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1
Shreve, Ronald L., and Mark Cloos. "Dynamics of sediment subduction, melange formation, and prism accretion." Journal of Geophysical Research 91, B10 (1986): 10229. http://dx.doi.org/10.1029/jb091ib10p10229.
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Safonova, I. Yu, and А. I. Khanchuk. "SUBDUCTION EROSION AT PACIFIC-TYPE CONVERGENT MARGINS." Tikhookeanskaya Geologiya 40, no. 6 (2021): 3–19. http://dx.doi.org/10.30911/0207-4028-2021-40-6-3-19.
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The paper presents a review of processes of subduction or tectonic erosion at the Pacific-type convergent margins (PTCM) including definition of “tectonic erosion”, its triggers, driving forces and consequences. We review examples of tectonic erosion at the Circum-Pacific PTCMs and at the fossil PTCMs of the Paleo-Asian Ocean (PAO) currently hosted by the Central-Asian Orogenic Belt (CAOB). Recent geological and stratigraphic studies have shown two types of PTCMs: accreting and eroding. Accreting PTCMs consist of older deposits of accretionary and frontal prisms and grow oceanward, i.e. the trench retreats. Eroding PTCMs are characterized by the destruction of the prism, approaching arc and trench and typically form during shallow-angle and fast subduction of an oceanic slab with oceanic floor topographic highs. The mechanism of tectonic erosion includes destruction of oceanic slab, island arcs, accretionary prism, fore-arc and related prism. Tectonic erosion is a common phenomenon at many Circum-Pacific PTCMs, e.g., in South America, Tonga and Nankai troughs, Alaska. Accretion and subduction of oceanic rises contributes greatly to the processes of formation, transformation and destruction of continental crust at PTCM. The episodes of tectonic erosion can be also reconstructed for an ancient ocean, for example, for the PAO, which evolution and suturing formed the CAOB. Many CAOB foldbelts (Altai, Tienshan, eastern Kazakhstan, Transbaikalia, Mongolia) carry signs of disap-pearance of big volumes of continental crust (arcs). Studying processes responsible not only for the formation of continental crust, but also for the disappearance of big volumes of crustal mate-rial is important for correct evaluation of the nature of intra-continental orogenic belts, e.g., CAOB, and development of reliable tectonic models.
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Polat, Ali, Thomas Kokfelt, Kevin C. Burke, Timothy M. Kusky, Dwight C. Bradley, Annika Dziggel, and Jochen Kolb. "Lithological, structural, and geochemical characteristics of the Mesoarchean Târtoq greenstone belt, southern West Greenland, and the Chugach – Prince William accretionary complex, southern Alaska: evidence for uniformitarian plate-tectonic processes." Canadian Journal of Earth Sciences 53, no. 11 (November 2016): 1336–71. http://dx.doi.org/10.1139/cjes-2016-0023.
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The Mesoarchean Târtoq greenstone belt, southern West Greenland, consists of tectonically imbricated slices of metamorphosed basalt, gabbro, peridotite, and sedimentary rocks and is intruded by felsic rocks (now mylonites) with well-preserved duplex structures, representing a relict accretionary prism. The Târtoq greenstone belt is a remnant of a supra-subduction zone ophiolite that originated as back-arc basin oceanic crust. Following the initiation of intra-oceanic subduction, the back-arc oceanic crust accreted to the overriding plate, forming an accretionary prism. The felsic mylonites are compositionally akin to Archean tonalite–trondhjemite–granodiorite suites. Field observations, along with geochemical and zircon U–Pb age data, indicate that the protoliths of the felsic mylonites were derived from partial melting of back-arc basalts in the accretionary prism and emplaced along thrust faults between 3012 ± 4 and 2993 ± 6 Ma. It is proposed that the partial melting of the basalts likely occurred in response to ridge subduction. The Upper Cretaceous turbiditic greywackes of the Chugach – Prince William accretionary complex in southern Alaska are intruded by Paleogene felsic dykes. These felsic dykes appear to have been derived from partial melting of subducted and (or) accreted oceanic crust during slab window magmatism. Archean granitoid–greenstone terrains share many geological characteristics of Phanerozoic subduction–accretion complexes such as the Alaskan and Altaid subduction–accretion complexes, consistent with the operation of uniformitarian geological processes in the Archean. The Archean Earth might have been dominated by numerous smaller plates and greater ridge length than today that would have resulted in more frequent ridge-accretionary prism interactions and larger volumes of tonalite–trondhjemite–granodiorite generation in subduction–accretion complexes.
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Cardace, Dawn, and Julie D. Morris. "Geochemical evidence for sediment accretion in the Costa Rica Frontal Prism." Geology 37, no. 10 (October 2009): 891–94. http://dx.doi.org/10.1130/g25631a.1.
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Tréhu, Anne M., Bridget Hass, Alexander de Moor, Andrei Maksymowicz, Eduardo Contreras-Reyes, Emilio Vera, and Michael D. Tryon. "Geologic controls on up-dip and along-strike propagation of slip during subduction zone earthquakes from a high-resolution seismic reflection survey across the northern limit of slip during the 2010 Mw 8.8 Maule earthquake, offshore Chile." Geosphere 15, no. 6 (November 7, 2019): 1751–73. http://dx.doi.org/10.1130/ges02099.1.
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Abstract A grid of closely spaced, high-resolution multichannel seismic (MCS) reflection profiles was acquired in May 2012 over the outer accretionary prism up dip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (offshore Chile) to complement a natural-source seismic experiment designed to monitor the post-earthquake response of the outer accretionary prism. We describe the MCS data and discuss the implications for the response of the accretionary prism during the earthquake and for the long-term evolution of the margin. The most notable observation from the seismic reflection survey is a rapid north-to-south shift over a short distance from nearly total frontal accretion of the trench sediments to nearly total underthrusting of undeformed trench sediments that occurs near the northern edge of slip in the 2010 earthquake. Integrating our structural observations with other geological and geophysical observations, we conclude that sediment subduction beneath a shallow décollement is associated with propagation of slip to the trench during great earthquakes in this region. The lack of resolvable compressive deformation in the trench sediment along this segment of the margin indicates that the plate boundary here is very weak, which allowed the outer prism to shift seaward during the earthquake, driven by large slip down dip. The abrupt shift from sediment subduction to frontal accretion indicates a stepdown in the plate boundary fault, similar to the stepovers that commonly arrest slip propagation in strike-slip faults. We do not detect any variation along strike in the thickness or reflective character of the trench sediments adjacent to the change in deformation front structure. This change, however, is correlated with variations in the morphology and structure of the accretionary prism that extend as far as 40 km landward of the deformation front. We speculate that forearc structural heterogeneity is the result of subduction of an anomalously shallow or rough portion of plate that interacted with and deformed the overlying plate and is now deeply buried. This study highlights need for three-dimensional structural images to understand the interaction between geology and slip during subduction zone earthquakes.
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Zagorevski, A., and V. McNicoll. "Evidence for seamount accretion to a peri-Laurentian arc during closure of Iapetus 1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.2 Geological Survey of Canada Contribution 20100465." Canadian Journal of Earth Sciences 49, no. 1 (January 2012): 147–65. http://dx.doi.org/10.1139/e11-016.
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The Red Indian Line is the fundamental Iapetus suture zone in the Newfoundland Appalchians along which the main tract of the Iapetus Ocean was consumed. Despite being the site of the closure of a wide ocean, few vestiges of the Iapetus plate have been accreted along Red Indian Line. Ordovician rocks in the Notre Dame Bay area preserve the only evidence for accretion of a seamount in Newfoundland. The seamount is characterized by alkali basalt and hypabyssal rocks that are juxtaposed with Darriwilian peri-Laurentian volcanic arc rocks (466 ± 4 and 467 ± 4 Ma) along a major mylonite zone. The mylonite zone lacks sedimentary rocks suggesting that the seamount was accreted to the arc along a sediment-starved interface and that significant subduction erosion took place along the Laurentian margin. Identification of subduction erosion indicates that an accretionary prism did not exist outboard of Laurentia in Newfoundland, in contrast to the well developed accretionary prisms of the Caledonides.
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Chen, F., G. H. Zhou, and J. Kong. "Anthropogenic Influences on the Hydrodynamic and Tidal Discharge in Tongzhou Bay, Nantong, China." Journal of Physics: Conference Series 2486, no. 1 (May 1, 2023): 012042. http://dx.doi.org/10.1088/1742-6596/2486/1/012042.
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Abstract In this study, we determined the variations of tidal flow field and tidal prism caused by human activities in Tongzhou bay and using MIKE 21 hydrodynamic model as analyzing tool. After the human activities, the hydrodynamic in sea area alongshore engineering is changed, the most obvious changes can reach over 0.1m/s; the tidal discharge decreases caused by the land accretion leading to the shrink of the area of Nantong near-shore waters, there is up to 12% reduction after planned reclamation during one spring tide period.
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Kawamura, Kiichiro, and Yujiro Ogawa. "Internal structure, active tectonics and dynamic topography of the eastern Nankai accretionary prism toe, Japan, and its tsunamigenic potential." Geological Magazine 158, no. 1 (October 30, 2018): 30–38. http://dx.doi.org/10.1017/s0016756818000699.
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AbstractThe eastern Nankai accretionary prism toe was surveyed to evaluate the nature and deformation of its frontal thrust. According to the determined porosities and yield strengths, turbidites were successively buried down to depths of 250–300 m before accretion, and were then exposed at the prism toe by uplift along the Tenryu frontal thrust during 3.4–1.98 Ma. Consolidation tests provided reasonable estimates of burial depth and, when combined with exposed sediment dates, yield prism toe uplift rates of 0.74–2.27 m ka–1. The displacement along the frontal thrust is estimated to be 500–900 m and the slip rates are 1.47–4.55 m ka–1, corresponding to the highest class of active faults on land in Japan. During the surveys of the Tenryu frontal thrust zone, we discovered a new active fault scarp that was several tens of centimetres high, interpreted to be a protothrust located c. 100 m south of the frontal thrust. This scarp is associated with chemosynthetic biocommunities. The thrust might potentially be the result of displacement during the East Nankai (To-Nankai) earthquake (Mw 8.1) in 1944. These lines of evidence indicate that the Tenryu frontal thrust is still active and that displacement along the thrust might induce a tsunami during future Tokai or To-Nankai earthquakes.
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Williams, Howard R. "Subprovince accretion tectonics in the south-central Superior Province." Canadian Journal of Earth Sciences 27, no. 4 (April 1, 1990): 570–81. http://dx.doi.org/10.1139/e90-053.
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Development of tectonic subprovinces as shear-bounded granite–greenstone and sediment-dominated terranes during the late Archaean is reviewed and interpreted from relationships between portions of the Wabigoon, Wawa, and Quetico subprovinces.Greenstone-dominated subprovinces (Wabigoon and Wawa) are complex successions of tholeiites, 2.76–2.70 Ga calc-alkaline volcanic centres, and derived sediments. Supracrustal rocks aggregated on a scale of tens of kilometres, forming homoclines, locally upright folded, intruded by granitoids, exhibiting variable fabric trends and strains, and cut by transcurrent shear zones. Small-scale (10–100 km) accretion juxtaposed these varied supracrustal sequences, which were engulfed granitoid magmas, to form greenstone belts.Sediment-dominated subprovinces (Quetico) are metamorphosed wacke sequences deposited during and after the volcanic climax in the period 2.70–2.69 Ga. Overthrust imbrication at both the Wabigoon–Quetico and the Quetico–Wawa contacts occurred along north-dipping shears, now vertical. Continued right-lateral convergence at subprovince margins induced progressive shortening within the Quetico Subprovince, producing a regional planar fabric. Abukuma–style metamorphism, migmatite formation, and S-type granite intrusions occurred during the period 2.67–2.65 Ga.Greenstone-belt developments, terminated during large-scale (100–1000 km) late neo-Archæan accretion, are preserved within elongate, batholith-dominated terranes separated by metasedimentary migmatite belts. Geochronological, lithotectonic, and metamorphic patterns on a scale of hundreds of kilometres are permissive of an accretionary model of greenstone terrane coalescence in which formation of long-lived, complex volcanic arcs and a complementary fore-arc accretionary prism culminated in large-scale accretion and the formation of stable continental crust.
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Devaney, Jonathan R., and Howard R. Williams. "Evolution of an Archean subprovince boundary: a sedimentological and structural study of part of the Wabigoon–Quetico boundary in northern Ontario." Canadian Journal of Earth Sciences 26, no. 5 (May 1, 1989): 1013–26. http://dx.doi.org/10.1139/e89-082.
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A prograded clastic wedge, represented by formation- to group-scale units of metasedimentary strata in the Beardmore–Geraldton Terrane, developed in a transitional zone at the southern margin of a volcanic arc between the Onaman–Tashota Terrane, part of the Wabigoon Subprovince to the north, and the Quetico Subprovince, an accretionary prism to the south. Megasequences or couplets with lower basaltic and upper clastic sedimentary parts are now exposed as regionally metamorphosed mafic volcanic and sedimentary belts, outlining thrust slices. Relatively proximal facies (belts) are juxtaposed on top of more distal ones, forming a regional stratigraphy of repetitive volcanic–sedimentary megasequences produced in an imbricate thrust stack. A variety of minor and regional structural features illustrate accretion and subsequent transpression. Isoclinal folding associated with dip-slip, overthrust shearing was followed by inhomogeneous ductile strain of dextral sense along weak lithologies and existing shear zones. Possible subduction-related accretion added a monotonous sequence of arc-derived wacke turbidites to the underside of the thrust-imbricated arc-margin succession. Post-tectonic melting in the northern section of this tectonically thickened accreted sediment gave rise to S-type granites.
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Dilek, Yildirim, and Yujiro Ogawa. "Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues." Geological Magazine 158, no. 1 (December 11, 2020): 1–12. http://dx.doi.org/10.1017/s0016756820001326.
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AbstractContinents grow mainly through magmatism, relamination, accretionary prism development, sediment underplating, tectonic accretion of seamounts, oceanic plateaus and oceanic lithosphere, and collisions of island arcs at convergent margins. The modern Pacific–Rim subduction zone environments present a natural laboratory to examine the nature of these processes. The papers in this special issue focus on the: (1) modern and ancient accretionary margins of Japan; (2) arc–continent collision zone in the Taiwan orogenic belt; (3) accreting versus non-accreting convergent margins of the Americas; and (4) several examples of ancient convergent margins of East Asia. Subduction erosion and sediment underplating are important processes, affecting the melt evolution of arc magmas by giving them special crustal isotopic characteristics. Oblique arc–continent collisions cause strong deformation partitioning that results in orogen-parallel extension, crustal exhumation and wrench faulting in the hinterland, and thrust faulting–folding in the foreland. Trench-parallel widths of subducting slabs exert major control on slab geometries, the degree of coupling–decoupling between the lower and upper plates, and subduction velocity partitioning. An initially large width of the subducting Palaeo-Pacific Plate against East Asia caused flat subduction and resistance to slab rollback during the Triassic Period. These conditions resulted in shortening across SE China. Foundering and delamination of the flat slab during the Early Jurassic Epoch led to slab segmentation and reduced slab widths, followed by slab steepening and rollback. This pull-away tectonics induced lithospheric extension and magmatism in SE China during Late Jurassic – Cretaceous time. Melting of subducted carbonaceous sediments commonly produces networks of silicate veins in CLM that may subsequently undergo partial melting, producing ultrapotassic magmas.
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Robertson, A. H. F. "Origin and emplacement of an inferred late Jurassic subduction-accretion complex, Euboea, eastern Greece." Geological Magazine 128, no. 1 (January 1991): 27–41. http://dx.doi.org/10.1017/s0016756800018021.
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AbstractIn northern Euboea, central eastern Greece, an up to 3 km-thick polygenetic melange (Pagondas complex) is structurally interleaved between a Triassic–Jurassic carbonate platform (Pelagonian Zone) and an overriding harzburgitic ophiolite. The melange mainly comprises late Triassic shallow-water limestone and calciturbidites, radiolarites, Triassic–Jurassic tholeiites, alkaline basalts and minor andesites. The units concerned range from kilometre-sized thrust sheets, and detached blocks, to broken formation and structureless, or bedded matrix-supported conglomerates (diamictite). The melange includes remnants of Neotethyan oceanic lithosphere, overlain by radiolarites, hemipelagic carbonates and distal calciturbidites derived from a Mesozoic carbonate platform. Tholeiites were erupted at a Triassic–Jurassic spreading axis, whilst within-plate-type alkali basalts are interpreted mainly as seamounts. Kilometre-scale detached blocks of shallow-water coralline limestone are identified as collapsed atolls, formed within an ocean and/or along the rifted continental margin. Volcaniclastic sediments are locally interbedded with radiolarite, and reflect post-volcanic erosion of the ocean floor. Intra-oceanic convergence began, apparently in late early Jurassic time, giving rise to the Euboea ophiolite above an inferred westwards-dipping subduction zone. The Pagondas Complex then developed as an accretionary prism. The subduction trench later collided with the Pelagonian passive margin, driving the hot Euobea ophiolite over the accretionary complex, to produce amphibolites and greenschists of the metamorphic sole. Trench–margin collision then drove the entire supra-subduction zone complex, apparently eastwards, downflexing the Pelagonian carbonate platform to form a foredeep in which late Jurassic (Kimmeridgian–Tithonian) radiolarian sediments accumulated. During emplacement, the accretionary complex was disrupted and partly resedimented as debris flows, turbiditic volcaniclastic sandstone and shale in a foredeep, or foreland basin setting.
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Cloos, Mark, and Ronald L. Shreve. "Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 1. Background and description." Pure and Applied Geophysics PAGEOPH 128, no. 3-4 (1988): 455–500. http://dx.doi.org/10.1007/bf00874548.
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Cloos, Mark, and Ronald L. Shreve. "Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 2. Implications and discussion." Pure and Applied Geophysics PAGEOPH 128, no. 3-4 (1988): 501–45. http://dx.doi.org/10.1007/bf00874549.
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Palyuk, Myroslav, Volodymyr Shlapinsky, Albert Medvedev, Bohdan Rizun, and Myroslav Ternavsky. "PROBLEMATIC ASPECTS OF THE FORMATION OF THE UKRAINIAN SEGMENT OF THE CARPATHIANS." Geology and Geochemistry of Combustible Minerals 3, no. 180 (December 18, 2019): 5–24. http://dx.doi.org/10.15407/ggcm2019.03.005.
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In the paper a model of the formation of the folded-covering-block structure of the Carpathians at a time interval that envelops Late-Hercynian and Alpine events is substantiated. Moreover, this concerns the Outer Carpathians, but the whole Carpathians arch was characterized without going into details, a critical estimate is expressed for application of such terms as terrains, accretion prism, suture, subduction and Transcarpathian fault. It is shown that formation of the Carpathians occurred through several stages under the influence of different-directed, manly horizontal, movements, as a result of which was destruction of early formed Hercynian continental crust, laying of geosynclinals troughs, formation and further transformation of the basement of the Flysch Carpathians, its collision with Eurasian continental edge, underling of the latter under flysh complex. After completion of these processes mainly vertical movements took place that lineally formed the structure of the Carpathians as folded-covering-block one. As a result of the last event (Pliocene-Pleistocene), a differential development of intensive fracturing occurred with the influx of hydrocarbons and filling traps formed up.
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Mulrennan, Monica E. "Changes since the Nineteenth Century to the Estuary-Barrier Complexes of North County Dublin." Irish Geography 26, no. 1 (January 23, 2015): 1–13. http://dx.doi.org/10.55650/igj.1993.453.
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Over the past 150 years, two estuary-barrier complexes on the north Dublin coastline have undergone considerable morphological changes. These include a reduction in the size of the estuaries, and estuary mouths, and the accretion of beach sediments and foredune ridges around the distal or southern ends of the barriers. Increased estuarine reclamation, and the construction of the Dublin to Belfast Railway across one of the estuaries, has reduced the volume of the tidal prism and weakened the ebb and flood currents, requiring an adjustment in the dimensions of the tidal channels and estuary mouths. Disruption of the tidal regime has led to substantial hydrodynamic and morphological changes, the southward extension of the barriers representing an attempt to restore the hydraulic equilibrium of these estuary/barrier complexes by reducing the cross section of the estuary mouth. Subsequent adjustments to these changes, combined with increasing recreational pressure, have been responsible for recent degradation and shoreline recession at the northern end of the barriers. A comprehensive understanding of the mechanisms of change currently operating along this coastline is essential to its effective management.
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TOBIN, HAROLD J., J. CASEY MOORE, MARY E. MACKAY, DANIEL L. ORANGE, and LAVERNE D. KULM. "Fluid flow along a strike-slip fault at the toe of the Oregon accretionary prism: Implications for the geometry of frontal accretion." Geological Society of America Bulletin 105, no. 5 (May 1993): 569–82. http://dx.doi.org/10.1130/0016-7606(1993)105<0569:ffaass>2.3.co;2.
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van Maanen, B., G. Coco, and K. R. Bryan. "On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2180 (August 2015): 20150115. http://dx.doi.org/10.1098/rspa.2015.0115.
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An ecomorphodynamic model was developed to study how Avicennia marina mangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution.
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McKibbin, Seann J., Bill Landenberger, and C. Mark Fanning. "First magmatism in the New England Batholith, Australia: forearc and arc–back-arc components in the Bakers Creek Suite gabbros." Solid Earth 8, no. 2 (April 5, 2017): 421–34. http://dx.doi.org/10.5194/se-8-421-2017.
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Abstract. The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite–gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ∼ 305 Ma) forearc basalt-like component with low Th ∕ Nb and with high Y ∕ Zr and Ba ∕ La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc–back-arc like gabbroic magmas (305–304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ∼ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ∼ 10 Myr) timescales for such melting.
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Khanchuk, A. I., A. A. Alenicheva, V. V. Golozubov, A. T. Kandaurov, Y. Y. Yurchenko, and S. A. Sergeev. "THE KHANKA MASSIF: HETEROGENEITY OF ITS BASEMENT AND REGIONAL CORRELATIONS." Tikhookeanskaya Geologiya 41, no. 4 (2022): 3–22. http://dx.doi.org/10.30911/0207-4028-2022-41-4-3-22.
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The results of geochronology studies on metagranitoids (U-Pb SIMS) and ophiolites (Sm-Nb) from the Khanka massif are considered. New and published data define the Early Neoproterozoic Matveevka-Nakhimov terrane with early suprasubduction magmatism of 935 and 915 Ma, intraplate and Pacific-type transform margin magmatism of 850-880 and 757 Ma, and the Late Neoproterozoic-Early Cambrian Dvoryan and Tafuin terranes with suprasubduction magmatism of 543, 520, 517 and 513 Ma. Between these two parts of the massif there is a suture (Voznesenka and Spassk terranes) formed by Ediacaran-Cambrian shelf deposits and a Cambrian accretionary prism with ophiolites older than 514 Ma. The greater part of the Khanka massif formed late in the Cambrian with the Kordonka island arc terrane accreted at the end of the Silurian. The Sergeevka terrane of the Ordovician island arc joined it through Early Cretaceous strike-slip movements. Heterogeneous structures of the main part of the Khanka massif can be traced to the north by the analogous stages of magmatism and metamorphism, where the Jiamusi massif (including the East Bureya terrane) is an Early Neoproterozoic block and the eastern Songnen massif (including the West Bureya terrane) is a Late Neoproterozoic-Cambrian block. Between these two blocks is the Spassk-Wuxingzhen-Melgin suture formed by their collision late in the Cambrian. The Bureya-Songnen-Jiamusi-Khanka superterrane formed as a part of the Gondwana supercontinent about 500 Ma ago through orogeny and accretion of the Rodinia supercontinent fragments.
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Babaie, Hassan A., Abbed Babaei, A. Mohamad Ghazi, and Mohsen Arvin. "Geochemical, 40Ar/39Ar age, and isotopic data for crustal rocks of the Neyriz ophiolite, Iran." Canadian Journal of Earth Sciences 43, no. 1 (January 1, 2006): 57–70. http://dx.doi.org/10.1139/e05-111.
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Trace-element data (including the rare-earth elements) in the crustal sequence of the Neotethyan Neyriz ophiolite in southwest Iran indicate normal mid-ocean ridge basalt (N-MORB) or island-arc tholeiite chemistry for the Tang-e Hana basalt. The data suggest that the Tang-e Hana rhyodacite, basalt, plagiogranite, and gabbro derived from a low-K tholeiitic parent magma. Trace-element distributions in amphibolite clasts, in the sole detachment of the ophiolite south of Lake Neyriz, correlate well with distributions in basalt clasts in the mélange and in the Tang-e Hana basalt. These trace elements suggest that the amphibolite originated from metamorphism and deformation of a tholeiitic basalt protolith. New 40Ar/39Ar incremental heating plateau ages from two hornblende plagiogranite specimens, in the crustal sequence in Tang-e Hana, are 92.07 ± 1.69 and 93.19 ± 2.48 Ma. Isotopic data for five Tang-e Hana basalts yield εNd values of +7.8 and +7.9, and 87Sr/86Sr values of 0.70368 to 0.70476. The isotopic compositions, ophiolite tectonostratigraphy, and correlation of the 40Ar/39Ar cooling (plagiogranite) and deformation (amphibolite) ages suggest emplacement of the Neyriz ophiolite either into an accretionary prism, through offscraping and subduction erosion, and (or) formation in a supra-subduction zone environment, around 8296 Ma. Progressive accretion probably led to the development of a fore-arc basin and deposition of Upper Cretaceous Eocene fore-arc and arc-derived sediments on the ophiolite.
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DRAUT, AMY E., PETER D. CLIFT, DAVID M. CHEW, MATTHEW J. COOPER, REX N. TAYLOR, and ROBYN E. HANNIGAN. "Laurentian crustal recycling in the Ordovician Grampian Orogeny: Nd isotopic evidence from western Ireland." Geological Magazine 141, no. 2 (March 2004): 195–207. http://dx.doi.org/10.1017/s001675680400891x.
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Because magmatism associated with subduction is thought to be the principal source for continental crust generation, assessing the relative contribution of pre-existing (subducted and assimilated) continental material to arc magmatism in accreted arcs is important to understanding the origin of continental crust. We present a detailed Nd isotopic stratigraphy for volcanic and volcaniclastic formations from the South Mayo Trough, an accreted oceanic arc exposed in the western Irish Caledonides. These units span an arc–continent collision event, the Grampian (Taconic) Orogeny, in which an intra-oceanic island arc was accreted onto the passive continental margin of Laurentia starting at ∼ 475 Ma (Arenig). The stratigraphy corresponding to pre-, syn- and post-collisional volcanism reveals a progression of εNd(t) from strongly positive values, consistent with melt derivation almost exclusively from oceanic mantle beneath the arc, to strongly negative values, indicating incorporation of continental material into the melt. Using εNd(t) values of meta-sediments that represent the Laurentian passive margin and accretionary prism, we are able to quantify the relative proportions of continent-derived melt at various stages of arc formation and accretion. Mass balance calculations show that mantle-derived magmatism contributes substantially to melt production during all stages of arc–continent collision, never accounting for less than 21% of the total. This implies that a significant addition of new, rather than recycled, continental crust can accompany arc–continent collision and continental arc magmatism.
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Bohdanova, Milena, and Oleh Hnylko. "OPHIOLITOCLASTIC BRECCIAS IN THE SECTION OF THE SOYMUL OLISTOSTROME FORMATION." SCIENTIFIC PAPERS OF DONNTU Series: “The Mining and Geology”, no. 1(27)-2(28)2022 (2022): 116–21. http://dx.doi.org/10.31474/2073-9575-2022-1(27)-2(28)-116-121.
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Purpose. Investigation .of the composition and features of the formation conditions of the Soymul olistostrome stratum in outcrops along the upper course of the Velyka Ugolka River in the Marmarosh Klippen Zone (Inner Ukrainian Carpathians), which is of important theoretical importance for the reproduction of the paleogeography of the basin and its tectonic history. Methodology. In this work there traditional structural-geological methods of field large-scale geomapping were used. Results. During the field work, geological mapping and documentation of the supporting outcrops of the Lower Cretaceous Soimul olistostrome was carried out. The material composition of the rocks in the outcrops was studied, the conditions of occurrence of olistoliths and matrix of the mixtites were investigated. A model of the formation of the Lower Cretaceous Soimul Formation is proposed Scientific novelty. For the first time, specific formations – ophiolithoclast breccias, several types of which are distinguished by the composition of fragments and cement – have been described in the outcrops among scattered fragments of ophiolitic assasia. Practical significance. In detailed geological mapping, the display of thrust and associated mixtite complexes (melanges and olistostomes) is a necessary condition for the reliability and conditionality of geological maps.The improvement of the theoretical and scientific-methodical basis of large-scale mapping of mixtites is also important for the identification of new tectonic criteria for the search for minerals, the forecast of dangerous geological processes, and geostable construction. In addition, the studied section, in our opinion, is a unique geotourism object of the Ukrainian Carpathians. Key words: accretion prism, olistostrome formation, ophiolite association, ophioliclast breccias, ophiocalcite.
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CHAN, GAVIN HEUNG-NGAI, JOHN MALPAS, COSTAS XENOPHONTOS, and CHING-HUA LO. "Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer–Bassit ophiolites: insights from 40Ar–39Ar geochronology." Geological Magazine 144, no. 5 (July 12, 2007): 797–810. http://dx.doi.org/10.1017/s0016756807003792.
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The Troodos ophiolite in Cyprus and Baer–Bassit ophiolite in Syria together form part of the Tethyan ophiolite belt. They were generated in a supra-subduction zone setting in Late Cretaceous times. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic ‘coloured mélange’ zones, which contain, among a variety of lithologies, metre- to kilometre-size blocks of metamorphic rocks. Precise 40Ar–39Ar laser step-heating experiments performed on four amphibolites from SW Cyprus and six from NW Syria, yield plateau ages ranging from 75.7±0.3 Ma to 88.9±0.8 Ma in Cyprus and 71.7±0.5 to 88.4±0.4 Ma in Syria. The older limits of these time spans are coeval with the age of the formation of the associated ophiolites. Unlike other metamorphic sole rocks which seem to form in relatively short time spans, these metamorphic rocks found in Cyprus and Syria are interpreted to have formed in Late Cretaceous times by accretion below the overriding Troodos and Baer–Bassit crust for a period of 15–18 Ma. The metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll-back and the rotation of the overriding plate until the cessation of subduction in Maastrichtian times. In Cyprus, the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed Mamonia passive margin sequence intercalated with rocks of the Troodos ophiolite during plate collision in the Maastrichtian. Concomitantly, in Syria, the Baer–Bassit ophiolite and subcreted metamorphic complex were emplaced onto the Arabian passive margin and fragmented into blocks and knockers, forming the Baer–Bassit mélange.
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Dril, S. I., M. I. Kuzmin, Ju V. Noskova, and O. V. Zarubina. "ISOTOPE Sm–Nd JUVENILE CRUST CHARACTERISTICS OF THE CENTRAL PART OF MONGHOL-OKHOTSK OROGENIC BELT." Доклады Российской академии наук. Науки о Земле 509, no. 2 (February 1, 2023): 184–89. http://dx.doi.org/10.31857/s2686739722602812.
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In the Phanerozoic, the production of the continental crust was associated with convergent geodynamic settings and, therefore, with intracontinental orogenic belts developed after the closure of paleooceans. Evaluation of the proportions of juvenile versus older recycled material is a key parameter for understanding how the crust in orogens formed and evolved. The Mongol-Okhotsk orogenic belt is one of the major structural part of Central Asia. Its central – Trans-Baikal part contains the well-reserved fragments of island-arc system as well as the entire spectrum of accretionary prism formations, allowing evaluation of the proportions of juvenile to recycled sedimentary material in the crust of this orogen. In this part of the belt, the best preserved fragments of juvenile crust are the Late Paleozoic volcanogenic-sedimentary sequences of the Kamensk and Urtui suites. The first suite is an indicator of the subduction along the northwestern margin of the Mongol-Okhotsk Paleocean beneath the Siberian paleocontinent, and the second one is an indicator of the subduction along the southeastern beneath the Argun superterrane. The entire compositional spectrum of volcanics from basalts to rhyolites demonstrate positive values εNd(254МА) = +1.4–(+3.8) and TNd(DM) = 896–920 MA. The basalts of the Urtui formation are also characterized by positive εNd(350МА) values, lying in the range of +1.7–(+6.0) at TNd(DM) = 773–939 MA. Therefore, the juvenile crust of the orogenic belt is characterized by positive ɛNd(t) values and model TNd(DM) age of 1000 Ma. The meta-sedimentary rocks of the accretion wedge of the Mongol-Okhotsk orogenic belt are significantly dominated by older recycled crustal material, whose source is likely the Late-Riphean formations of the Argun superterrane.
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Kosarev, A. М., V. N. Puchkov, Igor B. Seravkin, and Gulnara T. Shafigullina. "Geodynamic conditions of massive sulfide formation in the Magnitogorsk megazone." LITHOSPHERE (Russia) 21, no. 6 (December 28, 2021): 775–804. http://dx.doi.org/10.24930/1681-9004-2021-21-6-775-804.
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Research subject. Volcanism, rock geochemistry, geodynamics, and massive sulfide formation in the Magnitogorsk megazone (MMZ) of the Southern Urals in the Middle Paleozoic.Materials and Methods. Across the largest part of the massive sulfide deposits under investigation, the authors conducted route studies, including geological surveys of individual ore fields and quarries of deposits, core samples of deep wells and transparent sections. Representative analyses of petrogenic and microelements were performed using wet chemistry and ICP-MS in analytical centers in Russia and Europe. Along with the authors’ data, analytical materials published by Russian and foreign researchers were used. Geodynamic reconstructions were carried out taking into account regional data on gravics, thermal field, magnetometry, and seismic stu dies, including «Urseis-95».Results. The geodynamic reconstructions established that the main elements of the paleostructure of the Southern Urals in the Devonian were the subduction zone of the eastern dip and asthenospheric diapirs that penetrated into the «slab-window», which determined the type of volcanic belts, the composition and volume of volcanic rocks of pyrite-bearing complexes, and ore matter of pyrite deposits. The following geodynamic zones in the MMZ were identified: 1 – polychronous accretion prism; 2 – frontal and developed island arcs (D1e2–D2ef1); 3 – zone of back-arc spreading (D1e2); 4 – rear island arc (D2ef1).Conclusions. All investigated zones and ore areas are characterized by an autonomous development of volcanism, a special deep structure and a different composition, as well as by a different volume of massive sulfide deposits that vary in the Cu and Zn ratios and Pb, Ba, Au amounts. In the MMZ volcanic complexes, three groups of plume source basalts are distinguished. The results can be used in predictive-estimation and search operations for massive sulfide mineralization.
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Merriman, R. J., and B. Roberts. "Low-grade metamorphism in the Scottish Southern Uplands terrane: deciphering the patterns of accretionary burial, shearing and cryptic aureoles." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 91, no. 3-4 (2000): 521–37. http://dx.doi.org/10.1017/s0263593300008373.
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ABSTRACTSystematic studies of metapelitic grade linked with the geological re-survey of the Southern Uplands have been used to generate a contoured metamorphic map currently covering nearly two-thirds of the terrane. These studies, based on approximately one pelite sample per 2·5 km2, have used XRD measurements of clay mineral reaction progress, particularly illite crystallinity, to delineate zones of diagenesis and low-grade metamorphism in the imbricated Ordovician and Silurian strata. The regional pattern revealed by metapelitic zonal sequences does not agree with earlier observations that grade increases across the strike, from SE to NW. Instead, the map shows considerable variations in metamorphic trends, including patterns of grade increasing from older into younger strata, indicative of accretionary burial. Other patterns identified include those generated by high strain rates in the Moniaive Shear Zone (MSZ), and by extensive low-temperature cryptic aureoles associated with late granitic intrusions. The present pattern is the result of uplift that generated normal movement on reactivated thrust faults and differential block movement on NW-trending faults.Regional metamorphic patterns were generated by burial and underplating in an accretionary thrust stack. Subduction was initiated in the early Caradoc and probably ceased in the early Wenlock. Metapelitic patterns suggest that two levels of accretion are exposed in the terrane. Strata accreted to the toe of the prism and stacked above the décollement zone are typically at late diagenetic grade. Underplated strata below the décollement are typically at anchizonal grades with moderate to well-developed slaty cleavage. Coherent thrust-bounded tracts of strata at both levels were rotated and buried to produce a syntectonic depth-controlled pattern of meta-morphism. Shear zone metamorphism at depths of 12 km or more was probably confined to the underplated lower level of the thrust stack, and Devonian granitic intrusions were also emplaced mainly within the underplated strata.
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Tsuji, Takeshi, Jack Dvorkin, Gary Mavko, Norimitsu Nakata, Toshifumi Matsuoka, Ayako Nakanishi, Shuichi Kodaira, and Osamu Nishizawa. "VP/VS ratio and shear-wave splitting in the Nankai Trough seismogenic zone: Insights into effective stress, pore pressure, and sediment consolidation." GEOPHYSICS 76, no. 3 (May 2011): WA71—WA82. http://dx.doi.org/10.1190/1.3560018.
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To estimate variation of stress state and sediment consolidation in the Nankai plate subduction zone off southwest Japan, we measured the P-wave to S-wave velocity ratio (VP/VS) and S-wave splitting along the seismic line extending from the trench to the seismogenic zone. For this purpose, we used active-source seismic data recorded by multicomponent ocean bottom seismometers (OBS). Because it is difficult to identify the PS-converted reflection waveforms for each of the geological boundaries in this deep offshore region, we focused on the more easily identified PPS-refracted waveforms that register the conversion of the up-going P-waves to S-waves at the igneous crust surface. We estimated the average VP/VS ratio within the sedimentary section by using the time lag between the P-refracted waves and PPS-converted waves. This VP/VS ratio changes abruptly at the trough axis (i.e., the deformation front of the accretionary prism) arguably because of compaction associated with the accretion process. We observed relatively high VP/VS around the seismogenic megasplay fault, which may partially indicate the abnormal pore pressure and intensive fractures associated with the fault. To estimate the stress-induced fracture orientation and stress magnitude, we computed the fast S-wave polarization direction and estimated S-wave velocity anisotropy by applying the crosscorrelation method to the PPS-converted waves. To improve signal-to-noise ratio of the waveform for S-wave splitting analysis, we stacked PPS-converted waveforms on receiver gather. These anisotropic characteristics change at the seismogenic megasplay fault: the fast polarization direction is nearly parallel to the subduction direction seaward of the megasplay fault and is perpendicular to the subduction direction landward of the megasplay fault. This velocity anisotropy is especially strong around the megasplay fault. These results imply that the preferred fracture orientation, as well as the principal stress orientation, is oblique to the direction of plate subduction near the megasplay fault.
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Vargas-Cordero, I., U. Tinivella, F. Accaino, F. Fanucci, M. F. Loreto, M. E. Lascano, and C. Reichert. "Basal and Frontal Accretion Processes versus BSR Characteristics along the Chilean Margin." Journal of Geological Research 2011 (September 12, 2011): 1–10. http://dx.doi.org/10.1155/2011/846101.
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Multichannel seismic reflection data recorded between Itata (36°S) and Coyhaique offshores (43°S) were processed to obtain seismic images. Analysis of the seismic profiles revealed that weak and discontinuous bottom simulating reflectors were associated to basal accretion processes, while strong and continuous bottom simulating reflectors were associated to frontal accretion processes. This can be explained considering that during basal accretion processes, extensional tectonic movements due to uplifting can favour fluid escapes giving origin to weaker and most discontinuous bottom simulating reflectors. During frontal accretion processes (folding and thrusting), high fluid circulation and stable tectonic conditions however can be responsible of stronger and most continuous bottom simulating reflectors. Along the Arauco-Valdivia offshores, steep accretionary prisms, normal faults, slope basins, and thicker underplated sediment bed were associated to basal accretion, while along the Itata, Chiloe and Coyhaique offshores, small accretionary prisms, folding, and thinner underplated sediment bed were associated to frontal accretion.
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Lokhorst, Ivar R., Lisanne Braat, Jasper R. F. W. Leuven, Anne W. Baar, Mijke van Oorschot, Sanja Selaković, and Maarten G. Kleinhans. "Morphological effects of vegetation on the tidal–fluvial transition in Holocene estuaries." Earth Surface Dynamics 6, no. 4 (October 9, 2018): 883–901. http://dx.doi.org/10.5194/esurf-6-883-2018.
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Abstract. Vegetation enhances bank stability and sedimentation to such an extent that it can modify river patterns, but how these processes manifest themselves in full-scale estuarine settings is poorly understood. On the one hand, tidal flats accrete faster in the presence of vegetation, reducing the flood storage and ebb dominance over time. On the other hand flow-focusing effects of a tidal floodplain elevated by mud and vegetation could lead to channel concentration and incision. Here we study isolated and combined effects of mud and tidal marsh vegetation on estuary dimensions. A 2-D hydromorphodynamic estuary model was developed, which was coupled to a vegetation model and used to simulate 100 years of morphological development. Vegetation settlement, growth and mortality were determined by the hydromorphodynamics. Eco-engineering effects of vegetation on the physical system are here limited to hydraulic resistance, which affects erosion and sedimentation pattern through the flow field. We investigated how vegetation, combined with mud, affects the average elevation of tidal flats and controls the system-scale planform. Modelling with vegetation only results in a pattern with the largest vegetation extent in the mixed-energy zone of the estuary, which is generally shallower. Here vegetation can cover more than 50 % of the estuary width while it remains below 10 %–20 % in the outer, tide-dominated zone. This modelled distribution of vegetation along the estuary shows general agreement with trends in natural estuaries observed by aerial image analysis. Without mud, the modelled vegetation has a limited effect on morphology, again peaking in the mixed-energy zone. Numerical modelling with mud only shows that the presence of mud leads to stabilisation and accretion of the intertidal area and a slight infill of the mixed-energy zone. Combined modelling of mud and vegetation leads to mutual enhancement with mud causing new colonisation areas and vegetation stabilising the mud. This occurs in particular in a zone previously described as the bedload convergence zone. While vegetation focusses the flow into the channels such that mud sedimentation in intertidal side channels is prevented on a timescale of decades, the filling of intertidal area and the resulting reduction in tidal prism may cause the infilling of estuaries over centuries.
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Rahardiawan, Riza, and Catur Purwanto. "STRUKTUR GEOLOGI LAUT FLORES, NUSA TENGGARA TIMUR." JURNAL GEOLOGI KELAUTAN 12, no. 3 (February 16, 2016): 153. http://dx.doi.org/10.32693/jgk.12.3.2014.256.
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Tujuan penelitian seismik saluran banyak di Laut Flores, Nusa Tenggara Timur adalah untuk mengetahui kondisi geologi bawah permukaan dasar laut. Daerah penelitian merupakan daerah yang aktif secara tektonik dan diekspresikan dalam bentuk prisma akresi, vulkanik tidak aktif dan sesar-sesar aktif yang membentuk morfologi dasar laut. Berdasarkan penafsiran stratigrafi seismik lapisan bawah permukaan dasar laut terdiri dari empat satuan batuan: Batuan Dasar, Prisma Akresi, Gunungapi Bawah Laut, dan Sedimen Klastika. Sedimen Klastika ini dibagi menjadi lima unit.
Kata kunci: seismik, morfologi dasar laut, sesar aktif, Laut Flores
The purpose of the study of seismic multi channel in Flores Sea, East Nusa Tenggara is to recognize subsurface geology condition. The study area is an active tectonic that expressed by accretion prisms, inactive vulcanic and active faults form seabed morphology. Based on seismic stratigraphy interpretation, the study area is composed of four rocks units: Basement rocks, Accretionary Wedge, Seamount, and Clastic Sediments. This clactic sediment is divided into five units.
Keywords: seismic, seabed morphology, active fault, Flores Sea
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Wang, Junpeng, Xiawen Li, Wenbin Ning, Timothy Kusky, Lu Wang, Ali Polat, and Hao Deng. "Geology of a Neoarchean suture: Evidence from the Zunhua ophiolitic mélange of the Eastern Hebei Province, North China Craton." GSA Bulletin 131, no. 11-12 (April 24, 2019): 1943–64. http://dx.doi.org/10.1130/b35138.1.
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Abstract Mélanges characterize Phanerozoic convergent plate boundaries, but have rarely been reported from Archean orogens. In this paper, we document a Neoarchean ophiolitic mélange in the Eastern Hebei Province of the North China Craton. The Zunhua ophiolitic mélange is composed of a structural mixture of metapelites, ortho- and para-gneisses, and magnetite-quartzite mixed with exotic tectonic mafic blocks of metabasalts, metagabbroic rocks, and metadiabases, along with ultramafic blocks of serpentinized peridotites and podiform chromitites. The Zunhua ophiolitic mélange shows typical “block in matrix” structures. All units of the mélange have been intruded by granitic dikes and quartz veins that clearly cross-cut the foliation of blocks and matrix of the mélange. Laser-ablation–inductively coupled plasma–mass spectrometry zircon U-Pb dating of detrital zircons from the meta-sedimentary mélange matrix and intruding granitic dikes constrains the formation time of the Zunhua mélange to be between 2.52 and 2.46 Ga. Metamorphic rims on zircons from meta-sedimentary mélange matrix have ages of 2467 ± 27 Ma, confirming metamorphism of the mélange occurred at ca. 2.47 Ga. High-precision (scale 1:20 and 1:50) litho-structural mapping, along with detailed structural observations along several transects documents the internal fabrics and kinematics of the mélange, revealing a northwest to southeast directed transportation. The asymmetric structures in the mélange with folding and faulting events in the Zunhua mélange record kinematic information and are similar to the tectonic style of an accretionary wedge. Field relationships and geochemical analysis of various mafic blocks show that these blocks formed in an arc-related subduction tectonic environment. We suggest that the Zunhua mélange marks the suture zone of a Neoarchean arc-continent collisional event in the Central Orogenic Belt of the North China Craton. Combined with our previous studies, we demonstrate that a ca. 2.5 Ga tectonic suture exists between an arc/accretionary prism terrane in the Central Orogenic Belt and the Eastern Block of the North China Craton. We correlate this segment of the suture with other similar zones along strike, for >1000 km, including sections of the ca. 2.5 Ga in Dengfeng greenstone belt in the southern margin of the Central Orogenic Belt, and the ca. 2.5 Ga Zanhuang ophiolitic mélange in the center of the orogen. These relationships demonstrate that tectonic processes in the late Archean included subduction/accretion at convergent margins, and the horizontal movement of plates, in a style similar to modern-day accretionary convergent margins.
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Anderson, T. B., and G. J. H. Oliver. "The Orlock Bridge Fault: a major Late Caledonian sinistral fault in the Southern Uplands terrane, British Isles." Transactions of the Royal Society of Edinburgh: Earth Sciences 77, no. 3 (1986): 203–22. http://dx.doi.org/10.1017/s0263593300010841.
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ABSTRACTA detailed examination of the boundary between Peach and Home's (1899) Northern and Central Belts, in the Lower Palaeozoic rocks of the Southern Uplands of Scotland and their Irish continuation in Longford–Down, demonstrates it to be a major Caledonian sinistral wrench fault. Maps and descriptions of outcrops of the fault at Slieve Glah in County Cavan, at Orlock Bridge on the NE coast of Down, at Cairngarroch on the Rhinns of Galloway and at Garvald, 11 km SW of Dunbar, are presented. A distinctive fault fabric, clearly the result of repeated sinistral slip at the first three localities, characterises these outcrops along the 400 km trace. The fabric elements include: (1) lenticular shearing of arenites in the fault protolith, (2) a fault-associated phyllonitic fabric, with abundant pressure-solution seams, overprinting the regional S1, (3) numerous foliation-parallel quartz segregations, (4) refolding of the regional S1 cleavage, segregation veins and the phyllonitic fabric in at least two generations of steeply plunging, sinistrally-verging folds, (5) a non-penetrative crenulation cleavage, (6) a locally developed sinistral S–C fabric, and (7) typical protomylonite, mylonite and ultramylonite textures in thin sections of the fault rocks. The zone of fault-associated deformation varies from a few metres across at Garvald to over 1 km at Slieve Glah. The fault thus differs from other tract-defining faults in the Southern Uplands, particularly in its clear evidence of ductile, quasi-plastic, deformation at depth, in its lack of associated imbrication, in its significant refolding and overprinting of the regional S1 cleavage and in its uniquely large stratigraphic effects.The main fabric-generating movement postdates the regional, accretion-related, S1 cleavage but predates minor Caledonian (c. 400 Ma) intrusions. For its entire length the fault separates the Northern Belt, with proof only of Upper Ordovician turbidites, and the Central Belt, where turbidite deposition began in the Silurian. The age of the base of the turbidites decreases southward by some six graptolite zones at the fault trace. The fault thus either (a) excises the equivalent of four tracts from a single accretionary-prism terrane, or (b) juxtaposes two distinct terranes, one of late Ordovician and the other of Silurian age. In either event the sinistral slip is probably in excess of 400 km.
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Osman, Ariana, Ronald J. Steel, Ryan Ramsook, Cornel Olariu, and Si Chen. "The arrival of the paleo–Orinoco Delta at Trinidad: The Cruse Formation delta lobes and delivery to deepwater Atlantic." Journal of Sedimentary Research 90, no. 8 (August 19, 2020): 938–68. http://dx.doi.org/10.2110/jsr.2020.47.
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ABSTRACT Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas and repeated glacio-eustatic, climate-driven sea-level changes on a ca. 100 ky time scale. The paleo–Orinoco margin is no exception to this, as the paleo–Orinoco River Delta with its high sediment load prograded across Venezuela, then into the Southern and Columbus basins of Trinidad since the late Miocene, depositing a continental-margin sedimentary prism that is > 12 km thick, 200 km wide, and 500 km along dip. The Cruse Formation (> 800 m thick; 3 My duration) records the first arrival of the paleo–Orinoco Delta into the Trinidad area. It then accreted eastwards, outwards onto the Atlantic margin, by shallow to deepwater clinoform increments since the late Miocene and is capped by a major, thick flooding interval (the Lower Forest Clay). Previous research has provided an understanding of the paleo–Orinoco Delta depositional system at seismic and outcrop scales, but a clinoform framework detailing proximal to distal reaches through the main fairway of the Southern Basin has never been built. We integrate data from 58 wells and outcrop observations to present a 3-D illustration of 15 mapped Cruse clinoforms, in order to understand the changing character of the first Orinoco clastic wedge on Trinidad. The clinoforms have an undecompacted average height of 550 m, estimated continental slope of 2.5° tapering to 1°, and a distance from shelf edge to near-base of slope of > 10 km. The clinoform framework shows trajectory changes from strong shelf-margin progradation (C10–C13) to aggradation (C14–C20) and to renewed progradation (C21–24). Cruse margin progradational phases illustrate oblique clinothem geometries that lack well-developed topsets but contain up to 70 m (200 ft) thick, deepwater slope channels. This suggests a high supply of sediment during periods of repeated icehouse rise and fall of eustatic sea level, with fall outpacing subsidence rates at times, and delivery of sand to the deepwater region of the embryonic Columbus channel region. Also, evidence of wholesale shelf-edge collapse and canyon features seen in outcrop strongly suggest that deepwater conduits for sediment dispersal and bypass surfaces for Cruse basin-floor fans do exist. The change to a topset aggradational pattern with a rising shelf trajectory may be linked to increased subsidence associated with eastward migration of the Caribbean plate. The Cruse-margin topsets were dominated by mixed fluvial–wave delta lobes that were effective in delivery of sands to the basin floor. The preservation of a fluvial regime of the delta may have been impacted by basin geometry which partly sheltered the area from the open Atlantic wave energy at the shelf edge. Ultimately, understanding shelf-edge migration style as well as process-regime changes during cross-shelf transits of the delta will help to predict the location of bypassed sands and their delivery to deepwater areas.
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Gailler, Lydie-Sarah, Guillaume Martelet, Isabelle Thinon, Vincent Bouchot, Jean-Frédéric Lebrun, and Philippe Münch. "Crustal structure of Guadeloupe islands and the Lesser Antilles arc from a new gravity and magnetic synthesis." Bulletin de la Société Géologique de France 184, no. 1-2 (January 1, 2013): 77–97. http://dx.doi.org/10.2113/gssgfbull.184.1-2.77.
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Abstract Guadeloupe island (West French Indies) is one of the twenty islands that compose the Lesser Antilles arc, which results from the subduction of the Atlantic ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents a compilation and the processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe islands and at the scale of the Lesser Antilles arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer arc, the long wavelength positive anomaly is interpreted, at least along the Karukera spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism, as evidenced in bathymetry as well as on the islands. At the scale of Guadeloupe island, combined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre island ; ii) the ancient volcanic complexes of Basse-Terre island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The E-W models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate, associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles arc and Guadeloupe volcanic system.
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Iverson, N. R., T. S. Hooyer, U. H. Fischer, D. Cohen, P. L. Moore, M. Jackson, G. Lappegard, and J. Kohler. "Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation." Journal of Glaciology 53, no. 182 (2007): 323–40. http://dx.doi.org/10.3189/002214307783258431.
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AbstractTo avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m × 1.6 m × 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7–12 days, the glacier regelated downward into the prism to depths of 50–80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high pore-water pressure (70–100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.
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Uieda, Leonardo, and Valéria C. F. Barbosa. "Robust 3D gravity gradient inversion by planting anomalous densities." GEOPHYSICS 77, no. 4 (July 1, 2012): G55—G66. http://dx.doi.org/10.1190/geo2011-0388.1.
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We have developed a new gravity gradient inversion method for estimating a 3D density-contrast distribution defined on a grid of rectangular prisms. Our method consists of an iterative algorithm that does not require the solution of an equation system. Instead, the solution grows systematically around user-specified prismatic elements, called “seeds,” with given density contrasts. Each seed can be assigned a different density-contrast value, allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals. In real world scenarios, some sources might not be targeted for the interpretation. Thus, we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources. In our iterative algorithm, the estimated sources grow by the accretion of prisms in the periphery of the current estimate. In addition, only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations. Therefore, the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place, greatly reducing the demand for computer memory and processing time. Tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources, even when interfering signals produced by nontargeted sources are present. Inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of Quadrilátero Ferrífero, southeastern Brazil, we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations.
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Souto-Ceccon, Paola, Gonzalo Simarro, Paolo Ciavola, Andrea Taramelli, and Clara Armaroli. "Shoreline Detection from PRISMA Hyperspectral Remotely-Sensed Images." Remote Sensing 15, no. 8 (April 17, 2023): 2117. http://dx.doi.org/10.3390/rs15082117.
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Coastal managers, policymakers, and scientists use shoreline accretion/erosion trends to determine the coastline’s historical evolution and generate models capable of predicting future changes. Different solutions have been developed to obtain shoreline positions from Earth observation data in recent years, the so-called Satellite-Derived Shorelines (SDS). Most of the methodologies available in the literature use multispectral optical satellite imagery. This paper proposes two new methods for shoreline mapping at the subpixel level based on PRISMA hyperspectral imagery. The first one analyses the spectral signatures along defined beach profiles. The second method uses techniques more commonly applied to multispectral image analysis, such as Spectral Unmixing algorithms and Spatial Attraction Models. The results obtained with both methodologies are validated on three Mediterranean microtidal beaches located in two different countries, Italy and Greece, using image-based ground truth shorelines manually photointerpreted and digitised. The obtained errors are around 6 and 7 m for the first and second methods, respectively. These results are comparable to the errors obtained from multispectral data. The paper also discusses the capability of the two methods to identify two different shoreline proxies.
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McBeck, Jessica, Michele Cooke, Pauline Souloumiac, Bertrand Maillot, and Baptiste Mary. "The influence of detachment strength on the evolving deformational energy budget of physical accretionary prisms." Solid Earth 9, no. 6 (December 10, 2018): 1421–36. http://dx.doi.org/10.5194/se-9-1421-2018.
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Abstract. Tracking the evolution of the deformational energy budget within accretionary systems provides insight into the driving mechanisms that control fault development. To quantify the impact of these mechanisms on overall system efficiency, we estimate energy budget components as the first thrust fault pair develops in dry-sand accretion experiments. We track energy budget components in experiments that include and exclude a basal layer of glass beads in order to investigate the influence of detachment strength on work partitioning. We use the measurements of normal force exerted on the backwall to estimate external work, and measurements of strain observed on the sides of the sand packs to estimate the internal work, frictional work and work against gravity done within increments of each experiment. Thrust fault development reduces the incremental external work and incremental internal work, and increases the incremental frictional work and incremental gravitational work. The faults that develop within higher-friction detachment experiments produce greater frictional work than the faults in experiments with glass bead detachments because the slip distribution along the detachments remains the same, while the effective friction coefficient of the detachment differs between the experiments. The imbalance of the cumulative work budget suggests that additional deformational processes that are not fully captured in our measurements of the energy budget, such as acoustic energy, consume work within the deforming wedge.
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Stern, Robert J., Hadi Shafaii Moghadam, Mortaza Pirouz, and Walter Mooney. "The Geodynamic Evolution of Iran." Annual Review of Earth and Planetary Sciences 49, no. 1 (May 30, 2021): 9–36. http://dx.doi.org/10.1146/annurev-earth-071620-052109.
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Iran is a remarkable geoscientific laboratory where the full range of processes that form and modify the continental crust can be studied. Iran's crustal nucleus formed as a magmatic arc above an S-dipping subduction zone on the northern margin of Gondwana 600–500 Ma. This nucleus rifted and drifted north to be accreted to SW Eurasia ∼250 Ma. A new, N-dipping subduction zone formed ∼100 Ma along ∼3,000 km of the SW Eurasian margin, including Iran's southern flank; this is when most of Iran's many ophiolites formed. Iran evolved as an extensional continental arc in Paleogene time (66–23 Ma) and began colliding with Arabia ∼25 Ma. Today, Iran is an example of a convergent plate margin in the early stages of continent-continent collision, with a waning magmatic arc behind (north of) a large and growing accretionary prism, the Zagros Fold-and-Thrust Belt. Iran's crustal evolution resulted in both significant economic resources and earthquake hazards. ▪ Iran is a natural laboratory for studying how convergent plate margins form, evolve, and behave during the early stages of continental collision. ▪ Iran formed in the past 600 million years, originating on the northern flank of Gondwana, rifting away, and accreting to SW Eurasia. ▪ Iran is actively deforming as a result of collision with the Arabian plate, but earthquakes do not outline the position of the subducting slab. ▪ The Cenozoic evolution of Iran preserves the main elements of a convergent plate margin, including foredeep (trench), accretionary prism, and magmatic arc.
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Malinovsky, A. I., V. V. Golozubov, and S. A. Medvedeva. "COMPOSITION, SOURCE AREAS AND DEPOSITIONAL ENVIRONMENT OF LOWER CRETACEOUS SEDIMENTS IN THE NORTHERN SIKHOTE-ALIN." Tikhookeanskaya Geologiya 41, no. 6 (2022): 24–44. http://dx.doi.org/10.30911/0207-4028-2022-41-56-24-44.
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The structure, composition, source areas of Lower Cretaceous terrigenous sediments and geodynamic conditions for their deposition in the Northern Sikhote-Alin are considered. The study established that in terms of mineralogical and geochemical parameters the sandstones, being either petrogenic or first cycle deposits formed by the products of the breakdown of bedrock from the source areas, correspond to graywackes. They are characterized by low maturity, weak lithodynamic reworking of parental rocks, and high rates of deposition. The paleogeodynamic interpretation of the data suggests sedimentation in the Early Cretaceous along the continent-ocean boundary in the basin related to large-scale strike-slip motions along the transform faults. The source area combined sialic land formed by granite-metamorphic and sedimentary rocks, a mature and deeply eroded continental-margin arc, as well as fragments of Jurassic-Early Cretaceous accretion prisms of the Sikhote-Alin with ophiolites incorporated into their structure. All this allows for the studied deposits to be considered as part of the Early Cretaceous Zhuravlevka pull-apart terrane.
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Malinovsky, A. I. "HEAVY CLASTIC MINERALS AS AN INDICATOR OF GEODYNAMIC SETTINGS OF ACCUMULATION AND PROVENANCE OF CRETACEOUS SEDIMENTS OF THE WEST SAKHALIN TERRANE." Bulletin of Kamchatka Regional Association «Educational-Scientific Center». Earth Sciences, no. 1(49) (March 31, 2021): 68–86. http://dx.doi.org/10.31431/1816-5524-2021-1-49-68-86.
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The article discusses the results of studying heavy clastic minerals from the Cretaceous sandy rocks of the West Sakhalin Terrane, and also presents their paleogeodynamic interpretation. It is shown that in terms of mineralogical and petrographic parameters, the terrane sandstones correspond to typical graywackes and are petrogenic rocks formed mainly by destruction of igneous rocks of the source areas. The sediments were found to contain both sialic, granite-metamorphic association minerals, and femic, formed by products of the destruction of basic and ultrabasic volcanic rocks. The interpretation of the entire set of data on the content, distribution and microchemical composition of heavy minerals was carried out by comparing them with minerals from older rocks and modern sediments accumulated in known geodynamic settings. The results obtained indicate that during the Cretaceous, sedimentation occurred along the continent-ocean boundary in a basin associated with large-scale left-lateral transform movements of the Izanagi Plate relative to the Eurasian continent. The source area that supplied clastic material to that basin combined a sialic landmass composed of granite-metamorphic and sedimentary rocks, a mature deeply dissected ensialic island arc, and fragments of accretion prisms, in the structure of which involved ophiolites.
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Khanchuk, A. I., I. V. Kemkin, V. E. Kirillov, V. V. Ivanov, M. F. Kiryanov, and S. I. Trushin. "ULBAN TERRANE (ZONE) AS PART OF THE JURASSIC ACCRETIONAL COMPLEX OF THE SIKHOTE-ALIN OROGENIC BELT." Tikhookeanskaya Geologiya 43, no. 3 (2024): 3–18. http://dx.doi.org/10.30911/0207-4028-2024-43-3-3-18.
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New data are reported on the age of Triassic-Jurassic cherts replaced up the section by siliceous mudstones, and then by mudstones, which together with basalts form thin (up to hundreds of meters) plates and lenses that pinch out along the strike at different levels of the multi-kilometer terrigenous section of the Ulban terrane (zone). In the Nimelen subzone (the Albazino gold deposit area), their time interval of formation is Norian-Early Toarcian and that of host terrigenous deposits is Pliensbachian-Bathonian. In the Mewachan subzone, cherts and siliceous–clayey rocks are Middle Triassic-Callovian in age and terrigenous rocks are Middle-Late Jurassic (including Tithonian). A comparison of deposits of the Ulban terrane with deposits of the Samarka terrane which are well-studied and similar in age and composition allows us to consider the Ulban terrane (zone) as part of the Jurassic accretionary complex of the Sikhote-Alin orogenic belt. There are also sufficient indications to believe that its structural features are consistent with the subduction model. The basis for this is that the Triassic-Jurassic cherts and siliceous–clayey rocks accumulated for about 45 million years at a rate of about 1.8 m/million years characteristic for the oceanic plate sedimentary cover. At the same time, a gradual transition from cherts to mudstones is observed evidencing the movement of the oceanic plate into the subduction zone. The inclusion of its fragments in the terrigenous section is the result of their being detached in the trench and under the overhanging slab. Tectono-stratigraphic columns of the subzones of the Ulban terrane and a scheme of zoning of the Jurassic accretionary prism have been compiled with four structural-age levels along its entire length.
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Langeroodi, Danial, and Jens Hjorth. "Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-selected Highly Reddened Active Galactic Nuclei." Astrophysical Journal Letters 957, no. 2 (November 1, 2023): L27. http://dx.doi.org/10.3847/2041-8213/acfeec.
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Abstract Cold, substellar objects such as brown dwarfs have long been recognized as contaminants in color-selected samples of active galactic nuclei (AGNs). In particular, their near- to mid-infrared colors (1–5 μm) can closely resemble the V-shaped (f λ ) spectra of highly reddened accreting supermassive black holes (“little red dots”), especially at 6 < z < 7. Recently, a NIRCam-selected sample of little red dots over 45 arcmin2 has been followed up with deep NIRSpec multiobject prism spectroscopy through the UNCOVER program. By investigating the acquired spectra, we identify 3 of the 14 followed-up objects as T/Y dwarfs with temperatures between 650 and 1300 K and distances between 0.8 and 4.8 kpc. At 4.8 − 0.1 + 0.6 kpc, A2744-BD1 is the most distant brown dwarf discovered to date. We identify the remaining 11 objects as extragalactic sources at z spec ≳ 5. Given that three of these sources are strongly lensed images of the same AGN (A2744-QSO1), we derive a brown dwarf contamination fraction of 25% in this NIRCam selection of little red dots. We find that in the near-infrared filters, brown dwarfs appear much bluer than the highly reddened AGN, providing an avenue for distinguishing the two and compiling cleaner samples of photometrically selected highly reddened AGN.
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Hayes, Derek A., Scott E. Botterill, Michael J. Ranger, and Murray K. Gingras. "Fluvial character and architecture of an outcrop using sedimentology combined with UAV-based modeling, Cretaceous McMurray Formation, NE Alberta, Canada." Journal of Sedimentary Research 93, no. 5 (May 23, 2023): 273–92. http://dx.doi.org/10.2110/jsr.2022.039.
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ABSTRACT It is widely accepted that most occurrences of inclined heterolithic stratification (IHS) in the rock record form by laterally accreting point bars in freshwater fluvial, tidally influenced fluvial, or tidally dominated estuary channels. Despite the widespread distribution of IHS in the subsurface and outcropping strata of the lower Cretaceous McMurray Formation, the large-scale depositional architecture and lateral facies variability of these deposits remains controversial. The relatively limited lateral extent of many of the outcrops is a challenge, particularly when point-bar deposits on the scale of hundreds of meters to kilometers are interpreted in outcrops spanning anywhere from 100 to 300 meters laterally. This has in turn led researchers to leverage other datasets such as 3-D seismic to analyze the large-scale depositional architecture of the IHS, leading to two main interpretations for the IHS in the McMurray Formation: 1) a fluvially dominated environment owing to geomorphological features comparable to those in large modern fluvial systems, or 2) an estuarine environment owing to the presence of trace fossils characteristic of marine-derived faunal colonization in brackish-water settings and strong evidence of tidal modulation. The purpose of this study is to investigate the sedimentology and depositional architecture of IHS in a unique, kilometer-wide outcrop exposure of McMurray Formation strata and compare it to IHS observed at other McMurray Formation outcrops previously interpreted as estuarine channels. This is achieved by combining traditional field-based methods with Unmanned Aerial Vehicle-based outcrop modeling to create a 3-D outcrop model to visualize and analyze large point-bar geobodies deposited in a channel upwards of 25 meters deep and 750 meters wide exposed in outcrop at Crooked Rapids of the Athabasca River, west of the City of Fort McMurray. Importantly, this methodology uses bed orientation trends, paleocurrent data, and sedimentological observations to identify and map architectural elements, which constitute an eastward-accreting point bar crosscut by a southwestward-accreting counter point bar in the outcrop. The results strongly suggest that the IHS at Crooked Rapids was deposited in a freshwater fluvial environment. When compared to IHS deposited in estuarine depositional environments, fluvial IHS is driven by seasonal river discharge as opposed to the interplay between river discharge and the extent of the tidal prism. Therefore, fluvial IHS is: 1) dominantly sandstone with very minor waning-flow siltstone interbeds resulting from erosion by the succeeding freshet phase, and 2) completely devoid of bioturbation until flat-lying bar top or overbank strata is encountered. Using 3-D outcrop modeling to supplement sedimentological and ichnological observations strengthens the interpretation of complex fluvial geobodies and increases the overall understanding of the large-scale depositional architecture of point bars across the tidal–fluvial transition zone.
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Deville, Eric. "Dynamics of Brittle‐Viscous Accretionary Wedges as Revealed by Geophysical and Drilling Data and Analog Modeling of the Barbados Prism." Tectonics 42, no. 10 (October 2023). http://dx.doi.org/10.1029/2023tc007851.
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AbstractMega‐accretionary prisms do not exhibit the characteristics of the classical Coulomb wedge theory. In the example of the Barbados accretionary prism, a system of elongated extensional trenches (“basin‐&‐range” type) developed in the thickest zone of the tectonic wedge and this system has been active since at least Miocene times. Synchronously with this extension, compression occurred at the front of the accretionary prism (frontal accretion zone), and compression was also active at the inner edge of the prism (characterized by back‐thrusting). The interpretation proposed in this study invokes a spreading of the superficial part of the accretionary prism due to a viscous response associated to a tectonic thickening of the deepest parts of the prism. This interpretation is consistent with the fact that extension is limited to the axial part of the prism and coincides with the zone where the prism is the thickest. The deep zone of viscous behavior is interpreted as shale‐rich sedimentary domains intensively deformed by penetrative deformation. Analog sand‐silicone models monitored by X‐ray CT scanner have been used to simulate the distribution of the deformation in the Barbados accretionary prism as observed on available seismic reflection data. A bilayer model with an upper brittle zone and a lower ductile part is best suited to account for observed deformation. Compressive structures at the front and at the rear of the prism correlate with the zones of high concentration of maximum shear strain.
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Tan, Pingchuan, Weiwei Ding, and Jiabiao Li. "Exhumation history of the Hengchun Ridge and its implications for Taiwan orogenic processes." Frontiers in Earth Science 10 (August 24, 2022). http://dx.doi.org/10.3389/feart.2022.941040.
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The orogenic evolution of Taiwan is thought to have occurred with a steady and southward propagating trend since the Late Miocene. Recent studies suggest a two-stage collision for the Taiwan orogen and that the collision occurred simultaneously along the entirety of the island of Taiwan. To test this hypothesis, we evaluated 270 bathymetry profiles normal to the trench to constrain variations in the width, length, and crest of the Taiwan accretionary prism from the northern Central Ridge to the southern Hengchun Ridge. South of Taiwan Island, a gradual increase in the width and elevation of the accretionary prism of the Hengchun Ridge is noted. Assuming that the uplift of Hengchun Ridge is dominated by the accretion of hyper-stretched continental crust (HSCC), we estimated the uplift rate of the ridge (ca. 0.3 km/Ma) based on a linear regression between the HSCC and the observed depth of the prism crest. Using this uplift rate, we forward modeled the prism crest depth variations from 19.7°N to 23.5°N, and compared these values to observations. The model gives a good match to observations of the Hengchun Ridge, but significantly deeper depths to the north of Hengchun Peninsula. This suggests that the Taiwan orogeny had two stages: the first stage was dominated by structurally underplated HSCC, and the second is a combination of the arrival of the continental shelf and arc–continent collision. In addition to the widely accepted arc–continent collision, our study suggests that both the location and orientation of the continent–ocean boundary play important roles in orogeny.
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Schottenfels, Emily, Christine Regalla, and Yasuyuki Nakamura. "Influence of outer-rise faults on shallow décollement heterogeneity and sediment flux at the Japan trench." Seismica 3, no. 1 (January 15, 2024). http://dx.doi.org/10.26443/seismica.v3i1.386.
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We investigate the impact of outer-rise normal fault subduction on the structural evolution of the décollement and frontal prism in a portion of the Japan trench that hosted the 2011 Tohoku earthquake. We use seismic reflection data to map the relative occurrence of sediment accretion, sediment subduction, and frontal tectonic erosion in the shallow portion of the subduction zone and correlate these deformation styles to the magnitude of outer-rise fault throw and incoming plate sediment thickness. These data reveal spatial heterogeneity in the modes of deformation over distances of 5-10 km that necessitate correlative heterogeneity in the geometry and composition of the shallow décollement over similar length-scales. We find that sediment accretion predominantly occurs in regions where incoming plate sediment thickness is greater than fault throw. In these areas, the décollement appears to be non-planar and compositionally homogenous. Conversely, frontal tectonic erosion and slope failures are predominantly observed in regions where fault throw is greater than sediment thickness. In these areas, the décollement may be planar but compositionally heterogeneous. Additionally, spatial variations in near trench slip appear to correlate with the dominant deformation modes, suggesting that both sediment thickness and outer-rise fault throw may be important controls on shallow megathrust behavior.
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Hanegan, Kevin C., Duncan M. FitzGerald, Ioannis Y. Georgiou, and Zoe J. Hughes. "Long-term sea level rise modeling of a basin-tidal inlet system reveals sediment sinks." Nature Communications 14, no. 1 (November 6, 2023). http://dx.doi.org/10.1038/s41467-023-42895-y.
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AbstractMuch of the world’s population lives close to coastlines and this proximity is becoming increasingly impactful because of sea-level rise (SLR). Barrier islands and backbarrier saltmarshes, which comprise >10% of these coasts, are particularly susceptible. To better understand this risk, we model backbarrier morphologic and hydrodynamic evolution over a 200-year period of SLR, incorporating an erodible bed and a range of grain sizes. Here, we show that reduction in intertidal area creates negative feedback, shifting transport of coarse sediment (silt and sand) through the inlet from net export to net import. Imposing a modest marsh vertical accretion rate decreases the period of silt and sand import to 40 years (years 90 to 130) before being exported again. Clay is continuously exported thereby decreasing inorganic deposition on marshes and threatening their sustainability. Simulated marsh loss increases tidal prism and the volume of sand contained in ebb deltas, depleting coastal sand resources.
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Munari, U., V. Joshi, D. P. K. Banerjee, K. Čotar, S. Y. Shugarov, R. Jurdana-Šepić, R. Belligoli, et al. "The 2018 eruption and long term evolution of the new high-mass Herbig Ae/Be object Gaia-18azl = VES 263." Monthly Notices of the Royal Astronomical Society, July 30, 2019. http://dx.doi.org/10.1093/mnras/stz2078.
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Abstract We have been monitoring, at high cadence, the photometric and spectroscopic evolution of VES 263 following the discovery in 2018 of a brightening labeled as event Gaia-18azl. VES 263 is so far a neglected emission-line object discovered in the 1960s on objective prism plates, tentatively classified as a semi-regular AGB cool giant by automated analysis of ASASSN lightcurves. We have discovered that VES 263 is a bonafide massive pre-Main Sequence object (∼12 M⊙), of the Herbig AeBe type. It is located at 1.68±0.07 kpc distance, within the Cyg OB2 star-forming region, and it is highly reddened (EB − V=1.80±0.05) by interstellar extinction. In quiescence, the spectral energy distribution is dominated by the ∼20,000 K photospheric emission from the central B1II star, and at λ≥6μm by emission from circumstellar warm dust (T≤400○K). The 2018-19 eruption was caused by a marked brightening of the accretion disk around the B1II star as traced by the evolution with time of the integrated flux and the double-peaked profile of emission lines. At the peak of the eruption, the disk has a bulk temperature of ∼7500 K and a luminosity L ≥860 L⊙, corresponding to a mass accretion rate M≥1.1 × 10−5 M⊙ yr−1. Spectroscopic signature of possible bipolar jets (at −700 and +700 km s−1) of variable intensity are found. We have reconstructed from Harvard, Moscow and Sonneberg photographic plates the photometric history of VES 263 from 1896 to 1995.