scholarly journals A tectonic carpet of Variscan flysch at the base of a rootless accretionary prism in northwestern Iberia: U–Pb zircon age constrains from sediments and volcanic olistoliths

Solid Earth ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 835-867
Author(s):  
Emilio González Clavijo ◽  
Ícaro Dias da Silva ◽  
José R. Martínez Catalán ◽  
Juan Gómez Barreiro ◽  
Gabriel Gutiérrez-Alonso ◽  
...  
Keyword(s):  
Regional Scale ◽  
Source Area ◽  
Accretionary Prism ◽  
Upper Ordovician ◽  
Stratigraphic Sequence ◽  
Zircon Age ◽  
Provenance Areas ◽  
Thrust Sheets ◽  
Age Patterns ◽  
Tectonic Boundary

Abstract. The allochthonous complexes of Galicia–Trás-os-Montes Zone (NW Iberia) are part of a rootless tectonic stack which preserves part of a Variscan accretionary prism. They are formed by individual tectonic slices marked by specific tectonometamorphic evolutions, which were piled up in a piggy-back mode onto its relative autochthon, the Central Iberian Zone (CIZ). Allochthony decreases from the structurally upper thrust sheets towards the lower ones. The lowermost unit of the stack is known as the Parautochthon or Schistose Domain. It is characterized by a low metamorphic grade in contrast with higher temperatures and/or pressures estimated for the overlying allochthonous units and shares the stratigraphic sequence with the underlying autochthon. The Parautochthon is divided in two structural and stratigraphic sub-units: (i) the Lower Parautochthon (LPa) is made of synorogenic flysch-type sediments with varied turbiditic units and olistostrome bodies, showing Upper Devonian–lower Carboniferous age according to the youngest zircon populations and fossiliferous content; (ii) the Upper Parautochthon (UPa) is composed of highly deformed preorogenic upper Cambrian–Silurian volcano-sedimentary sequence comparable with the nearby autochthon and to some extent, also with the high-P and low-T Lower Allochthon laying structurally above. The UPa was emplaced onto the LPa along the Main-Trás-os-Montes Thrust, and the LPa became detached from the CIZ relative autochthon by a regional-scale structure, the Basal Lower Parautochthon Detachment, which follows a weak horizon of Silurian carbonaceous slates. A review on the detrital zircon studies on the synorogenic LPa complemented by zircon dating of 17 new samples is presented here. The results support the extension of the LPa underneath the NW Iberian allochthonous complexes, from Cabo Ortegal, to Bragança and Morais massifs. Its current exposure follows the lowermost tectonic boundary between the Galicia–Trás-os-Montes (allochthon) and Central Iberian (autochthon) zones. The youngest zircon age populations point to a maximum sedimentation age for the LPa formations ranging from Famennian to Serpukhovian and supports the piggy-back mode of emplacement of the Galicia–Trás-os-Montes Zone, of which it represents the latest imbricate. The zircon age populations in the LPa allow the sedimentary provenance areas to be constrained, showing the intervention of nearby sources (mostly the UPa) and/or multiply recycled and long-transport sediments with a typically north-central Gondwana age fingerprint, also found in the Lower Allochthon, UPa and Autochthon. Complementary geochronology of volcanic olistoliths trapped in the LPa sediments and of late Cambrian to Upper Ordovician rhyolites from the UPa is also presented. It shows a direct relationship between the major blocks source area (UPa) and the setting place (LPa). Old zircon age patterns show that the LPa sedimentary rocks were recycled from detrital rocks of the allochthon (advancing wedge) and the nearby autochthon (peripheral bulge).

scholarly journals A tectonic carpet of Variscan flysch at the base of an unrooted accretion prism in NW Iberia: U-Pb zircon age constrains from sediments and volcanic olistoliths

2020 ◽  
Author(s):  
Emilio González Clavijo ◽  
Ícaro Dias da Silva ◽  
José R. Martínez Catalán ◽  
Juan Gómez Barreiro ◽  
Gabriel Gutíerrez Alonso ◽  
...  
Keyword(s):  
General Structure ◽  
Source Area ◽  
Accretionary Prism ◽  
Upper Ordovician ◽  
Stratigraphic Sequence ◽  
Zircon Age ◽  
Upper Cambrian ◽  
Provenance Areas ◽  
Nw Iberia ◽  
Thrust Sheets

Abstract. The allochthonous complexes of Galicia – Trás-os-Montes Zone (NW Iberia) are part of the tectonic stack that unrooted the Variscan accretionary prism. They are formed by individual tectonic slices marked by specific tectono-metamorphic evolution, which was piled up in a piggy-back thrust complex onto its relative autochthon, the Central Iberian Zone (CIZ). Consequently, allochthony decreases towards lower, more external and younger thrust sheets. The lowermost unit of this pile of slivers is known as Schistose Domain or Parautochthon and bears low metamorphic grade, contrasting with the higher temperatures and pressures estimated for the upper allochthonous units, but sharing the stratigraphic sequence with the underlying autochthon. The Parautochthon is divided in two structural and stratigraphic sub-units: (i) the Lower (LPa) made of synorogenic flysch-type sediments with varied turbiditic units and olistostrome bodies, showing Upper Devonian-lower Carboniferous age on base of the youngest zircon populations and fossiliferous content; (ii) the Upper (UPa), composed of highly deformed pre-orogenic upper Cambrian-Silurian volcano-sedimentary sequence comparable with both the nearby autochthon and the HP-LT Lower Allochthon, laying structurally above. The UPa thrusted onto the LPa by the the Main-Trás-os-Montes Thrust; and the LPa detached from the CIZ relative autochthon by a regional structure (Basal Lower Parautochthon Detachment) which follows the favourable Silurian carbonaceous beds. A review on the detrital zircon studies of the synorogenic LPa complemented by 17 new samples geochronology is here presented. The results support the extension of the LPa underneath the NW Iberia allochthonous complexes, from Cabo Ortegal, to Bragança and Morais Massifs. Its current exposure follows the lowermost tectonic boundary between the Galicia – Trás-os-Montes (allochthon) and Central Iberian (autochthon) Zones. Youngest zircon age populations point to a maximum sedimentation age for the LPa formations ranging from Famennian to Serpukhovian and endorse the piggy-back evolution inside this unit, mimicking the general structure of the Galicia – Trás-os-Montes Zone. The zircon populations in the LPa allow constraining the sedimentary provenance areas, showing the intervention of nearby sources (mostly the UPa) and/or multiply recycled/long transport sediments with typically N-Central Gondwana age fingerprint, also found in the Lower Allochthon, UPa and Autochthon. Complementary geochronology of volcanic olistoliths trapped in the LPa sediments and of upper Cambrian to Upper Ordovician rhyolites from the UPa is also presented, showing a direct relation between the major block's source area (UPa) and the setting place (LPa). Old zircon age patterns show that the LPa sedimentary rocks were recycled from detrital rocks of the allochthon (advancing wedge) and the nearby autochthon (peripheral bulge).

scholarly journals Provenance connections between late Neoproterozoic and early Palaeozoic sedimentary basins of the Ross Sea region, Antarctica, south-east Australia and southern Zealandia

2013 ◽  
Vol 26 (2) ◽  
pp. 173-182 ◽  
Author(s):  
C.J. Adams ◽  
J.D. Bradshaw ◽  
T.R. Ireland
Keyword(s):  
Detrital Zircon ◽  
Ross Sea ◽  
Regional Scale ◽  
Sedimentary Basins ◽  
Zircon Age ◽  
Gondwana Margin ◽  
Age Patterns ◽  
Transantarctic Mountains ◽  
Late Neoproterozoic ◽  
Early Palaeozoic

AbstractThick successions of turbidites are widespread in the Ross–Delamerian and Lachlan orogens and are now dispersed through Australia, Antarctica and New Zealand. U-Pb detrital zircon age patterns for latest Precambrian, Cambrian and Ordovician metagreywackes show a closely related provenance. The latest Neoproterozoic–early Palaeozoic sedimentary rocks have major components, at c. 525, 550, and 595 Ma, i.e. about 40–80 million years older than deposition. Zircons in these components increase from the Neoproterozoic to Ordovician. Late Mesoproterozoic age components, 1030 and 1070 Ma, probably originate from igneous/metamorphic rocks in the Gondwanaland hinterland whose exact locations are unknown. Although small, the youngest zircon age components are coincident with estimated depositional ages suggesting that they reflect contemporaneous and minor, volcanic sources. Overall, the detrital zircon provenance patterns reflect the development of plutonic/metamorphic complexes of the Ross–Delamerian Orogen in the Transantarctic Mountains and southern Australia that, upon exhumation, supplied sediment to regional scale basin(s) at the Gondwana margin. Tasmanian detrital zircon age patterns differ from those seen in intra-Ross Orogen sandstones of northern Victoria Land and from the oldest metasediments in the Transantarctic Mountains. A comparison with rocks from the latter supports an allochthonous western Tasmania model and amalgamation with Australia in late Cambrian time.

Eclogite from central Yukon: a record of subduction at the western margin of ancient North America

1983 ◽  
Vol 20 (9) ◽  
pp. 1389-1408 ◽  
Author(s):  
Philippe Erdmer ◽  
Herwart Helmstaedt
Keyword(s):  
North America ◽  
North American ◽  
Stability Field ◽  
Western Margin ◽  
Thrust Sheets ◽  
The Stability ◽  
Basic Igneous Rock ◽  
Inclusion Trails ◽  
Tectonic Boundary ◽  
Host Rocks

Eclogite occurring in central Yukon, at Faro and near Last Peak, as lenses interleaved with muscovite–quartz blastomylonite has the chemical and field characteristics of group C rocks. From sigmoidal inclusion trails in garnet, from geothermometry and geobarometry, and from mineral parageneses, the eclogite is inferred to have a crustal protolith and to have followed a hysteretic, subduction-cycle P–T trajectory. Transformation of basic igneous rock into schist was followed by eclogite metamorphism during which pressure was at least 1000 MPa and temperature was between 600 and 700 °C. Uplifting involved passage through the stability field of glaucophane; the eclogite and its host rocks were then subjected to greenschist fades metamorphism and deformation, with temperature at approximately 400 °C. The rocks were emplaced as thrust sheets against or onto the western North American cratonal margin. The tectonic boundary ranges from nearly vertical, where it is outlined by a zone of steeply dipping mélange, to nearly horizontal beneath klippen of cataclastic rocks that lie on North American miogeoclinal strata. Together with occurrences of eclogite on strike, in Yukon, near Fairbanks (Alaska), and near Pinchi Lake (British Columbia), eclogite at Faro and near Last Peak implies that the Yukon Cataclastic Complex is a deeply eroded collision mélange that borders over 1000 km of the ancient continental margin.

scholarly journals Archaeopetrological approximation to the lithic procurement of the neolithic axes and adzes from Can Sadurní’s cave (Begues, NE Iberian Peninsula)

2016 ◽  
Vol 3 (2) ◽  
Author(s):  
Mar Rey-Solé ◽  
Gemma Alías ◽  
Mireia Ache ◽  
Elicinia Fierro ◽  
Manel Edo ◽  
...  
Keyword(s):  
Iberian Peninsula ◽  
Raw Materials ◽  
Source Area ◽  
Archaeological Site ◽  
Igneous Rocks ◽  
Contact Aureole ◽  
Stratigraphic Sequence ◽  
Materials Used ◽  
Granodiorite Porphyry ◽  
Ne Iberian Peninsula

Can Sadurní’s cave, located in Begues (NE Iberian Peninsula), in the Baix Llobregat region, is an archaeological site with a wide stratigraphic sequence covering from the Epipaleolithic hunter-gatherers societies at the beginning of the Holocene to Roman times. During the excavations of the last years a large number of different raw materials used for the manufacture of axes have been recovered.The present study is focused on the Neolithic sequence. 31 axes and adzes have been characterised petrographically with the aid of a binocular microscope and transmission microscope. A great variety of rocks constitute the raw materials of these stone tools, ranging from contact and regional metamorphic rocks to plutonic and porphyric igneous rocks. The formers are the most abundant (up to 78%) and include hornfels, spotted phyllites, marbles, quartzites, slates and phyllites. The igneous rocks consist of granodiorite, porphyry and aplites. Such a great assemblage of rocks matches in a geological context representative of a plutonic intrusion and its metamorphic contact aureole. Following that scenario we suggest that the most likely source area for all these materials occur at the Collserola hills, at 27 km far to the east from the cave, at the other side of the Llobregat River, where an Hercynian granodiorite and related igneous rocks intruding Ordovician metasedimentary materials are presented. 

scholarly journals The Imbert Formation of northern Hispaniola: a tectono-sedimentary record of arc-continent collision and ophiolite emplacement in the northern Caribbean subduction-accretionary prism

2015 ◽  
Vol 7 (2) ◽  
pp. 1827-1876 ◽  
Author(s):  
J. Escuder-Viruete ◽  
A. Suárez-Rodríguez ◽  
J. Gabites ◽  
A. Pérez-Estaún
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Middle Eocene ◽  
Accretionary Prism ◽  
Island Arc ◽  
Caribbean Island ◽  
Stratigraphic Sequence ◽  
Oblique Collision ◽  
The Caribbean ◽  
Ophiolitic Complex

Abstract. In northern Hispaniola, the Imbert Formation (Fm) has been interpreted as an orogenic "mélange" originally deposited as trench-fill sediments, an accretionary (subduction) complex formed above a SW-dipping subduction zone, or the sedimentary result of the early oblique collision of the Caribbean plate with the Bahama Platform in the middle Eocene. However, new stratigraphical, structural, geochemical and geochronological data from northern Hispaniola indicate that the Imbert Fm constitutes a coarsening-upward stratigraphic sequence that records the transition of the sedimentation from a pre-collisional forearc to a syn-collisional piggy-back basin. This piggy-back basin was transported on top of the Puerto Plata ophiolitic complex slab and structurally underlying accreted units of the Rio San Juan complex, as it was emplaced onto the North America continental margin units. The Imbert Fm unconformably overlies different structural levels of the Caribbean subduction-accretionary prism, including a supra-subduction zone ophiolite, and consists of three laterally discontinuous units that record the exhumation of the underlying basement. The distal turbiditic lower unit includes the latest volcanic activity of the Caribbean island arc; the more proximal turbiditic intermediate unit is moderately affected by syn-sedimentary faulting; and the upper unit is a (caotic) olistostromic unit, composed of serpentinite-rich polymictic breccias, conglomerates and sandstones, strongly deformed by syn-sedimentary faulting, slumping and sliding processes. The Imbert Fm is followed by subsidence and turbiditic deposition of the overlying El Mamey Group. The 40Ar / 39Ar plagioclase plateau ages obtained in gabbroic rocks from the Puerto Plata ophiolitic complex indicate its exhumation at ∼ 45–40 Ma (lower-to-middle Eocene), contemporaneously to the sedimentation of the overlying Imbert Fm. These cooling ages imply the uplift to the surface and submarine erosion of the complex to be the source of the ophiolitic fragments in the Imbert Fm, during of shortly after the emplacement of the intra-oceanic Caribbean island-arc onto the continental margin.

Neoproterozoic active margin in the northwestern Yangtze Block, South China: new clues from detrital zircon U–Pb geochronology and geochemistry of sedimentary rocks from the Hengdan Group

2020 ◽  
pp. 1-17
Author(s):  
Bo Hui ◽  
Yunpeng Dong ◽  
Feifei Zhang ◽  
Shengsi Sun ◽  
Shuai He
Keyword(s):  
South China ◽  
Detrital Zircon ◽  
Active Continental Margin ◽  
Geodynamic Setting ◽  
Provenance Analysis ◽  
Yangtze Block ◽  
Essential Information ◽  
Zircon Age ◽  
Age Patterns ◽  
Depositional Age

Abstract The Yangtze Block in South China constitutes an important Precambrian landmass in the present East Asian continent. The Neoproterozoic sedimentary successions of the Hengdan Group in the NW Yangtze Block record essential information for deciphering the Neoproterozoic tectonics along the NW margin. However, its depositional age, provenance and tectonic properties remain uncertain. Here, a combined analysis of detrital zircon U–Pb dating and geochemistry is performed on representative samples from the Hengdan Group. Concordant dating results of samples from the bottom and upper parts constrain the maximum depositional age at c. 720 Ma. Detrital zircon age patterns of samples reveal a uniformly pronounced age peak at c. 915–720 Ma, which is consistent with the magmatic pulses in domains at the NW end of the Yangtze Block. In addition, these samples display left-sloping post-Archaean Australian shale (PAAS)-normalized rare-earth element patterns and variable trace element patterns, resembling sediments accumulated in a basin related to an active continental margin geodynamic setting. Provenance analysis reveals that the main sources featured intermediate to felsic components, which experienced rapid erosion and sedimentation. These integrated new investigations, along with previous compilations, indicate that the Hengdan Group might have been deposited in a fore-arc basin controlled by subduction beneath the Bikou Terrane. Thus, such interpretation further supports proposals for subduction-related tectonics along the western margin of the Yangtze Block during the early Neoproterozoic.

The 1755 Lisbon earthquake and the beginning of closure of the Atlantic

2006 ◽  
Vol 14 (2) ◽  
pp. 193-205 ◽  
Author(s):  
A. RIBEIRO ◽  
L. MENDES-VICTOR ◽  
J. CABRAL ◽  
L. MATIAS ◽  
P. TERRINHA
Keyword(s):  
Source Area ◽  
Accretionary Prism ◽  
Sumatra Earthquake ◽  
Alert System ◽  
Tsunami Modelling ◽  
2004 Sumatra Earthquake ◽  
Lisbon Earthquake ◽  
History Of ◽  
History Of Europe ◽  
Gorringe Bank

The 1755 Lisbon earthquake and tsunami had one of the highest magnitudes in the history of Europe. The source mechanism requires generation at a subduction zone. Intensity distribution and tsunami modelling excludes the Gorringe Bank as a source area and suggests generation by the incipient convergence of the Atlantic with the Southwest Iberia and Morocco margin rather than at the less active Gulf of Cadiz Accretionary Prism. The comparison with the 2004 Sumatra earthquake and tsunami supports this interpretation. A tsunami warning alert system is urgent for the Atlantic.

Paleogeography of the Matapédia basin in the Gaspé Appalachians: initiation of the Gaspé Belt successor basin

2004 ◽  
Vol 41 (5) ◽  
pp. 553-570 ◽  
Author(s):  
Michel Malo
Keyword(s):  
Carbonate Platform ◽  
Source Area ◽  
Turbidity Currents ◽  
Northern Limit ◽  
Fine Grained ◽  
The North ◽  
Iapetus Ocean ◽  
Thrust Sheets ◽  
Siliciclastic Rocks ◽  
Lime Muds

The Matapédia basin consists of the uppermost Ordovician – lowermost Silurian deep-water, fine-grained carbonate–siliciclastic rocks of the Honorat (Garin Formation) and Matapédia groups (Pabos and White Head formations), the lower rock assemblage of the Gaspé Belt in the Gaspé Appalachians. Paleogeographic maps of eight time slices from the Caradocian to the Llandoverian are presented to better understand the tectonosedimentary evolution of the Matapédia basin. Deposition evolved from siliciclastic (Garin Fm.) to argillaceous limestones (Pabos Fm.), to limestones (White Head Fm.). The overall change from terrigenous (Garin Fm.) to limestone facies (White Head Fm.) reflects a change in the source area. Paleocurrent directions and composition of sandstones indicate an orogenic source area to the south for the Garin Formation, which is believed to be the inliers of the Humber and Dunnage zones in the southern Gaspé and New Brunswick Appalachians. Lime muds deposited by turbidity currents coming from the north suggest the Anticosti active carbonate platform as the source area for the White Head Formation. The Matapédia basin was filled from south to north. First deposits, the Garin Formation, occurred south of the Taconian thrust sheets (Humber Zone) and also south of the Grenville basement. This region was the domain of the Ordovician Iapetus Ocean (Dunnage Zone). The northern limit of the basin migrated northward during deposition of the Matapédia Group in Ashgillian–Llandoverian times and reached its actual northern limit at the very end of the Llandoverian (C6), when siliciclastic facies of the lower Chaleurs Group were deposited.

scholarly journals Variability of mineral dust deposition in the western Mediterranean basin and south-east of France

2016 ◽  
Vol 16 (14) ◽  
pp. 8749-8766 ◽  
Author(s):  
Julie Vincent ◽  
Benoit Laurent ◽  
Rémi Losno ◽  
Elisabeth Bon Nguyen ◽  
Pierre Roullet ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Mineral Dust ◽  
Sampling Site ◽  
Regional Scale ◽  
Western Mediterranean ◽  
Saharan Dust ◽  
Deposition Flux ◽  
Dust Deposition ◽  
Western Mediterranean Basin ◽  
Provenance Areas

Abstract. Previous studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than 1 year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA (Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie in French) have been deployed in the western Mediterranean region during 1 to 3 years depending on the station. The sites include, from south to north, Lampedusa, Majorca, Corsica, Frioul and Le Casset (southern French Alps). Deposition measurements are performed on a common weekly period at the five sites. The mean dust deposition fluxes are higher close to the northern African coasts and decrease following a south–north gradient, with values from 7.4 g m−2 year−1 in Lampedusa (35°31′ N, 12°37′ E) to 1 g m−2 year−1 in Le Casset (44°59′ N, 6°28′ E). The maximum deposition flux recorded is of 3.2 g m−2 wk−1 in Majorca with only two other events showing more than 1 g m−2 wk−1 in Lampedusa, and a maximum of 0.5 g m−2 wk−1 in Corsica. The maximum value of 2.1 g m−2 year−1 observed in Corsica in 2013 is much lower than existing records in the area over the 3 previous decades (11–14 g m−2 year−1). From the 537 available samples, 98 major Saharan dust deposition events have been identified in the records between 2011 and 2013. Complementary observations provided by both satellite and air mass trajectories are used to identify the dust provenance areas and the transport pathways from the Sahara to the stations for the studied period. Despite the large size of African dust plumes detected by satellites, more than 80 % of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different deposition sites in the Mediterranean studied area. The results tend to indicate that wet deposition is the main form of deposition for mineral dust in the western Mediterranean basin, but the contribution of dry deposition (in the sense that no precipitation was detected at the surface) is far from being negligible, and contributes 10 to 46 % to the major dust deposition events, depending on the sampling site.

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