A Discussion on global tectonics in Proterozoic times - The interrelations of fluid transport, deformation, geochemistry and heat flow in early Proterozoic shear zones in the Lewisian complex

1976 ◽  
Vol 280 (1298) ◽  
pp. 569-604 ◽  
Keyword(s):  
Grain Size ◽  
Heat Flow ◽  
Hydraulic Fracturing ◽  
Fluid Transport ◽  
Shear Zones ◽  
Size Reduction ◽  
Dyke Swarm ◽  
Large Temperature ◽  
Early Proterozoic ◽  
General Chemical

The Lewisian complex of northwest Scotland shows a pattern of evolution typical of a number of early Proterozoic provinces. During the period 2500-1600 Ma, deformation occurred along steeply dipping shear zones, resulting in both vertical and lateral movements. The largest of these shear zones, forming the northern boundary to the Scourian granulites (Archaean), must have penetrated to considerable depth, possibly to the mantle. Modal and chemical analysis of rocks from shear zones are presented and discussed in relation to rocks sampled outside shear zones. The mineralogy and composition of all rocks deformed in the shear zones have been considerably altered by synkinematic metasomatism. In the early stages, immediately prior to and during the intrusion of the regional doleritic dyke swarm, this metasomatic activity involved addition of H 2 O and Na to the rocks. Subsequently, more significant changes in rock chemistry occurred addition of H 2 O, K, Na, loss of Fe, Ca, Mg). These changes resulted from the interaction between large volumes of water and the rocks in the shear zones along which the fluid travelled. A combination of modal and chemical data allow general chemical reactions to be written which describe the evolution of the gneisses during reworking and retrogression from pyroxene bearing granulite facies rocks to hornblende and biotite bearing amphibolite facies rocks in shear zones. The reactions are written as ionic equilibria and suggest that the fluid phase in the shear zones had a low pH. Adiabatic transport of water upwards through the crust will result in moderate warming of the fluid, and can cause large temperature increases above the preexisting geothermal gradient in rocks through which the fluid travels. It is suggested that both deformation and metamorphism in these shear zones are related to transport of fluid by hydraulic fracturing. Grain size reduction by hydraulic fracturing increases the strain rate in the shear zones. Deformation may cease in a shear zone when the fluid pressure drops and hydraulic fracturing no longer occurs. Thus fluid transport, mineral reactions, chemical changes, grain size reduction and convective heat flow will cease. A close relation should exist between the intensity of deformation, the extent of metasomatism and the thermal history in these important shear belts.

scholarly journals Syn-kinematic hydration reactions, grain size reduction, and dissolution–precipitation creep in experimentally deformed plagioclase–pyroxene mixtures

Solid Earth ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 985-1009 ◽  
Author(s):  
Sina Marti ◽  
Holger Stünitz ◽  
Renée Heilbronner ◽  
Oliver Plümper ◽  
Rüdiger Kilian
Keyword(s):  
Grain Size ◽  
Confining Pressure ◽  
Shear Zones ◽  
Grain Boundary Sliding ◽  
Size Reduction ◽  
Deformation Mechanisms ◽  
Dislocation Creep ◽  
Exact Nature ◽  
Crystallographic Preferred Orientation ◽  
Mafic Rocks

Abstract. It is widely observed that mafic rocks are able to accommodate high strains by viscous flow. Yet, a number of questions concerning the exact nature of the involved deformation mechanisms continue to be debated. In this contribution, rock deformation experiments on four different water-added plagioclase–pyroxene mixtures are presented: (i) plagioclase(An60–70)–clinopyroxene–orthopyroxene, (ii) plagioclase(An60)–diopside, (iii) plagioclase(An60)–enstatite, and (iv) plagioclase(An01)–enstatite. Samples were deformed in general shear at strain rates of 3×10−5 to 3×10−6 s−1, 800 °C, and confining pressure of 1.0 or 1.5 GPa. Results indicate that dissolution–precipitation creep (DPC) and grain boundary sliding (GBS) are the dominant deformation mechanisms and operate simultaneously. Coinciding with sample deformation, syn-kinematic mineral reactions yield abundant nucleation of new grains; the resulting intense grain size reduction is considered crucial for the activity of DPC and GBS. In high strain zones dominated by plagioclase, a weak, nonrandom, and geometrically consistent crystallographic preferred orientation (CPO) is observed. Usually, a CPO is considered a consequence of dislocation creep, but the experiments presented here demonstrate that a CPO can develop during DPC and GBS. This study provides new evidence for the importance of DPC and GBS in mid-crustal shear zones within mafic rocks, which has important implications for understanding and modeling mid-crustal rheology and flow.

Self-consistent grain size evolution controls lithospheric shear zone formation during continental rifting

2021 ◽  
Author(s):  
Jonas B. Ruh ◽  
Leif Tokle ◽  
Whitney M. Behr
Keyword(s):  
Grain Size ◽  
Upper Mantle ◽  
Shear Zones ◽  
Size Reduction ◽  
Numerical Code ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Dominant Mechanism ◽  
Size Evolution ◽  
Growth Laws

<p>In geodynamic numerical models, grain-size-independent dislocation creep often solely defines the governing crystal-plastic flow law in the upper mantle. However, grain-size-dependent diffusion creep may become the dominant deformation mechanism if grain size is sufficiently small. Previous studies implying composite diffusion-dislocation creep rheologies and fixed grain size suggest that the upper mantle is stratified with the dominant mechanism being dislocation creep at shallow depths and diffusion creep further down. Studies with variable grain size in the upper mantle depending on common grain-size evolution models demonstrate that the contrary might be the case, where diffusion creep is acting within the mantle lithosphere and dislocation creep in the asthenosphere below. Diffusion creep as a dominant mechanism has important implications for the overall strength of the lithosphere and therefore for the dynamic evolution of lithospheric-scale extension and orogeny.</p><p>To investigate the importance of grain size and the effects of resulting crystal-plastic creep within the upper mantle, we developed a two-dimensional thermo-mechanical numerical code based on the finite difference method with a fully staggered Eularian grid and freely advecting Lagrangian markers. The model implies a composite diffusion-dislocation creep rheology and a dynamic grain-size evolution model based on the paleowattmeter including recently published olivine grain growth laws.</p><p>Results of upper mantle extension indicate olivine grain sizes of ~7 cm for large parts of the upper mantle below the LAB, while in the lithosphere grain size ranges from ~1 mm at the Moho to ~5 cm at the LAB. This grain size distribution indicates that dislocation creep dominates deformation in the entire upper mantle. However, diffusion creep activates along lithospheric-scale shear zones during rifting where intense grain size reduction occurs to local stress increase. We furthermore test the implications of wet and dry olivine rheology and respective crystal growth laws and interpret their effects on large-scale tectonic processes. Our results help explain strain localization during extension by strength loss related to grain size reduction and consequent diffusion creep activation.</p>

The Wathaman batholith: largest known Precambrian pluton

1984 ◽  
Vol 21 (10) ◽  
pp. 1082-1097 ◽  
Author(s):  
S. L. Fumerton ◽  
M. R. Stauffer ◽  
J. F. Lewry
Keyword(s):  
Shear Zones ◽  
Island Arc ◽  
Pacific Rim ◽  
Early Proterozoic ◽  
Northern Saskatchewan ◽  
Internal Deformation

The Early Proterozoic Wathaman batholith, in northern Saskatchewan and Manitoba, is a 900 km long, megacrystic granite–granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal–island-arc terranes of the "Trans-Hudson Orogen," of the western Churchill Province. Although the largest Precambrian batholith known, it is, apart from marginal complexities, remarkably homogeneous throughout and, unlike comparably sized and situated Phanerozoic batholiths, shows no evidence of multiple intrusion, nor does it have comagmatic early mafic phases. However, it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons. Taken as a whole the composite batholithic belt is similar in many aspects to Mesozoic Pacific rim batholithic belts, and like them probably was emplaced during plate collision.The batholith is affected by pervasive internal deformation, is bounded on the northwest by major blastomylonite zones, and is transected internally by splaying shear zones. It is a mid- to late-synkinematic Hudsonian intrusion, emplaced within a markedly compressional, crustal regime. On the basis of petrological, geochemical, and isotopic criteria the batholith is an "I-type" intrusion, but the origin of the magma and the emplacement mechanisms are still unresolved problems.

Dynamic strain aging and grain size reduction effects on the fatigue resistance of SA533B3 steels

2004 ◽  
Vol 324 (2-3) ◽  
pp. 140-151 ◽  
Author(s):  
J.Y Huang ◽  
J.R Hwang ◽  
J.J Yeh ◽  
C.Y Chen ◽  
R.C Kuo ◽  
...  
Keyword(s):  
Grain Size ◽  
Dynamic Strain Aging ◽  
Fatigue Resistance ◽  
Strain Aging ◽  
Size Reduction ◽  
Dynamic Strain

Grain size reduction by utilizing a very thin CrW seedlayer and dry-etching process in CoCrTaNiPt longitudinal media

2000 ◽  
Vol 87 (9) ◽  
pp. 6860-6862 ◽  
Author(s):  
Satoru Yoshimura ◽  
D. D. Djayaprawira ◽  
Tham Kim Kong ◽  
Yusuke Masuda ◽  
Hiroki Shoji ◽  
...  
Keyword(s):  
Grain Size ◽  
Dry Etching ◽  
Size Reduction ◽  
Etching Process

Grain size reduction effect of barium titanate embedded in silica xerogel

2008 ◽  
Vol 62 (17-18) ◽  
pp. 2947-2949 ◽  
Author(s):  
J.R. Martínez ◽  
J.A. de la Cruz-Mendoza ◽  
S.A. Palomares-Sánchez ◽  
G. Vázquez-García ◽  
G. Ortega-Zarzosa ◽  
...  
Keyword(s):  
Grain Size ◽  
Barium Titanate ◽  
Size Reduction ◽  
Silica Xerogel ◽  
Reduction Effect

The Influence of Lubricant Supply Conditions and Bearing Configuration on the Performance of (Semi) Floating Ring Bearing Systems for Turbochargers

2017 ◽  
Author(s):  
Luis San Andrés ◽  
Feng Yu ◽  
Kostandin Gjika
Keyword(s):  
Heat Flow ◽  
Thermal Energy ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Engine Oil ◽  
Large Temperature ◽  
Oil Viscosity ◽  
Supply Pressure ◽  
The Impact ◽  
Bearing System

Engine oil lubricated (semi) floating ring bearing (S)FRB systems in passenger vehicle turbochargers (TC) operate at temperatures well above ambient and must withstand large temperature gradients that can lead to severe thermo-mechanical induced stresses. Physical modeling of the thermal energy flow paths and an effective thermal management strategy are paramount to determine safe operating conditions ensuring the TC component mechanical integrity and the robustness of its bearing system. On occasion, the selection of one particular bearing parameter to improve a certain performance characteristic could be detrimental to other performance characteristics of a TC system. The paper details a thermohydrodynamic model to predict the hydrodynamic pressure and temperature fields and the distribution of thermal energy flows in the bearing system. The impact of the lubricant supply conditions (pressure and temperature), bearing film clearances, oil supply grooves on the ring ID surface are quantified. Lubricating a (S)FRB with either a low oil temperature or a high supply pressure increases (shear induced) heat flow. A lube high supply pressure or a large clearance allow for more flow through the inner film working towards drawing more heat flow from the hot journal, yet raises the shear drag power as the oil viscosity remains high. Nonetheless, the peak temperature of the inner film is not influenced much by the changes on the way the oil is supplied into the film as the thermal energy displaced from the hot shaft into the film is overwhelming. Adding axial grooves on the inner side of the (S)FRB improves its dynamic stability, albeit increasing the drawn oil flow as well as the drag power and heat flow from the shaft. The predictive model allows to identify a compromise between different parameters of groove designs thus enabling a bearing system with a low power consumption.

scholarly journals Grain size reduction strategies on Eurofer

2018 ◽  
Vol 17 ◽  
pp. 129-136 ◽  
Author(s):  
L. Pilloni ◽  
C. Cristalli ◽  
O. Tassa ◽  
I. Salvatori ◽  
S. Storai
Keyword(s):  
Grain Size ◽  
Size Reduction ◽  
Reduction Strategies

Influence of Severe Plastic Deformation on the PLC Effect and Mechanical Properties in Al 5XXX Alloy

2006 ◽  
Vol 114 ◽  
pp. 171-176 ◽  
Author(s):  
Joanna Zdunek ◽  
Pawel Widlicki ◽  
Halina Garbacz ◽  
Jaroslaw Mizera ◽  
Krzysztof Jan Kurzydlowski
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Grain Size ◽  
Severe Plastic Deformation ◽  
True Strain ◽  
Tensile Tests ◽  
Size Reduction ◽  
Hydrostatic Extrusion ◽  
Stress Strain ◽  
Chatelier Effect

In this work, Al-Mg-Mn-Si alloy (5483) in the as-received and severe plastically deformed states was used. Plastic deformation was carried out by hydrostatic extrusion, and three different true strain values were applied 1.4, 2.8 and 3.8. All specimens were subjected to tensile tests and microhardness measurements. The investigated material revealed an instability during plastic deformation in the form of serration on the stress-strain curves, the so called Portevin-Le Chatelier effect It was shown that grain size reduction effected the character of the instability.

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