Ocean subduction dynamics in the Alps

2021 ◽  
Author(s):  
Philippe Agard ◽  
Mark Handy
Keyword(s):  
Transition Zone ◽  
Continental Margin ◽  
North Atlantic ◽  
Subduction Zones ◽  
Mantle Transition Zone ◽  
Continental Subduction ◽  
The Alps ◽  
Slow Spreading ◽  
Selective Preservation

<p><strong>The Alps preserve abundant oceanic blueschists and eclogites that exemplify the selective preservation of fragments of relatively short-lived, small, slow-spreading North Atlantic-type ocean basins (here the ~400-700 km wide Alpine Tethys), whose subducting slabs reach down to the Mantle Transition Zone. Whereas none of the subducted fragments were returned during the first half of the subduction history, those exhumed afterwards experienced conditions typical of mature subduction zones worldwide. Sedimentary-dominated units were underplated intermittently, mostly at ~30-40 km depth, while mafic/ultramafic-dominated units subducted to ~80 km (In the W. Alps), whose protoliths had formed close to the continent, were offscraped from the slab only a few Ma before continental subduction. Spatiotemporal contrasts in burial and preservation of the fragments reveal how along-strike segmentation of the continental margin affects ocean subduction dynamics.</strong></p>

Ocean Subduction Dynamics in the Alps

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 9-16
Author(s):  
Philippe Agard ◽  
Mark R. Handy
Keyword(s):  
Transition Zone ◽  
Continental Margin ◽  
North Atlantic ◽  
Subduction Zones ◽  
Mantle Transition Zone ◽  
Continental Subduction ◽  
The Alps ◽  
Slow Spreading ◽  
Selective Preservation

The Alps preserve abundant oceanic blueschists and eclogites that exemplify the selective preservation of fragments of relatively short-lived, small, slow-spreading North Atlantic–type ocean basins whose subducting slabs reach down to the Mantle Transition Zone at most. Whereas no subducted fragments were returned during the first half of the subduction history, those exhumed afterwards experienced conditions typical of mature subduction zones worldwide. Sedimentary-dominated units were under-plated intermittently, mostly at ~30–40 km depth. Some mafic–ultramafic-dominated units formed close to the continent were subducted to ~80 km and offscraped from the slab only a few million years before continental subduction. Spatiotemporal contrasts in burial and preservation of the fragments reveal how along-strike segmentation of the continental margin affects ocean subduction dynamics.

Intraplate and petit-spot volcanism originating from hydrous mantle transition zone

2020 ◽  
Author(s):  
Jianfeng Yang ◽  
Manuele Faccenda
Keyword(s):  
Transition Zone ◽  
Northeast China ◽  
Subduction Zones ◽  
Japan Trench ◽  
Low Velocity ◽  
Iranian Plateau ◽  
Mantle Transition Zone ◽  
Mantle Minerals ◽  
Ocean Ridges ◽  
Pacific Slab

<p>Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, slab devolatilization at subduction zones, and mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China and the peculiar petit-spot volcanoes offshore the Japan trench cannot be readily associated with any of these mechanisms. Furthermore, the seismic tomography images show remarkable low velocity zones (LVZs) sit above and below the mantle transition zone which are coincidently corresponding to the volcanism. Here we show that most if not all the intraplate/petit-spot volcanism and LVZs present around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous transition zone. Numerical modelling results indicate that 0.2-0.3 wt.% H<sub>2</sub>O dissolved in mantle minerals which are driven out from the transition zone in response to subduction and retreat of a stagnant plate is sufficient to reproduce the observations. This suggests that critical amounts of volatiles accumulated in the mantle transition zone due to past subduction episodes and/or delamination of volatile-rich lithosphere could generate abundant dynamics triggered by recent subduction event. This model is probably also applicable to the circum-Mediterranean and Turkish-Iranian Plateau regions characterized by intraplate/petit-spot volcanism and LVZs in the underlying mantle.</p>

scholarly journals Interrelation of the stagnant slab, Ontong Java Plateau, and intraplate volcanism as inferred from seismic tomography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Masayuki Obayashi ◽  
Junko Yoshimitsu ◽  
Daisuke Suetsugu ◽  
Hajime Shiobara ◽  
Hiroko Sugioka ◽  
...  
Keyword(s):  
Transition Zone ◽  
Subduction Zones ◽  
Middle Eastern ◽  
P Wave ◽  
Ontong Java Plateau ◽  
Mantle Transition Zone ◽  
Slab Breakoff ◽  
Pacific Slab ◽  
Velocity Anomalies ◽  
Stagnant Slab

AbstractWe investigated the seismological structure beneath the equatorial Melanesian region, where is tectonically unique because an immense oceanic plateau, a volcanic chain and subduction zones meet. We conducted a multi-frequency P-wave tomography using data collected from an approximately 2-year-long seismic experiment around the Ontong Java Plateau (OJP). High-velocity anomalies were revealed beneath the center of the OJP at a depth of ~ 150 km, the middle-eastern edge of the OJP at depths of 200–300 km, and in the mantle transition zone beneath and around the OJP; low-velocity anomalies were observed along the Caroline volcanic island chain above 450 km depth. These anomalies are considered to be associated with the thick lithosphere of the OJP, remnant dipping Pacific slab, stagnant Pacific slab, and a sheet-like upwelling. The broad stagnant slab was formed due to rapid trench retreat from 48 to 25 Ma until when the OJP with thick lithosphere collided with a subduction boundary of the Pacific and Australian plates. This collision triggered slab breakoff beneath the arc where the dipping slab remained. The stagnant Pacific slab in the mantle transition zone restricted the plume upwelling from the lower mantle causing sheet-like deformed upwelling in the upper mantle.

Receiver Function mapping of mantle transition zone discontinuities beneath Western Alps using scaled 3-D velocity corrections

2021 ◽  
Author(s):  
Dongyang Liu ◽  
Liang Zhao ◽  
Anne Paul ◽  
Huaiyu Yuan ◽  
Stefano Solarino ◽  
...  
Keyword(s):  
Transition Zone ◽  
Receiver Function ◽  
Velocity Model ◽  
Western Alps ◽  
Orogenic Belt ◽  
P Wave ◽  
Mantle Transition Zone ◽  
3D Velocity Model ◽  
The Alps ◽  
European Plate

<p>The Alpine orogenic belt is the result of the continental collision and convergence between the Adriatic microplate and European plate during the Mesozoic. The Alps orogenic belt has a complex tectonic history and the deformation in and around the Alps are significantly affected by several microplates (e.g., Adriatic and Iberia) and blocks, in particular the Apennines, Betics, Dinarides. The mantle transition zone is delineated by seismic velocity discontinuities around the depths of 410 and 660 km which are generally interpreted as polymorphic phase changes in the olivine system and garnet-pyroxene system.The subduction depth of the European plate and the origin of the mantle flow behind the plate plays crucial roles for our understanding of regional geodynamic (Zhao et al., 2016; Hua et al., 2017). Therefore, we use receiver function method to study the seismic features of discontinuities beneath the Western Alps to constrain the structure of subducted plate and study the geodynamic origin of the low velocity anomaly behind the subduction zone and its relationship with the high-relief topography. </p><p>This study uses data collected from 293 permanent and temporary broadband seismic stations (e.g., CIFALPS). Teleseismic events are selected from 30<sup>o</sup> to 90<sup>o </sup>epicentral distrance with magnitudes (Mw) between 5.3 and 9.0. Data are carefully checked by automated and manual procedures to to give a total of 24904 receiver functions. Both 1D velocity model of the IASP91 and 3D velocity model of the EU60 (Zhu et al., 2015) are used for time-to-depth migration. The results show that using 3D velocity model to image the two discontinuities may obtain a more accurate structure image of the mantle transition zone.</p><p>In the northern part of the study area, along the alpine orogenic belt, we find a localized arc-shaped thinning area with a depressed 410 discontinuity, which is attributed to hot mantle upwellings. The uplift is hardly seen on the 660 discontinuity, suggesting that the thermal anomaly is unlikely to be interpreted as a mantle plume. The uplift of the 410-km can be interpreted as the European plate subducting to the depth of the upper transition zone. The depression of the 660-km  is likely attributed to the remnants from the oceanic mantle lithosphere that detached from the Eurasian plate after closure of the Alpine Tethys. Our results show a good agreement between the thinning area of MTZ and the area of topographic uplift, the mantle upwelling promotes the temperature increase which is conducive to the uplift of topographic.</p><p>Reference</p><p>Zhao L , Paul A , Marco G. Malusà, et al. Continuity of the Alpine slab unraveled by high-resolution P-wave tomography. Journal of Geophysical Research: Solid Earth, 2016, 121.</p><p>Hua, Y., D. Zhao, and Y. Xu (2017), P wave anisotropic tomography of the Alps, J. Geophys. Res. Solid Earth, 122, 4509–4528, doi:10.1002/2016JB013831.</p><p>Zhu H,Bozdag E and Tromp J.Seismic structure of the European upper mantle based on adjoint tomography.Geophys. J. Int. 2015, 201, 18–52</p>

Theoretical modeling of the regular olivine intergrowths in the mimetic paramorphosis after ringwoodite and wadsleyite

2018 ◽  
pp. 3-12
Author(s):  
B. B. Shkursky
Keyword(s):  
Transition Zone ◽  
Theoretical Modeling ◽  
Mantle Transition Zone ◽  
Misorientation Angles

Theoretical modeling of regular olivine grains misorientations in mimetic paramorphoses after ringwoodite and wadsleyite, the formation of which during the ascension of matter from the Mantle Transition Zone is expected, has been carried out. The coordinates of the misorientation axes and the misorientation angles, characterizing 10 operations of alignment in the pair intergrowths of olivine grains, eight of which are twins, are calculated. Possible conditions for the formation of mimetic paramorphoses predicted here, and the chances of their persistence are discussed. The calculated orientations are compared with the known twinning laws of olivine.

Multi-stage sulfur and carbon mobility in fossil continental subduction zones: new insights from carbonate-bearing orogenic peridotites

2021 ◽  
Author(s):  
Giulia Consuma ◽  
Sonja Aulbach ◽  
Roberto Braga ◽  
Laure A.J. Martin ◽  
Peter Tropper ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Continental Subduction ◽  
Multi Stage

scholarly journals A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge

Nature ◽  
2021 ◽  
Vol 589 (7843) ◽  
pp. 562-566
Author(s):  
Matthew R. Agius ◽  
Catherine A. Rychert ◽  
Nicholas Harmon ◽  
Saikiran Tharimena ◽  
J.-Michael Kendall
Keyword(s):  
Transition Zone ◽  
Mantle Transition Zone ◽  
Mid Atlantic Ridge
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