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1.
The formation and structural evolution of the Jungfrau syncline is described, based on excellent outcrops occurring in the Lötschental, in the Central Alps of Switzerland. The quality of the outcrops allows us to demonstrate that the External Massifs of the Swiss Alps have developed due to internal folding. The Jungfrau syncline, which separates the autochtonous Gastern dome from the Aar massif basement gneiss folds, is composed of slivers of basement rocks with their Mesozoic sedimentary cover. In the Inner Faflertal, a side valley of the Lötschental, the 200 m thick syncline comprises four units, the Gastern massif with a reduced Mesozoic sedimentary cover in a normal stratigraphic succession, two units of overturned basement rocks with their Mesozoic sedimentary cover, and the overturned lower limb of the Tschingelhorn gneiss fold of the Aar massif with lenses of its sedimentary cover. Stratigraphy shows that the lower units, related to the Gastern massif, are condensed and that the upper units, deposited farther away from a Gastern paleo-high, form a more complete sequence, linked to the Doldenhorn Meso-Cenozoic basin fill. The integration of these local observations with published regional data leads to the following model. On the northern margin of the Doldenhorn basin, at the northern fringe of the Alpine Tethys, the pre-Triassic crystalline basement and its Mesozoic sedimentary cover were folded by ductile deformation at temperatures above 300 °C and in the presence of high fluid pressures, as the Helvetic and Penninic nappes were overthrusted towards the northwest during the main Alpine deformation phase. The viscosity contrast between the basement gneisses and the sediments caused the formation of large basement anticlines and tight sedimentary synclines (mullion-type structures). The edges of basement blocks bounded by pre-cursor SE-dipping normal faults at the northwestern border of the Doldenhorn basin were deformed by simple shear, creating overturned slices of crystalline rocks with their sedimentary cover in what now forms the Jungfrau syncline. The localisation of ductile deformation in the vicinity of pre-existing SE-dipping faults is thought to have been helped by the circulation of fluids along the faults; these fluids would have been released from the Mesozoic sediments by metamorphic dehydration reactions accompanied by creep and dynamic recrystallisation of quartz at temperatures above 300 °C. Quantification of the deformation suggests a strain ellipsoid with a ratio (1+ e1 / 1+ e3) of approximately 1000. The Jungfrau syncline was deformed by more brittle NW-directed shear creating well-developed shear band cleavages at a late stage, after cooling by uplift and erosion. It is suggested that the external massifs of the Alps are basement gneiss folds created at temperatures of 300 °C by detachment through ductile deformation of the upper crust of the European plate as it was underthrusted below the Adriatic plate. 相似文献
2.
Hilmar von Eynatten Thomas Voigt Angela Meier Hans-Joachim Franzke Reinhard Gaupp 《International Journal of Earth Sciences》2008,97(6):1315-1330
The Harz Mountains and the adjacent Subhercynian Cretaceous Basin figure as the most prominent surface representative for
Late Cretaceous inversion structures in Central Europe. Facies, depositional architecture and provenance of the basin fill
reflect mechanisms and timing of the exhumation of the Harz. From Hauterivian to Early Santonian there is no evidence for
detrital input from the nearby Harz area. Sediments are mature quartzarenites derived from Paleozoic basement rocks and/or
recycled Permian to Mesozoic sedimentary rocks. This situation changed drastically in Middle to Late Santonian when freshly
exhumed and eroded Mesozoic sedimentary cover rocks of the Harz were delivered into the basin. Feldspar and lithoclasts reflect
erosion of Triassic and, in places, Jurassic to Turonian strata. Apatite and garnet in heavy mineral spectra are derived from
largely unweathered Lower Triassic Buntsandstein as indicated by apatite and garnet chemistry. In Early Campanian, Paleozoic
lithoclasts indicate erosion cutting down into the basement of the Harz. Simultaneous strong decrease of feldspar, garnet
and apatite suggest an almost complete removal of the 2–3 km thick Mesozoic cover of the Harz within only 2–4 Myr. This translates
into an exhumation rate of approximately 1 mm/a consistent with apatite fission track data from granitoid rocks of the Harz
Mountains. 相似文献
3.
The origin of the Woyla Terranes in Sumatra and the Late Mesozoic evolution of the Sundaland margin 总被引：3，自引：0，他引：3
A. J. Barber 《Journal of Asian Earth Sciences》2000,18(6):1024
The Jurassic–Cretaceous Woyla Group of northern Sumatra includes fragments of volcanic arcs and an imbricated oceanic assemblage. The arc rocks are intruded by a granitic batholith and are separated from the original continental margin of Sundaland by the oceanic assemblage. Rocks of the arc assemblage are considered to be underlain by a continental basement because of the occurrence of the intrusive granite and of tin anomalies identified in stream sediments. Quartzose sediments associated with the granite have been correlated with units in the Palaeozoic basement of Sumatra. From these relationships a model has been proposed in which a continental sliver was separated from the margin of Sundaland in the Late Jurassic to Early Cretaceous in an extensional strike-slip faulting regime, producing a short-lived marginal basin. The separated continental fragments have been designated the Sikuleh and Natal microcontinents. In the mid-Cretaceous the extensional regime was succeeded by compression, crushing the continental fragments back against the Sundaland margin, with the destruction of the marginal basin, now represented only by the imbricated oceanic assemblage. Modifications of this scenario are required by subsequent studies. Age-dating of the volcanic assemblage and intrusive granites in the Natal area showed that they formed part of an Eocene–Oligocene volcanic arc and are not relevant to the model. Thick-bedded radiolarian chert and palaeontological studies in the oceanic Woyla Group rocks of the Natal and Padang areas showed that they formed part of a more extensive and long-lived ocean basin which lasted from at least Triassic until mid-Cretaceous. This raised the possibility that the Sikuleh microcontinent might be allochthonous to Sumatra and encouraged plate tectonic reconstructions in which the Sikuleh microcontinent originated on the northern margin of Gondwanaland and migrated northwards across Tethys before colliding with Sundaland. Since these models were proposed, the whole of Sumatra has been mapped and units correlated with the Woyla Group have been recognised throughout western Sumatra. These units are reviewed and the validity of their correlation with the Woyla Group of northern Sumatra is assessed. From this review a revised synthesis for the Late Mesozoic tectonic evolution of the southwestern margin of Sundaland is proposed. 相似文献
4.
A. B. Kuzmichev M. K. Danukalova G. N. Aleksandrova V. A. Zakharov A. B. Herman B. L. Nikitenko V. B. Khubanov E. V. Korostylev 《Stratigraphy and Geological Correlation》2018,26(4):403-432
The model of geological structure of sedimentary cover of the Laptev Sea accepted by most geologists suggests that the lower seismic complex of the cover begins by the Aptian–Albian sedimentary rocks. They can be studied in natural outcrops of Kotelnyi Island. The section of the Tuor-Yuryakh Trough, which exposes the lower part of the Cretaceous complex, is described in the paper. It is composed of continental coaliferous rocks ~100 m thick. The marking beds divide it into five members, which are traced along the western wall of the trough at the distance up to 3 km. The spore–pollen complexes and plant megafossils indicate that almost the entire visible section of the mid-Cretaceous is Albian. Only its lower part no more than 14 m thick can probably belong to the Aptian. Marine facies with Albian foraminifers were found 15 m above the bottom of the Cretaceous complex. The section of the Cretaceous rocks is underlain by the Lower Jurassic marine clays and siltstones. The foraminifer assemblages of this part of the section are typical of the upper Sinemurian–Pliensbachian and fossil bivalves indicate late Sinemurian age of the host rocks. The hiatus ~70 Ma duration has no expression in the section and this boundary can de facto be substantiated only by microfossils. This vague contact between the Lower Jurassic and mid-Cretaceous rocks does not correspond to geophysical characteristics of the bottom of the lower seismic complex of the cover of the eastern part of the Laptev Sea. The latter is described as the most evident seismic horizon of the section of the cover, suggesting unconformable occurrence of the lower seismic complex on a peneplenized surface of lithified and dislocated rocks. This is mostly similar to the bottom of the Eocene sediments, which were observed on Belkovsky and Kotelnyi islands. The paper discusses possible application of our land results for interpretation of the shelf seismic sections of the Laptev Sea. It is concluded that local reasons are responsible for a vague boundary between the Lower Jurassic and mid-Cretaceous sequences in the section studied. Our observations support ideas on possible Aptian–Albian age of the rocks of the basement of the lower seismic complex; however, it is proposed to use also the previously popular idea on the Eocene age of the lower seismic complex of sedimentary cover of the eastern part of the Laptev Sea as one of the possible working scenarios. 相似文献
5.
Remnants of the Liguria-Piemont Ocean with its Jurassic ophiolitic basement are preserved in the South Pennine thrust nappes of eastern Switzerland. Analysis of South Pennine stratigraphy and comparison with sequences from the adjacent continental margin units suggest that South Pennine nappes are relics of a transform fault system. This interpretation is based on three arguments: (1) In the highly dismembered ophiolite suite preserved, Middle to Late Jurassic pelagic sediments are found in stratigraphic contact not only with pillow basalts but also with serpentinites indicating the occurrence of serpentinite protrusions along fracture zones. (2) Ophiolite breccias (»ophicalcites«) occurring along distinct zones within peridotite-serpentinite host rocks are comparable with breccias from present-day oceanic fracture zones. They originated from a combination of tectonic and sedimentary processes: i.e. the fragmentation of oceanic basement on the seafloor and the filling of a network of neptunian dikes by pelagic sediment with locally superimposed hydrothermal activity and gravitational collapse. (3) The overlying Middle to Late Jurassic radiolarian chert contains repeated intercalations of massflow conglomerates mainly comprising components of oceanic basement but clasts of acidic basement rocks and oolitic limestone also exist. This indicates a close proximity between continental and oceanic basement. The rugged morphology manifested in the mass-flow deposits intercalated with the radiolarites is draped by pelagic sediments of Early Cretaceous age. 相似文献
6.
徽成盆地是西秦岭造山带内一个具有代表性的盆地,保留较完整的地层记录.早白垩世田家坝组、周家湾组和鸡山组为一套砂砾岩沉积组合序列.本文通过对早白垩世砂岩的古水流恢复、砾石成分与含量、重矿物和地球化学分析,对沉积岩物源区特征和原型盆地进行探讨.古水流恢复和砾石成分统计表明,沉积物主要是近源堆积,主要来自于盆地南缘和北部.重矿物研究结果表明,早白垩世砂岩母岩以岩浆岩为主,并有少量变质岩/沉积岩.地球化学分析表明,早白垩世砂岩为成熟度较低的硬砂岩和长石/岩屑砂屑岩.稀土元素标准化配分曲线呈现轻稀土富集、重稀土平坦和弱Eu负异常特征.砂岩物源区组成判别图研究表明,早白垩世砂岩的物源区主要出露长英质火山岩.砂岩源区构造环境判别图解及特征指数分析表明,早白垩世砂岩源区主要形成于大陆岛弧和活动大陆边缘.结合区域资料和前人研究,表明早白垩世徽成地区发育走滑拉分盆地. 相似文献
7.
Transient mid-Cretaceous thermal uplift induced by lateral heating from passing oceanic lithosphere is often invoked as a mechanism for the formation of the Côte d'Ivoire–Ghana basement ridge in the Equatorial Atlantic. This heating event should have affected mid-Cretaceous sedimentary rocks along the ridge. However, organic maturity and clay mineral data on the thermal evolution of these rocks suggest that burial temperatures did not exceed 80 °C and that palaeo–geothermal gradients are not anomalous. Optical petrography and the stratigraphic pattern of temperature-sensitive parameters indicate that higher palaeotemperature estimates are related to admixtures of preheated, detrital organic and inorganic matter. Erosion brought the sediments to their present shallow burial depths. Lack of evidence for significant thermal alteration implies that either thermal exchange between oceanic and continental lithosphere along the Côte d'Ivoire–Ghana Transform Margin was negligible, or that lateral heating by oceanic lithosphere was not strong enough to affect the sedimentary cover of the basement ridge. 相似文献
8.
9.
《Geodinamica Acta》2003,16(1):21-38
The Tatric-Fatric-Veporic convergence zone of the Central Western Carpathians involved a basinal area that originated by Lower Jurassic rifting of Variscan continental crust. In mid-Cretaceous times shortening affected first the southern, Veporic margin of the basin, which was converted to the toe of the orogenic wedge prograding from the hinterland. A system of ductile basement/cover large-scale folds formed here by rotation of pre-existing, closely spaced, domino-type normal faults. However, the advancement of the wedge was likely accomplished by formation of a new thrust fault rooted in the ductile lower and/or middle crust. Afterwards, the basement of the lower plate Fatric basin was underthrust below the Veporic wedge; its sedimentary fill was detached and stacked to create the later Krížna decollement cover nappe. Underthrusting continued until the lower plate–Tatric margin collided with the orogenic wedge toe. Large basement slabs were peeled off this margin, shortened internally and thrust at moderate distances over the South Tatric ridge area. Pre-existing domino blocks were only slightly inverted here and passively transported above new thrust faults, which formed along weak crustal layers. It is inferred that the origin and geometry of large-scale, basement-involved structures generated in wide, intracontinental convergent zones is largely dependent on the lower versus upper plate position with distinctly different thermo-mechanical regimes operating during deformation. 相似文献
10.
This study investigates the isotopic composition (C, O, S and Sr) of carbonates, sulphates and sulphide cements in the rock
matrix and fracture fillings in geological formations of the Southeast basin of France, using core samples collected during
the Deep Geology of France programme (GPF Ardèche theme). The Southeast basin belongs to the Alpine Tethyan margin. It is
one of the thickest sedimentary basins in Europe, reaching upwards of 9 km in certain locations. The main fluid transfer from
the basin is related to the large Pb–Zn Mississippi Valley-type district along the southern margin of the Massif Central block.
A synthesis of the tectonic, mineralogical and petrographic investigations on the GPF boreholes shows that a major fluid circulation
event occurred across the Alpine margin of Tethys during the Early Jurassic (Hettangian–Bathonian). It produced a general
cementation of the rock porosity through precipitation of dolomite, sulphate and barite. Fracture fillings yield isotopic
signatures distinct from the matrix cements. Matrix cements have particular characteristics, i.e. δ34S and δ13C that agree with a marine origin. The δ34S values of Permo-Carboniferous to Triassic sulphides from fracture cements are interpreted as resulting from the thermo-chemical
reduction of sulphates. Fracture sulphates in the same geological formations yield δ34S values that define a relatively homogeneous end-member, whose composition is similar to sulphates in the Largentière Pb–Zn
ore deposit. The source of S is attributed to the Permo-Carboniferous succession. The borehole fracture fillings are attributed
to a major fluid circulation stage compatible with the Early Jurassic stage identified from the geological investigation of
the boreholes. The formation of the Largentière deposit is considered as resulting from the mixing of this Early Jurassic
fluid with continental hydrothermal fluids circulating in a basement horst, along its margin with the sedimentary basin. Other
Pb–Zn deposits may also be related to fluid migration along the basement/sedimentary cover interface in the eastern and western
parts of the Massif Central. This regional fluid circulation event may represent a geodynamic marker of the Jurassic extensional
phase. 相似文献
11.
Hayati KOÇ 《Arabian Journal of Geosciences》2017,10(22):499
The study area is located in the Central Taurides (southern Turkey), which is bounded by the K?rkkavak fault to the west and Ecemi? fault to the east. The sequences are studied in detail based on measured sections composed of the rocks deposited during the Cenomanian–Maastrichtian and located within different tectonic units previously described in the Taurides. The study materials include 217 thin section data from seven Cenomanian–Maastrichtian sequences of outcropping in different parts of the Central Taurides. The sediments deposited during the Cenomanian–Maastrichtian period in the Central Taurides are subdivided into eight units based on their lithological, paleontological, and textural properties. The lower boundaries of the upper Santonian and Campanian are unconformable contacts. The Upper Cretaceous sequence starts with the middle Cenomanian and represents a continuation of the Lower Cretaceous tidal flat and shelf lagoon sequence. Upper Turonian–Coniacian sediments are not observed due to the eustatic sea level drop. The second main transgression period of the Upper Cretaceous platform took place in the Santonian. This unit is represented by limestones composed of wackestones/packstones containing benthic foraminifera and rudist fragments, which are deposited in tidal flats and subtidal environments. The late Campanian starts with a transgression, and the environment transformed transitions into slope facies from inner platform facies, as a result of the thrust of ophiolitic rocks. In the following period, slope front and basin plain environments were dominant due to the increasing slope. Slumped pelagic limestones were deposited on the slope. Planktonic foraminiferal pelagic limestones were unconformably deposited on plaque limestone in the slope front environment depending on the increase in slope gradient and local faulting. As a result of decreasing tectonic activity, the sediments were deposited onto a stable basin plain. They were initially fed from the nearby carbonate platform and then by siliciclastic turbidites derived from the thrusted ophiolitic rocks. In this study, the lithostratigraphic properties of the Cenomanian–Maastrichtian units outcropping in various parts of the Central Taurides are described. The sedimentary deposits described here suggest different basinal conditions in the region. 相似文献
12.
D. Plašienka 《International Journal of Earth Sciences》1995,84(4):748-760
The Tatricum, an upper crustal thrust sheet of the Central Western Carpathians, comprises pre-Alpine crystalline basement and a Late Paleozoic-Mesozoic sedimentary cover. The sedimentary record indicates gradual subsidence during the Triassic, Early Jurassic initial rifting, a Jurassic-Early Cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods, and Middle Cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland. Passive rifting led to the separation of the Central Carpathian realm from the North European Platform. A passive margin, rimmed by peripheral half-graben, was formed along the northern Tatric edge, facing the Vahic (South Penninic) oceanic domain. The passive versus active margin inversion occurred during the Senonian, when the Vahic ocean began to be consumed southwards below the Tatricum. It is argued that passive to active margin conversion is an integral part of the general shortening polarity of the Western Carpathians during the Mesozoic that lacks features of an independent Wilson cycle. An attempt is presented to explain all the crustal deformation by one principal driving force - the south-eastward slab pull generated by the subduction of the Meliatic (Triassic-Jurassic Tethys) oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere. 相似文献
13.
The Northern, Central, and Southern zones are distinguished by stratigraphic, lithologic, and structural features. The Northern Zone is characterized by Upper Silurian–Lower Devonian sedimentary rocks, which are not known in other zones. They have been deformed into near-meridional folds, which formed under settings of near-latitudinal shortening during the Ellesmere phase of deformation. In the Central Zone, mafic and felsic volcanic rocks that had been earlier referred to Carboniferous are actually Neoproterozoic and probably Early Cambrian in age. Together with folded Devonian–Lower Carboniferous rocks, they make up basement of the Central Zone, which is overlain with a angular unconformity by slightly deformed Lower (?) and Middle Carboniferous–Permian rocks. The Southern Zone comprises the Neoproterozoic metamorphic basement and the Devonian–Triassic sedimentary cover. North-vergent fold–thrust structures were formed at the end of the Early Cretaceous during the Chukchi (Late Kimmerian) deformation phase. 相似文献
14.
15.
《Geodinamica Acta》2000,13(4):189-245
3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad subsiding area in an extensional framework, with a larger size than the present-day basin. During the Aalenian time, the subsidence pattern changes drastically (early stage of the central Atlantic opening). Further steps of the opening of the Ligurian Tethys (base Hettangian, late Pliensbachian;...) and its evolution into an oceanic domain (passive margin, Callovian) are equally recorded in the tectono-sedimentary history. The Lower Cretaceous was characterized by NE–SW compressive medium wavelength unconformities (late Cimmerian–Jurassic/Cretaceous boundary and intra-Berriasian and late Aptian unconformities) coeval with opening of the Bay of Biscay. These unconformities are contemporaneous with a major decrease of the subsidence rate. After an extensional period of subsidence (Albian to Turonian), NE–SW compression started in late Turonian time with major folding during the Late Cretaceous. The Tertiary was a period of very low subsidence in a compressional framework. The second folding stage occurred from the Lutetian to the Lower Oligocene (N–S compression) partly coeval with the E–W extension of the Oligocene rifts. Further compression occurred in the early Burdigalian and the Late Miocene in response to NE–SW shortening. Overall uplift occurred, with erosion, around the Lower/Middle Pleistocene boundary. 相似文献
16.
DANIELA FONTANA 《Sedimentology》1991,38(6):1085-1095
The Upper Cretaceous Pietraforte Formation, an allochthonous unit of the Ligurian domain in the northern Apennines, provides a case study of the importance of detrital carbonate grains for provenance determination in sandstones. The Pietraforte Formation is composed of turbidite sandstones with subordinate conglomerate, deposited in an external sector of the Ligurian ocean, close to the Adriatic margin. The sandstones have a lithic composition, characterized by abundant sedimentary and metasedimentary rock fragments (35–56% of the terrigenous framework), little feldspar (<7%) that is almost exclusively plagioclase, and a high ratio of fine- to coarse-grained polycrystalline quartzose grains to total quartzose grains (average Qp/Qt=0.37). Carbonate rock fragments dominate the lithic association of both sandstones and conglomerates and provide the most detailed information for provenance determination. They are composed primarily of dolostones and a wide variety of limestones containing identifiable age-diagnostic microfossils. Fossils and rock textures of carbonate clasts document the erosion of Upper Triassic to Lower Cretaceous shelf and pelagic carbonate units which can be matched with Mesozoic rock types present in the Tuscan domain of the northern Apennines. Compositional results constrain the source of the Pietraforte Formation sandstones to the western margin of the Adriatic plate, from uplifted sedimentary and metasedimentary rocks of the Tuscan domain and its low-grade metamorphic basement. Coeval intrabasinal sources provided additional supplies to the depositional basin of the Pietraforte Formation; this intrabasinal supply consists of shelf carbonate allochems, planktonic foraminifera and argillaceous rip-up clasts. The presence of carbonate grains from shallow-water environments may indicate the existence during deposition of marginal shelf areas favourable for carbonate allochem production. 相似文献
17.
Alvaro Nivia Giselle F. Marriner Andrew C. Kerr John Tarney 《Journal of South American Earth Sciences》2006,21(4):423
The Quebradagrande Complex of Western Colombia consists of volcanic and Albian–Aptian sedimentary rocks of oceanic affinity and outcrops in a highly deformed zone where spatial relationships are difficult to unravel. Berriasian–Aptian sediments that display continental to shallow marine sedimentary facies and mafic and ultramafic plutonic rocks are associated with the Quebradagrande Complex. Geochemically, the basalts and andesites of the Quebradagrande Complex mostly display calc-alkaline affinities, are enriched in large-ion lithophile elements relative to high field strength elements, and thus are typical of volcanic rocks generated in supra-subduction zone mantle wedges. The Quebradagrande Complex parallels the western margin of the Colombian Andes’ Central Cordillera, forming a narrow, discontinuous strip fault-bounded on both sides by metamorphic rocks. The age of the metamorphic rocks east of the Quebradagrande Complex is well established as Neoproterozoic. However, the age of the metamorphics to the west – the Arquía Complex – is poorly constrained; they may have formed during either the Neoproterozoic or Lower Cretaceous. A Neoproterozoic age for the Arquía Complex is favored by both its close proximity to sedimentary rocks mapped as Paleozoic and its intrusion by Triassic plutons. Thus, the Quebradagrande Complex could represent an intracratonic marginal basin produced by spreading-subsidence, where the progressive thinning of the lithosphere generated gradually deeper sedimentary environments, eventually resulting in the generation of oceanic crust. This phenomenon was common in the Peruvian and Chilean Andes during the Uppermost Jurassic and Lower Cretaceous. The marginal basin was trapped during the collision of the Caribbean–Colombian Cretaceous oceanic plateau, which accreted west of the Arquía Complex in the Early Eocene. Differences in the geochemical characteristics of basalts of the oceanic plateau and those of the Quebradagrande Complex indicate these units were generated in very different tectonic settings. 相似文献
18.
Through, long-lived structural-kinematic parageneses were established in the southeastern marginal part of the Baltic Shield on the basis of structural studies. These parageneses were formed and periodically rejuvenated from at least the Paleoproterozoic until the neotectonic stage of the evolution of this territory. A series of consecutive tectonic events related to the vertical and horizontal mobility of rocks of the crystalline basement and sedimentary cover had important implications for the formation of present-day structure of the southeastern margin of the Baltic Shield. These tectonic displacements developed for an extremely long time with retention of the main kinematic tendencies. At the end of the Paleoproterozoic, the volcanic and sedimentary rocks of the Vetreny Belt underwent tectonic stacking as a result of the countermotion of the crystalline masses of the Vodlozero Massif and the Belomorian-Lapland Belt. The clockwise rotation and lateral displacement of the Vodlozero Massif to the northeast provided the left-lateral transpression of the Vetreny Belt. Under these conditions, the Paleoproterozoic sequences experienced squeezing in the southeastern direction. This kinematic tendency was retained at the subsequent evolutional stages and eventually was recorded in the structure of the present-day boundary between the Baltic Shield and the Russian Platform. 相似文献
19.
Alastair Robertson Osman Parlak Timur Ustaömer Kemal Taslı Nurdan İnan Paulian Dumitrica 《Geodinamica Acta》2013,26(3-4):230-293
This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone.The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the ?zmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust.Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust.Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin.Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-of-sequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale.Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45?Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault.In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin. 相似文献
20.
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