DOI: 10.1016/j.epsl.2020.116260
论文题名: High-stress creep preceding coseismic rupturing in amphibolite-facies ultramylonites
作者: Papa S. ; Pennacchioni G. ; Menegon L. ; Thielmann M.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 541 语种: 英语
中文关键词: brittle-ductile transition
; EBSD
; lower crustal earthquake
; pseudotachylyte
; quartz rheology
; thermal runaway
英文关键词: Aggregates
; Biotite
; Creep
; Disintegration
; Grain boundary sliding
; Mica
; Quartz
; Seismology
; Amphibolite facies
; Brittle ductile transitions
; Constant temperature
; Deformation conditions
; Differential stress
; Metamorphic conditions
; Rate-limiting process
; Viscous grain-boundary sliding
; Strain rate
; amphibolite facies
; coseismic process
; deformation
; earthquake rupture
; numerical model
; pore space
; porosity
; stress-strain relationship
; Alps
; Western Alps
英文摘要: Coeval pseudotachylytes (solidified melts produced during seismic slip) and mylonites are generally regarded as the geological record of transient seismic events during dominant ductile flow. Thermal runaway has been proposed as a model to explain the pseudotachylyte-mylonite association. In the Mont Mary unit (Western Alps), pseudotachylyte fault veins occur along the amphibolite-facies (ca. 550 °C; 0.35 GPa) ultramylonitic foliation of paragneisses. These veins formed at the same metamorphic conditions of the ultramylonites, thus potentially recording thermal runaway. We analysed the microstructure of quartz in ultramylonite and of ultramylonite clasts in pseudotachylyte to investigate the possible occurrence of thermal runaway. Quartz aggregates show an evolution under constant temperature to ultrafine-grained recrystallised grain size (2.5 μm), reflecting creep under high differential stresses (> 200 MPa) and high strain rates (10−9 s−1), along very narrow foliation-parallel layers. In the ultrafine aggregates, viscous grain boundary sliding became dominant and promoted cavitation leading to disintegration of quartz aggregates and precipitation, in the pore space, of biotite, oriented parallel to the main ultramylonitic foliation. The strain rate-limiting process was aseismic fluid-assisted precipitation of biotite. The potential occurrence, at the deformation conditions of the Mont Mary ultramylonites, of thermal runaway in pure quartz layers was investigated by numerical modelling. The models predict a switch from stable flow to thermal runaway at background strain rates faster than 10−9 s−1 for critical differential stresses that are comparable to the brittle strength of rocks. Deformation of ultramylonites occurred close to the conditions for thermal runaway to occur, but based on the microstructural record we conclude that the Mont Mary pseudotachylyte-mylonite association is best explained by brittle failure, triggered by transients of high differential stress and strain rate causing a downward deflection of the brittle-ductile transition. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165202
Appears in Collections: 气候变化与战略
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作者单位: Department of Geosciences, University of Padova, Via Gradenigo 6, Padua, I-35131, Italy; School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL48AA, United Kingdom; The Njord Centre, Department of Geosciences, University of Oslo, Postbox 1048, Blindern, Oslo, 0316, Norway; Bayerisches Geoinstitut, University of Bayreuth, Universitätstraße 30, Bayreuth, 95440, Germany
Recommended Citation:
Papa S.,Pennacchioni G.,Menegon L.,et al. High-stress creep preceding coseismic rupturing in amphibolite-facies ultramylonites[J]. Earth and Planetary Science Letters,2020-01-01,541