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Title: Faulting of natural serpentinite: Implications for intermediate-depth seismicity

Abstract

The seismic potential of serpentinites at high pressure was investigated via deformation experiments on cored natural serpentinite samples, during which micro-seismicity was monitored by recording Acoustic Emissions (AEs). Deformation was performed at pressures of 3–5 GPa, using a Deformation-DIA device, and over a wide range of temperatures, both within and outside antigorite's stability field. Below 400 °C, serpentinite deformation involves “silent” semi-brittle mechanisms, even in cases where strain localization is observed. At high temperature (i.e., above 600 °C), despite conditions propitious to dehydration embrittlement (i.e., fast strain rates and reaction kinetics), joint deformation and dehydration lead to ductile shear, without generation of AEs. Brittle behavior was observed in a narrow temperature window ca. 500 °C. In this latter case, AEs are consistently observed upon faulting and extremely sharp strain localization is observed in recovered samples. The resulting microstructures are consistent with the inverse ductile-to-brittle transition proposed by Proctor and Hirth (2016) in antigorite. This may therefore be a source of seismicity in subducting slabs at mantle pressures and temperatures from 500 to 600 °C. However, the acoustic signal observed here is orders of magnitude weaker than what is obtained at low PT conditions with brittle failure, consistently with low radiationmore » efficiency of serpentinite faulting (Prieto et al., 2013) and suggests that other mechanisms are responsible for large intermediate-depth earthquakes. In fact, the present results are in line with a recent study (Ferrand et al., 2017), that suggests that intermediate earthquakes are likely induced by mechanical instabilities due to dehydration in partly hydrated peridotites.« less

Authors:
; ORCiD logo; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
NSFFOREIGN
OSTI Identifier:
1372241
Resource Type:
Journal Article
Resource Relation:
Journal Name: Earth and Planetary Science Letters; Journal Volume: 474; Journal Issue: C
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; high pressure; acoustic emission; serpentinite dehydration; intermediate depth earthquakes; synchrotron x-ray diffraction; deformation-DIA

Citation Formats

Gasc, Julien, Hilairet, Nadège, Yu, Tony, Ferrand, Thomas, Schubnel, Alexandre, and Wang, Yanbin. Faulting of natural serpentinite: Implications for intermediate-depth seismicity. United States: N. p., 2017. Web. doi:10.1016/j.epsl.2017.06.016.
Gasc, Julien, Hilairet, Nadège, Yu, Tony, Ferrand, Thomas, Schubnel, Alexandre, & Wang, Yanbin. Faulting of natural serpentinite: Implications for intermediate-depth seismicity. United States. doi:10.1016/j.epsl.2017.06.016.
Gasc, Julien, Hilairet, Nadège, Yu, Tony, Ferrand, Thomas, Schubnel, Alexandre, and Wang, Yanbin. 2017. "Faulting of natural serpentinite: Implications for intermediate-depth seismicity". United States. doi:10.1016/j.epsl.2017.06.016.
@article{osti_1372241,
title = {Faulting of natural serpentinite: Implications for intermediate-depth seismicity},
author = {Gasc, Julien and Hilairet, Nadège and Yu, Tony and Ferrand, Thomas and Schubnel, Alexandre and Wang, Yanbin},
abstractNote = {The seismic potential of serpentinites at high pressure was investigated via deformation experiments on cored natural serpentinite samples, during which micro-seismicity was monitored by recording Acoustic Emissions (AEs). Deformation was performed at pressures of 3–5 GPa, using a Deformation-DIA device, and over a wide range of temperatures, both within and outside antigorite's stability field. Below 400 °C, serpentinite deformation involves “silent” semi-brittle mechanisms, even in cases where strain localization is observed. At high temperature (i.e., above 600 °C), despite conditions propitious to dehydration embrittlement (i.e., fast strain rates and reaction kinetics), joint deformation and dehydration lead to ductile shear, without generation of AEs. Brittle behavior was observed in a narrow temperature window ca. 500 °C. In this latter case, AEs are consistently observed upon faulting and extremely sharp strain localization is observed in recovered samples. The resulting microstructures are consistent with the inverse ductile-to-brittle transition proposed by Proctor and Hirth (2016) in antigorite. This may therefore be a source of seismicity in subducting slabs at mantle pressures and temperatures from 500 to 600 °C. However, the acoustic signal observed here is orders of magnitude weaker than what is obtained at low PT conditions with brittle failure, consistently with low radiation efficiency of serpentinite faulting (Prieto et al., 2013) and suggests that other mechanisms are responsible for large intermediate-depth earthquakes. In fact, the present results are in line with a recent study (Ferrand et al., 2017), that suggests that intermediate earthquakes are likely induced by mechanical instabilities due to dehydration in partly hydrated peridotites.},
doi = {10.1016/j.epsl.2017.06.016},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 474,
place = {United States},
year = 2017,
month = 9
}
  • The transition from shallow interplate thrusting to intermediate-depth seismicity is often poorly observed, but critical for understanding the fate of the downgoing slab. In order to better examine the transition, 1448 earthquakes are relocated from data recorded by a regional seismic network in the eastern Aleutian arc, using an improved three-dimensional velocity model and accurate ray tracing. Single-event first-motion solutions are determined from these rays for 31 slab events. The interplate thrust zone is a planar fault zone, dipping 10-15[degrees] at 25-35 km depth, and is no more than 5-10 km wide. Most intermediate-depth earthquakes are localized to a planemore » no wider than 5 km near the top of the descending plate. Fault-plane solution orientations for these events vary by several tens of degrees in orientation, although 73% show T axes aligned within 45[degrees] of the slab dip. A parallel seismic zone, 20-25 km deeper into the slab, also shows down-dip plunges of T axes for 3 to 5 solutions. The fault-plane solutions are poorly explained by plate bending ur unbending about a neutral fiber. Hypocenters show that intermediate-depth events are confined near the subducted oceanic crust, supporting compositional rather than pure thermal control of intermediate-depth seismicity. One explanation is that the upper-plane events are an indirect consequence of phase changes in subducted crust. Perhaps similar processes are important in producing earthquakes in the lower, parallel zone. 26 refs., 4 figs.« less
  • No abstract prepared.
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