Towards understanding the roll-back subduction of narrow oceanic domains: inferences from the modelling of Carpathians subduction zone

2020 ◽  
Author(s):  
István Bozsó ◽  
Ylona van Dinther ◽  
Liviu Matenco ◽  
István Kovács
Keyword(s):  
Subduction Zones ◽  
Plastic Properties ◽  
Thermal Distribution ◽  
The Carpathians ◽  
Vrancea Zone ◽  
Weakness Zones ◽  
Fully Coupled ◽  
Roll Back ◽  
Oceanic Slab ◽  
Geodynamic Reconstructions

<p>Numerous subduction systems in the Meditteranean realm are derived from the subduction of narrow oceanic domains, which are too narrow to generate the means of a fully coupled two-dimensional thermo-mechanical numerical model that takes into account the visco-elasto-plastic properties of different lithospheric domains. The results show that the narrow extent of the Ceahlau-Severin Ocean commonly assumed by paleogeographic reconstruction cannot generate roll-back upon subduction, in particular for models that must assume that slabs do not penetrate the 660 km discontinuity. Therefore, we propose that the subduction of the Carpathians system must have an inherited component from a previous orogenic evolution, which will ensure sufficient slab-pull to generate roll-back in the Carpathians realm. The model is constrained by recent results in terms of mantle structure and geodynamic reconstructions, while multiple compositional, thermal distribution and geometrical scenarios are tested in successive models. In all of our models, roll-back is achieved, which indicates that the proposed inherited component can sufficiently explain the roll-back subduction of the aforementioned narrow oceans. The subducting oceanic slab does not penetrate the 660 km discontinuity, this is in agreement with seismic tomographic results from various Mediterranean subduction zones. The exact onset and dynamics of the roll-back are mostly controlled by the thermic age of the ocean and the convergence kinematics of the continental slabs. An outlook on possible future improvements to the model, such as taking into account pre-existing rheological weakness zones in the lithosphere, is discussed and the opportunity of a seismo-thermo-mechanical modelling to investigate the seismic cycle in the Vrancea-zone is highlighted.</p>

scholarly journals First structural observation around the hinge of the Mongolian Orocline (Central Asia): Implications for the geodynamics of oroclinal bending and the evolution of the Mongol-Okhotsk Ocean

2021 ◽  
Author(s):  
Pengfei Li ◽  
Min Sun ◽  
Tserendash Narantsetseg ◽  
Fred Jourdan ◽  
Wanwan Hu ◽  
...  
Keyword(s):  
Central Asia ◽  
Subduction Zones ◽  
Plate Tectonics ◽  
Large Scale ◽  
Central Mongolia ◽  
3D Geometry ◽  
Hinge Zone ◽  
Subduction System ◽  
Negative Buoyancy ◽  
Oceanic Slab

To understand the origin of curved subduction zones has been one of the major challenges in plate tectonics. The Mongol-Okhotsk Orogen in Central Asia is characterized by the development of a U-shaped oroclinal structure that was accompanied by the continuous subduction of the Mongol-Okhotsk oceanic plate. Therefore, it provides a natural laboratory to understand why and how a subduction system became tightly curved. In this study, we provide the first structural observation around the hinge of the Mongolian Orocline (the Zag zone in Central Mongolia), with an aim to constrain the oroclinal geometry and to link hinge zone structures with the origin of the orocline. Our results show that rocks in the Zag zone are characterized by the occurrence of a penetrative foliation that is commonly subparallel to bedding. Both bedding and dominant fabric in the Zag zone are steeply dipping, and their strike orientations in a map view follow a simple curve around the hinge of the Mongolian Orocline, thus providing the first structural constraint for 3D geometry of the orocline. A secondary penetrative fabric parallel to the axial plane of the orocline was not observed, indicating a low degree of orogen-parallel shortening during oroclinal bending. Combining with available geological and geophysical data, we conclude that the Mongolian Orocline was developed in a period of Permian to Jurassic, and its origin was linked to the subduction of the Mongol-Okhotsk oceanic slab. We consider that the low-strain oroclinal bending likely resulted from the along-strike variation in trench retreat, which was either triggered by the negative buoyancy of the Mongol-Okhotsk oceanic slab, or driven by the relative rotation of the Siberian and North China cratons. Our results shed a light on 3D geometry and geodynamic mechanisms of large-scale oroclinal bending in an accretionary orogen.

scholarly journals CARPATHIANS

2020 ◽  
pp. 27-37
Author(s):  
S. Verbitsky ◽  
R. Pronishin ◽  
V. Prokopishin ◽  
A. Stetskiv ◽  
M. Chuba ◽  
...  
Keyword(s):  
Seismic Station ◽  
Seismic Energy ◽  
Earthquake Source ◽  
National Academy Of Sciences ◽  
The Carpathians ◽  
Carpathian Region ◽  
Vrancea Zone ◽  
Active Zones ◽  
Maximum Earthquake ◽  
Academy Of Sciences

The article describes seismic observations in the Carpathian region in 2014, which were carried out, as before, by two organizations from two states: in Ukraine – the Seismicity Department of the Carpathian region of the Institute of Geophysics of the National Academy of Sciences of Ukraine, in Moldova – the Seismology Laboratory of the Institute of Geology and Seismology of the Academy of Sciences of Moldova. In Ukraine, 20 stationary digital stations and 3 temporary ones worked in the Dniester energy complex with a processing center in Lviv, in Moldova - six stations with a center in Chisinau. Different programs, local hodo-graphs and magnitudes were used. The consolidated catalog of earthquakes was created in Lviv. A map of epi-centers and a table of the distribution of earthquakes of different classes by region are given. The total number of earthquakes in 2014 was NΣ=81 in the range KP =5.2–14.3 with the interval of hypocenter depths h=1–154 km and the total seismic energy ΣE=2.11·1014 J. Of these, 18 earthquakes with depths h=77–154 km located in the Vrancea zone. The maximum earthquake with KP=14.3 was registered on November 22 in the Precarpathian Trough with hрР=37 km. In the Vrancha mountains the maximum earthquake occurred on March 29 with the KP=12.5 and hрР=136 km. In the Precarpathian and Transcarpathian regions, all earthquakes were weaker. The most powerful event in Transcarpathia was a perceptible earthquake that occurred near the Trostnyk seismic station on November 15 with KP=8.9. The earthquake source is located in the Earth's crust at a depth of h=10 km. The earthquake was felt by the population of the Dyakovo, Trostnyk, Fanchykovo villages with the intensity of 5 and 4–5. In general, in all the seismically active zones of the Carpathians in 2014, there was a slight increase in the level of seismicity compared to that in 2013.

Subduction dynamics and rheology control on forearc and backarc subsidence: Numerical models and observations from the Mediterranean  

2021 ◽  
Author(s):  
Attila Balazs ◽  
Claudio Faccenna ◽  
Taras Gerya ◽  
Kosuke Ueda ◽  
Francesca Funiciello
Keyword(s):  
Subduction Zones ◽  
Numerical Models ◽  
Accretionary Wedge ◽  
Suction Force ◽  
Continental Subduction ◽  
Backarc Basins ◽  
The Mediterranean ◽  
Forearc Basins ◽  
Back Arc ◽  
Roll Back

<p>The dynamics of oceanic and continental subduction zones is linked to the rise and demise of forearc and backarc basins in the overriding plate. Subsidence and uplift rates of these distinct sedimentary basins are controlled by variations in plate convergence and subduction velocities and determined by lithospheric rheological structure and different lithospheric thicknesses.</p><p>In this study we conducted a series of high-resolution 2D numerical models applying the thermo-mechanical code 2DELVIS (Gerya and Yuen, 2007). The model, based on finite differences and marker-in-cell techniques, solves the mass, momentum, and energy conservation equations for incompressible media; assumes elasto-visco-plastic rheologies and involves erosion, sedimentation and hydration processes.</p><p>The models show the evolution of wedge-top basins lying on top of the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger and before the slab reaches the 660 km discontinuity. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative dynamics topographic signals.</p><p>Extensional back-arc basins are either localized along inherited crustal or lithospheric weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. During trench retreat and slab roll-back the older volcanic arc area becomes part of the back-arc region. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Onset of continental subduction and soft collision is linked to the rapid uplift of the forearc basins; however, the back-arc region records ongoing extension. Finally, during hard collision the forarc and back-arc basins are ultimately under compression.</p><p>Our results are compared with the evolution of the Mediterranean and based on the reconstructed plate kinematics, subsidence and heat flow evolution we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.</p>

Linking geodynamic subduction models to self-consistent 3D dynamic earthquake rupture and tsunami simulations

2020 ◽  
Author(s):  
Sara Aniko Wirp ◽  
Alice-Agnes Gabriel ◽  
Elizabeth H. Madden ◽  
Iris van Zelst ◽  
Lukas Krenz ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Surface Boundary ◽  
Seismic Cycle ◽  
Earthquake Rupture ◽  
Dynamic Rupture ◽  
Cycle Model ◽  
Earthquake Dynamics ◽  
Rupture Mode ◽  
Fully Coupled ◽  
Tsunami Models

<p>3D imaging reveals striking along-trench structural variations of subduction zones world-wide (e.g., Han et al, JGR 2018). Subduction zones include basins, sediments, splay and back-thrusting faults that evolve over a large time span due to tectonic processes, and may crucially affect earthquake dynamics and tsunami genesis. Such features should be taken into account for realistic hazard assessment. Numerical modeling bridges time scales of millions of years of subduction evolution to seconds governing dynamic earthquake rupture, as well as spatial scales of hundreds of kilometers of megathrust geometry to meters of an earthquake rupture front.</p><p>Recently, an innovative framework linking long-term geodynamic subduction and seismic cycle models to dynamic rupture models of the earthquake process and seismic wave propagation at coseismic timescales was presented (van Zelst et al., JGR 2019). This workflow was extended in a simple test case to link the 2D seismic cycle model to a three-dimensional earthquake rupture mode, which was then linked to a tsunami model  (Madden et al., EarthArxiv, doi:10.31223/osf.io/rzvn2). Here, we couple a 2D seismic cycle model to 3D earthquake and tsunami models and assess the geophysical aspects of this coupling. We extract all 2D material properties, stresses and the strength of the megathrust, and its geometry, from the seismic cycling model at a time step right before a typical megathrust event to use as initial conditions for the 3D dynamic rupture models. We explore the effects of along-arc variations of megathrust curvature, sediment content, and closeness to failure of the wedge on earthquake dynamics by studying the effects on slip, rupture velocity, stress drop and seafloor deformation.</p><p>In a next step, the dynamic seafloor displacements are linked to tsunami simulations that use depth-integrated (hydrostatic) shallow water equations. This approach efficiently models wave propagations and large-scale horizontal flows. We also present novel, fully coupled 3D dynamic rupture-tsunami simulations (Krenz et al., AGU19; Abrahams et al., AGU19; Lotto and Dunham et al., 2015, Computational Geosciences) which solve simultaneously for the solid earth and ocean response, taking gravity into account via a modified free surface boundary condition.</p><p>Earthquake rupture modeling and the fully-coupled tsunami modeling utilize SeisSol (www.seissol.org), a flagship code of the ChEESE project (www.cheese-coe.eu). SeisSol is an open source software package using unstructured tetrahedral meshes that are optimally suited for the complex geometries of subduction zones. The here presented links between geodynamic subduction and seismic cycling model with earthquake dynamics and tsunami models better account for the complexity of subduction zones and help evaluate the effects of along arc heterogeneities on earthquake and tsunami behavior and advance physics-based assessments of earthquake-tsunami hazards.</p>

scholarly journals Continental versus oceanic subduction zones

2016 ◽  
Vol 3 (4) ◽  
pp. 495-519 ◽  
Author(s):  
Yong-Fei Zheng ◽  
Yi-Xiang Chen
Keyword(s):  
Subduction Zones ◽  
Mantle Wedge ◽  
Ultrahigh Pressure ◽  
Metamorphic Rocks ◽  
Crustal Rocks ◽  
Incompatible Elements ◽  
Ultrahigh Temperature ◽  
Subducting Slab ◽  
Oceanic Slab ◽  
Metasomatized Mantle

Abstract Subduction zones are tectonic expressions of convergent plate margins, where crustal rocks descend into and interact with the overlying mantle wedge. They are the geodynamic system that produces mafic arc volcanics above oceanic subduction zones but high- to ultrahigh-pressure metamorphic rocks in continental subduction zones. While the metamorphic rocks provide petrological records of orogenic processes when descending crustal rocks undergo dehydration and anataxis at forearc to subarc depths beneath the mantle wedge, the arc volcanics provide geochemical records of the mass transfer from the subducting slab to the mantle wedge in this period though the mantle wedge becomes partially melted at a later time. Whereas the mantle wedge overlying the subducting oceanic slab is of asthenospheric origin, that overlying the descending continental slab is of lithospheric origin, being ancient beneath cratons but juvenile beneath marginal arcs. In either case, the mantle wedge base is cooled down during the slab–wedge coupled subduction. Metamorphic dehydration is prominent during subduction of crustal rocks, giving rise to aqueous solutions that are enriched in fluid-mobile incompatible elements. Once the subducting slab is decoupled from the mantle wedge, the slab–mantle interface is heated by lateral incursion of the asthenospheric mantle to allow dehydration melting of rocks in the descending slab surface and the metasomatized mantle wedge base, respectively. Therefore, the tectonic regime of subduction zones changes in both time and space with respect to their structures, inputs, processes and products. Ophiolites record the tectonic conversion from seafloor spreading to oceanic subduction beneath continental margin, whereas ultrahigh-temperature metamorphic events mark the tectonic conversion from compression to extension in orogens.

scholarly journals Mariana-type ophiolites constrain the establishment of modern plate tectonic regime during Gondwana assembly

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jinlong Yao ◽  
Peter A. Cawood ◽  
Guochun Zhao ◽  
Yigui Han ◽  
Xiaoping Xia ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
Surface Erosion ◽  
Plate Tectonic ◽  
Mountain Ranges ◽  
Tectonic Regime ◽  
Subduction Initiation ◽  
The Earth ◽  
Tethys Ocean ◽  
Roll Back

AbstractInitiation of Mariana-type oceanic subduction zones requires rheologically strong oceanic lithosphere, which developed through secular cooling of Earth’s mantle. Here, we report a 518 Ma Mariana-type subduction initiation ophiolite from northern Tibet, which, along with compilation of similar ophiolites through Earth history, argues for the establishment of the modern plate tectonic regime by the early Cambrian. The ophiolite was formed during the subduction initiation of the Proto-Tethys Ocean that coincided with slab roll-back along the southern and western Gondwana margins at ca. 530-520 Ma. This global tectonic re-organization and the establishment of modern plate tectonic regime was likely controlled by secular cooling of the Earth, and facilitated by enhanced lubrication of subduction zones by sediments derived from widespread surface erosion of the extensive mountain ranges formed during Gondwana assembly. This time also corresponds to extreme events recorded in climate and surface proxies that herald formation of the contemporary Earth.

scholarly journals Effects of episodic slow slip on seismicity and stress near a subduction-zone megathrust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Saeko Kita ◽  
Heidi Houston ◽  
Suguru Yabe ◽  
Sachiko Tanaka ◽  
Youichi Asano ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Slow Slip ◽  
Plate Interface ◽  
B Values ◽  
Megathrust Earthquakes ◽  
Cyclic Processes ◽  
Stress Orientations ◽  
Oceanic Slab

AbstractSlow slip phenomena deep in subduction zones reveal cyclic processes downdip of locked megathrusts. Here we analyze seismicity within a subducting oceanic slab, spanning ~50 major deep slow slip with tremor episodes over 17 years. Changes in rate, b-values, and stress orientations of in-slab seismicity are temporally associated with the episodes. Furthermore, although stress orientations in the slab below these slow slips may rotate slightly, in-slab orientations 20–50 km updip from there rotate farther, suggesting that previously-unrecognized transient slow slip occurs on the plate interface updip. We infer that fluid pressure propagates from slab to interface, promoting episodes of slow slip, which break mineral seals, allowing the pressure to propagate tens of km further updip along the interface where it promotes transient slow slips. The proposed methodology, based primarily on in-slab seismicity, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes.

Subduction and roll-back of narrow oceanic slabs: Back-arc basin modelling of the Carpathians subduction zone

2021 ◽  
Author(s):  
István Bozsó ◽  
Ylona van Dinther ◽  
Liviu Matenco ◽  
Attila Balázs ◽  
István Kovács
Keyword(s):  
Subduction Zone ◽  
Pannonian Basin ◽  
Suture Zone ◽  
The Carpathians ◽  
Mediterranean Systems ◽  
Set Up ◽  
Sag Basin ◽  
Back Arc ◽  
Roll Back ◽  
Oceanic Domain

<p>The Carpathians subduction system evolved similarly to many Mediterranean systems where extensional back-arc basins and separate large sag basins develop in the overriding plate. The evolution of such basins can be explained in the context of roll-back of narrow oceanic slabs. Their evolution is linked to extensional and sag back-arc basins, retreating orogenic systems and slab detachment. A recent example of slab detachment can be studied by the Vrancea slab beneath the SE Carpathians.<br>Significant effort has been dedicated to modelling such Mediterranean-style subduction systems, and in most cases the model was set up with a narrow oceanic domain, which has an increased difficulty to create rollback due to reduced buoyancy of the slab.<br>Our approach is to use a two-dimensional thermo-mechanical numerical model that introduces an inherited oceanic domain, which adds to the younger, narrow ocean developed in the later stages.<br>Our model can produce sustained subduction of the oceanic slab associated with roll-back and slab detachment. In most of our models a retro-arc sag basin develops, which can be interpreted as the Transylvanian Basin. This sag basin is one of the most consistent features of our model. At larger distances from the subduction zone, the extensional back-arc of the Pannonian basin can be modelled by introducing an lithospheric weakness zone, which represents a suture zone inherited from a previous orogenic evolution. Such a suture zone is compatible with the overall orogenic evolution of the Alps-Carpathians-Dinarides system. We furthermore discuss the limitations of our 2D modeling in the overall 3D settings of the Carpathians system and possibilities of future integration.</p>

Transition from the lithospheric to asthenospheric mantle-derived magmatism in the Early Jurassic along eastern Bangong–Nujiang Suture, Tibet: Evidence for continental arc extension induced by slab rollback

2020 ◽  
Vol 133 (1-2) ◽  
pp. 134-148
Author(s):  
Wang-Chun Xu ◽  
Hong-Fei Zhang ◽  
Li-Ran Chen ◽  
Bi-Ji Luo ◽  
Liang Guo ◽  
...  
Keyword(s):  
Mantle Source ◽  
Subduction Zones ◽  
Granulite Facies ◽  
Early Jurassic ◽  
Basement Complex ◽  
Granulite Facies Metamorphism ◽  
Asthenospheric Mantle ◽  
Isotopic Compositions ◽  
Slab Rollback ◽  
Oceanic Slab

Abstract The transition of the geochemical signature in mafic rocks along the eastern Bangong–Nujiang suture in Tibet contains important information about geodynamic processes in the upper mantle. This study recognized two episodes of Early Jurassic gabbros from the Kaqiong terrane, a microblock within the Bangong–Nujiang suture zone. Early gabbros (ca. 197–191 Ma) appear as lenses in the basement complex and were overprinted by amphibolite/granulite-facies metamorphism at ca. 180 Ma. Later undeformed hornblende gabbros (ca. 177–175 Ma) occur as dikes intruding into the basement complex. The early metagabbros are characterized by arc-like geochemical features and enriched Nd-Hf isotopic compositions (whole rock ∑Nd(t) = –0.7 to +0.3; zircon ∑Hf(t) = –5.7 to –2.2), which suggests formation by partial melting of an enriched lithospheric mantle source. In contrast, the later hornblende gabbros have depleted Nd-Hf isotopic compositions (whole rock ∑Nd(t) = +6.1 to +7.1; zircon ∑Hf(t) = +10.7 to +16.8) and normal mid–oceanic–ridge basalt (N–MORB)-type rare earth element (REE) features. They also show variable enrichments of fluid mobile elements (e.g., Rb, U, Pb), indicative of the input of slab-derived fluids in their mantle source. Thus, the hornblende gabbros were most likely originated from the asthenospheric mantle metasomatized by subducted oceanic slab-derived fluids. The transition in geochemical and isotopic compositions of these mantle-derived magmas reveals a long-lasting lithosphere extension and thinning along the southern margin of the Qiangtang terrane in the Early Jurassic. Combined with geological observations, we propose that this transition has resulted from the southward rollback of the subducting Bangong–Nujiang Tethyan oceanic slab. The slab rollback could have initiated the overriding plate extension and the asthenosphere upwelling. Wider implications of this study are that an onset of slab rollback could be an important trigger for the transition of magmatic geochemistry in subduction zones.

scholarly journals Transition from slab roll-back to slab break-off in the central Apennines, Italy: Constraints from the stratigraphic and thermochronologic record

2021 ◽  
Author(s):  
Maria Giuditta Fellin ◽  
Malwina San Jose ◽  
Claudio Faccenna ◽  
Sean D. Willett ◽  
Domenico Cosentino ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Phase Evolution ◽  
Mediterranean Area ◽  
Accretionary Wedge ◽  
The West ◽  
Central Apennines ◽  
Two Phase ◽  
Transitional State ◽  
Intermontane Basins ◽  
Roll Back

Stratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab roll-back. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3−4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post−5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between <2 km in most areas and ≥3−4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab.

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