Fluid and deformation induced metamorphic processes around Moho beneath continent collision zones: Examples from the exposed root zone of the Caledonian mountain belt, W-Norway

Austrheim, Håkon

doi:10.1016/j.tecto.2013.08.030

Cited by 94 publications

(116 citation statements)

References 115 publications

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“…The absence of hydration associated with pseudotachylyte development in the shear zones described here also indicates that the switch between seismic brittle fracture (pseudotachylyte) and ductile shearing was not induced by infiltration of fluids. This is in marked contrast to what has been previously described in the Bergen Arc (Austrheim, 2013, and references therein) and Lofoten area (Menegon et al, 2017) of Norway, where fluid influx promoted by propagation of the earthquake fracture and associated weakening due to metamorphic reaction localized subsequent ductile shearing. In the absence of elevated pore fluid pressure, high stresses are necessary to fracture rocks under dry, lower-crustal conditions (Sibson and Toy, 2006;Menegon et al, 2017).…”

Section: Resultscontrasting

confidence: 89%

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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Section: Resultscontrasting

confidence: 89%

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

et al. 2018

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“…John et al, 2009) and are expected to result in extensive development of pseudotachylytes in granitoid rocks (e.g. Austrheim, 2013, and references therein), which, however, have not been observed in the sample studied here.…”

Section: Significance Of the Switch In Deformation Mode And Implicatimentioning

confidence: 70%

“…Guermani and Pennacchioni, 1998;Pennacchioni and Mancktelow 2007); most of these studies consider deformation at shallow to intermediate crustal depths (Fusseis and Handy, 2008;Mazzoli et al, 2009;, although case studies under conditions of upper amphibolite to granulite (White, 1996;Pennacchioni and Cesare, 1997;Pittarello et al, 2013;Altenberger et al, 2013) and eclogite facies (Austrheim and Boundy, 1994;Austrheim, 2013, and references therein) were also investigated.…”

Section: Introductionmentioning

confidence: 99%

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

Molli

Menegon

Malasoma³

2017

Solid Earth

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Abstract. The switching in deformation mode (from distributed to localized) and mechanisms (viscous versus frictional) represent a relevant issue in the frame of crustal deformation, being also connected with the concept of the brittle-"ductile" transition and seismogenesis. In a subduction environment, switching in deformation mode and mechanisms and scale of localization may be inferred along the subduction interface, in a transition zone between the highly coupled (seismogenic zone) and decoupled deeper aseismic domain (stable slip). However, the role of brittle precursors in nucleating crystal-plastic shear zones has received more and more consideration being now recognized as fundamental in some cases for the localization of deformation and shear zone development, thus representing a case in which switching deformation mechanisms and scale and style of localization (deformation mode) interact and relate to each other. This contribution analyses an example of a millimetrescale shear zone localized by brittle precursor formed within a host granitic protomylonite. The studied structures, developed in ambient pressure-temperature (P -T ) conditions of low-grade blueschist facies (temperature T of ca. 300 • C and pressure P ≥ 0.70 GPa) during involvement of Corsican continental crust in the Alpine subduction. We used a multidisciplinary approach by combining detailed microstructural and petrographic analyses, crystallographic preferred orientation by electron backscatter diffraction (EBSD), and palaeopiezometric studies on a selected sample to support an evolutionary model and deformation path for subducted continental crust. We infer that the studied structures, possibly formed by transient instability associated with fluctuations of pore fluid pressure and episodic strain rate variations, may be considered as a small-scale example of fault behaviour associated with a cycle of interseismic creep and coseismic rupture or a new analogue for episodic tremors and slow-slip structures. Our case study represents, therefore, a fossil example of association of fault structures related to stick-slip strain accommodation during subduction of continental crust.

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“…As the pressurization and heating procedure required to attain the experimental Pc-T conditions takes place within 5-8 h, the sample material is brought rapidly to a metastable state. Although this rapid change in P -T conditions is unique to experiments, there is widespread evidence from observations of natural rocks that, similarly, metastable mineral assemblages can be sustained even at high-grade conditions and to large overstepping of reaction boundaries when rocks are dry (e.g., Rubie, 1986;Austrheim, 1987;Wayte et al, 1989;Krabbendam et al, 2000;Austrheim, 2013;Jamtveit et al, 2016). Only where fluid infiltrates are mineral reactions enabled and equilibrium can be attained.…”

Section: Importance Of Dissolution-precipitation Creep In Natural Rocksmentioning

confidence: 99%

Syn-kinematic hydration reactions, grain size reduction, and dissolution–precipitation creep in experimentally deformed plagioclase–pyroxene mixtures

et al. 2018

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Abstract. It is widely observed that mafic rocks are able to accommodate high strains by viscous flow. Yet, a number of questions concerning the exact nature of the involved deformation mechanisms continue to be debated. In this contribution, rock deformation experiments on four different water-added plagioclase-pyroxene mixtures are presented: (i) plagioclase(An60-70)-clinopyroxene-orthopyroxene, (ii) plagioclase(An60)-diopside, (iii) plagioclase(An60)-enstatite, and (iv) plagioclase(An01)-enstatite. Samples were deformed in general shear at strain rates of 3 × 10 −5 to 3 × 10 −6 s −1 , 800 • C, and confining pressure of 1.0 or 1.5 GPa. Results indicate that dissolution-precipitation creep (DPC) and grain boundary sliding (GBS) are the dominant deformation mechanisms and operate simultaneously. Coinciding with sample deformation, syn-kinematic mineral reactions yield abundant nucleation of new grains; the resulting intense grain size reduction is considered crucial for the activity of DPC and GBS. In high strain zones dominated by plagioclase, a weak, nonrandom, and geometrically consistent crystallographic preferred orientation (CPO) is observed. Usually, a CPO is considered a consequence of dislocation creep, but the experiments presented here demonstrate that a CPO can develop during DPC and GBS. This study provides new evidence for the importance of DPC and GBS in mid-crustal shear zones within mafic rocks, which has important implications for understanding and modeling mid-crustal rheology and flow.

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Fluid and deformation induced metamorphic processes around Moho beneath continent collision zones: Examples from the exposed root zone of the Caledonian mountain belt, W-Norway

Cited by 94 publications

References 115 publications

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

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

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

Syn-kinematic hydration reactions, grain size reduction, and dissolution–precipitation creep in experimentally deformed plagioclase–pyroxene mixtures

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