Crystallographic preferred orientations and misorientations in some olivine rocks deformed by diffusion or dislocation creep

Fliervoet, Timon; Drury, M. R.; Chopra, Prame

doi:10.1016/s0040-1951(98)00250-9

Cited by 87 publications

(55 citation statements)

References 69 publications

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“…In fact, in the misorientation distribution data shown by Obbard et al (2006), there was no difference between the correlated and un-correlated distributions. This implies that misorientations are controlled by the strong CPO (Fliervoet et al, 1999). In addition, there is a lack of 5 • -15 • misorientation boundaries, which would be expected if polygonisation was the main grain-size-reducing mechanism (Trimby et al, 1998(Trimby et al, , 2000.…”

Section: Characteristics Of Grain Dissection In Simulation and Naturementioning

confidence: 99%

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

et al. 2017

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The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modeling and analyzed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighboring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modeling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures.

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Section: Characteristics Of Grain Dissection In Simulation and Naturementioning

confidence: 99%

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

et al. 2017

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“…Plagioclase and clinopyroxene, which are the major rock forming minerals in the studied granulites, also exhibit evidence for deformation by both grain-size-insensitive and grain-size-sensitive deformation mechanisms. Evidence for intragranular deformation by dislocation creep includes (1) phase segregation and formation of compositional layering (Kenkmann and Dresen, 2002); (2) undulose extinction of porphyroclasts; (3) a high number of low-angle (< 10 • ) misorientation angles; (4) a large number of low-angle misorientation axes with strongly clustered distributions (Fliervoet et al, 1999); and (5) misorientation axes consistent with the orientations of tilt boundaries for known slip systems in plagioclase. Furthermore, dynamic recrystallization accommodated by subgrain rotation recrystallization is inferred from microstructures such as (1) recrystallized grains lacking significant internal deformation; (2) recrystallized grains with twins oriented at a low angle to the twins in adjacent porphyroclasts; and (3) core-and-mantle structures (e.g., Drury and Urai, 1990).…”

Section: Deformation Mechanisms In the Baja California Lithospherementioning

confidence: 99%

Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

et al. 2017

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Abstract. The rheology of lower crust and its transient behavior in active strike-slip plate boundaries remain poorly understood. To address this issue, we analyzed a suite of granulite and lherzolite xenoliths from the upper Pleistocene–Holocene San Quintín volcanic field of northern Baja California, Mexico. The San Quintín volcanic field is located 20 km east of the Baja California shear zone, which accommodates the relative movement between the Pacific plate and Baja California microplate. The development of a strong foliation in both the mafic granulites and lherzolites, suggests that a lithospheric-scale shear zone exists beneath the San Quintín volcanic field. Combining microstructural observations, geothermometry, and phase equilibria modeling, we estimated that crystal-plastic deformation took place at temperatures of 750–890 °C and pressures of 400–560 MPa, corresponding to 15–22 km depth. A hot crustal geotherm of 40 ° C km−1 is required to explain the estimated deformation conditions. Infrared spectroscopy shows that plagioclase in the mafic granulites is relatively dry. Microstructures are interpreted to show that deformation in both the uppermost lower crust and upper mantle was accommodated by a combination of dislocation creep and grain-size-sensitive creep. Recrystallized grain size paleopiezometry yields low differential stresses of 12–33 and 17 MPa for plagioclase and olivine, respectively. The lower range of stresses (12–17 MPa) in the mafic granulite and lherzolite xenoliths is interpreted to be associated with transient deformation under decreasing stress conditions, following an event of stress increase. Using flow laws for dry plagioclase, we estimated a low viscosity of 1.1–1.3×1020 Pa ⋅ s for the high temperature conditions (890 °C) in the lower crust. Significantly lower viscosities in the range of 1016–1019 Pa ⋅ s, were estimated using flow laws for wet plagioclase. The shallow upper mantle has a low viscosity of 5.7×1019 Pa ⋅ s, which indicates the lack of an upper-mantle lid beneath northern Baja California. Our data show that during post-seismic transients, the upper mantle and the lower crust in the Pacific–Baja California plate boundary are characterized by similar and low differential stress. Transient viscosity of the lower crust is similar to the viscosity of the upper mantle.

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“…Ji et al, 2001;Lawlis, 1998;McDonnell et al, 2000). Existing data on the resultant microstrctures in such controlled experiments indicate that orthopyroxene is deforming by dislocation creep where as the olivines are dominated by GBS (Fliervoet et al, 1999). These experiments, however, were done in uniaxial compression to strains 161 less than 24%, and the LPOs show evidence for diffusion creep as well as GBS.…”

Section: Viscosity Variations In Naturally-deformed Peridotitesmentioning

confidence: 99%

Petrologic and microstructural constraints on focused melt transport in dunites and the rheology of the shallow mantle

Braun¹

2004

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Crystallographic preferred orientations and misorientations in some olivine rocks deformed by diffusion or dislocation creep

Cited by 87 publications

References 69 publications

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

Petrologic and microstructural constraints on focused melt transport in dunites and the rheology of the shallow mantle

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