Evolution in H2O contents during deformation of polycrystalline quartz: An experimental study

Palazzin, Giulia; Raimbourg, Hugues; Stünitz, Holger; Heilbronner, Renée; Neufeld, Kai; Précigout, Jacques

doi:10.1016/j.jsg.2018.05.021

Cited by 32 publications

(24 citation statements)

References 75 publications

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“…This has been shown to have major effects on the mechanisms of strain accommodation in other major phases as quartz (e.g. Palazzin et al, ) and hence impact the deformation style.…”

Section: Discussionmentioning

confidence: 99%

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

Airaghi

Bellahsen

Dubacq

et al. 2020

Journal Metamorphic Geology

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Pre-kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts, but rarely dated and accounted for in orogenic cycle reconstructions. Studying pre-kinematic alteration is challenging because of its usual obliteration by subsequent syn-kinematic metamorphism often occurring at conditions typical of the brittle-ductile transition. It is, however, to be expected that pre-kinematic alteration has major implications for the rheology of the upper crust. In the 305 Ma-old Variscan basement of the Bielsa massif (located in the Axial Zone of the Pyrenees), successive fluid-rock interaction events are recorded in granites below 350°C. Combined microstructural and petrographic analysis, low-T thermobarometry and in situ U-Th/Pb dating of anatase, titanite and monazite show extensive pre-orogenic (pre-Alpine) and pre-kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270-350°C at 230-300 Ma. This event is followed by a second fluid-rock interaction stage marked by new crystallization of phyllosilicates at 200-280°C and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes. U-Pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40-70 Ma, consistent with independent regional geology constraints. The Variscan basement was therefore softened at late to post-Variscan time, at least 150-200 Ma before the main Alpine shortening while Alpine-age compression (c. 35-50 Ma) leads to the formation of a dense net of mylonites. The associated deformation, both distributed at the scale of the Bielsa massif and localized at decametric scale in mylonitic corridors, precedes the strain localization along the major thrusts of the Axial Zone. The Bielsa massif is a good example where inherited, pre-orogenic upper crustal softening controls the deformation patterns in granitic basement units through low-grade metamorphic reactions. K E Y W O R D SAxial Zone, Bielsa, chlorite-white mica thermobarometry, mylonites, U-Th/Pb anatase-titanitemonazite dating 184 | AIRAGHI et Al.

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“…This has been shown to have major effects on the mechanisms of strain accommodation in other major phases as quartz (e.g. Palazzin et al, ) and hence impact the deformation style.…”

Section: Discussionmentioning

confidence: 99%

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

Airaghi

Bellahsen

Dubacq

et al. 2020

Journal Metamorphic Geology

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“…H 2 O loss from detrital grain interiors may have been due to pipe diffusion (Cordier et al, 1988;Bakker and Jansen, 1994) during SGR recrystallization or decrepitation of inclusions (Tarantola et al, 2010), with delivery to grain boundaries. Once at grain margins, continued loss of H 2 O from the deforming quartzites may have proceeded by grain boundary diffusion and impurity sweeping by mobile grain boundaries during BLG recrystallization (Palazzin et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

Water loss during dynamic recrystallization of Moine thrust quartzites, northwest Scotland

Kronenberg

Ashley

Francsis

et al. 2020

Geology

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Infrared absorption measurements of molecular water in sheared Cambrian quartzites in the footwall to the Moine thrust reveal a decrease in water content from 4080 to 1570 ppm with increasing recrystallization traced toward the overlying thrust at the Stack of Glencoul in northwest Scotland. These results are contrary to the expected correlation between shear strain and water content for quartz deformed by dislocation creep and water-weakening processes. The observed inverse correlation indicates that fluid inclusions and hydrous defects within grains were lost by mobile grain boundary sweeping and grain boundary diffusion. Although reduced water contents might lead to hardening as chemical weakening is diminished, quartz mylonites in the immediate footwall (5 mm) to the thrust are characterized by intense strain localization and contain the least water, and there is little evidence of shear zone widening. Water weakening appears to have been important throughout the quartz mylonites, controlled by the presence of water, not by water concentration. Fluids present within relict inclusions and at grain boundaries may have governed the high water fugacities critical for water weakening.

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“…Holyoke and Tullis (2006a) found in hightemperature experiments a strong relation between the interconnection of weaker phases and strain localization. It has also been shown by Pec et al, (2016) and Palazzin et al, (2018) that the bulk strength of a given sample remains high if the weak shear bands are not, or poorly connected. Numerical studies also support the idea that phase arrangement can dramatically affect the bulk strength (e.g.…”

Section: Geometrical Aspects: Connectivity Of Shear Zones and Weakenimentioning

confidence: 97%

The role of deformation-reaction interactions to localize strain in polymineralic rocks: Insights from experimentally deformed plagioclase-pyroxene assemblages

Mansard

Stünitz

Raimbourg

et al. 2020

Journal of Structural Geology

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show abstract

Evolution in H2O contents during deformation of polycrystalline quartz: An experimental study

Cited by 32 publications

References 75 publications

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

Water loss during dynamic recrystallization of Moine thrust quartzites, northwest Scotland

The role of deformation-reaction interactions to localize strain in polymineralic rocks: Insights from experimentally deformed plagioclase-pyroxene assemblages

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