scholarly journals Lateral propagation–induced subduction initiation at passive continental margins controlled by preexisting lithospheric weakness

2020 ◽  
Vol 6 (10) ◽  
pp. eaaz1048 ◽  
Author(s):  
Xin Zhou ◽  
Zhong-Hai Li ◽  
Taras V. Gerya ◽  
Robert J. Stern
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Three Dimensional ◽  
Passive Margin ◽  
Continental Margins ◽  
Subduction Initiation ◽  
Passive Margins ◽  
The North ◽  
Lateral Propagation

Understanding the conditions for forming new subduction zones at passive continental margins is important for understanding plate tectonics and the Wilson cycle. Previous models of subduction initiation (SI) at passive margins generally ignore effects due to the lateral transition from oceanic to continental lithosphere. Here, we use three-dimensional numerical models to study the possibility of propagating convergent plate margins from preexisting intraoceanic subduction zones along passive margins [subduction propagation (SP)]. Three possible regimes are achieved: (i) subducting slab tearing along a STEP fault, (ii) lateral propagation–induced SI at passive margin, and (iii) aborted SI with slab break-off. Passive margin SP requires a significant preexisting lithospheric weakness and a strong slab pull from neighboring subduction zones. The Atlantic passive margin to the north of Lesser Antilles could experience SP if it has a notable lithospheric weakness. In contrast, the Scotia subduction zone in the Southern Atlantic will most likely not propagate laterally.

Forced subduction initiation at passive continental margins: Numerical modeling

2020 ◽  
Author(s):  
Xinyi Zhong ◽  
Zhong-Hai Li
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Passive Margin ◽  
Complex Case ◽  
Subduction Initiation ◽  
Boundary Force ◽  
Time Required

<p>Subduction initiation (SI) induced by the tectonic boundary force may play a significant role in the Wilson cycle. In the previous analog and numerical models, the constant convergent velocity is generally applied, which may lead to large boundary forces for SI. In this study, we begin with testing the simple case of SI at passive margin with constant convergent force. The results indicate that the boundary force required to trigger the SI at passive margin with a thin and young oceanic lithosphere is much lower than that with a thick and old one. It is consistent with the multiple Cenozoic subduction zones in the Southwest Pacific, which are young ocean basin within 40 Ma and compressed by the India-Australia plate. Furthermore, we extended our model to explore a more complex case, forced SI during the collision-induced subduction transference, which is critical for Tethyan evolution. Both collision and SI processes are integrated in the numerical models. The results indicate that the forced convergence, rather than pure free subduction, is required to trigger and sustain the SI in the neighboring passive margin after collision of terrane. In addition, a weak passive margin can significantly promote the occurrence of subduction initiation, by decreasing required boundary force within reasonable range of plate tectonics. However, the lengths of subducted oceanic slab and accreting terrane play secondary roles in the occurrence of SI after collision. Under the favorable conditions of collision-induced subduction transference, the time required for subduction initiation after collision is generally within 10 Myrs, which is consistent with the general geological records of Neo-Tethys. In contrast, both Atlantic passive margin and Indian passive margin are old and stable with absence of subduction initiation in the present, which remains an open question.</p>

scholarly journals Evidence of oceanic plate delamination in the Northern Atlantic

2021 ◽  
Author(s):  
Joao Duarte ◽  
Nicolas Riel ◽  
Chiara Civiero ◽  
Sonia Silva ◽  
Filipe Rosas ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Numerical Models ◽  
Oceanic Lithosphere ◽  
Continental Lithosphere ◽  
Subduction Initiation ◽  
Passive Margins ◽  
Velocity Anomaly ◽  
New Class ◽  
Lisbon Earthquake ◽  
Mountain Belts

Abstract The Earth’s surface is constantly being recycled by plate tectonics. Subduction of oceanic lithosphere and delamination of continental lithosphere constitute the two most important mechanisms by which the Earth’s lithosphere is recycled into the mantle. Delamination or detachment in continental regions typically occurs below mountain belts due to a weight excess of overthickened lithospheric mantle, which detaches from overlying lighter crust, aided by the existence of weak layers within the continental lithosphere. Oceanic lithosphere is classically pictured as a rigid plate with a strong core that does not allow for delamination to occur. Here, we propose that active delamination of oceanic lithosphere occurs offshore Southwest Iberia. The process is assisted by the existence of a lithospheric serpentinized layer that allows the lower part of the lithosphere to decouple from the overlying crust. Tomography images reveal a sub-lithospheric high-velocity anomaly below this region, which we interpret as a delaminating block of old oceanic lithosphere. We present numerical models showing that for a geological setting mimicking offshore Southwest Iberia delamination of oceanic lithosphere is possible and may herald subduction initiation, which is a long-unsolved problem in the theory of plate tectonics. We further propose that such oceanic delamination is responsible for the highest-magnitude earthquakes in Europe, including the M8.5-8.7 Great Lisbon Earthquake of 1755 and the M7.9 San Vincente earthquake of 1969. In particular, our numerical models, in combination with calculations on seismic potential, provide a solution for the instrumentally recorded 1969 event below the flat Horseshoe abyssal plain, away from mapped tectonics faults. Delamination of old oceanic lithosphere near passive margins constitutes a new class of subduction initiation mechanisms, with fundamental implications for the dynamics of the Wilson cycle.

scholarly journals Evolution and demise of passive margins through grain mixing and damage

2021 ◽  
Vol 118 (4) ◽  
pp. e2011247118
Author(s):  
David Bercovici ◽  
Elvira Mulyukova
Keyword(s):  
Plate Tectonics ◽  
Ocean Basin ◽  
Passive Margin ◽  
Continental Margins ◽  
Sea Floor ◽  
Passive Margins ◽  
Grain Damage ◽  
Lithospheric Plates ◽  
Compositional Gradients ◽  
Ocean Lithosphere

How subduction—the sinking of cold lithospheric plates into the mantle—is initiated is one of the key mysteries in understanding why Earth has plate tectonics. One of the favored locations for subduction triggering is at passive margins, where sea floor abuts continental margins. Such passive margin collapse is problematic because the strength of the old, cold ocean lithosphere should prohibit it from bending under its own weight and sinking into the mantle. Some means of mechanical weakening of the passive margin are therefore necessary. Spontaneous and accumulated grain damage can allow for considerable lithospheric weakening and facilitate passive margin collapse. Grain damage is enhanced where mixing between mineral phases in lithospheric rocks occurs. Such mixing is driven both by compositional gradients associated with petrological heterogeneity and by the state of stress in the lithosphere. With lateral compressive stress imposed by ridge push in an opening ocean basin, bands of mixing and weakening can develop, become vertically oriented, and occupy a large portion of lithosphere after about 100 million y. These bands lead to anisotropic viscosity in the lithosphere that is strong to lateral forcing but weak to bending and sinking, thereby greatly facilitating passive margin collapse.

scholarly journals Kinematic Boundary Conditions Favouring Subduction Initiation at Passive Margins Over Subduction at Mid-oceanic Ridges

2021 ◽  
Vol 9 ◽  
Author(s):  
A. Auzemery ◽  
E. Willingshofer ◽  
P. Yamato ◽  
T. Duretz ◽  
F. Beekman
Keyword(s):  
Convergence Rate ◽  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Continental Margins ◽  
Subduction Initiation ◽  
Passive Margins ◽  
Geodynamic Processes ◽  
The Alps ◽  
The Relationship

We perform numerical modelling to simulate the shortening of an oceanic basin and the adjacent continental margins in order to discuss the relationship between compressional stresses acting on the lithosphere and the time dependent strength of the mid-oceanic ridges within the frame of subduction initiation. We focus on the role of stress regulating mechanisms by testing the stress–strain-rate response to convergence rate, and the thermo-tectonic age of oceanic and continental lithospheres. We find that, upon compression, subduction initiation at passive margin is favoured for thermally thin (Palaeozoic or younger) continental lithospheres (<160 km) over cratons (>180 km), and for oceanic basins younger than 60 Myr (after rifting). The results also highlight the importance of convergence rate that controls stress distribution and magnitudes in the oceanic lithosphere. Slow convergence (<0.9 cm/yr) favours strengthening of the ridge and build-up of stress at the ocean-continent transition allowing for subduction initiation at passive margins over subduction at mid-oceanic ridges. The results allow for identifying geodynamic processes that fit conditions for subduction nucleation at passive margins, which is relevant for the unique case of the Alps. We speculate that the slow Africa–Europe convergence between 130 and 85 Ma contributes to the strengthening of the mid-oceanic ridge, leading to subduction initiation at passive margin 60–70 Myr after rifting and passive margin formation.

Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

2021 ◽  
pp. M57-2021-31
Author(s):  
Harald Brekke ◽  
Halvor S. S. Bunkholt ◽  
Jan I. Faleide ◽  
Michael B. W. Fyhn
Keyword(s):  
Lower Jurassic ◽  
Passive Margin ◽  
Continental Margins ◽  
Axial Line ◽  
Continental Breakup ◽  
The North ◽  
Tectonic Development ◽  
Definition Of ◽  
Conjugate Margins ◽  
Greenland Margin

AbstractThe geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

Juxtaposition of diverse, subduction-related tectonic blocks with contrasting metamorphic features and ages in the Paleoproterozoic Aketashitage orogen, NW China: Implications for Precambrian orogeny

2020 ◽  
Author(s):  
Qian W.L. Zhang ◽  
Jia-Hui Liu ◽  
Zhen M.G. Li ◽  
Meng-Yan Shi ◽  
Yi-Chao Chen ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Inductively Coupled Plasma ◽  
Subduction Zones ◽  
Plate Tectonics ◽  
Secondary Ion Mass Spectrometry ◽  
Orogenic Belt ◽  
Early Precambrian ◽  
Inductively Coupled ◽  
The North ◽  
Depositional Age

The comprehensive investigation of orogenic-related litho-structural assemblages, metamorphism, and geochronology in early Precambrian orogens can help us better understand the features of plate tectonics in early Earth. The Paleoproterozoic Aketashitage orogenic belt is located at a key position in northwestern China and connects the North China craton, Tarim craton, Altaids orogen, and Tethys orogen. Garnet-bearing mafic and paragneissic granulite occur as interlayers or blocks preserved within paragneissic matrix, and two to three generations of metamorphic mineral assemblages were identified. Geothermobarometry and pseudosection modeling yielded clockwise metamorphic P-T paths passing from 7.5‒8.6 kbar/575‒715 °C (M1) through 7.4‒12.2 kbar/715‒895 °C (M2) and finally to 5.2‒7.3 kbar/710‒800 °C (M3) for the mafic and paragneissic granulite as well as amphibolite, which is indicative of metamorphic features of subduction/collision zones. Peak metamorphic P-T conditions of all the samples lie in the medium P/T facies series, suggesting that the thermal gradient (∼20‒31 °C/km) of this Paleoproterozoic orogenic belt was obviously higher than most of the Phanerozoic subduction zones. Secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and monazite yielded metamorphic ages of ca. 1.98−1.96 Ga in the eastern part of the orogen, ca. 1.86−1.85 Ga in the western part, and a maximum depositional age of ca. 2.06 Ga for paragneiss. Compared with previous studies, the Aketashitage orogen is composed of unordered juxtaposition of diverse, subduction-related tectono-metamorphic blocks with different protoliths, metamorphic grades, and ages preserved within the paragneissic matrix deposited in the Paleoproterozoic, which is highly similar to Phanerozoic mélange. A Paleoproterozoic subduction-metamorphic-exhumation-accretionary process was deciphered, similar to that found in accretionary/orogenic wedge in Phanerozoic orogens. The juxtaposition of diverse, subduction-related tectonic blocks with contrasting ages and metamorphic features can serve as a marker of early Precambrian orogens and plate tectonics.

Middle Ordovician (Darriwilian) conodonts from southern Tibet, the Indian passive margin: implications for the age and correlation of the roof of the world

2020 ◽  
pp. 1-25
Author(s):  
Svend Stouge ◽  
David A. T. Harper ◽  
Renbin Zhan ◽  
Jianbo Liu ◽  
Lars Stemmerik
Keyword(s):  
Middle Part ◽  
Passive Margin ◽  
Continental Margins ◽  
Oceanic Circulation ◽  
Mount Everest ◽  
Southern Tibet ◽  
Middle Ordovician ◽  
The North ◽  
Carbon Isotope Excursion ◽  
Central Tibet

Abstract New occurrences of middle–late Darriwilian (Middle Ordovician) conodonts are reported from the Nyalam region, southern Tibet. The conodont-yielding strata, referred to the Chiatsun Group, accumulated on the north Indian continental margin of northern Gondwana. These Middle Ordovician conodonts include the informal species Histiodella sp. A in the middle part of the Lower Formation of the Chiatsun Group succeeded by a fauna of the Pygodus serra Zone in the upper part of that formation. Pygodus anserinus is recorded from the base of the Upper Formation of the Chiatsun Group. The Nyalam succession and its conodont taxa allow for precise correlation of the strata preserved on top of Mount Qomolangma (Mount Everest), eastern Tibet and the Peri-Gondwana Lhasa (north central Tibet), South China, North China, Tarim Basin and Thailand-Malaysia (Sibumasu Terrane) terranes and/or microcontinents. The middle Darriwilian positive increase in δ13Ccarb values (carbon isotope excursion, or MDICE) is recorded from most terranes, and can be related to a late middle Darriwilian global short-term cooling and sea-level drop. The cooling event prompted temperate- to warm-water taxa to migrate towards the palaeoequator and constrained the Australasian Province to locations near and at the palaeoequator. The intensified oceanic circulation and upwelling on continental margins probably caused some characteristic taxa to become extinct. The incoming fauna was mainly of cool-water taxa. The conodont specimens from southern Tibet are black to pale grey, corresponding to conodont colour index (CAI) values of 5 to 6, which demonstrates that the host sedimentary rocks were once heated to more than 360°C.

Bringing slow slip processes into focus

2020 ◽  
Author(s):  
Rebecca Bell
Keyword(s):  
High Resolution ◽  
Subduction Zones ◽  
Seismic Velocity ◽  
Numerical Models ◽  
Fluid Pressure ◽  
Geophysical Methods ◽  
Rock Properties ◽  
Slow Slip ◽  
Velocity Models ◽  
The North

<p>The discovery of slow slip events (SSEs) at subduction margins in the last two decades has changed our understanding of how stress is released at subduction zones. Fault slip is now viewed as a continuum of different slip modes between regular earthquakes and aseismic creep, and an appreciation of seismic hazard can only be realised by understanding the full spectrum of slip. SSEs may have the potential to trigger destructive earthquakes and tsunami on faults nearby, but whether this is possible and why SSEs occur at all are two of the most important questions in earthquake seismology today. Laboratory and numerical models suggest that slow slip can be spontaneously generated under conditions of very low effective stresses, facilitated by high pore fluid pressure, but it has also been suggested that variations in frictional behaviour, potentially caused by very heterogeneous fault zone lithology, may be required to promote slow slip.</p><p>Testing these hypotheses is difficult as it requires resolving rock properties at a high resolution many km below the seabed sometimes in km’s of water, where drilling is technically challenging and expensive. Traditional geophysical methods like travel-time tomography cannot provide fine-scale enough velocity models to probe the rock properties in fault zones specifically. In the last decade, however, computational power has improved to the point where 3D full-waveform inversion (FWI) methods make it possible to use the full wavefield rather than just travel times to produce seismic velocity models with a resolution an order of magnitude better than conventional models. Although the hydrocarbon industry have demonstrated many successful examples of 3D FWI the method requires extremely high density arrays of instruments, very different to the 2D transect data collection style which is still commonly employed at subduction zones.</p><p> The north Hikurangi subduction zone, New Zealand is special, as it hosts the world’s most well characterised shallow SSEs (<2 km to 15 km below the seabed).  This makes it an ideal location to collect 3D data optimally for FWI to resolve rock properties in the slow slip zone. In 2017-2018 an unprecedentedly large 3D experiment including 3D multi-channel seismic reflection, 99 ocean bottom seismometers and 194 onshore seismometers was conducted along the north Hikurangi margin in an 100 km x 15 km area, with an average 2 km instrument spacing. In addition, IODP Expeditions 372 and 375 collected logging-while drilling and core data, and deployed two bore-hole observatories to target slow slip in the same area. In this presentation I will introduce you to this world class 3D dataset and preliminary results, which will enable high resolution 3D models of physical properties to be made to bring slow slip processes into focus.  </p>

An analytical model concerning the possible initiation of subduction between the India and Africa plates, caused by the Morondova plume

2020 ◽  
Author(s):  
Bernhard Steinberger ◽  
Douwe van Hinsbergen
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Eastern Mediterranean ◽  
Plate Boundary ◽  
Plate Motion ◽  
Mantle Flow ◽  
Plate Motions ◽  
Subduction Initiation ◽  
Euler Pole ◽  
Geodynamic Processes

<p>Identifying the geodynamic processes that trigger the formation of new subduction zones is key to understand what keeps the plate tectonic cycle going, and how plate tectonics once started. Here we discuss the possibility of plume-induced subduction initiation. Previously, our numerical modeling revealed that mantle upwelling and radial push induced by plume rise may trigger plate motion change, and plate divergence as much as 15-20 My prior to LIP eruption. Here we show that, depending on the geometry of plates, the distribution of cratonic keels and where the plume rises, it may also cause a plate rotation around a pole that is located close to the same plate boundary where the plume head impinges: If that occurs near one end of the plate boundary, an Euler pole of the rotation may form along that plate boundary, with extension on one side, and convergence on the other.  This concept is applied to the India-Africa plate boundary and the Morondova plume, which erupted around 90 Ma, but may have influenced plate motions as early as 105-110 Ma. If there is negligible friction, i.e. there is a pre-existing weak plate boundary, we estimate that the total amount of convergence generated in the northern part of the India-Africa plate boundary can exceed 100 km, which is widely thought to be sufficient to initiate forced, self-sustaining subduction. This may especially occur if the India continental craton acts like an “anchor” causing a comparatively southern location of the rotation pole of the India plate. Geology and paleomagnetism-based reconstructions of subduction initiation below ophiolites from Pakistan, through Oman, to the eastern Mediterranean reveal that E-W convergence around 105 Ma caused forced subduction initiation, and we tentatively postulate that this is triggered by Morondova plume head rise. Whether the timing of this convergence is appropriate to match observations on subduction initiation as early as 105 Ma depends on the timing of plume head arrival, which may predate eruption of the earliest volcanics. It also depends on whether a plume head already can exert substantial torque on the plate while it is still rising – for example, if the plate is coupled to the induced mantle flow by a thick craton.</p>

scholarly journals Boninitic blueschists record subduction initiation and subsequent accretion of an arc–forearc in the northeast Proto-Tethys Ocean

Geology ◽  
2021 ◽  
Author(s):  
Dong Fu ◽  
Bo Huang ◽  
Tim E. Johnson ◽  
Simon A. Wilde ◽  
Fred Jourdan ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Oceanic Lithosphere ◽  
Island Arc ◽  
Early Paleozoic ◽  
Subduction Initiation ◽  
North Qilian Orogenic Belt ◽  
Mariana Arc ◽  
Tethys Ocean ◽  
North Qilian

Subduction of oceanic lithosphere is a diagnostic characteristic of plate tectonics. However, the geodynamic processes from initiation to termination of subduction zones remain enigmatic mainly due to the scarcity of appropriate rock records. We report the first discovery of early Paleozoic boninitic blueschists and associated greenschists from the eastern Proto-Tethyan North Qilian orogenic belt, northeastern Tibet, which have geochemical affinities that are typical of forearc boninites and island arc basalts, respectively. The boninitic protoliths of the blueschists record intra-oceanic subduction initiation at ca. 492–488 Ma in the eastern North Qilian arc/forearc–backarc system, whereas peak blueschist facies metamorphism reflects subsequent subduction of the arc/forearc complex to high pressure at ca. 455 Ma. These relations therefore record the life circle of an intra-oceanic subduction zone within the northeastern Proto-Tethys Ocean. The geodynamic evolution provides an early Paleozoic analogue of the early development of the Izu–Bonin–Mariana arc and its later subduction beneath the extant Japanese arc margin. This finding highlights the important role of subduction of former upper plate island arc/forearcs in reducing the likelihood of preservation of initial subduction-related rock records in ancient orogenic belts.

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