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| Titel |
Experimental deformation and recrystallization of olivine – processes and timescales of damage healing during postseismic relaxation at mantle depths |
| VerfasserIn |
C. A. Trepmann, J. Renner, A. Druiventak |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 4, no. 2 ; Nr. 4, no. 2 (2013-11-11), S.423-450 |
| Datensatznummer |
250084943
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| Publikation (Nr.) |
 copernicus.org/se-4-423-2013.pdf |
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| Zusammenfassung |
| Experiments comprising sequences of deformation (at 300 or 600 °C) and annealing at varying temperature (700 to 1100 °C), time
(up to 144 h) and stress (up to 1.5 GPa) were carried out in a
Griggs-type apparatus on natural olivine-rich peridotite samples to simulate
deformation and recrystallization processes in deep shear zones that reach
mantle depth as continuations of seismically active faults. The resulting
olivine microfabrics were analysed by polarization and electron microscopy
(SEM/EBSD, TEM). Core-and-mantle-like microstructures are the predominant
result of our experiments simulating rapid stress relaxation (without or
with minor creep) after a high-stress deformation event: porphyroclasts
(> 100 μm) are surrounded by new grains comprising
fragments and recrystallized grains with a wide range in size (2 to
40 μm). Areas with small grains (≤ 10 μm) trace former
high-strain zones generated during initial high-stress deformation even
after annealing at a temperature of 1100 °C for 70 h. A weak
crystallographic preferred orientation (CPO) of new olivine grains is
related to the orientation of the original host crystals but appears
unrelated to the strain field. Based on these findings, we propose that
olivine microstructures in natural shear-zone peridotites with a large range
in grain size, localized fine-grained zones, and a weak CPO not related to
the strain field are diagnostic for a sequence of high-stress deformation
followed by recrystallization at low stresses, as to be expected in areas of
seismic activity. We extended the classic Avrami-kinetics equation by
accounting for time-dependent growth kinetics and constrained the involved
parameters relying on our results and previous studies devoted to the
kinetics of defect processes in olivine. Extrapolation to natural conditions
suggests that the observed characteristic microstructure may develop within
as little as tens of years and less than ten thousands of years. These
recrystallization microstructures have a great diagnostic potential for past
seismic activity because they are expected to be stable over geological timescales, since driving forces for further modification are not sufficient to
erase the characteristic heterogeneities. |
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