High-temperature Dislocation Creep Research Articles

Deformation Behavior and Inferred Seismic Properties of Tonalitic Migmatites at the Time of Pre‐melting, Partial Melting, and Post‐Solidification

AbstractAs seismic data from the lower crust becomes more readily available, it is important to link seismic properties to the ongoing processes within lower crustal evolution. This includes high temperature, pre‐ and post‐migmatization solid state deformation as well as melt‐present deformation. We selected two tonalitic migmatites with variable former melt content (one metatexite and one diatexite) from the lower crustal Daqingshan area, northern North China Craton to assess the link between seismic properties and rock structure and rheology. Field observation along with microstructural features suggest that the characteristics of hornblende and plagioclase within the residuum of the metatexite can be used to derive information on the pre‐melt deformation. Residuum's plagioclase CPO (crystallographic preferred orientations) is consistent with high temperature dislocation creep as the main deformation mechanism; similarly, hornblende shows a strong CPO related to dislocation creep. During syn‐melt (melt present) conditions, phenocrysts of plagioclase in the metatexite's neosome and K‐feldspar and peritectic hornblende in the diatexite's neosome are present. The rheology of the rock was dominated by melt; hence is inferred to follow Newtonian flow. After melt crystallization deformation is minor but again dominated by dislocation creep. The seismic properties (seismic velocity, anisotropy, Vp/Vs ratio, etc.) for pre‐ and post‐melt have similar values expected values for solid mafic rocks, whilst the syn‐melt seismic velocities are generally lower and Vp/Vs ratios and seismic anisotropies are higher.

Grain-size reduction of feldspar and flow of deformed granites within the Gaoligong shear zone, southwestern Yunnan, China

Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due to the complexity of their mineral compositions, crystal structures, as well as changing deformation conditions. The refined microstructure, fabric and composition of major minerals in the deformed granitic rocks within the Gaoligong shear zone (GLGSZ), southwestern Yunnan, China, were studied. With increasing mylonitization, two fabric types of end-members have been distinguished (type-I banded granitic mylonite and type-II banded ultramylonite). The two types of deformed granitic rocks have the same mineral assemblage, but different mineral modes. The type-I banded granitic mylonite has a greater proportion of K-feldspar (mostly present as porphyroclasts)>plagioclase>quartz±biotite, however, the type-II banded ultramylonite has a greater proportion of fine-grained plagioclase>K-feldspar>quartz±biotite. The crystallographic preferred orientation (CPO) patterns of quartz combined with two-feldspar geothermometer, confirm that the quartz grains in the type-I and type-II granitic rock have undergone high-temperature dislocation creep deformation. The K-feldspar grains in the matrix of type-II banded ultramylonite show a dominant (100) [010] slip system with dislocation creep recrystallization, while the fine-grained plagioclase grains present a weak CPO pattern with superplastic flow. The K-feldspar porphyroclasts show grain-size reduction associated with mineral composition and fabric transformation. The myrmekite formation with the fine-grained neocrystallization of plagioclase and quartz significally replaced the K-feldspar porphyroclasts. Finally, the fine-grained neocrystallization plagioclases were formed further into the high strain localized ultramylonites with superplastic flow.

High-pressure, high-temperature deformation of dunite, eclogite, clinopyroxenite and garnetite using in situ X-ray diffraction

The rheology of eclogite, garnetite and clinopyroxenite in the peridotitic upper mantle was experimentally investigated in a large volume press combined with in situ synchrotron X-ray diffraction techniques to study the impact on mantle convection resulting from the subduction of oceanic lithosphere. Experiments were carried out over a range of constant strain rates (2×10−6–3×10−5 s−1), pressures (4.3 to 6.7 GPa) and temperatures (1050 to 1470 K). Results show substantial strength variations among eclogitic garnet and clinopyroxene and peridotitic olivine. At low temperatures (<1200 K), eclogite is over 1 GPa stronger than dunite. On the other hand, at high temperatures (>1400 K) eclogite is weaker than dunite by 0.2 GPa or more. Garnetite and clinopyroxenite exhibit higher strength than dunite at approximately 1200 K. However, at higher temperature (1370 K), clinopyroxenite is significantly weaker than garnetite (and dunite) by more than a factor of five. We explain these observations by transitions in deformation mechanisms among the mineral phases. In clinopyroxene, high temperature dislocation creep resulting in a strength reduction replaces low temperature twinning. Whereas garnet remains very rigid at all experimental conditions when nominally anhydrous (‘dry’). Microstructural observations show phase segregation of clinopyroxene and garnet, development of a crystallographic and shape preferred orientation in the former but not in the latter, suggesting an overall weak seismic anisotropy. Detection of eclogite bodies in the peridotite-dominated mantle may only be possible via observation of high VP/VS1 ratios. A comparable or weaker rheology of eclogite to dunite suggests effective stirring and mixing of eclogite in the convecting mantle.

Relaxation mechanisms at grain boundaries for ambient-temperature creep of h.c.p. metals

The role of grain boundaries (GBs) for ambient-temperature creep of h.c.p. metals was investigated using pure Zn with several grain sizes. To reveal the relaxation mechanism of ambient-temperature creep, scanning electron microscopy and atomic force microscopy were performed to evaluate the amount of grain boundary sliding. Grain orientation variations were then measured using electron backscatter diffraction to investigate a lattice rotation after ambient-temperature creep. The results obtained by these experiments are as follows: (1) Strong grain size dependency, i.e. larger grain size showed lower total true strain. This is different from high temperature dislocation creep. (2) Grain boundary steps of a few tenths of a micrometer gave evidence of grain boundary sliding during ambient-temperature creep. (3) Lattice rotation of a few degrees was observed near GBs, which indicates that dislocations piled up at GBs. (4) Grain boundary sliding is considered as accommodation process of piled-up dislocations with an apparent activation energy of 18 kJ/mol.

Relationships between melt-induced rheological transitions and finite strain: Observations from host rock pendants of the Tuolumne Intrusive Suite, Sierra Nevada, California

Finite strain analysis in the northern (Piute Meadow pendant (PMP)) and eastern (Saddlebag Lake pendant (SLP)) host rock pendants of the Tuolumne Intrusive Suite (TIS) reveals plane strain geometries in the pendants and a steep strain gradient in the SLP. Average regional z-axis shortening in both pendants is ca. 43% and increases to ca. 70 and 85% in the SLP within ca. 100 m to the pluton contact. Microstructures in the SLP adjust to increasing temperatures and partial melting near the margin. Beyond the pluton margin, weakly elongate quartz grains with lobate grain boundaries, patchy to sweeping undulose extinction, deformation bands, and incipient subgrains are consistent with low-temperature dislocation creep. Towards the margin, quartz grain boundaries become increasingly irregular and display “chessboard” patterns indicating high-temperature dislocation creep. Grain size is markedly smaller near the margin and despite large finite strain grains do not show evidence for crystal-plastic deformation. Cuspate strain-free interstices are interpreted to mimic former anatectic melt. Outcrop-scale migmatization, coincidence with abruptly increasing finite strain, and microfracturing towards the margin implies that fracture-induced mechanical grain size reduction may have triggered the transition to melt-assisted granular flow, ultimately resulting in drastic rheological weakening.

Effects of pressure on high-temperature dislocation creep in olivine

Effects of pressure on high-temperature, dislocation creep in olivine ((Mg, Fe) 2 SiO 4 ) aggregates have been determined under both water-poor ('dry') and water-saturated ('wet') conditions. New experimental data were obtained at pressures of 1-2 GPa under 'dry' and 'wet' conditions using a newly developed high-resolution dislocation density measurement technique to estimate the creep strength. These data are compared with previous data at lower and higher pressures to determine the pressure dependence of high-temperature dislocation creep in olivine aggregates. We find that the creep strength under 'dry' conditions increases monotonically with increasing pressure, whereas the creep strength under 'wet' conditions changes with pressure in a non-monotonic fashion: it first decreases rapidly with increasing pressure and then becomes less sensitive to pressure at above 1 GPa. Such behaviour can be described by the following formula: where the subscripts d and w refer to parameters for 'dry' and 'wet' conditions respectively. The present study gives A d = 10 6.1 -0.2 s m1 (MPa) mn , , and r = 0 for 'dry' conditions, and A w m10 2.9 -0.1 s m1 (MPa) mn mr , , and r = 1.20 -0.05 for 'wet' conditions ( n = 3.0 -0.1 for both 'dry' and 'wet' conditions). The large activation volume for 'wet' conditions can be interpreted as due to the additional contribution from the activation volume for dissolution of OH in the olivine structure ( ). The value of r ( ,1.2) is consistent with a model in which creep in olivine is rate controlled by the motion of positively charged jogs through the diffusion of silicon via an interstitial mechanism.

Crystal plasticity of natural garnet: New microstructural evidence

Research Article| November 01, 2000 Crystal plasticity of natural garnet: New microstructural evidence David J. Prior; David J. Prior 1Department of Earth Sciences, Liverpool University, Liverpool L69 3BX, UK Search for other works by this author on: GSW Google Scholar John Wheeler; John Wheeler 1Department of Earth Sciences, Liverpool University, Liverpool L69 3BX, UK Search for other works by this author on: GSW Google Scholar Frank E. Brenker; Frank E. Brenker 2Institut für Mineralogie und Geochemie, Universität zu Köln, Zülpicher Straße 49b, 50674 Köln, Germany Search for other works by this author on: GSW Google Scholar Ben Harte; Ben Harte 3Department of Geology and Geophysics, Edinburgh University, Edinburgh EH9 3JW, UK Search for other works by this author on: GSW Google Scholar Mike Matthews Mike Matthews 4Johnson Matthey Ltd., Blounts Court, Sonning Common, Reading RG4 9NH, UK Search for other works by this author on: GSW Google Scholar Author and Article Information David J. Prior 1Department of Earth Sciences, Liverpool University, Liverpool L69 3BX, UK John Wheeler 1Department of Earth Sciences, Liverpool University, Liverpool L69 3BX, UK Frank E. Brenker 2Institut für Mineralogie und Geochemie, Universität zu Köln, Zülpicher Straße 49b, 50674 Köln, Germany Ben Harte 3Department of Geology and Geophysics, Edinburgh University, Edinburgh EH9 3JW, UK Mike Matthews 4Johnson Matthey Ltd., Blounts Court, Sonning Common, Reading RG4 9NH, UK Publisher: Geological Society of America Received: 24 May 2000 Revision Received: 03 Aug 2000 Accepted: 07 Aug 2000 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (11): 1003–1006. https://doi.org/10.1130/0091-7613(2000)28<1003:CPONGN>2.0.CO;2 Article history Received: 24 May 2000 Revision Received: 03 Aug 2000 Accepted: 07 Aug 2000 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David J. Prior, John Wheeler, Frank E. Brenker, Ben Harte, Mike Matthews; Crystal plasticity of natural garnet: New microstructural evidence. Geology 2000;; 28 (11): 1003–1006. doi: https://doi.org/10.1130/0091-7613(2000)28<1003:CPONGN>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Scanning electron microscope (SEM) orientation contrast images of mantle nodules show that garnets contain cellular domains of different crystallographic orientation. Electron backscatter diffraction shows small crystallographic mismatches (<3°) across cell boundaries. A transmission electron microscope examination of an area containing these substructures shows that the cell boundaries comprise arrays of dislocations and are subgrain boundaries. The observed garnet substructures relate to high-temperature dislocation creep and recovery. This is the first time that subgrains have been shown to occur in a significant volume of an individual garnet. Wider application of new SEM techniques may enable us to use garnet microstructures to determine deformation conditions more exactly and will aid interpretation of garnet microchemical data. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Creep of Al-3wt.%Mg as measured with the incremental loading method

The deformation behaviour of Al-3wt.%Mg polycrystals was studied in the temperature interval from 295 to 674 K on a creep apparatus, applying the incremental loading method. The temperature dependences of the stresses which first cause plastic strain as well as the stress sensitivities of the strain rate indicate that different deformation mechanisms are operating. At temperatures below 0.5 T m, the intersection of forest dislocations is the most likely rate-controlling mechanism, superimposed at the lowest applied temperatures by effects of dynamic strain ageing. Above 0.5 T m there is diffusion-controlled high-temperature dislocation creep. The differences in results due to the use of the method and its limitations are discussed.

Electromigration threshold of thin-film conductors

The connection between the mechanical properties of a thin film conductor and its electromigration threshold ( jl) th, where j is the current density and l is the conductor length is analysed. It is assumed that electrodiffusion can lead to elastic strain of the conductor (electrodiffusional stresses). As is shown for aluminium, the electromigration threshold value is determined by the level of compressive stresses at which the electrodiffusional stresses intensively relax via a dislocation glide (at T ≲ 470 K) or high-temperature dislocation creep (at T ≳ 470 K). Expressions are proposed for estimation of ( jl) th for thin film conductors made of various materials. It is assumed that the value of the electromigration threshold is determined by the parameter μ (Z ∗ϱ) , where μ is the shear modulus, Z ∗ the effective charge, ϱ the resistivity of a thin film material. In descending order of ( jl) th, metals may be arranged into five groups: noble metals (gold, copper, aluminium, silver); IIB group metals (cadmium, zinc); refractory metals (molybdenum, tantalum, tungsten, chromium, titanium); platinum metals (nickel, iridium, rhodium, palladium, platinum) and soft low-melting point metals (indium, tin, lead). Among d-elements ( jl) th decreases with the increase of the group number in each period of the periodic table. To increase the electromigration resistance of the conductors of integrated circuit metallization, the dispersion hardened alloys based on metals with a high value of μ (Z ∗ϱ) , for example, aluminium, gold, silver or copper should be used.

Superplasticity in a Zn-1·1 wt.% Al alloy

In the paper the results of the deformation behaviour study in a Zn-1·1 wt. % Al alloy are presented. The influence of temperature ranging from 223 K (0·34Tm) to 645 K (0·98 Tm) on the flow stress, strain rate sensitivity parameterm and activation energy was investigated at various strain rates. The superplastic behaviour was observed in a very broad temperature interval the limits of which were dependent on the strain rate. The best superplastic properties—ductility A>1000 % and parameterm≊0·7—were established at strain rates\(\dot \varepsilon \cong 10^{ - 4} s^{ - 1} \) at temperatureT=520 K. Superplastic characteristics were found in coarser-grained samples with grain sizes up to 50 μm. An intensive grain growth occurring at temperaturesT370 K was found to be probably responsible for the origin of anomalies in temperature dependences of the flow stress and parameterm. The activation energy established in the region of superplastic behaviour was much lower than the activation energy measured in the non-superplastic region. The valueQ≊90 kJ/mol obtained in the non-superplastic region at very high temperatures is comparable with the activation energy of lattice selfdiffusion in pure Zn or heterodiffusion of Al in Zn along the hexagonalc-axis. This result suggests that the deformation mechanism in the non-superplastic region has a nature similar to the high-temperature dislocation creep. The activation energyQ e〈20;40〉 kJ/mol obtained in the superplastic region cannot be compared with activation energies of any known diffusion types in Zn. The explanation of this discrepancy could be find in the presence of other temperature dependent terms the contributions of which to the temperature dependence of the flow stress were neglected. The structure study confirmed the decrease in the contribution of grain boundary sliding when passing from the superplastic to the non-superplastic region.

Transition from cataclastic flow to dislocation creep of feldspar: Mechanisms and microstructures

Research Article| July 01, 1987 Transition from cataclastic flow to dislocation creep of feldspar: Mechanisms and microstructures Jan Tullis; Jan Tullis 1Department of Geological Sciences, Brown University Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Richard A. Yund Richard A. Yund 1Department of Geological Sciences, Brown University Providence, Rhode Island 02912 Search for other works by this author on: GSW Google Scholar Geology (1987) 15 (7): 606–609. https://doi.org/10.1130/0091-7613(1987)15<606:TFCFTD>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jan Tullis, Richard A. Yund; Transition from cataclastic flow to dislocation creep of feldspar: Mechanisms and microstructures. Geology 1987;; 15 (7): 606–609. doi: https://doi.org/10.1130/0091-7613(1987)15<606:TFCFTD>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Feldspar aggregates exhibit cataclastic flow over a wide range of conditions between low-temperature faulting and high-temperature dislocation creep; this is due to the ease of cracking on the two good cleavages and the difficulty of dislocation motion. Albite aggregates experimentally deformed at moderate to high pressures in the cataclastic flow regime are macroscopically ductile; their optical microstructures show little evidence of crushing and resemble those expected for dislocation creep. However, transmission electron microscopy (TEM) shows no dislocations or very limited dislocation mobility, but does show abundant distributed microcracks and microcrush zones that contain <0.1-µm-diameter grains. Cataclastic flow is likely to be an important deformation mechanism in nature, but it may have been overlooked because its optical microstructures have been misinterpreted and because the extreme grain size reduction facilitates transitions to other phases and deformation mechanisms. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.