scholarly journals Time-Transgressive Salinic and Acadian Orogenesis, Magmatism and Old Red Sandstone Sedimentation in Newfoundland

2014 ◽  
Vol 41 (2) ◽  
pp. 138 ◽  
Author(s):  
Cees R. Van Staal ◽  
Alexandre Zagorevski ◽  
Vicki J. McNicoll ◽  
Neil Rogers
Keyword(s):  
Volcanic Rocks ◽  
Leading Edge ◽  
Foreland Basins ◽  
Red Beds ◽  
Deformation Front ◽  
Red Sandstone ◽  
Slab Breakoff ◽  
Accreted Terranes ◽  
Good Proxy ◽  
Red Bed

We propose an intimate relationship between Silurian terrestrial red bed sedimentation (Old Red Sandstone), slab breakoff-related magmatism and deformation in the Newfoundland Appalachians. Red bed sedimentation started during the Early Silurian, and records the progressive rise of the Salinic mountains in the tectonic hinterland of the orogen. The red beds were mainly deposited in molasse-style foreland basins in front of an east-propagating terminal Salinic deformation front. New U–Pb zircon dating of volcanic rocks interlayered with the Silurian red beds in key structural locations yielded ages ranging between 425 and 418 Ma, which, combined with the existing geochronological database, suggests that the sedimentary rocks are progressively younger from west to east and overstep the accreted Gondwana-derived terranes. We propose that deposition of the red beds is a good proxy for the time of cratonization of the accreted terranes. Eastward migration of the Salinic deformation front was accompanied by eastward-widening of a slab-breakoff-related asthenospheric window. The latter is interpreted to have formed due to a combination of progressive steepening of the down-going plate following entrance of the leading edge of the Gander margin and its eduction. Gander margin eduction (reversed subduction) is proposed to have been instigated by the trench migration of the Acadian coastal arc built upon the trailing edge of the Gander margin, which developed contemporaneously with the Salinic collision. The resultant thinning of the lithosphere beneath the Salinic orogen, built upon the leading edge of the Gander margin immediately prior to the onset of the Early Devonian Acadian orogeny, set the stage for generation of the widespread bloom of Acadian magmatism.SOMMAIRENous proposons qu’il y a eu une relation intime entre la sédimentation des couches rouges continentales au Silurien (vieux-grès-rouges), un magmatisme lié à une rupture de segments de croûte, et la déformation appalachienne à Terre-Neuve.  La sédimentation des couches rouges qui a débuté au début du Silurien témoigne du soulèvement progressif des monts saliniques de l’arrière-pays tectonique de l’orogène.  Les couches rouges se sont déposées sous forme de molasses dans des bassins d’avant-pays, à l’avant du front de déformation salinique terminale qui se déployait vers l’est.  De nouvelles datations U-Pb sur zircon de roches volcaniques interstratifiées avec des couches rouges siluriennes en des lieux structurels stratégiques montrent des âges qui varient entre 425 Ma et 418 Ma, ce qui, combiné aux bases de données géochronologiques existantes permet de penser que les roches sédimentaires sont progressivement plus jeunes d’ouest en est, et qu’elles surplombent les terranes accrétés du Gondwana.  Nous suggérons que les couches rouges sont de bons indicateurs temporels de la cratonisation des terranes accrétés.  La migration vers l’est du front de la déformation salinique a été accompagnée par un élargissement vers l’est d’une fenêtre asthénosphérique liée à une rupture de la croûte.  Cette dernière aurait été provoquée par la combinaison de l’enfoncement progressif de la plaque qui a suivi l’entrée du bord d’attaque de la marge de Gander, et son éduction.  Nous proposons que l’éduction (l’inverse de la subduction) de la marge de Gander a été provoquée par la migration de la fosse tectonique côtière acadienne, induite par la migration du bord d’attaque de la marge de Gander, contemporaine de la collision salinique.  L’amincissement de la lithosphère sous l’orogène salinique qui en a résulté, et qui s’est déployé au bord d’attaque de la marge de Gander juste avant l’enclenchement de l’orogénie acadienne au début du Dévonien, a préparé le terrain du déploiement à grande échelle du magmatisme acadien.

scholarly journals Influence Mechanism of Different Flow Patterns on the Softening of Red-Bed Soft Rock

2019 ◽  
Vol 7 (5) ◽  
pp. 155 ◽  
Author(s):  
Zhen Liu ◽  
Xinfu He ◽  
Cuiying Zhou
Keyword(s):  
Quantitative Analysis ◽  
Soft Rock ◽  
Flow Patterns ◽  
Specific Method ◽  
Red Beds ◽  
Rock Interaction ◽  
Red Sandstone ◽  
Influence Mechanism ◽  
Water Conditions ◽  
Red Bed

As a typical representative of red beds, the softening and disintegration of red sandstone when it encounters water is an important cause of initiated engineering disasters. However, research on the softening of this kind of rock has mainly focused on the still water–rock interaction. There is still a lack of quantitative analysis and a mechanistic explanation for the basic experimental study of dynamic water–rock interactions. Therefore, based on the independently developed multifunctional open channel hydraulic test equipment, the still water was used as the reference by designing the saturation test of red sandstone under two typical flow patterns—laminar flow and turbulent flow—and combined with a three-dimensional numerical simulation; specifically, the chemical, physical and mechanical effects of different flow patterns on the softening of red sandstone are discussed, and the mechanism of the influence of different flow patterns on the softening of red sandstone was further revealed. The results show that under different flow patterns, as the flow of water increased, the alkalinity of the circulating solution became stronger, the speed of stabilization of the ion concentration became faster, the development of the microscopic structure of the corresponding rock became higher and the decrease in mechanical strength became greater. The flow state affects the processes of rock softening and breaking by acting on the rock from the three aspects of chemistry, physics and mechanics. The study makes up for the deficiency of the quantitative analysis index of rock softening under dynamic water conditions and further improves the influence mechanism of different flow patterns on soft rock softening in red beds under dynamic water conditions. This research also provides a specific method for the protection of estuarine and coastal bank slopes with rich red-bed soft rock dissection under different flow patterns.

scholarly journals Accretion, Soft and Hard Collision: Similarities, Differences and an Application from the Newfoundland Appalachian Orogen

2020 ◽  
Vol 47 (3) ◽  
pp. 103-118
Author(s):  
Cees Van Staal ◽  
Alexandre Zagorevski
Keyword(s):  
Volcanic Rocks ◽  
Leading Edge ◽  
Qualitative Assessment ◽  
Fault System ◽  
Accretionary Wedge ◽  
The North ◽  
Show Evidence ◽  
Accreted Terranes ◽  
Mountain Belts ◽  
Laurentian Margin

We argue there is no distinction between accretion and collision as a process, except when accretion is used in the sense of incorporating small bodies of sedimentary and/or volcanic rocks into an accretionary wedge by off-scraping or underplating. There is also a distinction when these terms are used in classifying mountain belts into accretionary and collisional orogens, although such classifications are commonly based on a qualitative assessment of the scale and nature of the accreted terranes and continents involved in formation of mountain belts. Soft collisions occur when contractional deformation and associated metamorphism are principally concentrated in rocks of the leading edge of the partially pulled-down buoyant plate and the upper plate forearc terrane. Several young arc-continent collisions show evidence for partial or wholesale subduction of the forearc such that the arc is structurally juxtaposed directly against lower plate rocks. This process may explain the poor preservation of forearcs in the geological record. Soft collisions generally change into hard collisions over time, except if the collision is rapidly followed by formation of a new subduction zone due to step-back or polarity reversal. Thickening and metamorphism of the arc's suprastructure and retro-arc part of upper plate due to contractional deformation and burial are the characteristics of a hard collision or an advancing Andean-type margin. Strong rheological coupling of the converging plates and lower and upper crust in the down-going continental margin promotes a hard collision. Application of the soft–hard terminology supports a structural juxtaposition of the Taconic soft collision recorded in the Humber margin of western Newfoundland with a hard collision recorded in the adjacent Dashwoods block. It is postulated that Dashwoods was translated dextrally along the Cabot-Baie Verte fault system from a position to the north of Newfoundland where the Notre Dame arc collided ca. 10 m.y. earlier with a wide promontory in a hyperextended segment of the Laurentian margin.

The Caledonoid faults of northern Lleyn (North Wales)

1970 ◽  
Vol 107 (3) ◽  
pp. 235-247 ◽  
Author(s):  
W. E. Tremlett
Keyword(s):  
Volcanic Rocks ◽  
Strike Slip ◽  
Metamorphic Rocks ◽  
Red Sandstone ◽  
North Wales ◽  
Dextral Strike Slip

SummaryEvidence of substantial dextral strike-slip displacements along the Caledonoid fault-set of northern Lleyn is revealed by the distribution of Pre-Cambrian igneous and metamorphic rocks, Ordovician volcanic rocks and Caledonian ‘early granodioritic’ intrusions. These apparently occurred prior to some smaller sinistral strike-slip movements which left total net dextral displacements of 91/2 km. Both types of movement were completed before the Caledonoid faults were disrupted by NNW sinistral faulting and more intrusions of Lower Old Red Sandstone age were emplaced.

Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia

2021 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
Donghai Zhang
Keyword(s):  
Subduction Zones ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Ocean Basin ◽  
Magma Source ◽  
Central Asian ◽  
Slab Rollback ◽  
Slab Breakoff ◽  
Subduction Fluids ◽  
Arc Setting

<p>Oceanic subduction and its last underthrusted part can both triggers arc-like magmatism. As the existence of multi-subduction zones in the Central Asian Orogenic Belt, controversy still surrounds on when and especially how the subduction of the (Paleo-Asian Ocean) PAO terminated. We present geochronological, geochemical, and Lu-Hf isotopic data for a suite of basalt-andesites, dacite-rhyolites and later trachyandesite-mugearitic dykes from the Khan-Bogd area in the Gobi Tianshan Zone (GTZ) of the southern Mongolia. U-Pb dating of zircons indicate the basalt-andesites and dacite-rhyolites were formed at ~334-338 Ma, and the dykes at ~300 Ma. These Early Carboniferous volcanic rocks display high U/Th, Ba/Th, low La/Sm and variable Zr/Nb ratios, implying the involvement of subduction fluids or sediment melt. They display arc geochemical features such as calc-alkaline and metaluminous nature and positive Ba and U and negative Nb, Ta and Ti anomalies. Moreover, their continental geochemical signals (e.g. positive Pb, K anomalies) and some old captured zircons implying a continental arc setting. Comparatively, the ~300 Ma dykes are characterized by high alkaline contents, which are common for coeval (~320-290 Ma) and widespread post-subductional granites there. Given a mainly crust-derived magma source for those granites, these dykes likely reflect a mantle disturbance due to: (1) their relative low SiO<sub>2 </sub>(51.71-55.85 wt. %) and high Mg# (40.3-67.3) values, and (2) positive zircon Ɛ<sub>Hf</sub>(t) (most > 12). Considering a slab rollback model during the Carboniferous and Triassic, the mantle disturbance was possibly induced by the oceanic slab breakoff. Combined with previous work, this ~320-290 Ma slab breakoff-induced extension marks the closure of a wide secondary ocean (North Tianshan-Hegenshan ocean) north of the main ocean basin of the PAO. This research was financially supported by NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).</p>

Magmatic record of continuous Neo-Tethyan subduction after initial India-Asia collision in the central part of southern Tibet

2020 ◽  
Author(s):  
Feng Huang ◽  
Tyrone O. Rooney ◽  
Ji-Feng Xu ◽  
Yun-Chuan Zeng
Keyword(s):  
Mantle Wedge ◽  
Leading Edge ◽  
Continental Collision ◽  
Southern Tibet ◽  
Mafic Rocks ◽  
Lhasa Terrane ◽  
Slab Breakoff ◽  
Geodynamic Processes ◽  
Generation Mechanisms ◽  
Transitional Phase

The Lhasa Terrane in southern Tibet is the leading edge of the Tibet-Himalaya Orogen and represents a fragmentary record of terminal oceanic subduction. Thus, it is an ideal region for studying magmatism and geodynamic processes that occurred during the transition from oceanic subduction to continental collision and/or oceanic slab breakoff. Here we examine a suite of early Cenozoic mafic rocks (ca. 57 Ma) within the central part of Lhasa Terrane, southern Tibet, which erupted during a transitional phase between the onset of India-Asia continental collision and Neo-Tethyan slab breakoff. These rocks display a geochemical affinity with magmas produced by fluid-fluxed melting of the mantle wedge within a subduction zone environment. The whole-rock element and Sr-Nd isotope compositions of these mafic rocks are similar to those of Cretaceous subduction-related magmatism in southern Tibet, demonstrating the sustained influence of the Neo-Tethys Ocean slab on the mantle wedge during the onset of the collision of India and Asia. The results of our geochemical forward modeling constrain the conditions of melt generation at depths of 1.3−1.5 GPa with significant fluid additions from the Neo-Tethyan slab. These results provide the first petrological and geochemical evidence that slab flux-related magmatism continued despite the commencement of continental collision. While existing studies have suggested that magmas were derived from melting of the Neo-Tethyan slab during this period, our new results suggest that additional magma generation mechanisms were active during this transitional phase.

Late Miocene sediment delivery from the axial drainage system of the East Carpathian foreland basin to the Black Sea

Geology ◽  
2020 ◽  
Vol 48 (8) ◽  
pp. 761-765 ◽  
Author(s):  
Arjan de Leeuw ◽  
Stephen J. Vincent ◽  
Anton Matoshko ◽  
Andrei Matoshko ◽  
Marius Stoica ◽  
...  
Keyword(s):  
Black Sea ◽  
Late Miocene ◽  
Drainage System ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Danube River ◽  
The Black Sea ◽  
Foreland Basins ◽  
Continental Scale ◽  
Slab Breakoff

Abstract We describe a late Miocene to early Pliocene axial drainage system in the East Carpathian foreland, which was an important sediment supplier to the Black Sea and the Dacian Basin. Its existence explains the striking progradation of the northwest Black Sea shelf prior to the onset of sediment supply from the continental-scale Danube River in the late Pliocene to Pleistocene. This axial drainage system evolved due to the diachronous along-strike evolution of the Carpathians and their foreland; continental collision, overfilling, slab breakoff, and subsequent exhumation of the foreland occurred earlier in the West Carpathians than in the East Carpathians. After overfilling of the western foreland, excess sediment was transferred along the basin axis, giving rise to a 300-km-wide by 800-km-long, southeast-prograding river-shelf-slope system with a sediment flux of ∼12 × 103 km3/m.y. Such late-stage axial sediment systems often develop in foreland basins, in particular, where orogenesis is diachronous along strike. Substantial lateral sediment transport thus needs to be taken into account, even though evidence of these axial systems is often eroded following slab breakoff and inversion of their foreland basins.

Reduction spots in the Mesoproterozoic age: implications for life in the early terrestrial record

2010 ◽  
Vol 9 (4) ◽  
pp. 209-216 ◽  
Author(s):  
Samuel C. Spinks ◽  
John Parnell ◽  
Stephen A. Bowden
Keyword(s):  
Formation Mechanism ◽  
Microbial Reduction ◽  
Deep Biosphere ◽  
Isotopic Data ◽  
Red Beds ◽  
Geological Record ◽  
Microbial Life ◽  
Terrestrial Environments ◽  
Red Bed

AbstractReduction spots are common within continental red beds in the geological record. The method of formation of reduction spots is a subject of debate, but they are thought to be the result of the reducing nature of microbial life present in the sediment during burial, which caused localized reduction in sediment that was otherwise oxidized during diagenesis. Reduction spots often have dark concretionary cores commonly enriched in elements such as vanadium and uranium. This enrichment is also believed to be associated with the microbial reduction of the sediment. Isotopic data from sulphides present in the cores of analogue Triassic reduction spots are consistent with a potential microbial formation mechanism.Here we report the presence of reduction spots with vanadium-rich mica (roscoelite) – enriched cores within a terrestrial red bed sequence of the Mesoproterozoic age. These findings may be a possible indicator of life within the terrestrial geological record during the Mesoproterozoic age, a time when such evidence is otherwise very rare. These findings suggest that life had not only colonized terrestrial environments during the Mesoproterozoic age, but had established a deep biosphere in the sediment.

A 1.25 Ga depositional age for the “Paleoproterozoic” Mapedi red beds, Kalahari manganese field, South Africa: New constraints on the timing of oxidative weathering and hematite mineralization

Geology ◽  
2019 ◽  
Vol 48 (1) ◽  
pp. 44-48 ◽  
Author(s):  
Birger Rasmussen ◽  
Janet R. Muhling ◽  
Jian-Wei Zi ◽  
Harilaos Tsikos ◽  
Woodward W. Fischer
Keyword(s):  
South Africa ◽  
Climatic Conditions ◽  
Red Beds ◽  
The West ◽  
Zircon Age ◽  
Great Oxidation Event ◽  
Depositional Age ◽  
Red Bed

Abstract The Great Oxidation Event (GOE) is marked by the loss of readily oxidizable detrital minerals and the onset of oxidative weathering. One of the oldest post-GOE weathering surfaces, which extends for almost 350 km along strike, occurs in Griqualand West, South Africa. It is best preserved east of the Blackridge thrust, where oxidized paleoweathering profiles are developed below the unconformity at the base of Mapedi-Gamagara red beds. In the Maremane Dome, the red beds preserve pisolitic hematite laterites, which indicate a highly oxygenated atmosphere and suggest hot and humid climatic conditions. The Mapedi and Gamagara Formations are undated east of the Blackridge thrust but were thought to be lithological correlatives of the ≥1.91 Ga Mapedi red bed sequence to the west. Here, we report a U-Pb zircon age of 1.25 Ga for a felsic tuff in red beds of the Mapedi Formation in the Kalahari manganese field. The new tuff age shows that the Mapedi red beds east of the thrust were deposited >650 m.y. after the Mapedi Formation to the west, and therefore they are part of a distinct Mesoproterozoic sequence. Based on lithologic and sedimentological similarities, the Mapedi-east and Gamagara formations are likely to be correlatives that were deposited on an ancient weathering surface at ca. 1.25 Ga. Our findings suggest that key evidence for a highly oxygenated atmosphere during the early Paleoproterozoic actually formed at ca. 1.25 Ga during a major episode of Mesoproterozoic oxidative weathering.

New 40Ar/39Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada

1998 ◽  
Vol 35 (5) ◽  
pp. 495-503 ◽  
Author(s):  
Stephen S Harlan ◽  
Ernest M Duebendorfer ◽  
Jack E Deibert
Keyword(s):  
Las Vegas ◽  
Volcanic Rocks ◽  
Normal Fault ◽  
Vertical Axis ◽  
Lake Mead ◽  
Basin And Range Province ◽  
Red Sandstone ◽  
Las Vegas Valley ◽  
Western Lake ◽  
Southern Nevada

New 40Ar/39Ar dates on volcanic rocks interlayered with synextensional Miocene sedimentary rocks in the western Lake Mead area and southern end of the Las Vegas Range provide tight constraints on magmatism, basin formation, and extensional deformation in the Basin and Range province of southern Nevada. Vertical axis rotations associated with movement along the Las Vegas Valley shear zone occurred after 15.67 ± 0.10 Ma (2 sigma ), based on a 40Ar/39Ar date from a tuff in the Gass Peak formation in the southern Las Vegas Range. Basaltic magmatism in the western Lake Mead area began as early as 13.28 ± 0.09 Ma, based on a date from a basalt flow in the Lovell Wash Member of the Horse Spring Formation. Isotopic dating of a basalt from the volcanic rocks of Callville Mesa indicates that these rocks are as old as 11.41 ± 0.14 Ma, suggesting that volcanic activity began shortly after formation of the Boulder basin, the extensional basin in which the informally named red sandstone unit was deposited. The red sandstone unit is at least as old as 11.70 ± 0.08 Ma and contains megabreccia deposits younger than 12.93 ± 0.10 Ma. This result shows that formation of the Boulder basin was associated with development of topographic relief that was probably generated by movement along the Saddle Island low-angle normal fault. Stratal tilting associated with extension occurred both prior to and after 11.5 Ma.

Sedimentology of the Partry Series in the Partry Mountains, Co. Mayo, Eire

1967 ◽  
Vol 104 (6) ◽  
pp. 585-607 ◽  
Author(s):  
John McManus
Keyword(s):  
Shallow Water ◽  
Marine Environment ◽  
Volcanic Rocks ◽  
Sedimentary Structures ◽  
Welded Tuff ◽  
Water Origin ◽  
Red Bed

AbstractThe Lettereeneen fault, a newly recognized structure, brings the Mweelrea and Maumtrasna Groups of the Partry Series (Caradocian-Llandeilian age) into contact. The stratigraphy of the Mweelrea Group, of red bed facies, is followed from the presence of welded tuff horizons; no such markers exist in the Maumtrasna Group which lies unconformably upon the former.Sedimentary structures of shallow water origin occur in each group. Three types of conglomerate recognized in the area are examined. The immature feldspathic sandstones increase in arkosity upwards.A proluvial or proluvio-marine environment of deposition is suggested, with debris derived from an eastward extension of the metamorphosed Dalradian rocks of the Connemara Cordillera and foothills of sedimentary and volcanic rocks.

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