Paraskevi Io Ioannidi

Vrije Universiteit Amsterdam

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Samuel Angiboust

Centre National de la Recherche Scientifique

Onno Oncken

Freie Universität Berlin

Philippe Agard

Sorbonne Université

Laëtitia Le Pourhiet

Institut des Sciences de la Terre de Paris

Marcos Moreno

Pontificia Universidad Católica de Chile

Iskander Muldashev

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Jacqueline E. Reber

Iowa State University

Shae McLafferty

Iowa State University

Kyle Bogatz

Iowa State University

Gabriele Morra

University of Louisiana at Lafayette

Cooperative Institutions

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Iowa State University

University of Potsdam

Centre National de la Recherche Scientifique

Université Paris Cité

ETH Zurich

University of Oslo

Institut des Sciences de la Terre de Paris

Sorbonne Université

Institut Universitaire de France

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Rheological Properties of Natural Subduction Zone Interface: Insights from "Digital" Griggs Experiments

AGUFM (2017)

Paraskevi Io Ioannidi Laëtitia Le Pourhiet Marcos Moreno Philippe Agard Onno Oncken

Interface (matter)

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Deformation along the roof of a fossil subduction interface in the transition zone below seismogenic coupling: The Austroalpine case and new insights from the Malenco Massif (Central Alps)

Geosphere (2020)

Paraskevi Io Ioannidi Samuel Angiboust Onno Oncken Philippe Agard Johannes Glodny

Abstract A network of fossil subduction plate interfaces preserved in the Central Alps (Val Malenco, N Italy) is herein used as a proxy to study deformation processes related to subduction and subsequent underplating of continental slices (in particular the Margna and Sella nappes) at depths reported to in the former brittle-ductile transition. Field observations, microfabrics, and mapping revealed a network of shear zones comprising mostly mylonites and schists but also rare foliated cataclasites. These shear zones are either located at the contacts of the two nappes or within the boundaries of the Sella unit. Microprobe results point to two different white mica generations, with higher-pressure (Si-rich) phengites rimming lower-pressure (Si-poor) phengites. Garnet is locally observed overgrowing resorbed pre-Alpine cores. Pressure-temperature estimates based on pseudosection modeling point to peak burial deformation conditions of ∼0.9 GPa and 350–400 °C, at ∼30 km depth. Rb/Sr geochronology on marbles deformed during the Alpine event yields an age of 48.9 ± 0.9 Ma, whereas due to incomplete recrystallization, a wide range of both Rb/Sr and 40Ar/39Ar apparent ages is obtained from deformed orthogneisses and micaschists embracing 87–44 Ma. Based on our pressure-temperature, structural and geochronological observations, the studied shear zones last equilibrated at depths downdip of the seismogenic zone in an active subduction zone setting. We integrate these new results in the frame of previous studies on other segments of the same Alpine paleosubduction interface, and we propose that this system of shear zones represents deformation conditions along the subduction interface(s) in the transition zone below the seismogenic zone during active subduction.

Mylonite

Massif

Lineation

Phengite

Underplating

continental collision

Thermochronology

10.1130/ges02149.1

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Citations (10)

Deciphering the Alpine Deformation History of a Potential Fossil Subduction Interface in the Depth of the Seismogenic Zone (Central Alps)

EGUGA (2017)

Paraskevi Io Ioannidi Onno Oncken Samuel Angiboust Philippe Agard

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The Effective Rheology of Natural Subduction Shear Zones: Insights from Numerical Simple Shear Experiments

EGU General Assembly Conference Abstracts (2017)

Paraskevi Io Ioannidi Laëtitia Le Pourhiet Marcos Moreno Philippe Agard Onno Oncken

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Deformation and Frictional Failure of Granular Media in 3D Analog and Numerical Experiments

Pure and Applied Geophysics (2024)

Paraskevi Io Ioannidi Shae McLafferty Jacqueline E. Reber Gabriele Morra Dion Weatherley

Abstract Frictional sliding along grain boundaries in brittle shear zones can result in the fragmentation of individual grains, which ultimately can impact slip dynamics. During deformation at small scales, stick–slip motion can occur between grains when existing force chains break due to grain rearrangement or failure, resulting in frictional sliding of granular material. The rearrangement of the grains leads to dilation of the granular package, reducing the shear stress and subsequently leading to slip. Here, we conduct physical experiments employing HydroOrbs, an elasto-plastic material, to investigate grain comminution in granular media under simple shear conditions. Our findings demonstrate that the degree of grain comminution is dependent on both the normal force and the size of the grains. Using the experimental setup, we benchmark Discrete Element Method (DEM) numerical models, which are capable of simulating the movement, rotation, and fracturing of elasto-plastic grains subjected to simple shear. The DEM models successfully replicate both grain comminution patterns and horizontal force fluctuations observed in our physical experiments. They show that increasing normal forces correlate with higher horizontal forces and more fractured grains. The ability of our DEM models to accurately reproduce experimental results opens up new avenues for investigating various parameter spaces that may not be accessible through traditional laboratory experiments, for example, in assessing how internal friction or cohesion affect deformation in granular systems.

Comminution

Brittleness

Cohesion (chemistry)

Shear band

10.1007/s00024-024-03464-6

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Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

Earth and Planetary Science Letters (2024)

Samuel Angiboust Paraskevi Io Ioannidi Iskander Muldashev

A paradox exists between the great number of intermediate-depth earthquakes occurring along active subduction interfaces worldwide and the extreme scarcity of paleo-seismic events recorded in exhumed metasediments from ancient subducted slabs. Recrystallization associated with exhumation-related overprinting generally contributes to the nearly-complete erasing of markers of unstable slip events in metamorphic rocks. We herein focus on a sample from an ancient deep thrust from a Cretaceous High-Pressure paleo-accretionary complex in Chilean Patagonia. A representative, moderately foliated micaschist exhibits broken garnet crystals that host a dense network of healed micro-fractures. While garnet fragments appear thoroughly disaggregated along the main foliation, the rock matrix that completely recrystallized has lost the record of brittle deformation. We employ a 2D visco-elasto-plastic numerical modelling approach in order to investigate the mechanical conditions that enable the fracturing of isolated garnet grains in a relatively weak matrix. The rupture of these stiff grains is achieved in our models at strain rates faster than 10−10 /s to 10−12 /s for elevated pore fluid pressures (80 to 99 % of the lithostatic value, respectively). Since high pore fluid pressures prevail in deep subduction interface settings, it is suggested that the rupture of these garnet crystals occurred through cataclastic deformation via (transient) slip rate acceleration, perhaps as a consequence of localized slip associated with slow to conventional earthquakes. Upon slip rate deceleration, viscous disaggregation of the broken garnet clasts occurred along with the erasing of the matrix cataclastic fabric.

Cataclastic rock

Overprinting

Pressure solution

10.1016/j.epsl.2024.118794

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Citations (3)

The Impact of Matrix Rheology on Stress Concentration in Embedded Brittle Clasts

Geochemistry Geophysics Geosystems (2022)

Paraskevi Io Ioannidi Kyle Bogatz Jacqueline E. Reber

Abstract Frictional failure is the dominant deformation mechanism for rocks in the upper crust while in the middle crust rocks begin to deform viscously. Within this transition, brittle and viscous phases coexist, forming semi‐frictional materials. While semi‐frictional deformation on large scales might play an important role in understanding the transition between earthquakes and slow slip/creep, it can also be observed at smaller scales. Here, we use field observations of the Papoose Flat pluton in eastern California to study deformation of heterogeneous materials during shearing. Clast concentration varies between 2% and 12% by area. Field and microscopic observations show that the matrix deforms viscously, while the clasts fail in a brittle manner. We systematically document clast concentration and spacing with respect to clast fracturing and observe increasing frictional failure of clasts with increasing clast concentration. To test which matrix viscosities impose enough stresses on the clasts to lead to frictional deformation, we complement field observations with 2D numerical models. Maps with 7% by area randomly placed circular clasts are created and deformed under simple shear kinematic conditions. We test different matrix viscosities, from constant low and high viscosity (10 17 and 10 19 Pa.s, respectively), to dislocation creep for granite. Clasts in the vicinity of other clasts are affected by stresses around their neighbors. This effect decreases with increasing clast distance. Our field observations and numerical results suggest that the viscous phase can impose significant stresses onto the brittle phase, causing failure even at very low clast concentrations and in the absence of clast‐clast interactions.

Brittleness

Shearing (physics)

Stress field

Matrix (chemical analysis)

10.1029/2021gc010127

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Citations (12)

Effective rheology of a two-phase subduction shear zone: Insights from numerical simple shear experiments and implications for subduction zone interfaces

Earth and Planetary Science Letters (2021)

Paraskevi Io Ioannidi Laëtitia Le Pourhiet Philippe Agard Samuel Angiboust Onno Oncken

Matrix (chemical analysis)

10.1016/j.epsl.2021.116913

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Citations (14)

Deformation Patterns Recorded by the Hanging Wall of a Former Subduction Interface in the Seismogenic Zone (Central Alps)

AGU Fall Meeting Abstracts (2016)

Paraskevi Io Ioannidi Onno Oncken Samuel Angiboust Philippe Agard Marcos Moreno

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Garnet fracturing reveals ancient unstable slip events hosted in plate interface metasediments

EarthArXiv (California Digital Library) (2023)

Samuel Angiboust Paraskevi Io Ioannidi Iskander Muldashev

A paradox exists between the great number of intermediate-depth earthquakes occurring along active subduction interfaces worldwide and the extreme scarcity of paleo-seismic events recorded in exhumed metasedimentary rocks from ancient subduction zones. Recrystallization, shearing as well as exhumation-related overprinting generally contribute to the nearly-complete erasing of markers of unstable slip events in metamorphic rocks. We herein focus on a sample from an ancient deep thrust from a Cretaceous High-Pressure paleo-accretionary complex in Chilean Patagonia. A representative, moderately foliated micaschist exhibits broken garnet crystals that host a dense network of healed micro-fractures. While garnet fragments appear thoroughly disaggregated along the main foliation, the matrix that has completely recrystallized hardly records brittle deformation. We employ a 2D visco-elasto-plastic numerical modelling approach in order to investigate the mechanical conditions that enable the fracturing of isolated garnet grains in a relatively weak matrix. The rupture of these stiff grains is achieved in our models at strain rates faster than 10-10 /s to 10-12 /s for elevated pore fluid pressures (80 to 99% of the lithostatic value, respectively). Since high pore fluid pressures prevail in deep subduction interface settings, it is suggested that the rupture of these garnet crystals occurred through cataclastic deformation via (transient) slip rate acceleration, perhaps as a consequence of localized slip associated with slow to normal earthquakes. Upon slip rate deceleration, viscous disaggregation of the broken garnet clasts occurred along with the erasing of the matrix cataclastic fabric.

Cataclastic rock

Overprinting

Pressure solution

10.31223/x5cq36

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