Paleowattmeters: A scaling relation for dynamically recrystallized grain size

Austin, N. J.; Evans, Brian

doi:10.1130/g23244a.1

Cited by 214 publications

(273 citation statements)

References 25 publications

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“…Sample CMHT2 without inclusions has a recrystallized grain size of ≈23.3±4.3 µm and a strength of ≈21.2 MPa (crossed circle), plotting close to the field boundary. The boundary is well predicted by the paleowattmeter (Austin and Evans, 2009;Austin and Evans, 2007). In the process zone of SH-bearing samples CMHT3 and CMHT2 the recrystallized grain size is 12 ± 3 and 10.4 ±1.9 µm, respectively, with bulk flow strength of ≈ 20 MPa (open circles).…”

Section: Aggregate Strengthmentioning

confidence: 70%

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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Section: Aggregate Strengthmentioning

confidence: 70%

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

et al. 2014

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“…For the damage partitioning fraction we assume small values within the range 10 −4 ≤ f I ≤ 10 −2 , which is comparable to that inferred by Rozel et al (2011) and Austin & Evans (2007), although these studies were more relevant for damage directly to grains via dynamic recrystallization. The choice of can be estimated by inferring the values necessary to yield R 0 = 2 µm, which were the typical experimental grain sizes.…”

Section: Scales and Numbersmentioning

confidence: 96%

Melt-band instabilities with two-phase damage

Rudge

Bercovici

2015

Geophysical Journal International

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S U M M A R YDeformation experiments on partially molten rocks in simple shear form melt bands at 20• to the shear plane instead of at the expected 45• principal compressive stress direction. These melt bands may play an important role in melt focusing in mid-ocean ridges. Such shallow bands are known to form for two-phase media under shear if strongly non-Newtonian power-law creep is employed for the solid phase, or anisotropy imposed. However laboratory experiments show that shallow bands occur regardless of creep mechanism, even in diffusion creep, which is nominally Newtonian. Here we propose that a couple of forms of two-phase damage allow for shallow melt bands even in diffusion creep.

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“…According to Kidder et al (2016), quartz grain sizes may record short term stress changes in non-steady state deformation. Stresses calculated from a grain size of 200 µm down to a minimum grain size of 1 µm, are on the order of less than 10 to up to 500 MPa (Austin andEvans, 2007, Stipp andTullis, 2003).…”

Section: Non-steady State Stress Estimatesmentioning

confidence: 99%

“…While the mylonites in the Fregon Subdomain typically show a grain size of 50 to 100 µm, implying stresses on the order of tens of MPa (e.g. Austin and Evans, 2007;Stipp et al, 2006;Stipp and Tullis, 2003;Twiss, 1977), the formation of brittle fractures and pseudotachylytes in dry rock requires stresses on the order of more than 1 GPa (Byerlee, 1978). According to Kidder et al (2016), quartz grain sizes may record short term stress changes in non-steady state deformation.…”

Section: Non-steady State Stress Estimatesmentioning

confidence: 99%

Weak and slow, strong and fast: How shear zones evolve in a dry continental crust (Musgrave Ranges, Central Australia)

Hawemann¹,

Mancktelow²,

Pennacchioni³

et al. 2018

Preprint

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Key Points: Ductile shearing localizes on precursor pseudotachylytes and fractures. Stress fluctuations range from 10 MPa to at least <1 GPa  Earthquakes in the lower crust can be locally triggered by stress concentrations without the transfer of stresses from the upper crust. KeywordsPseudotachylyte, lower crust, localization of deformation, stress, earthquake AbstractThe Davenport Shear Zone in Central Australia is a strike-slip fault zone developed during the Petermann Orogeny (~ 550 Ma) in an intracontinental lower crustal setting, with conditions of shearing estimated at upper amphibolite to eclogite facies (~ 650 °C, 1.2 GPa). This five kilometer thick mylonite zone encloses several large low-strain domains, allowing a thorough study of the initiation of shear zones and their progressive development. Quartzofeldspathic gneisses and granitoids contain rheologically different layers, such as quartz-rich pegmatite dykes, mafic bands and dykes, which should preferentially localize viscous deformation if favourably orientated. This is not observed, except for long, continuous and fine grained dolerite dykes. Instead, many shear zones, typically only a few millimeters to centimeters in width but extending for tens of meters, commonly exploited pseudotachylytes and are sometimes parallel to a network of little overprinted brittle fractures. The recrystallized mineral assemblage in the sheared pseudotachylyte is similar to that in the host gneiss, without associated fluid-rock interaction. Lack of localization in quartz-rich, coarser grained (typically >50 microns) rocks compared to mafic dykes, precursor factures and pseudotachylytes implies that localization in the dry lower crust preferentially occurs along elongate planar layers with a relatively fine grain size. Transient high stress events repeatedly initiated fractures, providing finer grained, weaker, planar precursors that localized subsequent ductile shear zones. This intimate interplay between brittle and ductile deformation suggests a local source for lower crustal earthquakes, rather than downward migration of earthquakes from the shallower, usually more seismogenic part of the crust.

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Paleowattmeters: A scaling relation for dynamically recrystallized grain size

Cited by 214 publications

References 25 publications

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

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

Melt-band instabilities with two-phase damage

Weak and slow, strong and fast: How shear zones evolve in a dry continental crust (Musgrave Ranges, Central Australia)

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