显增加.  相似文献   

15.
为了通过碎屑岩的物源对比讨论古亚洲洋的闭合过程,笔者选择西拉木伦河北侧林西双井子地区和南侧奈曼旗下石碑地区的志留纪地层进行碎屑岩锆石U-Pb年代学研究。北侧样品LX0831-11为粉砂质板岩,采于西拉木伦河北岸上志留统杏树洼组。碎屑锆石年龄分为三组:385~531Ma(N=52)、872~1097Ma(N=11)、1344~1901Ma(N=11),碎屑锆石的最小年龄限定地层沉积下限为中-晚泥盆世。南侧样品130417-06为石英岩屑砂岩,采于奈曼旗下石碑组顶部砂岩中。碎屑锆石年龄分为四组:370~523Ma(N=34)、884~1481Ma(N=21)、1573~1900Ma(N=6)、2369~2588Ma(N=8),碎屑锆石的最小年龄限定地层沉积下限为晚泥盆世。这两个分别来自西拉木伦河南、北两侧原志留纪样品,显示一致的志留-泥盆纪及晚元古代碎屑锆石年龄谱,表明两者从泥盆纪开始即具有相同的沉积物源;而代表兴蒙造山带的元古代碎屑锆石在奈曼旗地区的出现,说明泥盆纪以来兴蒙造山带的剥蚀物已到达华北板块北缘。因此,本次碎屑锆石年代学研究暗示华北板块与其北部松辽地块在中-晚泥盆世之前已经完成拼合过程,即此时两者间已不存在古亚洲洋。  相似文献   

16.
In the Eastern Lachlan Orogen, the mineralised Molong and Junee‐Narromine Volcanic Belts are two structural belts that once formed part of the Ordovician Macquarie Arc, but are now separated by younger Silurian‐Devonian strata as well as by Ordovician quartz‐rich turbidites. Interpretation of deep seismic reflection and refraction data across and along these belts provides answers to some of the key questions in understanding the evolution of the Eastern Lachlan Orogen—the relationship between coeval Ordovician volcanics and quartz‐rich turbidites, and the relationship between separate belts of Ordovician volcanics and the intervening strata. In particular, the data provide evidence for major thrust juxtaposition of the arc rocks and Ordovician quartz‐rich turbidites, with Wagga Belt rocks thrust eastward over the arc rocks of the Junee‐Narromine Volcanic Belt, and the Adaminaby Group thrust north over arc rocks in the southern part of the Molong Volcanic Belt. The seismic data also provide evidence for regional contraction, especially for crustal‐scale deformation in the western part of the Junee‐Narromine Volcanic Belt. The data further suggest that this belt and the Ordovician quartz‐rich turbidites to the east (Kirribilli Formation) were together thrust over ?Cambrian‐Ordovician rocks of the Jindalee Group and associated rocks along west‐dipping inferred faults that belong to a set that characterises the middle crust of the Eastern Lachlan Orogen. The Macquarie Arc was subsequently rifted apart in the Silurian‐Devonian, with Ordovician volcanics preserved under the younger troughs and shelves (e.g. Hill End Trough). The Molong Volcanic Belt, in particular, was reworked by major down‐to‐the‐east normal faults that were thrust‐reactivated with younger‐on‐older geometries in the late Early ‐ Middle Devonian and again in the Carboniferous.  相似文献   

17.
对塔里木盆地塘古兹巴斯凹陷志留系与奥陶系(S/O3)、上泥盆统与志留系(D3d/S)2个区域角度不整合的三层结构特征及属性进行详细研究,分析了不整合面下构造变形特征、不整合面结构类型分布、不整合面上初始沉积砾岩成分及其物源.发现加里东中期该区形成了塔里木盆地独特的不整合结构,构造不整合(S/O3)明显地受北东东-南西西走向逆冲断裂系控制,在凹陷北部逆冲断裂系上盘发育中等角度单斜不整合和褶皱不整合,沿断裂带形成了多个角度不整合带;加里东晚期不整合(D3 d/S)区域上呈现由南向北的剥蚀特征,局部受继承性再活动的断裂控制存在北东东向的中角度单斜不整合带,且构成了加里东中期及晚期的叠合不整合.两期不整合面上的初始沉积砂砾岩有明显差异,加里东中期不整合面上初始沉积以近源的沉积岩为主、物源来自被动大陆边缘;晚期不整合面上的初始沉积砾岩主要为硅质岩和变质岩,物源主要来自较远的被动大陆边缘及大陆岛弧.综合分析表明,晚奥陶世末塘古兹巴斯凹陷主要受到阿尔金、西昆仑的构造作用;中志留世-晚泥盆世主要受到西昆仑及阿尔金碰撞造山活动共同作用.在加里东构造运动中晚期,凹陷中控制不整合发育的NEE向逆冲断裂系与南阿尔金断裂在活动时限、强度、区域应力场上具有可比性.加里东中、晚期不整合的三层结构及其属性是反映阿尔金-西昆仑早古生代构造运动发生、发展、终结动态演化过程的良好证据.  相似文献   

18.
New data on the ages of detrital zircons from folded basement rocks and cover sediments of the Severnaya Zemlya archipelago and Izvestiy TSIK islands have been obtained. The basement age is defined as Cambrian (pre-Ordovician). The Ordovician and Silurian sandstones were mainly formed by erosion of the basement rocks. The Devonian sandstones were formed by debris sourced from the Caledonian orogen. The Carboniferous–Early Permian molasse was formed simultaneously with the erosion of the Carboniferous granitoids and weathering of the Ordovician volcanic arc rocks and the Cambrian basement. The North Kara basin was formed in the Ordovician as a back-arc basin. It experienced its main compression deformations at the boundary of the Devonian and Carboniferous and in the Carboniferous.  相似文献   

19.
虎林盆地北部坳陷地层包括下白垩统裴德组、下云山组、上云山组、珠山组，渐新统虎林组和中新统富锦组。北部坳陷砂岩-泥岩由常量、微量和稀土元素组成，揭示早白垩世砂岩-泥岩源区构造背景为活动大陆边缘，渐新统斗新统砂岩-泥岩多呈现出从活动大陆边缘向大陆岛弧转换的地球化学特征。结合沉积相特征和岩屑所反映的源区岩性特点，认为早白垩世时期物源主要来自于坳陷北部完达山造山带和南部古隆起；渐新统物源则主要来自盆地东北部的完达山造山带，并且碎屑岩的原始物质均来自上地壳。  相似文献   

20.
Abstract

Magmatic-textured zircon from medium- to high-K calc-alkaline Warraweena Volcanics (WV) in two drill holes have yielded concordant U–Pb dates of 417?±?3.5 and 414?±?4.0?Ma and are interpreted as maximum emplacement ages. The Warraweena volcanics were previously considered to be either Neoproterozoic or Macquarie arc equivalents. Whole-rock εNdt values of these volcanics are +4.5 and +4.8. Along strike of the drill holes, Devonian zircon U–Pb ages (411?±?5.5?Ma) were obtained from coherent S-type rhyolite flows that have highly negative εNdt values (–7.9 and –7.8). These are a component of the Oxley volcanics. The ages of the Warraweena and Oxley volcanics are identical within uncertainty.

The Oxley volcanics (OV) are interbedded with predominantly fine- to medium-grained metasedimentary and so imply a Lower Devonian deposition age for these host rocks. Based on their geophysical characteristics, the metasediments are widely distributed. These metasedimentary rocks yield a wide range of maximum depositional ages, from Early Devonian to earliest Ordovician–latest Cambrian, similar to the Cobar Basin. The absence of complex fabric development typical of Ordovician supracrustal rocks in the region, and conformity with the OV where observable suggest the widespread sedimentation was synchronous with rift-related volcanism in the Early Devonian.

Regionally, the WV is temporally, geochemically and isotopically (εNd values) similar to the calc-alkaline Louth Volcanics located over 100?km to the southwest of the WV. Louth Volcanics define a complexly folded belt in geophysical data. Other potentially correlative Early Devonian igneous rocks occur in the nearby Cobar Superbasin and elsewhere in the eastern Lachlan Orogen and are considered to represent the products of a post-orogenic, nascent continental back-arc rift system.  相似文献   

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