Syntectonic Recrystallization Research Articles

Preferred orientation of silicate spinel inferred from experimentally deformed aggregates of trevorite.

Syntectonic recrystallization experiments have been done on the synthetic fine-grained aggregate of trevorite (NiFe2O4; a spinel type mineral) analogous to the γ-(Mg, Fe)2SiO4 in the upper mantle by means of a constant strain rate apparatus under various physical conditions: strain rates from 10-3 to 10-6 s-1, homologous temperatures from 0.56 to 0.80, and confining pressure of 0.6 GPa. An X-ray pole figure goniometry is employed to describe the quantitative orientation distribution of spinel crystallites in uniaxially deformed aggregates. The obtained inverse pole figures indicate that two types of preferred orientation have been produced during the axial deformations both in compression and tension. The lower temperature and faster strain rate yield the preferred orientation of type I: [1 1 0]//compression axis and [1 0 0]//tension axis, while the higher temperature and slower strain rate yield type II: [1 0 0]//compression axis and [1 0 0]//tension axis. The generation of the two types of preferred orientation is caused by grain rotation due to slip in constituent grains in an aggregate, and syntectonic recrystallization, respectively. The present results suggest (1)γ-(Mg, Fe)2SiO4 has a considerable degree of preferred orientation in the upper mantle, (2) the preferred orientation is probably of type II rather than of type I under the mantle conditions, and (3) the detectable degree of shear wave anisotropy is expected in the spinel layer of the earth's upper mantle as a result of preferred orientation.

Polyphase deformation of the massive sulphide ore of the Black Angel Mine, central West Greenland

The massive Fe-Zn-Pb sulphide sheets constituting the Angel Zone ore body of the Black Angel Mine, show evidence of three phases of deformation at greenschist facies metamorphic grade. During an early phase an originally layered sulphide ore type was isoclinally folded. Subsequent thrusting parallel to the ore body transformed the layered ore into massive and porphyroclastic ore tectonites. Late, open folds refolded the earlier structures and caused localized differential mobilization of the sulphides. The microstructures of the layered ore tectonite indicate a period with static grain growth, interpreted as the result of prograde metamorphism, followed by a dynamic recrystallization under low stress and at low strain rates, which is correlated with the early isoclinal folding. The microstructures of the massive and the porphyroclastic ore tectonites indicate syntectonic recrystallization under high stress and at high strain rates, corresponding to the thrusting of the ore bodies. The microstructures of the mobilized sulphides show evidence of repeated plastic/cataclastic deformation and recrystallization, corresponding to highly variable strain and strain rate conditions during the mobilization. Post-deformational annealing took place at elevated temperature and was largely controlled by inhibition-dependent grain growth and to a minor extent by orientation-dependent grain growth.

Surface-wave propagation in an ocean basin with an anisotropic upper mantle: numerical modelling

Summary. The characteristics of surface-wave propagation in ocean basins are examined numerically for models with two types of anisotropic alignment in the upper mantle: one resulting from glide-plane slip in olivine with horizontal or vertical slip-planes, and the other from syntectonic recrystallization of olivine in a zone of horizontal shear. Glide-plane slip can cause highly anomalous inclined-Rayleigh particle-motion in the third-generalized mode (corresponding to the isotropic second-Rayleigh mode). The amplitude of this anomaly is rather insensitive to details of the structure. Syntectonic recrystallization can cause an anomalous combination of inclined-and tilted-Rayleigh motion in all modes. The variation with period of the amplitude of the anomaly in the fundamental mode can indicate the approximate depth to the anisotropic layer. In both types of alignment, the sense of tilt and the inclination varies with direction of propagation in a manner characteristic of the structural symmetry.

Surface-wave propagation in an ocean basin with an anisotropic upper mantle: observations of polarization anomalies

Summary. Observations of surface waves crossing ocean basins indicate that, at least in some cases, a better interpretation of what was previously considered to be the simultaneous arrival of fundamental Love and second Rayleigh modes, with similar group velocities, is the coupled motion of the second-generalized mode surface wave propagating in an anisotropic upper-mantle. This mode displays the polarization anomalies expected from anisotropic alignments caused by syntectonic recrystallization of olivine in a zone of horizontal shear. The polarity of the pattern of anomalies, found in waves crossing the Pacific Basin, suggests that the lithosphere is dragging the asthenosphere.

Microstructural development of fine-grained quartz aggregates by syntectonic recrystallization

Experimental study of syntectonic recrystallization of fine-grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition. Agate was axially compressed with a constant-strain-rate apparatus. Experiments were conducted at 4 kbar solid confining pressure, 700–1000°C and 10 −4-10 −6 sec −1 to 10%–45% strain. In all runs, deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium. Two different types of microstructure were distinguished in the deformed specimens. One is P-type which is characterized by equant, equidimensional, and polygonal grains. The other is S-type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis. The P-type microstructure is developed at higher temperatures and slower strain rates, while the S-type developed at lower temperatures and faster strain rates. The transition between the S- and P-types is found to be very sharp.

Creep and Fabrics of Polycrystalline Ice Under Shear and Compression

Abstract Creep tests were performed in torsion and torsion–compression on polycrystalline ice at temperatures near the melting point. Syntectonic recrystallization occurs at strains of the order of 2–3%, leading to a rapid increase in strain-rate. It is shown that the increase of creep-rate during tertiary creep arises from the development of fabrics favouring the glide on basal planes but also from the softening processes associated with recrystallization. The c-axis fabric of recrystallized ice developed in simple shear consists of two-maxima, one at the pole of the permanent shear plane and the other between the normal of the second plane of maximum shearing stress and the principal direction of compression. In torsion–compression, a three- or four-maximum fabric is formed according to the intensity of different components of the stress tensor. The maxima are clustered around the principal direction of compression. Processes of fabric formation are discussed. The experimentally developed fabrics are probably produced by the strain-induced recrystallization, for which the driving force is provided by differences in stored plastic strain energy. However the degree of preferred orientation of ice c-axes must be a function of the total strain when syntectonic recrystallization becomes less important. In this case, fabrics are principally formed by plastic flow and a steady state is obtained for very high strains.

Creep and Fabrics of Polycrystalline Ice Under Shear and Compression

AbstractCreep tests were performed in torsion and torsion–compression on polycrystalline ice at temperatures near the melting point. Syntectonic recrystallization occurs at strains of the order of 2–3%, leading to a rapid increase in strain-rate. It is shown that the increase of creep-rate during tertiary creep arises from the development of fabrics favouring the glide on basal planes but also from the softening processes associated with recrystallization. The c-axis fabric of recrystallized ice developed in simple shear consists of two-maxima, one at the pole of the permanent shear plane and the other between the normal of the second plane of maximum shearing stress and the principal direction of compression. In torsion–compression, a three- or four-maximum fabric is formed according to the intensity of different components of the stress tensor. The maxima are clustered around the principal direction of compression. Processes of fabric formation are discussed. The experimentally developed fabrics are probably produced by the strain-induced recrystallization, for which the driving force is provided by differences in stored plastic strain energy. However the degree of preferred orientation of ice c-axes must be a function of the total strain when syntectonic recrystallization becomes less important. In this case, fabrics are principally formed by plastic flow and a steady state is obtained for very high strains.

High temperature flow and dynamic recrystallization in carrara marble

Specimens of Carrara marble have been experimentally deformed at temperatures between 600° and 1050° and at strain rates between 10 −2 and 10 −6 sec −1. No single empirical flow law could be found for the whole range of experimental conditions covered. Instead it was found that three deformation regimes, each with its characteristic microstructural imprint, can be established. Above 1000 bar differential stress a relatively low strain rate sensitivity of the flow stress is observed and twinning is predominant (regime 1). Regime 2 extends down to 200 bar flow stress and exhibits the unusually high stress exponent n = 7–8 in the power law creep equation earlier found by Heard and Raleigh (1972) in Yule marble. The original grains exhibit a “core and mantle” structure. Only in regime 3 below 200 bar differential stress does one find lower values for n of around 4, and now a mosaic of equi-axed subgrains occupies entire grains. Extensive recrystallization and grain boundary migration was found at the higher temperatures. The grain size produced by dynamic in-situ recrystallization was found to be inversely proportional to the applied flow stress. Scanning electron microscopy observations on split cylinders suggests substantial amounts of grain boundary sliding in the low Stress region. The unusually high dislocation densities at low flow stresses as measured under the transmission electron microscope are interpreted to arise through strains induced during cooling under pressure after the deformation experiment. In view of the fact that the different calcite rocks so far investigated under elevated temperatures and low flow stresses exhibit rather different flow laws, caution is indicated when extrapolating such empirical flow laws to geological conditions. The size of dynamically recrystallized grains may directly lead to a paleostress estimate at the time of recrystallization. A subsequent work softening effect through a change in mechanism induced by syntectonic recrystallization may play an important role in the formation of shear zones and mylonite layers.

Temporal development of fabric in uniaxially stressed polycrystalline media?A theory

We present a kinetic theory for the development of lattice-preferred orientation in a uniaxiallystressed aggregate consisting of elastically uniaxial crystals. The fabric is brought about by grain-boundary migration alone; other fabric-producing mechanisms, such as plastic deformation, syntectonic recrystallization, and dissolution/reprecipitation, are specifically excluded from the theory. The formulation statistically averages the mass transfer between a typical crystal and its adjacent neighbors over all the possible crystallographic orientations of these neighbors and over all the possible orientations of the interfaces between the neighbors and the crystal of interest. The rate of mass exchange between two adjacent crystals is proportional (1) to the difference between chemical potentials and (2) to the surface area common to them. With these assumptions we find an equation for the massfraction density of crystals that have a given orientation (with respect to the stress) at any given time. The theory predicts that beyond a certain time a gap develops in the distribution of crystal orientations allowed: the only crystals that continue to exist are those for which the c-axis is within a certain, timedependent range about the stress.

Microstructural and chemical studies of sheared anorthosites, Roneval, South Harris

Microstructural and chemical variations accompanying the mylonitisation of the Roneval anorthosites were studied. The plagioclase in the anorthosite studied has compositions of ca. An 65 or of An 48 if garnet is present. Huttenlocher and Boggild lamellae are present in undeformed grains of both compositions. The mylonites developed by syntectonic recrystallization with grains containing two sets of lamellae recrystallizing preferentially. Those grains with a composition of An 65 become more albitic whereas those of An 65 became more anorthitic during recrystallization. All grains have sodium enriched rims. Grain boundary sliding processes appear to have been the main deformation mechanism in the mylonites after recrystallization.

Seismic anisotropy in the oceanic upper mantle: Evidence from the Bay of Islands Ophiolite Complex

Olivine fabrics in 17 field‐oriented ultramafics and mafics from three widely‐spaced traverses in the Bay of Islands Ophiolite Complex, Newfoundland, display a remarkably uniform symmetry in which the olivine a crystallographic axes are aligned subprependicular to the sheeted dikes and the b and c axes lie within the plane of the sheeted dikes. The ultramafics studied consist entirely of tectonites; any olivine formed at the ridge crest by cumulus processes has since been re‐oriented by translation gliding and/or syntectonic recrystallization. Deformation has extended from the ultramafics into the overlying gabbro, which suggests that in many oceanic regions the deepest levels of layer 3 consist of gabbroic tectonites. Compressional wave velocities computed from these petrofabrics display 5–6% anisotropy in the plane of the Mohorovičić discontinuity, with Vp fast parallel to the direction of spreading inferred from dike orientations. Since this pattern is identical to that observed for the oceanic upper mantle, it is concluded that the Bay of Islands Complex is a segment of oceanic crust and upper mantle. Shear wave velocity contours calculated from the same fabrics indicate that the upper mantle is nearly isotropic in terms of the maximum shear wave velocity, , but that the difference in velocity, ΔVs, between shear waves of orthogonal polarization traveling in the same direction may be sufficiently large parallel to the intersection of the Mohorovičić discontinuity and the sheeted dikes to allow detection of two distinct shear wave arrivals.

Experimental deformation of diopside and websterite

Diopside single-crystals, oriented favorably for twin gliding on both systems: (001) [100] and (100)[001] have been deformed in a Griggs apparatus using talc as pressure medium. The latter mechanism is dominant at temperatures ( T) below 1050° C at strain rates (ϵ) of 10 −3 sec −1, and below 800° C at ϵ ̇ = 10 −6 sec −1 ; at higher temperatures translation gliding on (100)[001] accompanied by syntectonic recrystallization is dominant but other glide systems also operate. Tests at a single set of conditions, T- and ϵ-incremental tests and stress-relaxation experiments have been carried out on websterite (68% CPX, 32% OPX), both in talc (“wet”) and talc-AlSiMag (“dry”) assemblies. Most tests were performed in the high-T regime, where syntectonic recrystallization and “relatively nonselective” glide are dominant. The mean size of recrystallized clinopyroxenes ( D, μ m ) appears to be related to stress (σ, kb) as D = 60σ −0.9 . The mechanical data fit the power law ϵ ̇ = A exp(-Q/RT)σ n , where for the “wet” experiments A = 10 5.9 kb −n sec −1 , Q = 91.2 kcal/mole , n = 5.3; for σ < 3.5 kb n appears to decrease to 3.3. For the “dry” experiments A = 10 2.2, Q = 77.9 , and n = 4.3 for σ < 7.0 kb. Clinopyroxene in the upper mantle occurs as ca. 0–15% mixed phase in peridotites and websterites occur as thin layers. Stresses in these materials will then be near those in the olivine-rich matrix. At ϵ ̇ = 10 −14/ sec , the equivalent viscosity of dry websterite is less than that of dry dunite at depths to 60 km but it increases rapidly at higher pressures; at 240 km it is 10 6 greater than that of dunite. This may account for the low strains and passive behavior observed for clinopyroxene crystals in most peridotites and websterites, that presumably have formed at great depth. Attenuated folds of websterite in peridotite—evidence of more ductile behavior—may then have formed at shallower levels; alternatively they may have formed under “wet” conditions.

Palaeoanisotropy in the upper mantle

CARTER1 has reviewed advances in understanding the steady-state flow of rocks with particular reference to the behaviour and anisotropic alignment of rocks in the upper mantle. Some form of high-temperature creep is clearly responsible for the distribution of continents and their first-order structures2. The difficulty is specifying the exact mechanism and the possible anisotropic alignments. Appropriate upper mantle temperatures and pressures can be achieved in the laboratory3, but any results must be extrapolated to rates of deformation lower by some five or six orders of magnitude. Carter et al.2 conclude, although there are conflicting views4, that the syntectonic recrystallisation suggested by Ave Lallemant and Carter5 is the dominant deformational process. This will be most effective at the higher temperatures at the base of the lithosphere where crystals, orientated by the deformations, have their alignments fixed as the lithosphere cools. All the deformational processes suggested for the upper mantle are capable of orientating crystalline structures, and aligned azimuthal-anisotrophy may be expected at any depth in the lithosphere.

Boundary between subbasal I and subbasal II fields of quartz deformation in geological conditions

The Sangun crystalline schists of the Hirose district, Yamaguchi Prefecture, Southwest Japan, show progressive metamorphism from the pumpellyitechlorite facies, through the pumpellyite-actinolite facies, to the epidoteglaucophane-schist facies. The quartz fabrics produced during the main phase of metamorphism have been examined in this paper. Quartz microstructures in the low-temperature zone of the pumpellyite-chlorite facies are characterized by undulatory extinction and deformation lamellae which are referred to as type I subbasal lamellae, suggesting that the quartz deformation occurred in the subbasal I field. In the pumpellyite-actinolite facies, the epidote-glaucophane-schist facies and the high-temperature zone of the pumpellyite-chlorite facies, the quartz fabrics are characterized by small quartz grains produced by syntectonic recrystallization of coarsegrained quartz and crossed-girdle orientations of c-axes whose inclination angles are between 17° and 25°, suggesting that the quartz deformation occurred in the subbasal II field. The boundary between subbasal I and subbasal II fields of quartz deformation during the main phase of metamorphism appears to have been placed in the pumpellyite-chlorite facies. The temperature and confining pressure at the boundary are inferred to be at ca. 250 °C and 5–7 kb respectively.

The Origin of the Double Maximum Pattern of Optic Axes in Quartzite Mylonite

The double maximum pattern of optic axes is found in quartzite mylonites that have undergone extensive plastic deformation and partial recrystallization as shown by highly elongate grains with small strain free grains along the grain boundaries. The optic axis pattern is characterized by two maxima of [0001] at 45° to the foliation and perpendicular to the lineation. The pattern has orthorhombic symmetry. However, X-ray analysis of a specimen from the Moine thrust zone in N.W. Scotland has revealed that the actual symmetry of the specimen is monoclinic and that {1011} is parallel to foliation and poles to {4041} are parallel to the direction of maximum elongation (= lineation). As both the texture and preferred orientation correspond to those observed by Tullis et al. (1973) in experimentally produced mylonites (although the symmetries are different), it is concluded that basal slip, prismatic slip, Dauphine twinning, subsidiary syntectonic recrystallization and loss of strength due to water weakening obs...

Structure of the Vulcan Peak alpine-type peridotite, southwestern Oregon

Research Article| February 01, 1976 Structure of the Vulcan Peak alpine-type peridotite, southwestern Oregon ROBERT A. LONEY; ROBERT A. LONEY 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar GLEN R. HIMMELBERG GLEN R. HIMMELBERG 2Department of Geology, University of Missouri, Columbia, Missouri 65201 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT A. LONEY 1U.S. Geological Survey, Menlo Park, California 94025 GLEN R. HIMMELBERG 2Department of Geology, University of Missouri, Columbia, Missouri 65201 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (2): 259–274. https://doi.org/10.1130/0016-7606(1976)87<259:SOTVPA>2.0.CO;2 Article history First Online: 01 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 ROBERT A. LONEY, GLEN R. HIMMELBERG; Structure of the Vulcan Peak alpine-type peridotite, southwestern Oregon. GSA Bulletin 1976;; 87 (2): 259–274. doi: https://doi.org/10.1130/0016-7606(1976)87<259:SOTVPA>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 SocietyGSA Bulletin Search Advanced Search Abstract The Vulcan Peak alpine-type peridotite forms part of the Josephine ultramafic complex in the Klamath Mountains geologic province. The peridotite is a partly serpentinized highly deformed harzburgite-dunite complex, in which three episodes of high-temperature plastic deformation are recognized. The first deformation was the most intense and produced the dominant metamorphic foliation and scattered folds in crosscutting layers and in the foliation itself. The first deformation seems also to have produced an olivine fabric in which X is normal to the foliation. The second deformation superposed a similar and pervasive fabric on the first, in which X olivine is normal to a spotty weak subvertical north-striking foliation that crosscuts the first foliation. These olivine fabrics are analogous to fabrics produced experimentally by either gliding or syntectonic recrystallization at temperatures in the range 1000° to 1200°C. This temperature range agrees with the temperatures of formation calculated from the distribution of Mg and Fe in mineral pairs. The third deformation was characterized by a limited plasticity, in which deformation was restricted to scattered narrow northeast-striking subvertical plastic shear zones. The sense of movement on the shear zones is consistently down on the northwest. A homotactic olivine fabric is present in the shear zones, consisting of a strong Z-point maximum approximately parallel to the zone. This fabric suggests glide on the system {Ok1} [100], which has been produced experimentally in the temperature range 800° to 1000°C.After the high-temperature and presumably deep-seated plastic deformation, the relatively cold peridotite was thrust, probably in post-Middle Jurassic time, northward against a complex of igneous and high-grade metamorphic rocks. Later, probably in Late Cretaceous or Tertiary time, the peridotite and the complex were thrust together westward against the low-grade Dothan Formation. 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.

Experimental deformation and recrystallization of a peristerite

Partial syntectonic recrystallization has been produced in an experimentally deformed plagioclase (peristerite An4.5). The recrystallized grains are scattered through the strongly deformed matrix and appear to have developed by a nucleation and growth mechanism.

Experimental deformation of natural chalcopyrite at temperatures up to 300 degrees C over the strain rate range 10 (super -2) to 10 (super -6) sec (super -1)

Natural chalcopyrite from two localities was experimentally deformed in compression under 1.5 kilobars of confining pressure at temperatures up to 300 degrees C over the strain rate range 10 (super -2) to 10 (super -6) sec (super -1) . At 25 degrees and 100 degrees C the stress-strain behavior was relatively independent of temperature and strain rate and the deformation proceeded predominantly by intragranular and grain-boundary fracturing (microfracturing). From 150 degrees to 300 degrees C strength decreased with increasing temperature and decreasing strain rate, and the dominant mode was intragranular slip and deformation twinning. The higher temperature behavior of the two different experimental materials was similar in spite of differences in impurity and grain size. The low-temperature microfracturing strength, however, was higher in the finer grained, less pure chalcopyrite.Extrapolation of the experimental data for steady state plastic flow to representative geological strain rates indicates stress differences in the order of 250 to 1,000 bars at 100 degrees C, 80 to 500 bars at 200 degrees C, and 30 to 300 bars at 300 degrees C. These values are not expected to vary with confining pressure. Syntectonic recrystallization might lower these stress differences even further.Chalcopyrite is expected to flow plastically in the crust except for very shallow conditions where low confining pressures and temperatures and relatively high stress differences prevail.In etched polished sections evidence of naturally deformed chalcopyrite can be provided by slip lines, deformation twins, subgrains, high-energy serrated grain boundaries, distorted twin boundaries, and elongation (straining) of grains. Such evidence may be partially or wholly obliterated by subsequent recrystallization.

Systematics of large-scale tectonics and age progressions in Alpine and Circum-Pacific blueschist belts

The early Alpine tectonics and relatively high-pressure metamorphic parageneses of the Helvetic, Pennine and Sesia—Lanzo realms are compared with analogous circumpacific terranes in western California, southwestern Japan, west-central Chile, and southern Alaska. Petrotectonic relationships appear to be compatible with a process involving syntectonic recrystallization and pervasive deformation in an imbricated subduction zone for each of these regions. Successive underthrusting of younger portions of the downgoing low-density material, followed by decoupling and rise towards the surface may account for the systematic decrease in both age and metamorphic intensity proceeding away from the old plate junction in these terranes. The environs of the present Aleutian trench serve as a modern analogue. Several other circumpacific blueschist belts (i.e., New Zealand, New Caledonia and eastern Papua) exhibit possible departures of timing, metamorphic polarity or direction of tectonic transport from that appropriate to the imbricated convergent plate-junction model presented in this paper, but the overall metamorphic sequences and tectonic settings are nevertheless strikingly similar. Many relatively high-pressure belts seem to be characterized by the occurrence of a major post-metamorphic transcurrent fault. This phenomenon suggests that blueschist belts, which must be exhumed rapidly in order to preserve the relatively high-pressure, low-temperature mineral assemblages, typically are obliterated through higher-temperature recrystallization unless a profound change from convergent to conservative plate motion occurs. Variation in convergence rate is yet another important factor, more rapid underflow promoting generation of blueschistic metamorphic parageneses, slower underflow favoring shallow decoupling and buoyant return towards the earth's surface of the successive underplatings. Other things being equal, a steeper angle of underflow would provide lower temperatures at a given depth for the subducted slab, thus promoting glaucophane schist-type metamorphism.

Mechanisms of preferred orientations of olivine in tectonite peridotite

Preferred orientations of olivine have been produced by syntectonic recrystallization in dunite samples that have been deformed moderately in a general stress field at high temperatures and pressures: X -olivine maxima ( X = [010]) developed parallel to σ 1 and Z -olivine maxima ( Z = [100]) developed parallel to σ 3 . Similar fabrics are expected to form by mechanical rotation due to translation gliding on (010)[100], but much larger strains are required. The experimental results indicate that the orientation patterns are caused by preferred growth of newly formed nuclei that have low coefficients of resolved shear stress for slip on (010)[100].