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Title: Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist

Abstract

The origin of intermediate-depth seismicity has been debated for decades. A substantial fraction of these events occurs within the upper plane of Wadati–Benioff double seismic zones believed to represent subducting oceanic crust. We deformed natural lawsonite-rich blueschist samples under eclogite-facies conditions (1.52.5 GPa to maximum temperatures ranging from 762 to 1073 K, during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite–eclogite and the breakdown reaction of lawsonite was only crossed in case of the highest final temperature; ii) heating while deforming at a pressure <2 GPa to a maximum temperature of 1121 K associated with crossing the breakdown reaction of lawsonite and successively entering the stability fields of epidote–blueschist and eclogite–amphibolite but not of lawsonite–eclogite. Upon entering the Lws-Ecl stability field samples exhibited brittle failure, accompanied by the radiation of AEs. In-situ X-ray diffraction and microstructural analysis demonstrate that fractures are topologically related to the formation of omphacite. Amorphous material was detected along the fractures by transmission-electron microscopy without evidence for free-water. Since the newly formed omphacite crystals are small compared to the initial grains, we interpret the observed mechanical instability as a transformation-induced runaway under stress triggered during the transition from lawsonite–blueschist tomore » lawsonite–eclogite. In contrast, we find no microstructural evidence that the breakdown of lawsonite, and hence the liberation of water leads to the fracturing in samples that experienced the highest quench temperatures of 1073 and 1121 K, although some AEs were detected during an experiment performed at 1.5 GPa. Our experimental results challenge the concept of “dehydration embrittlement”, which ascribes the genesis of intermediate-depth earthquakes to the breakdown of hydrous phases in the subducting oceanic plate. Instead we suggest that grain-size reduction (transformational faulting) during the transition from lawsonite–blueschist to lawsonite–eclogite leads to brittle failure of the deviatorically loaded samples.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE
OSTI Identifier:
1338985
Resource Type:
Journal Article
Resource Relation:
Journal Name: Earth and Planetary Science Letters; Journal Volume: 459; Journal Issue: C
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; intermediate-depth seismicity; eclogitization; transformational faulting; shear heating; dehydration embrittlement; lawsonite–blueschist

Citation Formats

Incel, Sarah, Hilairet, Nadège, Labrousse, Loïc, John, Timm, Deldicque, Damien, Ferrand, Thomas, Wang, Yanbin, Renner, Jörg, Morales, Luiz, and Schubnel, Alexandre. Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist. United States: N. p., 2017. Web. doi:10.1016/j.epsl.2016.11.047.
Incel, Sarah, Hilairet, Nadège, Labrousse, Loïc, John, Timm, Deldicque, Damien, Ferrand, Thomas, Wang, Yanbin, Renner, Jörg, Morales, Luiz, & Schubnel, Alexandre. Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist. United States. doi:10.1016/j.epsl.2016.11.047.
Incel, Sarah, Hilairet, Nadège, Labrousse, Loïc, John, Timm, Deldicque, Damien, Ferrand, Thomas, Wang, Yanbin, Renner, Jörg, Morales, Luiz, and Schubnel, Alexandre. Wed . "Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist". United States. doi:10.1016/j.epsl.2016.11.047.
@article{osti_1338985,
title = {Laboratory earthquakes triggered during eclogitization of lawsonite-bearing blueschist},
author = {Incel, Sarah and Hilairet, Nadège and Labrousse, Loïc and John, Timm and Deldicque, Damien and Ferrand, Thomas and Wang, Yanbin and Renner, Jörg and Morales, Luiz and Schubnel, Alexandre},
abstractNote = {The origin of intermediate-depth seismicity has been debated for decades. A substantial fraction of these events occurs within the upper plane of Wadati–Benioff double seismic zones believed to represent subducting oceanic crust. We deformed natural lawsonite-rich blueschist samples under eclogite-facies conditions (1.52.5 GPa to maximum temperatures ranging from 762 to 1073 K, during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite–eclogite and the breakdown reaction of lawsonite was only crossed in case of the highest final temperature; ii) heating while deforming at a pressure <2 GPa to a maximum temperature of 1121 K associated with crossing the breakdown reaction of lawsonite and successively entering the stability fields of epidote–blueschist and eclogite–amphibolite but not of lawsonite–eclogite. Upon entering the Lws-Ecl stability field samples exhibited brittle failure, accompanied by the radiation of AEs. In-situ X-ray diffraction and microstructural analysis demonstrate that fractures are topologically related to the formation of omphacite. Amorphous material was detected along the fractures by transmission-electron microscopy without evidence for free-water. Since the newly formed omphacite crystals are small compared to the initial grains, we interpret the observed mechanical instability as a transformation-induced runaway under stress triggered during the transition from lawsonite–blueschist to lawsonite–eclogite. In contrast, we find no microstructural evidence that the breakdown of lawsonite, and hence the liberation of water leads to the fracturing in samples that experienced the highest quench temperatures of 1073 and 1121 K, although some AEs were detected during an experiment performed at 1.5 GPa. Our experimental results challenge the concept of “dehydration embrittlement”, which ascribes the genesis of intermediate-depth earthquakes to the breakdown of hydrous phases in the subducting oceanic plate. Instead we suggest that grain-size reduction (transformational faulting) during the transition from lawsonite–blueschist to lawsonite–eclogite leads to brittle failure of the deviatorically loaded samples.},
doi = {10.1016/j.epsl.2016.11.047},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 459,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}