Transition from fracturing to viscous flow in granulite facies perthitic feldspar (Lofoten, Norway)

Menegon, Luca; Stünitz, Holger; Nasipuri, Pritam; Heilbronner, Renée; Svahnberg, Henrik

doi:10.1016/j.jsg.2012.12.004

Cited by 74 publications

(64 citation statements)

References 60 publications

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“…These aggregates formed as a result of the following hydration reaction:

Clinopyroxene + {Plagioclase}_{1} + H_{2} normalO = Amphibole ((), Pargasite) + {Plagioclase}_{2} + Quartz

where the subscripts 1 and 2 refer to primary and recrystallized plagioclase, respectively. Such reaction has been observed also in other feldspar rich lower crustal shear zones in Lofoten, and indicates P‐T conditions of 0.65–0.8 GPa, 700–730 °C (Menegon et al, ).…”

Section: The Lofoten Areamentioning

confidence: 56%

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

et al. 2019

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Rock rheology and density have first‐order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid‐driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall‐rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake‐generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid‐rock interactions, and creep flow.

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“…These aggregates formed as a result of the following hydration reaction:

Clinopyroxene + {Plagioclase}_{1} + H_{2} normalO = Amphibole ((), Pargasite) + {Plagioclase}_{2} + Quartz

Section: The Lofoten Areamentioning

confidence: 56%

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

et al. 2019

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“…Kjøll et al, 2015) that localized rigid body rotation of fragments around the Y direction (e.g. Trepmann et al, 2007;Menegon et al, 2013). The rotation around Y of (1) the crystallographic directions of the host grain and (2) the recrystallized grains (in this case for large misorientation > 10 • ) is confirmed by the plots of the misorientation axis in sample coordinates (Fig.…”

Section: Quartz In the Host Rockmentioning

confidence: 66%

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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“…Even under high‐temperature conditions where plastic deformation of minerals takes place, fracturing and nucleation of new grains as small fragments have been identified in naturally and experimentally deformed rocks. For feldspar, see for example, Tullis and Yund [], Fitz Gerald and Stünitz [], Kruse et al [], McLaren and Pryer [], Stünitz et al [], Brander et al [], Fukuda et al [], Fukuda and Okudaira [], and Menegon et al []; for quartz, see Trepmann and Stöckhert [], Vernooij et al [], and Trepmann et al []; for orthopyroxene, see Raimbourg et al []; and for hornblende, see Imon et al [, ] and Díaz Aspiroz et al []. Particularly for plagioclase and quartz, fracture‐related small fragments act as nuclei for new grains, which are characterized by low aspect ratios and weak or absent crystallographic preferred orientation [e.g., Stünitz et al , ; Trepmann et al , ].…”

Section: Introductionmentioning

confidence: 99%

High‐temperature fracturing and subsequent grain‐size‐sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust?

et al. 2015

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The mechanism of shear zone formation in lower crustal, relatively "dry" rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10-20 μm wide fractures show little displacement. The fine-grained plagioclase and orthopyroxene in the fractures lack a crystallographic preferred orientation (CPO) or a systematic crystallographic orientation with respect to the host grains. Fractures grade into narrow shear zones, which are composed of fine (10-20 μm), equant grains of recrystallized plagioclase, amphibole, and pyroxene. Recrystallized plagioclase and pyroxene have compositions different from the magmatic grains, suggesting that they have formed by nucleation and growth. Based on conventional plagioclase-amphibole thermobarometry, the shear zones have formed at temperatures and pressures of 700-750°C and 0.5-0.6 GPa. The observed primary minerals cut by fractures suggest high-temperature fracturing in the absence of high pore pressures, which implies a high strength of the lower crustal gabbros and high stresses at fracturing. The shear zones are characterized by the lack of CPO and a small grain size, suggesting that the mechanism of deformation of the fine-grained plagioclase and orthopyroxene has been grain boundary sliding accommodated by diffusive mass transfer. The amphibole grains have strong CPOs, which most likely result from oriented growth and/or rigid body rotations during deformation. The process that initiated the fracturing and subsequent viscous creep in the Hasvik gabbro may have resulted from a process of coseismic loading followed by creep during decaying stress in the lower crust.

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Transition from fracturing to viscous flow in granulite facies perthitic feldspar (Lofoten, Norway)

Cited by 74 publications

References 60 publications

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

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

High‐temperature fracturing and subsequent grain‐size‐sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust?

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