scholarly journals Rupture of wet mantle wedge by self-promoting carbonation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Atsushi Okamoto ◽  
Ryosuke Oyanagi ◽  
Kazuki Yoshida ◽  
Masaoki Uno ◽  
Hiroyuki Shimizu ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Mantle Wedge ◽  
Carbonaceous Material ◽  
Hydrous Minerals ◽  
Carbon And Oxygen Isotope ◽  
Episodic Tremor And Slip ◽  
Ductile Flow ◽  
Episodic Tremor ◽  
Isotope Analyses ◽  
Volume Decrease

AbstractMore than one teramole of carbon per year is subducted as carbonate or carbonaceous material. However, the influence of carbonation/decarbonation reactions on seismic activity within subduction zones is poorly understood. Here we present field and microstructural observations, including stable isotope analyses, of carbonate veins within the Higuchi serpentinite body, Japan. We find that the carbon and oxygen isotope compositions of carbonate veins indicate that carbonic fluids originated from organic materials in metasediments. Thermodynamic calculations reveal that carbonation of serpentinite was accompanied by a solid volume decrease, dehydration, and high magnesium mobility. We propose that carbonation of the mantle wedge occurs episodically in a self-promoting way and is controlled by a solid volume contraction and fluid overpressure. In our conceptual model, brittle fracturing and carbonate precipitation were followed by ductile flow of carbonates and hydrous minerals; this might explain the occurrence of episodic tremor and slip in the serpentinized mantle wedge.

scholarly journals Melting of subducted sediments reconciles geophysical images of subduction zones

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
M. W. Förster ◽  
K. Selway
Keyword(s):  
Subduction Zones ◽  
Source Region ◽  
Volcanic Rocks ◽  
Electrically Conductive ◽  
Small Magnitude ◽  
Volcanic Arcs ◽  
Frictional Strength ◽  
Episodic Tremor And Slip ◽  
Episodic Tremor ◽  
Sediment Melting

AbstractSediments play a key role in subduction. They help control the chemistry of arc volcanoes and the location of seismic hazards. Here, we present a new model describing the fate of subducted sediments that explains magnetotelluric models of subduction zones, which commonly show an enigmatic conductive anomaly at the trenchward side of volcanic arcs. In many subduction zones, sediments will melt trenchward of the source region for arc melts. High-pressure experiments show that these sediment melts will react with the overlying mantle wedge to produce electrically conductive phlogopite pyroxenites. Modelling of the Cascadia and Kyushu subduction zones shows that the products of sediment melting closely reproduce the magnetotelluric observations. Melting of subducted sediments can also explain K-rich volcanic rocks that are produced when the phlogopite pyroxenites melt during slab roll-back events. This process may also help constrain models for subduction zone seismicity. Since melts and phlogopite both have low frictional strength, damaging thrust earthquakes are unlikely to occur in the vicinity of the melting sediments, while increased fluid pressures may promote the occurrence of small magnitude earthquakes and episodic tremor and slip.

Brittle-ductile deformation in high-pressure continental units and deep episodic tremor and slip

2021 ◽  
Author(s):  
Francesco Giuntoli ◽  
Giulio Viola
Keyword(s):  
High Pressure ◽  
Subduction Zones ◽  
Ductile Deformation ◽  
The European Union ◽  
Subduction Channel ◽  
Geological Record ◽  
Horizon 2020 ◽  
Mylonitic Foliation ◽  
Episodic Tremor And Slip ◽  
Episodic Tremor

<p>The geological record of deep seismic activity in subduction zones is generally limited due to common rock overprinting during exhumation and only a few regions allow studying well-preserved exhumed deep structures. The Northern Apennines (Italy) are one such area, granting access to continental units (Tuscan Metamorphic Units) that were subducted to high-pressure conditions, were affected by brittle-ductile deformation while accommodating deep tremor and slip and then exhumed back to surface, with only minor retrogression.</p><p>Our approach is based on detailed fieldwork, microstructural and petrological investigations. Field observations reveal a metamorphosed broken formation composed of boudinaged metaconglomerate levels enveloped by metapelite displaying a pervasive mylonitic foliation. Shear veins occur in both lithologies, but are more common and laterally continuous in the metapelite. They are mostly parallel to the foliation and composed of iso-oriented stretched quartz and Mg-carpholite (XMg>0.5) fibres, which are single-grains up to several centimetres long. These fibres define a stretching direction coherent with that observed in the metaconglomerate and metapelite, which is marked by K-white mica and quartz. Thermodynamic modeling constrains the formation of the high-pressure veins and the mylonitic foliation to ~ 1 GPa and 350°C, corresponding to c. 30-40 km depth in the subduction channel.</p><p>Shear veins developed in subducted (meta)sediments are a key indicator of episodic tremor and slip (e.g. <sup>1</sup>). We propose that these structures reflect the repeated alternation of localised brittle failure, with shear veins development, and more diffuse viscous deformation. These cycles were probably related to the fluctuation of pore pressure that repeatedly reached lithostatic values. Concluding, these structures can be considered the geological record of episodic tremors and slip occurring at >30 km of depth in the Apenninic subduction channel.</p><p>1. Fagereng, Å., Remitti, F. & Sibson, R. H. Incrementally developed slickenfibers — Geological record of repeating low stress-drop seismic events? Tectonophysics <strong>510</strong>, 381–386 (2011).</p><p>This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 839779.</p>

The rheology of talc at high P-T conditions with implications for subduction-zone dynamics

2020 ◽  
Author(s):  
Yuval Boneh ◽  
Matej Pec ◽  
Greg Hirth
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Microstructural Analysis ◽  
Stability Field ◽  
Localized Deformation ◽  
Hydrous Minerals ◽  
Regional Seismicity ◽  
Pressure Threshold ◽  
Confining Pressures

<p>Subduction-zone dynamics, kinematics, and seismicity are strongly affected by the rheology of hydrous phyllosilicates. Although there is growing evidence for hydrous minerals in the subducting plate, mantle wedge, and the interface between the plates, we are continuing to learn more about the rheological behavior of phyllosilicates at the relevant pressures. Talc is stable to depths of ≈100 km and has been found in fault rocks and subduction-zones mélanges as the product of metasomatism and/or mineral breakdown (e.g., breakdown of antigorite). The frictional strength of talc under low to intermediate pressures (up to ~400 MPa) was studied and demonstrated some of the mineral’s unique rheology; however, there is a lack of data for pressures of P > 0.5 GPa. Here we present the first rheological and microstructural analysis of experimentally deformed talc under pressure and temperature conditions relevant for the rheology of a subducted slab or mantle wedge.</p><p>We analyzed the mechanical and microstructural evolution of 15 samples of natural talc cylinders deformed using a high P-T deformation ‘Griggs’ type apparatus. We used natural samples comprise of >98 % talc and analyzed the post-mortem microstructure and chemistry of the samples using optical microscopy, scanning electron microscopy, and electron microprobe. The experiments were performed at confining pressures from 0.5 to 2 GPa and temperatures of 25 to 700°C; all within the talc stability field. Results show that the strength of talc at 25°C or 400°C is pressure-dependent up to the highest pressure tested (2 GPa). This behavior is attributed to brittle/semi-brittle mechanisms. At higher temperatures (500-700° C) and above a pressure threshold the strength becomes independent of pressure (e.g., when P > 1 GPa at T = 600 ° C), indicating that dilatant cracking is suppressed at these pressures. However, microstructural analysis indicates that fracturing is evident in all samples at all conditions examined. Interestingly, samples deformed at higher temperatures (>600°C) show more localized deformation. A synthesis of results from this study and previously published studies demonstrate that the strength of talc only becomes temperature-dependent at higher pressures. It is suggested that an increasing P-T geotherm of a subducted slab is likely to induce weakening and localization of talc-rich layers with possible implications for the mechanism to induce/hinder regional seismicity and affect the plate-coupling between the subducted and riding plates.   </p>

scholarly journals Cascading rupture of patches of high seismic energy release controls the growth process of episodic tremor and slip events

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Keita Nakamoto ◽  
Yoshihiro Hiramatsu ◽  
Takahiko Uchide ◽  
Kazutoshi Imanishi
Keyword(s):  
Energy Release ◽  
Subduction Zones ◽  
Seismic Energy ◽  
High Energy ◽  
Plate Interface ◽  
Waveform Data ◽  
Seismic Energy Release ◽  
Slow Earthquakes ◽  
Episodic Tremor And Slip ◽  
Episodic Tremor

AbstractSlip phenomena on plate interfaces reflect the heterogeneous physical properties of the slip plane and, thus, exhibit a wide variety of slip velocities and rupture propagation behaviors. Recent findings on slow earthquakes reveal similarities and differences between slow and regular earthquakes. Episodic tremor and slip (ETS) events, a type of slow earthquake widely observed in subduction zones, likewise show diverse activity. We investigated the growth of 17 ETS events beneath the Kii Peninsula in the Nankai subduction zone, Japan. Analyses of waveform data recorded by a seismic array enabled us to locate tremor hypocenters and estimate the migration patterns and spatial distribution of the energy release of tremor events. Here, we describe three major features in the growth of ETS events. First, independent of their start point and migration pattern, ETS events exhibit patches of high seismic energy release on the up-dip part of the ETS zone, suggesting that the location of these patches is controlled by inherent physical or frictional properties of the plate interface. Second, ETS events usually start outside the high-energy patches, and their final extent depends on whether the patches participate in the rupture. Third, we recognize no size dependence in the initiation phase of ETS events of different sizes with comparable start points. These features demonstrate that the cascading rupture of high-energy patches governs the growth of ETS events, just as the cascading rupture of asperities governs the growth of regular earthquakes.

scholarly journals Decoupling of inorganic and organic carbon during slab mantle devolatilisation

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
P. Bouilhol ◽  
B. Debret ◽  
E. C. Inglis ◽  
M. Warembourg ◽  
T. Grocolas ◽  
...  
Keyword(s):  
High Pressure ◽  
Organic Carbon ◽  
Subduction Zones ◽  
Inorganic Carbon ◽  
Mantle Wedge ◽  
Isotope Composition ◽  
Sr Isotope ◽  
Ultra High Pressure ◽  
Isotope Analyses ◽  
Inorganic And Organic

AbstractSerpentinites are an important sink for both inorganic and organic carbon, and their behavior during subduction is thought to play a fundamental role in the global cycling of carbon. Here we show that fluid-derived veins are preserved within the Zermatt-Saas ultra-high pressure serpentinites providing key evidence for carbonate mobility during serpentinite devolatilisation. We show through the O, C, and Sr isotope analyses of vein minerals and the host serpentinites that about 90% of the meta-serpentinite inorganic carbon is remobilized during slab devolatilisation. In contrast, graphite-like carbonaceous compounds remain trapped within the host rock as inclusions within metamorphic olivine while the bulk elemental and isotope composition of organic carbon remains relatively unchanged during the subduction process. This shows a decoupling behavior of carbon during serpentinite dehydration in subduction zones. This process will therefore facilitate the transfer of inorganic carbon to the mantle wedge and the preferential slab sequestration of organic carbon en route to the deep mantle.

scholarly journals Cascading Rupture of Patches of High Seismic Energy Release Controls the Growth Process of Episodic Tremor and Slip Events

2020 ◽  
Author(s):  
Keita Nakamoto ◽  
Yoshihiro Hiramatsu ◽  
Takahiko Uchide ◽  
Kazutoshi Imanishi
Keyword(s):  
Energy Release ◽  
Subduction Zones ◽  
Seismic Energy ◽  
High Energy ◽  
Plate Interface ◽  
Waveform Data ◽  
Seismic Energy Release ◽  
Slow Earthquakes ◽  
Episodic Tremor And Slip ◽  
Episodic Tremor

Abstract Slip phenomena on plate interfaces reflect the heterogeneous physical properties of the slip plane and thus exhibit a wide variety of slip velocities and rupture propagation behaviors. Recent findings on slow earthquakes reveal similarities and differences between slow and regular earthquakes. Episodic tremor and slip (ETS) events, a type of slow earthquake widely observed in subduction zones, likewise show diverse activity. We investigated the growth of 17 ETS events beneath the Kii Peninsula in the Nankai subduction zone, Japan. Analyses of waveform data recorded by a seismic array enabled us to locate tremor hypocenters and estimate the migration patterns and spatial distribution of the energy release of tremor events. Here we describe three major features in the growth of ETS events. First, independent of their start point and migration pattern, ETS events exhibit patches of high seismic energy release on the up-dip part of the ETS zone, suggesting that the location of these patches is controlled by inherent physical or frictional properties of the plate interface. Second, ETS events usually start outside the high-energy patches, and their final extent depends on whether the patches participate in the rupture. Third, we recognize no size dependence in the initiation phase of ETS events of different sizes with comparable start points. These features demonstrate that the cascading rupture of high-energy patches governs the growth of ETS events, just as the cascading rupture of asperities govern the growth of regular earthquakes.

Limited subduction of water to mid-upper mantle depths predicted by the phase assemblages in hydrated peridotites with natural chemical composition at high-PT conditions

2021 ◽  
Author(s):  
Nestor Cerpa ◽  
Diane Arcay ◽  
José Alberto Padrón-Navarta
Keyword(s):  
Experimental Data ◽  
Sea Level ◽  
Subduction Zones ◽  
Thermal State ◽  
Water Flux ◽  
Geochemical Evolution ◽  
Hydrous Minerals ◽  
Global Sea Level ◽  
Global Water

<p>The water exchange between the Earth’s surface and the deep interior is a prime process for the geochemical evolution of our planet and its dynamics. The degassing of water from the mantle takes place through volcanism whereas mantle regassing occurs through the subduction of H<sub>2</sub>O chemically bound to hydrous minerals. The (im)balance between degassing and regassing controls the budget of surficial liquid water over geological timescales, i.e, the long-term global sea level. Continental freeboard constraints show that the mean-sea level has remained relatively constant in the last 540 Ma (changes less than about 100 m), thus suggesting a limited imbalance. However, thermopetrological models of water fluxes at present-day subduction zones predict that regassing exceeds degassing by about 50% which, if extrapolated to the past, would have induced a drop inconsistent with the estimations of the long-term sea-level. We have made the case that these inconsistencies arise from thermodynamic predictions for the hydrated lithospheric mantle mineralogy that are poorly constrained at a high pressure (P) and temperature (T). In our study, we thus have revised the global-water flux calculations in subduction zones using petrological constraints on post-antigorite assemblages from recent laboratory experimental data on natural peridotites under high-PT conditions [e.g. Maurice et al, 2018].</p><p>We model the thermal state of all present-day mature subduction zones along with petrological modeling using the thermodynamic code Perple_X and the most updated version of the thermodynamic database of Holland and Powell [2011]. For the modeling of peridotite, we build a hybrid phase diagram that combines thermodynamic calculations at moderate PT and experimental data at high PT (> 6 GPa- 600˚C). Our updated thermopetrological model reveals that the hydrated mantle efficiently dehydrates upon the breakdown of the hydrous aluminous-phase E before reaching 250 km in all but the coldest subduction zones. Further subducting slab dehydration is expected between 300-350 km depths, regardless of its thermal state, as a result of lawsonite breakdown in the gabbroic crust. Overall, we predict that present-day global water retention in subducting plates beyond a depth of 350 km barely exceeds the estimations of mantle degassing for average thicknesses of subducting serpentinized mantle subducting at the trenches of up to 6 km. Finally, our models quantitatively support the steady-state sea level scenario over geological times.</p><p> </p><p>Maurice, J., Bolfan-Casanova, N., Padrón-Navarta, J. A., Manthilake, G., Hammouda, T., Hénot, J. M., & Andrault, D. (2018). The stability of hydrous phases beyond antigorite breakdown for a magnetite-bearing natural serpentinite between 6.5 and 11 GPa. <em>Contributions to Mineralogy and Petrology</em>, 173(10), 86.</p><p>Holland, T. J. B., & Powell, R. (2011). An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids. <em>Journal of Metamorphic Geology</em>, 29(3), 333-383.</p>

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