Amphibolite-facies pseudotachylytes in Premosello metagabbro and felsic mylonites (Ivrea Zone, Italy)

Pittarello, Lidia; Pennacchioni, Giorgio; Toro, Giulio Di

doi:10.1016/j.tecto.2012.08.001

Cited by 59 publications

(56 citation statements)

References 68 publications

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“…The combination of these factors would ultimately determine the arresting depth of large earthquakes, which can be deeper than the low-velocity VW zone where earthquakes can nucleate. This possibility is supported by geological studies which find occurrence of seismic slip in the mostly ductile regime (12,(104)(105)(106)(107)(108)(109), and has been conjectured in several synoptic models of the shear zone (13,110,111). These considerations motivate our model M2.…”

Section: Supplementary Textsupporting

confidence: 80%

Deeper penetration of large earthquakes on seismically quiescent faults

Jiang

Lapusta

2016

Science

119

110

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A microseismic turn off Certain strike-slip faults do not have the expected number of microearthquakes between larger earthquakes. Jiang and Lapusta suggest that this behavior is down to what the last big earthquake looked like. They found that microseismicity turns off if an earthquake's rupture runs deeper than the fault's locking depth. This appears to be the case along the famous San Andreas Fault and also along other strike-slip faults around the world. The discovery may allow for better estimates of historic earthquake magnitudes and improve hazard assessments. Science , this issue p. 1293

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Section: Supplementary Textsupporting

confidence: 80%

Deeper penetration of large earthquakes on seismically quiescent faults

Jiang

Lapusta

2016

Science

119

110

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“…Modified after Evins et al (2010). Brune, 1972;Sibson, 1975), can be locally abundant in exposures of lower crust (Altenberger et al, 2011(Altenberger et al, , 2013Austrheim and Boundy, 1994;Clarke and Norman, 1993;Steltenpohl, 2009, 2011;Pittarello et al, 2012;Orlandini et al, 2013;Menegon et al, 2017). The metamorphic conditions of these sections correspond to depths well below the usual brittle-ductile transition zone for crustal rocks (< 15 km) and thus the assumed lower limit for earthquake nucleation.…”

Section: Introductionmentioning

confidence: 99%

“…Sibson (1980) reported mutually overprinting pseudotachylytes and mylonites from the Outer Hebrides Thrust (NW Scotland) and similar observations were made by Moecher and Steltenpohl (2009) and Menegon et al (2017) in the Lofoten region (N Norway), by Hobbs et al (1986) in the Redbank Shear Zone (Arunta Block, Central Australia), and by in the Woodroffe Thrust (Central Australia). Mutual overprinting has been interpreted to reflect the generation of pseudotachylytes and mylonitization under the same conditions (Altenberger et al, 2011(Altenberger et al, , 2013Clarke and Norman, 1993;Moecher and Steltenpohl, 2011;Pennacchioni and Cesare, 1997;Pittarello et al, 2012;Ueda et al, 2008;White, 1996White, , 2004White, , 2012. A possible explanation for the generation of earthquakes in these mid-to lower-crustal rocks is the downward migration of the brittle-ductile transition through the transfer of stress from the upper crust after a seismic event (Ellis and Stöckhert, 2004;Handy and Brun, 2004).…”

Section: Introductionmentioning

confidence: 99%

Pseudotachylyte as field evidence for lower-crustal earthquakes during the intracontinental Petermann Orogeny (Musgrave Block, Central Australia)

et al. 2018

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Abstract. Geophysical evidence for lower continental crustal earthquakes in almost all collisional orogens is in conflict with the widely accepted notion that rocks, under high grade conditions, should flow rather than fracture. Pseudotachylytes are remnants of frictional melts generated during seismic slip and can therefore be used as an indicator of former seismogenic fault zones. The Fregon Subdomain in Central Australia was deformed under dry sub-eclogitic conditions of 600-700 • C and 1.0-1.2 GPa during the intracontinental Petermann Orogeny (ca. 550 Ma) and contains abundant pseudotachylyte. These pseudotachylytes are commonly foliated, recrystallized, and cross-cut by other pseudotachylytes, reflecting repeated generation during ongoing ductile deformation. This interplay is interpreted as evidence for repeated seismic brittle failure and post-to inter-seismic creep under dry lower-crustal conditions. Thermodynamic modelling of the pseudotachylyte bulk composition gives the same PT conditions of shearing as in surrounding mylonites. We conclude that pseudotachylytes in the Fregon Subdomain are a direct analogue of current seismicity in dry lower continental crust.

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“…In the brittle-ductile transition regime and at lower temperatures, shear zone formation often occurs at brittle precursors (Brander et al, 2012;Fusseis and Handy, 2008;Pennacchioni and Mancktelow, 2007;Pittarello et al, 2012), or by ductile fracturing (Dimanov et al, 2007;Menegon et al, 2013;Rybacki et al, 2008;Rybacki et al, 2010;Shigematsu et al, 2009;Spiess et al, 2012;White, 2012). Ultimately, strain weakening associated with localization may result from (e.g., Burlini and Bruhn, 2005): (1) grain size reduction by dynamic recrystallization or metamorphic reaction that produce new stress-free grains and/or a switch to grain size-sensitive deformation mechanisms, (2) structural softening in polyphase materials induced by the formation of interconnected weak layers at high strain, (3) geometric softening resulting from shape and crystallographic preferred orientation, (4) chemical weakening resulting in a change of point defects concentration, (5) fluid-induced dissolution-precipitation creep or reduction of the effective pressure causing embrittlement, (6) partial melting, leading to mechanical weakening and fast diffusion along wet grain boundaries, (7) transformation plasticity caused by mineral phase change, and (8) shear heating.…”

Section: Introductionmentioning

confidence: 99%

Strain localization during high temperature creep of marble: The effect of inclusions

et al. 2014

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The deformation of rocks in the Earth's middle and lower crust is often localized in ductile shear zones. To better understand the initiation and propagation of high-temperature shear zones induced by the presence of structural and material heterogeneities, we performed deformation experiments in the dislocation creep regime on Carrara marble samples containing weak (limestone) or strong (novaculite) second phase inclusions. The samples were mostly deformed in torsion at a bulk shear strain rate of ≈ 1.9x10 -4 s -1 to bulk shear strains γ between 0.02 and 2.9 using a Paterson-type gas deformation apparatus at 900°C temperature and 400 MPa confining pressure. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at γ > 0.1 -0.2.Peak shear stress at the imposed conditions is about 20 MPa, which is ≈8% lower than the strength of intact samples. Strain progressively localized within the matrix with increasing bulk strain, but decayed rapidly with increasing distance from the inclusion tip.Microstructural analysis shows twinning and recrystallization within this process zone, with a strong crystallographic preferred orientation, dominated by {r} and (c) slip in .Recrystallization-induced weakening starts at local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. In contrast, torsion of a sample containing strong inclusions deformed at similar stress as inclusion-free samples but do not show localization. The experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips. Recrystallizationinduced grain size reduction may only locally promote grain boundary diffusion creep. Accordingly, the bulk strength of the twisted aggregate is close to or slightly below the lower (isostress) strength bound, determined from the flow strength and volume fraction of matrix and inclusions.

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Amphibolite-facies pseudotachylytes in Premosello metagabbro and felsic mylonites (Ivrea Zone, Italy)

Cited by 59 publications

References 68 publications

Deeper penetration of large earthquakes on seismically quiescent faults

Deeper penetration of large earthquakes on seismically quiescent faults

Pseudotachylyte as field evidence for lower-crustal earthquakes during the intracontinental Petermann Orogeny (Musgrave Block, Central Australia)

Strain localization during high temperature creep of marble: The effect of inclusions

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