Chapter 21 Middle thrust sheets in the Caledonide orogen, Sweden: the outer margin of Baltica, the continent–ocean transition zone and late Cambrian–Ordovician subduction–accretion

2020 ◽  
Vol 50 (1) ◽  
pp. 517-548 ◽  
Author(s):  
David G. Gee ◽  
Iwona Klonowska ◽  
Per-Gunnar Andréasson ◽  
Michael B. Stephens
Keyword(s):  
Transition Zone ◽  
Foreland Basin ◽  
Ultrahigh Pressure ◽  
Dyke Swarm ◽  
Metasedimentary Rocks ◽  
Late Cambrian ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Augen Gneiss ◽  
Ocean Ridge

AbstractNappes of continental outer and outermost margin affinities (Middle Allochthon) were transported from locations west of the present Norwegian coast and thrust eastwards onto the Baltoscandian foreland basin and platform. They are of higher metamorphic grade than underlying thrust sheets and most are more penetratively deformed. These allochthons are treated here in three groups. The lower thrust sheets comprise Paleoproterozoic crystalline basement (e.g. Tännäs Augen Gneiss Nappe) and greenschist facies, Neoproterozoic, siliciclastic metasedimentary rocks (e.g. Offerdal Nappe). These are overthrust by a Cryogenian−Ediacaran succession intruded by c. 600 Ma dolerites (Baltoscandian Dyke Swarm) with an affinity to mid-ocean ridge basalt containing normal to enriched incompatible element contents (Särv Nappes). The upper sheets are dominated by higher-grade allochthons (Seve Nappe Complex) with similar, mainly siliciclastic sedimentary protoliths, more mafic magmatism and some solitary ultramafic bodies. Within this early Ediacaran continent−ocean transition zone (COT) assemblage, generally metamorphosed in amphibolite facies, some nappes experienced migmatization, and eclogites are present. Evidence of ultrahigh-pressure metamorphism has been obtained from garnet peridotites and eclogites; recently, microdiamonds have been discovered in paragneisses. Subduction of the COT started by the late Cambrian and accretion continued through the Ordovician, prior to the Baltica–Laurentia collision. Thrusting of all these Middle allochthons onto the foreland basin exceeds a distance of 400 km.

Chapter 19 Regional context and tectonostratigraphic framework of the early–middle Paleozoic Caledonide orogen, northwestern Sweden

2020 ◽  
Vol 50 (1) ◽  
pp. 481-494 ◽  
Author(s):  
David G. Gee ◽  
Michael B. Stephens
Keyword(s):  
Foreland Basin ◽  
Metasedimentary Rocks ◽  
Mafic Intrusions ◽  
Late Cambrian ◽  
Iapetus Ocean ◽  
Nappe Complex ◽  
Middle Paleozoic ◽  
Thrust Sheets ◽  
Seve Nappe Complex ◽  
Augen Gneiss

AbstractThe Scandian mountains in northwestern Sweden are dominated by the eastern part of the Scandinavian Caledonides, an orogen that terminated during the middle Paleozoic with Himalayan-style collision of the ancient continents of Baltica and Laurentia. In this foreland region, far-transported higher allochthons from an exotic continental margin (Rödingsfjället Nappe Complex) and underlying mostly oceanic-arc basin character (Köli Nappe Complex) were emplaced at least 700 km onto the Baltoscandian margin of Baltica. The thrust sheets below the Iapetus Ocean terranes were derived from the transition zone to Baltica (Seve Nappe Complex), comprising mainly siliciclastic metasedimentary rocks, hosting abundant metamorphosed c. 600 Ma mafic intrusions. They preserve evidence of subduction (eclogites, garnet peridotites and microdiamonds in host paragneisses), starting in the late Cambrian; exhumation continued through the Ordovician. Underlying allochthons derived from the outer margin of Baltica are less-metamorphosed Neoproterozoic sandstone-dominated successions, also intruded by Ediacaran dolerite dykes (Särv Nappes); they are located tectonically above similar-aged metasandstone and basement slices, devoid of dykes (Offerdal and Tännäs Augen Gneiss nappes and equivalents). Lowermost allochthons (Jämtlandian Nappes and equivalents), from the inner Baltoscandian margin, provide evidence of Cryogenian rifting, Ediacaran–Cambrian drifting and platformal sedimentation, followed by foreland basin development in the Ordovician and Silurian.

Origin of the Indus ophiolite linked to the mantle transition zone (410–660 km)

2021 ◽  
Author(s):  
Souvik Das ◽  
Asish R. Basu
Keyword(s):  
Transition Zone ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Ultrahigh Pressure ◽  
Historical Contingency ◽  
Mantle Transition Zone ◽  
Contingency Model ◽  
Mid Ocean Ridge ◽  
Consistent Change ◽  
Ocean Ridge

ABSTRACT The southeast Ladakh (India) area displays one of the best-preserved ophiolite sections in this planet, in places up to 10 km thick, along the southern bank of the Indus River. Recently, in situ, ultrahigh-pressure (UHP) mineralogical evidence from the mantle transition zone (MTZ; ∼410–660 km) with diamond and reduced fluids were discovered from two peridotite bodies in the basal mantle part of this Indus ophiolite. Ultrahigh-pressure phases were also found by early workers from podiform chromitites of another coeval Neo-Tethyan ophiolite in southern Tibet. However, the MTZ phases in the Indus ophiolite are found in silicate peridotites, but not in metallic chromitites, and the peridotitic UHP phases show systematic and contiguous phase transitions from the MTZ to shallower depth, unlike the discrete UHP inclusions, all in Tibetan chromitites. We observe consistent change in oxygen fugacity (fO2) and fluid composition from (C-H + H2) to (CO2 + H2O) in the upwelling peridotitic mantle, causing melting to produce mid-ocean-ridge basalt (MORB). At shallow depths (<100 km) the free water stabilizes into hydrous phases, such as pargasitic amphibole, capable of storing water and preventing melting. Our discoveries provide unique insights into deep sub-oceanic-mantle processes, and link deep-mantle upwelling and MORB genesis. Moreover, the tectonic setting of Neo-Tethyan ophiolites has been a difficult problem since the birth of the plate-tectonics concept. This problem for the origin of ophiolites in mid-ocean-ridge versus supra-subduction zone settings clearly confused the findings from Indus ophiolites. However, in this contribution, we provide arguments in favor of mid-ocean-ridge origin for Indus ophiolite. In addition, we venture to revisit the “historical contingency” model of E.M. Moores and others for Neo-Tethyan ophiolite genesis based on the available evidence and have found that our new results strongly support the “historical contingency” model.

Thermal history of thrust sheets in an orogenic wedge: 40Ar/39Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

2000 ◽  
Vol 137 (4) ◽  
pp. 437-446 ◽  
Author(s):  
OLAF M. SVENNINGSEN
Keyword(s):  
Shear Zones ◽  
Passive Margin ◽  
Fault System ◽  
Dyke Swarm ◽  
Slow Cooling ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Seve Nappe Complex ◽  
The Baltic ◽  
The Individual

The Seve Nappe Complex in the Scandinavian Caledonides contains the fragmented late Precambrian continent–ocean transition between Baltica and the Iapetus Ocean. This passive margin was fragmented and thrust eastwards over the Baltic Shield during Caledonian orogenesis. The individual thrust sheets in the Seve Nappe Complex went through different P–T–t evolutions, resulting in dramatic metamorphic contrasts: eclogite-bearing nappes are juxtaposed with nappes showing no evidence of Caledonian deformation or metamorphism in their interiors. Strain localization to the marginal parts of the thrust sheets left records of both pre-orogenic (rift) and early orogenic (subduction and subsequent uplift) processes in the thrust sheets of the Seve Nappe Complex. Even though it has been transported several hundred kilometres, only the margins of the eastern part of the Sarektjåkkå Nappe are affected by penetrative Caledonian deformation. This part of the Sarektjåkkå Nappe is dominated by pristine tholeiitic dykes and cross-bedded sandstones. The dykes are 608±1 Ma old and make up 70–80% of the nappe. Widely spaced thin shear zones of the Ruopsok fault system represent the only Caledonian penetrative deformation in the interior of the nappe. Previously published Ar–Ar dates indicate cooling below the closure temperature of hornblende at c. 470 Ma, but numerous ages have been recorded. Ar dating of biotite and muscovite from a cross-laminated metapsammite in the Sarektjåkkå Nappe gave well-defined ages of 428.5±3.6 and 432.4±3.8 Ma, respectively. Muscovite from a shear zone in the Ruopsok Fault System gave 428.2±4.0 Ma, whereas hornblende from the same locality did not yield interpretable data. The results indicate that these rocks were completely degassed at some unknown time, presumably at the emplacement of the dyke swarm. No subsequent excess argon contamination can be detected. A likely candidate for the degassing event is the emplacement of the dykes at 608 Ma. The interior of the nappe, and thus the entire nappe complex, cooled below ∼ 350 °C at around 430 Ma. Cooling from more than 500 °C at c. 470 Ma to 350 °C at c. 430 Ma suggests an average cooling rate of [les ] 4 °C/Ma. A prolonged period of slow cooling (≈exhumation?) following the initial, rapid uplift of the eclogite-bearing nappes and Early Ordovician construction of the Seve Nappe Complex is suggested.

scholarly journals ARCABOUÇO TECTÔNICO E ESTRATIGRÁFICO DA FAIXA RIACHO DO PONTAL, DIVISA PERNAMBUCO-PIAUI-BAHIA

2013 ◽  
Author(s):  
Fabrício de Andrade Caxito ◽  
Alexandre Uhlein
Keyword(s):  
Plate Tectonics ◽  
Central Zone ◽  
Fold Belt ◽  
Northern Margin ◽  
External Zone ◽  
Metasedimentary Rocks ◽  
Late Neoproterozoic ◽  
Brasiliano Orogeny ◽  
Augen Gneiss ◽  
Ocean Ridge

A faixa brasiliana Riacho do Pontal bordeja a margem norte do Cráton do São Francisco e pode ser subdividida em três domíniosou zonas tectônicas de características geológicas contrastantes, de norte para sul: zonas Interna, Central, e Externa. A Zona Interna édominada por rochas metavulcanosedimentares intrudidas por rochas plutônicas relacionadas à Orogênese Cariris Velhos (augen-gnaissesda Suíte Afeição, ~1.0-0.9 Ga). A Zona Central é caracterizada pelo Complexo Monte Orebe, composto por metabasaltos de geoquímicasimilar aos basaltos de cadeia oceânica e rochas metassedimentares de ambiente marinho profundo. A Zona Externa é caracterizada pelosistema de nappes Casa Nova, composto por duas unidades: A Formação Barra Bonita na base, que representa uma sequência plataformaldesenvolvida na borda norte do paleocontinente São Francisco; e a Formação Mandacaru no topo, que representa uma sequência marinhaprofunda turbidítica, provavelmente sin-orogênica. Essas rochas foram afetadas por deformação compressiva (D1-D2-D3) com odesenvolvimento do sistema de nappes vergentes para sul, durante o Neoproterozoico (~630-575 Ma), seguida por deformaçãotranscorrente (D4) nos estágios tardios da Orogênese Brasiliana. Toda a faixa é intrudida por múltiplas gerações de plútons graníticos esieníticos sin a pós-colisionais, de idade neoproterozóica a cambriana (~630-530 Ma). A Faixa Riacho do Pontal representa um ciclo deplacas tectônicas completo no Neoproterozoico tardio, envolvendo a colisão do cráton do São Francisco a sul com os blocos litosféricos daProvíncia Borborema a norte.Palavras chave: Orogênese Brasiliana, Faixa Riacho do Pontal, Cráton do São Francisco ABSTRACTTECTONIC AND STRATIGRAPHIC FRAMEWORK OF THE RIACHO DO PONTAL FOLD BELT, PERNAMBUCO-PIAUI-BAHIA BORDER.The Riacho do Pontal Fold Belt borders the northern margin of the São Francisco Craton and can be subdivided into three tectonic domainsor zones of distinct geology, from north to south: the Internal, Central, and External zones. The Internal Zone is composed bymetavulcanosedimentary rocks intruded by plutonic rocks related to the Cariris Velhos Orogeny (Afeição Suite augen-gneiss, ~1.0-0.9 Ga);rocks of this age are absent in the other zones. The Central Zone is characterized by the Monte Orebe Complex, composed by metabasaltswhose geochemistry is similar to mid-ocean ridge basalts and deep marine metasedimentary rocks. The External Zone is characterized bythe Casa Nova nappe system, composed by two units: (a) the Barra Bonita Formation at the base, representing a platformal sequencedeveloped at the northern São Francisco Craton margin; and (b) the Mandacaru Formation at the top, which represents a syn-orogenicdeep marine unit. These rocks were affected by compressive deformation (D1-D2-D3) with the development of a south-verging nappesystem, during the Neoproterozoic (~630-575 Ma), followed by strike-slip deformation (D4) at the late stages of the Brasiliano Orogeny.The whole fold belt is intruded by multiple generations of syn- to post-collisional granitic and syenitic plutons, of Neoproterozoic toCambrian age (~630-530 Ma). The Riacho do Pontal Fold Belt represents a complete plate tectonics cycle at the late Neoproterozoic,involving the collision of the São Francisco Craton to the South with the crustal blocks of the Borborema Province towards North.Keywords: Brasiliano Orogeny, Riacho do Pontal Fold Belt, São Francisco Craton

scholarly journals Revised Timing of Cenozoic Atlantic Incursions and Changing Hinterland Sediment Sources during Southern Patagonian Orogenesis

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Julie C. Fosdick ◽  
R. A. VanderLeest ◽  
J. E. Bostelmann ◽  
J. S. Leonard ◽  
R. Ugalde ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Atlantic Coast ◽  
Foreland Basin ◽  
Late Eocene ◽  
Coarse Grained ◽  
Plate Convergence ◽  
Metasedimentary Rocks ◽  
Sediment Routing ◽  
Thrust Sheets ◽  
Major Shift

Abstract New detrital zircon U-Pb geochronology data from the Cenozoic Magallanes-Austral Basin in Argentina and Chile ~51° S establish a revised chronostratigraphy of Paleocene-Miocene foreland synorogenic strata and document the rise and subsequent isolation of hinterland sources in the Patagonian Andes from the continental margin. The upsection loss of zircons derived from the hinterland Paleozoic and Late Jurassic sources between ca. 60 and 44 Ma documents a major shift in sediment routing due to Paleogene orogenesis in the greater Patagonian-Fuegian Andes. Changes in the proportion of grains from hinterland thrust sheets, comprised of Jurassic volcanics and Paleozoic metasedimentary rocks, provide a trackable signal of long-term shifts in orogenic drainage divide and topographic isolation due to widening of the retroarc fold-thrust belt. The youngest detrital zircon U-Pb ages confirm timing of Maastrichtian-Eocene strata but require substantial age revisions for part of the overlying Cenozoic basinfill during the late Eocene and Oligocene. The upper Río Turbio Formation, previously mapped as middle to late Eocene in the published literature, records a newly recognized latest Eocene-Oligocene (37-27 Ma) marine incursion along the basin margin. We suggest that these deposits could be genetically linked to the distally placed units along the Atlantic coast, including the El Huemul Formation and the younger San Julián Formation, via an eastward deepening within the foreland basin system that culminated in a basin-wide Oligocene marine incursion in the Southern Andes. The overlying Río Guillermo Formation records onset of tectonically generated coarse-grained detritus ca. 24.3 Ma and a transition to the first fully nonmarine conditions on the proximal Patagonian platform since Late Cretaceous time, perhaps signaling a Cordilleran-scale upper plate response to increased plate convergence and tectonic plate reorganization.

Chapter 23 Swedish Caledonides: key components of an early–middle Paleozoic Himalaya-type collisional orogen

2020 ◽  
Vol 50 (1) ◽  
pp. 577-599 ◽  
Author(s):  
David G. Gee
Keyword(s):  
North Atlantic Ocean ◽  
Mafic Magma ◽  
Ultrahigh Pressure ◽  
Uhp Metamorphism ◽  
Foreland Basins ◽  
The North ◽  
Late Cambrian ◽  
Orogenic Wedge ◽  
Middle Paleozoic ◽  
Thrust Sheets

AbstractCaledonian collision of continents Laurentia and Baltica, with at least 1000 km of lateral shortening, dominates the bedrock along the northern margins of the North Atlantic Ocean. Scandian (Silurian–Devonian) underthrusting of Laurentia by Baltica resulted in stacking of the main orogenic wedge and its migration onto the platform edge of Baltica. Complementary thrust sheets, exposed in northeastern Greenland, telescoped the Laurentian continental margin. The Swedish part of the Caledonides, comprising the foreland segment along the central half of this mountain belt, includes the key components of: (1) the Baltoscandian inner margin, including Ordovician and Silurian foreland basins; (2) the Neoproterozoic extended outer margin dominated by mafic magma and continent–ocean transition zone; (3) Iapetus oceanic terranes; and (4) evidence that substantial parts of the outermmost Baltoscandian margin experienced deep subduction and high- and ultrahigh-pressure (HP/UHP) metamorphism during late Cambrian–Ordovician accretion. This evidence, integrated with the Norwegian Caledonides, defines an orogenic pro-wedge comparable to that in the Himalaya today. Orthogonal Scandian collision, lasting for about 60 million years (c. 440–380 Ma), involved late Silurian–Early Devonian HP/UHP metamorphism of the underthrusting Baltoscandian basement. By the Middle Devonian, the hinterland was experiencing orogen-parallel folding and axial extension, accompanying exhumation, while the orogenic pro-wedge continued to migrate eastwards on to the platform.

Chapter 22 Upper and uppermost thrust sheets in the Caledonide orogen, Sweden: outboard oceanic and exotic continental terranes

2020 ◽  
Vol 50 (1) ◽  
pp. 549-575 ◽  
Author(s):  
Michael B. Stephens
Keyword(s):  
Continental Margin ◽  
Amphibolite Facies ◽  
Magmatic Activity ◽  
Volcanic Arcs ◽  
Late Cambrian ◽  
Marine Sedimentation ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Tectonothermal Event ◽  
Gabbroic Pluton

AbstractThree separate stacks of thrust sheets (Köli Nappe Complex) constitute the Upper Allochthon in the Caledonide orogen, Sweden. This thrust complex is dominated by late Cambrian–Ordovician successions deposited in subduction-related, marginal oceanic basins. Magmatic activity at c. 488 Ma (Lower Köli) and c. 492–476 Ma (Middle Köli) is linked to rifted volcanic arcs and Zn–Cu–Fe–(Pb–Au–Ag) sulphide mineralization; serpentinite bodies with talc deposits are also conspicuous. Renewed magmatic activity, both plutonic (Upper and Middle Köli) and mafic volcanic (Middle and Lower Köli), occurred at c. 440–434 Ma during crustal extension. Late Ordovician shallow-marine sedimentation, deepening upwards into an early Silurian succession also prevailed (Lower Köli). Silurian (c. 430 Ma and later) folding, eastwards-vergent thrusting and greenschist or lower amphibolite facies metamorphism preceded upright, orogen-parallel and orogen-transverse open folding. Juxtaposition of an arc-related terrane to an ancient continental margin, comprising slices of gneiss and marble, in the Middle Köli occurred prior to c. 437 Ma and the eastwards-vergent thrusting; remnants of an Ordovician amphibolite facies tectonothermal event are also preserved in the Upper Köli. The tectonic roof to the Köli complex contains amphibolite facies mica schist, gneiss and marble, derived from the Laurentian continental margin, and a major gabbroic pluton (Rödingsfjället Nappe Complex, Uppermost Allochthon).

Chapter 20 Lower thrust sheets in the Caledonide orogen, Sweden: Cryogenian–Silurian sedimentary successions and underlying, imbricated, crystalline basement

2020 ◽  
Vol 50 (1) ◽  
pp. 495-515 ◽  
Author(s):  
David G. Gee ◽  
Michael B. Stephens
Keyword(s):  
Foreland Basin ◽  
Late Ordovician ◽  
Crystalline Basement ◽  
Ultrahigh Pressure ◽  
Foreland Basins ◽  
Orogenic Wedge ◽  
Thrust Sheets ◽  
Rifted Margin ◽  
Early Late

AbstractThe Jämtlandian Nappes and their equivalents further north, belonging to the lower thrust sheets in the Caledonide orogen of Sweden, comprise a mega-duplex of Cryogenian–Silurian sedimentary rocks sandwiched between structurally higher allochthons and a basal décollement. Further west towards the hinterland, crystalline basement is increasingly involved in this thrusting, imbricate stacking occurring beneath the décollement in antiformal windows. The sedimentary successions were derived from the Cryogenian rifted margin of Baltica, the Ediacaran–Cambrian drifted margin, and Ordovician and Silurian foreland basins. During the Early–Late Ordovician (Floian–Sandbian), hinterland-derived turbidites were deposited in response to early Caledonian accretion of subducted complexes belonging to the outermost margin of Baltica, now preserved in the higher allochthons. Following a quiescent period during the Late Ordovician (Hirnantian) and early part of the Llandovery, collision of Laurentia and Baltica reactivated the foreland basins, with flysch and molasse deposition during the Llandovery–Wenlock. Collisional shortening during this Scandian orogenic episode continued into the Devonian. High- and ultrahigh-pressure (HP/UHP) metamorphism accompanied Baltica's underthrusting of Laurentia in the deep hinterland, and prominent basement-cored antiforms developed towards the foreland during the advance of the orogenic wedge over the foreland basin onto the Baltoscandian platform.

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