Hydration-induced climb dissociation of dislocations in naturally deformed mantle olivine     

Martyn R. Drury 《Physics and Chemistry of Minerals》1991,18(2):106-116

Widely dissociated dislocations have been observed in mantle olivine from the Erro-Tobbio peridotite in N.W. Italy. Analysis of diffraction contrast in transmission electron microscopy (TEM) indicates that the dissociation reaction involves the climb dissociation on (001) and {021} planes of b=[001] unit dislocations into partial dislocations with Burgers vectors approximately equal to 1/x 011. In the most extreme case a unit dislocation dissociates into four partials which bound three planar defects. The unusually wide dissociation and the greater extent of dissociation in olivine from amphibole-bearing rocks suggests that the dissociation is related to hydration. The occurrence of fluid inclusions along the dislocations confirms that the partials and planar defects are saturated with volatiles. Analysis of possible planar defect structures in Fo₉₀ shows that; (i) the most likely partial Burgers vectors are b=0 3/11 1/4; (ii) two of the planar defects are cation-deficient and can be stabilised by segregation of H⁺ to produce (Mg, Fe) (OH)₂ layers which are iso-structural with the OH-rich interlayer of the humite group minerals; (iii) the central planar defect is formed by removing a stoichiometric olivine (002) layer so does not produce any local chemical changes. The climb dissociation provides a possible mechanism for the transformation of olivine to a humite group mineral. OH-rich interlayers may nucleate on dislocations and extend into the crystal by climb resulting in a gradual increase of (Mg, Fe) (OH)₂ content. The only addition of material required is hydrogen which can rapidly diffuse into olivine. If the dissociation is stable and occurs at high temperatures and pressures it may significantly influence the nature and kinetics of deformation mechanisms and the olivine — spinel shear transformation mechanism in hydrated olivine.  相似文献   

Rare-earth and LIL element fractionation in high-grade charnockitic gneisses,south Norway     

D Field  S.A Drury  D.C Cooper 《Lithos》1980,13(3):281-289

High-Fe, intermediate-acid, charnockitic gneisses in the Arendal-Tromøy area of the Svecofennian terrain of southeast Norway comprise two chemically contrasting zones - one with normal large-ion-lithophile (LIL) element characteristics, and the other IIL-deficint. The noramal -LiLL-deficient varitties also have low ΣEEE, commonly with positive Eu anomalies. The normal-LIL rocks are enriched in ?REE, exhibit fractionated patterns and have negative Eu anomalies. Modelling shows that both the LIL and REE patterns are consistent with an essentially primary fractionation process involving the separation of cumulus (LIL-deficient) phases from andesitic-dacitic magma emplaced directly under the high-grade conditions, with the normal-LIL rocks crystallising from the residual melt. This process is interpreted as a deep-seated component of the magma system which culminated in the emplacement of some higher level rapakivi granite late in the Svecofennian event. The model presented does not require anorthosite to be part of the same magma system.  相似文献   

Partial melt in the asthenosphere: Evidence from electrical conductivity data     

M.J. Drury 《Physics of the Earth and Planetary Interiors》1978,17(2):P16-P20

Modelled conductivity variations with depth in the upper mantle obtained from geomagnetic induction and magnetotelluric results are compared to predicted conductivity variations obtained from laboratory measurements on dry material assumed to occur in the mantle. Higher than predicted conductivities at the base of the oceanic lithosphere suggest the presence of highly conductive partial melt. Using a known relationship between observed conductivity and the conductivity and volume fraction of the fluid, estimates of the melt volume fraction have been made assuming the melt to be in continuously connected network. In the sub-oceanic asthenosphere these values range from approximately 0.45 to 9%, whereas in sub-continental asthenosphere the partial melt volume fraction appears to be too low to increase the bulk conductivity. The partial melt content of the sub-continental asthenosphere may reach a few percent if the melt exists in isolated pockets. The apparent difference in melt content in sub-oceanic and sub-continental asthenosphere is discussed in terms of the different velocities of Pacific-type plates (which carry no continental block) and Atlantic-type plates (which carry a continental block).  相似文献   

Control issues relating to real‐time substructuring experiments using a shaking table     

S. A. Neild  D. P. Stoten  D. Drury  D. J. Wagg 《地震工程与结构动力学》2005,34(9):1171-1192

Real‐time substructuring is a method of dynamically testing a structure without experimentally testing a physical model of the entire system. Instead the structure can be split into two linked parts, the region of particular interest, which is tested experimentally, and the remainder which is tested numerically. A transfer system, such as a hydraulic actuator or a shaking table, is used to impose the displacements at the interface between the two parts on the experimental substructure. The corresponding force imposed by the substructure on the transfer system is fed back to the numerical model. Control of the transfer system is critical to the accuracy of the substructuring process. A study of two controllers used in conjunction with the University of Bristol shaking table is presented here. A proof‐of‐concept one degree‐of‐freedom mass–spring–damper system is substructured such that a portion of the mass forms the experimental substructure and the remainder of the mass plus the spring and the damper is modelled numerically. Firstly a linear controller is designed and tested. Following this an adaptive substructuring strategy is considered, based on the minimal control synthesis algorithm. The deleterious effect of oil‐column resonance common to shaking tables is examined and reduced through the use of filters. The controlled response of the experimental specimen is compared for the two control strategies. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Evidence for dominant grain-boundary sliding deformation in greenschist- and amphibolite-grade polymineralic ultramylonites from the Redbank Deformed Zone, Central Australia   总被引：1，自引：0，他引：1  

Timon F. Fliervoet  Stanley H. White  Martyn R. Drury 《Journal of Structural Geology》1997,19(12):1495-1520

Microstructural and textural investigations by scanning (SEM) and transmission electron microscopy (TEM) techniques have been performed on samples taken across two quartzo-feldspathic mylonite zones from the Redbank Deformed Zone, Central Australia. One has been deformed at greenschist-facies (GS), the second at amphibolite-facies (Am), conditions. With increasing strain the rock type changes from protomylonite to mylonite to ultramylonite. The protomylonites and mylonites consist of alternating quartz and polymineralic quartz-feldspar bands. At the highest strains a homogeneous, fine-grained polymineralic ultramylonite occurs. Shear-zone geometry and microscale structures indicate that these ultramylonites experienced higher strains and were weaker than the encapsulating protomylonites and mylonites. TEM and SEM studies of the ultramylonites reveal a rectangular to square grain shape, a continuous alignment of grain and interphase boundaries across several grain diameters, a grain size (GS 0.5 μm; Am 5–11 μm) less than the equilibrium subgrain size, and open and void-containing grain and interphase boundaries. Analysis of local textures by electron back-scatter diffraction (EBSD) in the SEM showed a very weak crystallographic preferred orientation (CPO) for the quartz. The grain misorientation relationships are not consistent, with dislocation creep being the dominant deformation mechanism. All structures are of the type expected if grain-boundary sliding processes had contributed significantly to the deformation. Consequently, the deformation of such quartzo-feldspathic rocks, and by implication the rheology of the Redbank Deformed Zone, must have been controlled by the mechanical properties of these fine-grained polymineralic ultramylonites, deforming by grain-boundary sliding processes. This is in contrast to the pure quartz bands which deformed by dislocation-creep mechanisms and were less important in the rheology of the Redbank Deformed Zone.  相似文献   

Large strain deformation studies using polycrystalline magnesium as a rock analogue. Part I: grain size paleopiezometry in mylonite zones     

S.H. White  M.R. Drury  S.E. Ion  F.J. Humphreys 《Physics of the Earth and Planetary Interiors》1985,40(3):201-207

The results of large strain deformation studies of polycrystalline magnesium are reported. Shear zones develop at temperatures below 0.65 Tm for strain rates between 10^?4?10^?5 s^?1. The zones are characterised by small recrystallised grains and are analogues of mylonite zones in crustal and mantle rocks. Their development is marked by a stress drop but the recrystallised grains in the zones do not re-equilibrate and remain equilibrated to the peak stress. However, the recrystallised grains in the areas bordering the shear zones undergo a strain dependent coarsening and their sizes re-equilibrate to the relaxed stresses at natural strains of 1. The geological implications of these results are discussed.  相似文献   

Virtual MHD Jets on Grids     

Thibaut Lery  CÉline Combet  Gareth Murphy  Luke O. C. Drury 《Astrophysics and Space Science》2005,298(1-2):375-378

As network performance has outpaced computational power and storage capacity, a new paradigm has evolved to enable the sharing of geographically distributed resources. This paradigm is known as Grid computing and aims to offer access to distributed resource irrespective of their physical location. Many national, European and international projects have been launched during the last years trying to explore the Grid and to change the way we are doing our everyday work. In Ireland, we have started the CosmoGrid project that is a collaborative project aimed to provide high performance super-computing environments. This will help to address complex problems such as magnetohydrodynamic outflows and jets in order to model and numerically simulate them. Indeed, the numerical modeling of plasma jets requires massive computations, due to the wide range of spatial-temporal scales involved. We present here the first jet simulations and their corresponding models that could help to understand results from laboratory experiments.  相似文献   

Recent developments and goals in texture research of geological materials     

B. Leiss  K. Ullemeyer  K. Weber  H. G. Brokmeier  H. -J. Bunge  M. Drury  U. Faul  F. Fueten  A. Frischbutter  H. Klein  W. Kuhs  P. Launeau  G. E. Lloyd  D. J. Prior  Ch. Scheffzük  T. Weiss  K. Walther  H. -R. Wenk 《Journal of Structural Geology》2000,22(11-12)

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Recognising the crystallographic signature of recrystallisation processes in deformed rocks: a study of experimentally deformed rocksalt     

Patrick W. Trimby  Martyn R. Drury  Christopher J. Spiers 《Journal of Structural Geology》2000,22(11-12)

The microstructural development of synthetic rocksalt experimentally deformed at 100–200°C can be dominated either by grain boundary migration recrystallisation or by subgrain rotation recrystallisation, depending on water content. Samples taken from both regimes have been analysed using automated electron backscatter diffraction in order to collect crystallographic orientation and misorientation data. The frequency distribution of boundary misorientations, the boundary hierarchy characteristics and the nature of any crystallographic preferred orientation (CPO) have been used to determine the crystallographic signature of both recrystallisation processes. Dominant subgrain rotation recrystallisation results in many low to medium angle (4–20°) boundaries, a strong CPO and a continuous boundary hierarchy. Dominant grain boundary migration recrystallisation results in few low or medium angle boundaries, and a discrete boundary hierarchy. The causes of these differences and the potential application of crystallographic signatures to the study of naturally deformed rocks are discussed.  相似文献   

Super-silicic garnet microstructures from an orogenic garnet peridotite, evidence for an ultra-deep (>6 GPa) origin   总被引：1，自引：0，他引：1  

Van Roermund  Drury  Barnhoorn  & De Ronde 《Journal of Metamorphic Geology》2000,18(2):135-147.

We report the field, petrographic and mineral chemical characteristics of relict super‐silicic (=majoritic) garnet microstructures from the Otrøy peridotites in the Western Gneiss Region, Norway. The evidence for the former existence of super‐silicic garnet consists of two‐pyroxene exsolution microstructures from garnet. Estimates of the initial composition of the super‐silicic garnet imply pressures of 6–6.5 GPa, indicating that the Otrøy garnet peridotites were derived from depths >185 km. The garnet peridotites consist of inter‐banded variable compositions with c. 50% garnet peridotite and 50% garnet‐free peridotite. Two distinct garnet types were identified: (a) normal matrix garnet, grain‐size ≤4 mm, and (b) large isolated single garnet crystals and/or (polycrystalline) garnet nodules up to 10 cm in size. Large garnet nodules occur only within limited bands within the garnet peridotites. The relicts of super‐silicic garnet were exclusively found in some (not all) of the larger garnet nodules. Petrographic observations revealed that the microstructure of nodular garnet consists of the following four characteristic elements. (1) Individual garnet nodules are polycrystalline, with grain sizes of 2–8 mm. Garnet grain boundaries are straight with well‐defined triple junctions. (2) Some garnet triple junctions and garnet grain boundaries are decorated by interstitial orthopyroxene. (3) Cores of larger polycrystalline garnet contain two‐pyroxene exsolution microstructures. (4) Precipitation‐free rims (2 mm thick) surround garnet cores containing the exsolved pyroxene microstructure. Pyroxene exsolution from super‐silicic garnet was subsequently followed by brittle–ductile deformation of garnet. Both exsolved pyroxene needles and laths become undulous or truncated by fractures. Simultaneous garnet plasticity is indicated by the occurrence of high densities of naturally decorated dislocations. Transmission electron microscopy observations indicate that decoration is due to Ti‐oxide precipitation. Estimates of the P–T conditions for mineral chemical equilibration were obtained from geothermobarometry. The mineral compositions equilibrated at mantle conditions around 805±40 °C and 3.2±0.2 GPa. These P–T estimates correspond to cold continental lithosphere conditions at depths of around 105 km. From a combination of both depth estimates it can be concluded that the microstructural memory of the rock extends backwards to twice as great a depth range as obtained by thermobarometric methods. Available geochronological and geochemical data of Norwegian garnet peridotites suggest a multi‐stage, multi‐orogenic exhumation history.  相似文献