Fluid-assisted strain localization in the shallow subcontinental lithospheric mantle

Hidas, Károly; Tommasi, Andréa; Garrido, Carlos J.; Padrón‐Navarta, José Alberto; Mainprice, David; Vauchez, Alain; Barou, Fabrice; Marchesi, Claudio

doi:10.1016/j.lithos.2016.07.038

Cited by 42 publications

(55 citation statements)

References 93 publications

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“…4a)27. This feature differs from the distal protolith where an A-type fabric has been documented2225. Moreover, in some layers, the [010] and [001] axes are more dispersed and distributed as girdles normal to the shear direction.…”

Section: Resultsmentioning

confidence: 92%

“…This rate of water diffusion excludes in situ measurements of water content in our samples (see the methods section). The systematic occurrence of E-type fabric, more or less combined with D-type fabric, also suggests that water was present everywhere in the study area before strain localization, contrary to the distal protolith where a dry A-type fabric has been described2225. The most likely scenario is, therefore, that the D-type fabric overprinted the E-type fabric during strain localization.…”

Section: Discussionmentioning

confidence: 93%

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Water pumping in mantle shear zones

et al. 2017

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Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is thus crucial to understanding how water impacts Earth's geodynamics. Here we demonstrate that ductile flow exerts a dynamic control on water-rich fluid circulation in mantle shear zones. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. We also give evidence of cracking induced by fluid pressure where the highest amount of water is expected. These results emphasize long-term fluid pumping attributed to creep cavitation and associated phase nucleation during grain size reduction. Considering the ubiquitous process of grain size reduction during strain localization, our findings shed light on multiple fluid reservoirs in the crust and mantle.

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Section: Resultsmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 93%

Water pumping in mantle shear zones

et al. 2017

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“…6, 7, 8, and 9) highlights that extreme grain size reduction (<50µm) and phase mixing are always associated with strongly sutured, interpenetrating phase boundaries (in particular between olivine and pyroxenes) and with the crystallization of reactional plagioclase or hydrous minerals Strating et al, 1993;Furusho and Kanagawa, 1999;Newman et al, 1999;Warren and Hirth, 2006;Toy et al, 2010;Kaczmarek and Tommasi, 2011;Hidas et al, 2013;El Messbahi et al, 2014;Hidas et al, 2015). In mylonites with no evidence for reactions, recrystallized grain sizes are usually ≥ 100µm and phase segregation rather than mixing is the rule (e.g., Falus et al, 2008;Behr and Hirth, 2014).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…ACCEPTED MANUSCRIPT and Tommasi, 2011;Frets et al, 2014;Précigout and Hirth, 2014;Hidas et al, 2015). Additional activation of (solid-state or fluid-assisted) diffusional processes or grain boundary sliding is, however, required for producing the almost random CPO that characterizes most ultramylonites (e.g., Newman et al, 1999;Warren and Hirth, 2006;Toy et al, 2010;Kaczmarek and Tommasi, 2011;Précigout and Hirth, 2014;Hidas et al, 2015).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…This variation in the symmetry of the CPO records changes on the deformation regime or on the relative activity of the different slip systems Tommasi et al, 2000). (Mehl et al, 2003;Soustelle and Tommasi, 2010;Hidas et al, 2015) or melts Tommasi et al, 2006). Olivine CPO marked by [001] maximum parallel to the lineation (D-and C-types of Karato et al, 2008) are still rarer (~5%).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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Heterogeneity and anisotropy in the lithospheric mantle

2015

Self Cite

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International audienceThe lithospheric mantle is intrinsically heterogeneous and anisotropic. These two properties govern the repartition of deformation, controlling intraplate strain localization and development of new plate boundaries. Geophysical and geological observations provide clues on the types, ranges, and characteristic length scales of heterogeneity and anisotropy in the lithospheric mantle. Seismic tomography points to variations in geothermal gradient and hence in rheological behavior at scales of hundreds of km. Seismic anisotropy data substantiate anisotropic physical properties consistent at scales of tens to hundreds of km. Receiver functions imply lateral and vertical heterogeneity at scales < 10 km, which might record gradients in composition or anisotropy. Observations on naturally deformed peridotites establish that compositional heterogeneity and Crystal Preferred Orientations (CPOs) are ubiquitous from the mm to the km scales. These data allow discussing the processes that produce/destroy heterogeneity and anisotropy and constraining the time scales over which they are active. This analysis highlights: (i) the role of deformation and reactive percolation of melts and fluids in producing compositional and structural heterogeneity and the feedbacks between these processes, (ii) the weak mechanical effect of mineralogical variations, and (iii) the low volumes of fine-grained microstructures and difficulty to preserve them. In contrast, olivine CPO and the resulting anisotropy of mechanical and thermal properties are only modified by deformation. Based on this analysis, we propose that strain localization at the plate scale is, at first order, controlled by large-scale variations in thermal structure and in CPO-induced anisotropy. In cold parts of the lithospheric mantle , grain size reduction may contribute to strain localization, but the low volume of fine-grained domains limits this effect

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Ultramylonite generation via phase mixing in high‐strain experiments

Cross

Skemer

2017

JGR Solid Earth

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Dynamic recrystallization and phase mixing are considered to be important processes in ductile shear zone formation, as they collectively enable a permanent transition to the strain‐weakening, grain‐size sensitive deformation regime. While dynamic recrystallization is well understood, the underlying physical processes and timescales required for phase mixing remain enigmatic. Here, we present results from high‐strain phase mixing experiments on calcite‐anhydrite composites. A poorly mixed starting material was synthesized from fine‐grained calcite and anhydrite powders. Samples were deformed in the Large Volume Torsion apparatus at 500°C and shear strain rates of 5 × 10−5 to 5 × 10−4 s−1, to finite shear strains of up to γ = 57. Microstructural evolution is quantified through analysis of backscattered electron images and electron backscatter diffraction data. During deformation, polycrystalline domains of the individual phases are geometrically stretched and thinned, causing an increase in the spatial density of interphase boundaries. At moderate shear strains (γ ≥ 6), domains are so severely thinned that they become “monolayers” of only one or two grain's width and form a thin compositional layering. Monolayer formation is accompanied by a critical increase in the degree of grain boundary pinning and, consequently, grain‐size reduction below the theoretical limit established by the grain‐size piezometer or deformation mechanism field boundary. Ultimately, monolayers neck and disaggregate at high strains (17 <γ <57) to complete the phase mixing process. This “geometric” phase mixing mechanism is consistent with observations of mylonites, where layer (i.e., foliation) formation is associated with strain localization, and layers are ultimately destroyed at the mylonite‐ultramylonite transition.

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Fluid-assisted strain localization in the shallow subcontinental lithospheric mantle

Cited by 42 publications

References 93 publications

Water pumping in mantle shear zones

Water pumping in mantle shear zones

Heterogeneity and anisotropy in the lithospheric mantle

Ultramylonite generation via phase mixing in high‐strain experiments

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