Twin Gliding Research Articles

EBSD analysis of rhombohedral twinning in hematite crystals of naturally deformed iron formations

The rhombohedral twinning in hematite has an important role in the accommodation of the deformation of hematite single crystals and hematite aggregates. It is a contact twinning and occurs as lamellae parallel to the \{10{\overline 1}2\} planes of hematite as a result of twin gliding on such planes. On account of the recent applications of electron backscatter diffraction (EBSD) techniques in a wide range of microstructural studies, the determination of symmetry operations that relate crystals in a deformed crystalline aggregate is crucial for the full textural characterization. This study presents an EBSD-based crystallographic analysis of the rhombohedral twinning on hematite crystals of a naturally deformed banded iron formation. Manipulations of theoretical pole figures depicting the symmetry relation of the rhombohedral twinning and misorientation and crystallographic data obtained by EBSD are used to establish the rotational relationship between twin and parent crystals. A method for determining pairs of axes and angles of rotation was developed which can be extended to any other twin laws or misorientation patterns in any other crystal system. It was found that the hematite rhombohedral twins are related to the parent crystal by an approximately 85° rotation about the 〈02{\overline 2}1〉 directions. Hence it could be determined that this consists of a macroscopic twinning element which is an alternative to the conventional ones used to describe the symmetry of the twin. It also matches microscopic twinning elements for the rhomb twinning law. Additionally, this method allows the determination of the crystallographic orientation of the twin lamellae and which particular 〈02{\overline 2}1〉 axis satisfies the 85°〈02{\overline 2}1〉 pair of rotation. The use of an unambiguous angle–axis pair of rotation allows the identification of twin boundaries in complex and finely grained aggregates and the distinction of twinning laws in a particular crystal.

Micro-and submicrostructural evidence for high-temperature brittle-ductile transition deformation of hornblende: Case study of high-grade mylonites from Diancangshan, western Yunnan

OM (optical microscope)/TEM (transmission electron microscope) micro-and submicrostructural analysis of hornblende rocks sheared at high temperatures from the Diancangshan area, western Yunnan reveals evidence for deformation in the brittle-ductile transition of hornblende at middle crustal level (about 637°C and 0.653 GPa) and mechanisms of deformation in the transitional regime are further discussed. Sheared hornblende rocks at middle crustal level have typical mylonitic microstructures, shown by coarse porphyroclasts and fine matrix grains. Different mineral phases in the rocks show distinct deformation characteristics. Hornblende and feldspar grains are intensely deformed with obvious grainsize reduction, but quartz grains are recrystallized dominantly by grain growth. Hornblende grains show typical brittle-ductile transition nature. Initial crystallographic orientations of porphyroclasts have strong effects on the behavior of grains during deformation. There are mainly two types of porphyroclasts, type I “hard” porphyroclasts and type II “soft” porphyroclasts, with [001] perpendicular and parallel to external shear stresses respectively. “Hard” porphyroclasts generally occur as competent grains that are rarely deformed or sometimes deformed by fracturing and dislocation tangling. “Soft” porphyroclasts are highly deformed primarily by dislocation tangling (as shown in the cores of the porphyroclasts), but twinning, dislocation glide and climb probably due to hydrolytic weakening also contribute to dynamic recrystallization of the porphyroclasts into fine grains in the matrix. The micro-and submicrostructures of the two types of porphyroclasts and fine-grained matrix provide powerful evidence for the behavior of brittle-ductile transition of hornblende grains. It is concluded that twinning nucleation is one of the most important processes that operate during dynamic recrystallization of hornblende crystals at the brittle-ductile transition. (100) [001] twin gliding and dislocation creep (dislocation glide and climb) are mutually enhanced during twinning nucleation. As a newly discovered mechanism of dynamic recrystallization, it may have played more important roles than ever recognized during dynamic recrystallization of crystals with twins in the brittle-ductile transition.

Determining paleostress orientations from faults and calcite twins: a case study near the Sainte-Victoire Range (southern France)

This paper presents the results of the analyses of striated faults and calcite twins near a highly deformed, polyphase range, the Sainte-Victoire Mountain (southern France). We thus show that combining both paleostress indicators provides a reliable way to reconstruct polyphase tectonic evolution involving homoaxial compressional stresses. From a regional point of view, the paleostress orientations have been accurately determined. These orientations correspond to three main stages of the stress field evolution since the late Cretaceous: N–S compression (late Cretaceous to late Eocene), E–W extension (Oligocene) and ENE-WSW compression (early Miocene). During the Pyrenean N–S compression, several substages of folding, strike-slip or reverse faulting have been detected. These early tectonic events account for compressional deformations older than the late Eocene major shortening of the Provence sedimentary cover. From the methodological point of view, tectonic investigations based on both paleostress indicators (macroscopic and microscopic) were consistent and complementary. Calcite twins often allowed determination of paleostress tensors in sites where microfaults are absent for a given tectonic event. The greater sensibility of twinning to stress is related to the lower differential stress required to activate twin gliding, compared with brittle failure. Despite local stress deviations related to structural inhomogeneities, the regional stress field remains homogeneous, and provides a basis for interpreting deformation at all scales.

Relationships of rock cleavage fabrics to incremental and accumulated strain in the conococheague formation, U.S.A.

Pressure solution coupled with twin gliding, and recrystallization acted to form two geometrically distinct cleavages in the Conococheague Formation, northwest Virginia and West Virginia. Limestone layers contain a penetrative cleavage ( S p ) formed by pervasive pressure solution (Coble creep), with twin gliding in more highly deformed zones. Dolomite layers contain a spaced solution cleavage ( S s ) formed by pressure solution, also with twin gliding in highly deformed zones. Recrystallization textures occur in highly deformed zones of limestones and dolomites. Incremental strain shows that layering was initially inclined as much as 30° to shortening, and that the deformation was locally non-coaxial, as viewed by the deforming material on the fold limbs. Spaced cleavage zones are curved, and closely match the initial and final orientations of incremental elongation. Penetrative cleavage parallels the elongation axis of accumulated strain (measured using deformed ooids). Pressure solution surfaces in dolomites concentrate insoluble materials. Deformation, together with twin gliding, and recrystallization are greatest in the hinge zones of folds and least on shallowly dipping limbs of asymmetric folds. The deformation mechanism path of calcite and dolomite are similar; changing from pressure solution to twin gliding with recrystallization as strain rate (strain energy density) increases.

Strain analysis and fold shape in a limestone layer and implications for layer rheology

Folds are developed in thin limestone layers within slates of the McKay Formation exposed to the east of the Rocky Mountain Trench, British Columbia, Canada. They possess geometrical characteristics expected of development by buckling. Strain in the profile plane of a selected fold is similar to that predicted by tangential longitudinal strain, except that magnitudes are too low for the observed curvature. This is attributed to inhomogeneity of strain on the scale of measurement, largely because of pressure solution. Material removed by pressure solution from the inner arc of the fold appears to form veins perpendicular to the hinge, a direction of tectonic stretching. Bedding-parallel stylolites developed diagenetically prior to tectonism. Layer-parallel shortening during the initiation of buckling was less than 20%, and probably less than 10%. The mean arclength/thickness ratio is 6.5 and 7.1, with a dispersion of 0.48 and 0.37 for local and regional populations of 29 and 212 folds, respectively. Application of buckling theory to this data suggests that folding followed a non-linear flow law. The viscosity contrast between limestone and slate would be higher and the power law exponent lower, if initial irregularities in the layers were in the form of a constant amplitude spectrum rather than one of white roughness. The data do not allow a choice of initial amplitude spectrum to be made, nor do they closely constrain estimates of n the power law exponent and viscosity contrast. Deformation in the limestone layers was accommodated by intracrystalline flow (twin gliding), pressure solution, and extensional veining (the last two linked by diffusive mass transfer). The first two dominated deformation in the profile plane of the fold and the last, in association with fracturing, allowed for extension parallel to the hinge. Experimental and theoretical considerations suggest that deformation by a combination of these processes should be non-linear. The non-linear flow law deduced from buckling analysis is consistent with expectations based on observations of active deformation mechanisms.

Development of preferred orientation in plane strain deformed limestone: Experiment and theory

Carbonate rocks deform preferentially by twin gliding on e={01¯18} and slip on r ={10¯14} and f={02¯21}. In polycrystalline aggregates strong textures develop. We report on experimentally produced textures in triaxial plane strain geometry with orthorhombic symmetry at 200° C and 400° C. Pole figure of the experimentally deformed specimens are compared quantitatively with theoretical simulations based on the Taylor theory using both slip and mechanical twinning as mechanisms. Agreement at low and high temperature is satisfactory and documents that models developed for f.c.c. metals can be applied to low symmetry minerals provided that deformation mechanisms are known and that mechanical twinning is properly accounted for. Comparison with experimental results indicates that strain was nearly homogeneous at the conditions considered and the same may apply to many geological textures. Three texture types are described which are differentiated mainly by the relative importance of e twinning.

Strain analysis of experimental superposed deformation using calcite twin lamellae

Specimens of Indiana limestone have been experimentally deformed twice with the maximum compression direction of the second deformation parallel, perpendicular, or at 45° to the maximum compression direction of the first deformation in order to determine how useful the least-squares strain-gage technique for calcite twin lamellae ( Groshong, 1972, 1974) is in mapping superposed deformations. The superposed deformations were achieved by axially shortening cylindrical specimens (4.76 cm in diameter by 10.00 cm long) to 5.3% strain in dry triaxial compression tests at 100 MPa confining pressure, 10 −4 sec −1 strain rate, and room temperature. Each of these deformed specimens was then cored parallel, perpendicular, or at 45° to the load axis to obtain smaller cylindrical specimens (1.25 cm in diameter by 3.10 cm long) for subsequent deformation under identical experimental conditions with axial shortenings ranging from 2.8 to 8.3%. The straingage technique permits one to compute not only the principal strains associated with the total superposed deformation of the specimen but also to compute an expected shear strain for each measured twin set. Since the sense of shear for twin gliding in calcite is fixed (positive), unfavorably oriented twins for a computed strain tensor yield apparent negative shear strains. Separate analysis of the measured twin sets on the basis of positive and negative expected shear strains permits the recognition of each of the two perpendicular superposed deformations, but for coaxial superposed deformations the technique calculates only the total strain of both deformations. For the single and coaxial deformations the calculated strains are within 10% of the experimental axial compressive strains and the angular difference in direction is only 3°. For perpendicular superposed deformations the error in the magnitude and direction of the calculated strains relative to the experimental strain are twice as large as those for the single or coaxial deformations. When the maximum compression direction of the second deformation is 45° to the maximum compression direction of the first deformation, these errors are four times larger.

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.

Dynamic interpretation of deformation twins in haematite

Abstract Turner's (1953) technique of the “dynamic interpretation of deformation twins” has been tested in the case of twin gliding on r={10Ī1} in haematite, using an experimentally deformed, haematite ore from Malmberget. Microscopic-structure studies show that r-twin gliding preferably occurs in haematite grains suitably oriented in relation to the applied stress, i.e. in grains which have high resolved shear stresses in the observed glide systems. The distribution of the “derived principal-stress axes” in heavily twinned grains agrees with the axially symmetric stress orientation during the deformation. In a naturally deformed haematite ore from S tripa, analysis of the preferred orientation of [0001] of haematites with various internal structures reveals that the weak [0001] -maximum perpendicular to s in the ore has been generated by postcrystalline r-twinning. The derived principal-stress axes in the most strongly twinned grains indicate a stress field which, during the formation of the r-twins, had the maximum compressive stress subparallel to the fabric axis a and the least principal stress subparallel to the fabric axis c.

Use of calcite twin lamellae to infer differential stress

The equation that relates the resolved shear stress coefficient ( S 1 ), differential stress (Δσ), and the critical resolved shear stress ( t c ) necessary to produce twin gliding is t r = S t * Δσ. If we assume an infinite number of possible crystal orientations, it is possible to determine the percentage of grains that has a given value of the resolved shear stress coefficient ( S 1 ) on one, two, or three twin sets. Therefore, if the percentage of grains exhibiting one, two, or three twin sets is known, the differential stress can be determined in terms of the critical resolved shear stress using the above equation. The method has been developed for the case of randomly oriented grains deformed in an irrotational, uniaxial stress field. The method also assumes that all twinning is observable and has occurred in only those orientations where twinning is theoretically possible. Twin gliding has previously been shown to be a mechanism of creep in calcite, and in many cases the method may actually overestimate the magnitude of the differential stress. The validity of this technique of differential stress magnitude determination has been tested by its application to six experimentally deformed samples of Indiana limestone. The calculated differential stresses are within 21 percent of the experimental values for strains of less than 3 to 4 percent. At larger strain values reasonably accurate differential stress values may also be determined, but this requires a greater degree of interpretation. Comparison of samples that contain naturally deformed crystals of both calcite and dolomite suggests that the critical resolved shear stress for dolomite is approximately five times greater than that for calcite.

Strain, fractures, and pressure solution in natural single-layer folds

Research Article| October 01, 1975 Strain, fractures, and pressure solution in natural single-layer folds R. H. GROSHONG, JR. R. H. GROSHONG, JR. 1Cities Service Oil Company, Exploration & Production Research, Box 50408, Tulsa, Oklahoma 74150 Search for other works by this author on: GSW Google Scholar Author and Article Information R. H. GROSHONG, JR. 1Cities Service Oil Company, Exploration & Production Research, Box 50408, Tulsa, Oklahoma 74150 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (10): 1363–1376. https://doi.org/10.1130/0016-7606(1975)86<1363:SFAPSI>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 R. H. GROSHONG; Strain, fractures, and pressure solution in natural single-layer folds. GSA Bulletin 1975;; 86 (10): 1363–1376. doi: https://doi.org/10.1130/0016-7606(1975)86<1363:SFAPSI>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 Intragranular strain has been measured by the twinned calcite strain-gage technique from the hinges and limbs of three single-layer minor folds with limb dips of 15°, 48°, and 67°. The folds are in unmetamorphosed, Silurian-age limestone beds enclosed in shale, in the Appalachian Valley and Ridge province of central Pennsylvania. In all three folds, the maximum compressive strain axes are subparallel to bedding and tend to plunge toward the inner arcs of the hinges. The principal deviatoric compressive strains in the fold cross sections range from −0.48 ± 0.77 to −4.75 ± 0.78 percent; the largest compressive strains are in the gentlest fold and the smallest ones are in the tightest fold. Syntectonic stylolites are abundant in the folds and approximate a fanning cleavage. Filled extension fractures occur normal to bedding on the outer arc of the hinges of the two tightest folds. Filled fractures on the limbs of the same folds began as extension fractures subparallel to bedding and evolved into throughgoing thrust faults. A significant amount of the folding deformation is evidently accomplished by pressure solution and by displacement on fractures.The folds are interpreted as buckle folds and distinguished from transverse bends and passive folds on the basis of the mechanical contrast between the limestone and enclosing shale beds and the orientation and distribution of the principal strain axes, stylolites, and fractures. The orientations of the principal strain axes are best fit by buckle-fold models. Strain models of pure bending, layer-parallel shear, and shear parallel to the hinge plane are shown to be inadequate by themselves even as first-order approximations.A simple rheological model including intragranular strain (twin and translation gliding, grain boundary adjustments) and pressure solution fits the inferred relationships between these features. The model presumes that intragranular strain has a yield stress, whereas pressure solution does not, and that at high stresses pressure solution is more important than intragranular strain. The model predicts that when conditions are suitable for pressure solution, more of the strain will occur by this mechanism than by twin gliding and related mechanisms. This can explain the overall low values of measured intragranular strain. 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.

Preferred orientation in experimentally deformed limestone

Over sixty syntectonic deformation experiments in uniaxial compression have been done on fine-grained limestones in the stability fields of calcite I, calcite II and aragonite. X-ray techniques and spherical harmonic analysis of the data were used to determine preferred orientation quantitatively, and inverse pole-figures were derived for these axially symmetric specimens. They display in most cases strong preferred orientation which varies as a function of the experimental conditions, mainly temperature and pressure. At temperatures below 350° C recrystallization is lacking and flattened grains indicate that translation, twin gliding and kinking have been the dominant deformation mechanisms. The inverse pole-figure shows a maximum at c with a shoulder towards or a second maximum at e. This is in agreement with preferred orientation observed in experimentally deformed Yule marble and can be explained as the product of dominant twin gliding on e and translation gliding on r (Turner et al., 1956). At high temperatures (900–1000° C) strong grain growth (from 4 to 50 microns) indicates that the fabric recrystallized. Grains are equidimensional and clear with a marble-like texture. The inverse pole-figure shows a single maximum at r, and c-axes are oriented in a small circle around the axis of compression, σ1. Such a pattern of preferred orientation would be expected on thermodynamic grounds assuming that recrystallized grains will be oriented in such a way that the strain energy is a maximum (e.g. MacDonald, 1960). Decrease in confining pressure caused a decrease of the maximum at c and the formation of a secondary maximum at highangle positive rhombs in the inverse pole-figure. This can be interpreted as r translation dominating over e twinning. In all deformation experiments an equilibrium in preferred orientation was reached after 20 percent shortening. The strength of preferred orientation decreased with increasing temperature. Aragonite was produced within its hydrostatic stability field at temperatures above 500° C. Close to the phase boundary, coarse-grained textures showed preferred orientation with poles to (010) parallel to σ1. At higher pressures the fabric is fine-grained and [001] is aligned parallel to σ1. Evidence is given that the phase change from calcite to aragonite in these deformation experiments is a diffusive and not a martensitic transformation.

�ber Beanspruchung und Verformung von Gesteinen

7 coaxial (p1>p2=p3) and 6 real triaxial (p1>p2>p3) compression tests (0,5 to 6 hours duration) on cubic samples of homogeneous, statistically low anisotropic marble from Auerbach (Germany) were made at room temperature and different ratios of the main pressures and rates of loading. 3 samples of strong anisotropic marble of Drama (Greece) were deformed at p1∶p2∶p3=8∶4∶1 and constant rate of loading in the three orientations: parallel, at 45° and perpendicular to the foliation (12 hours duration). As can be deduced from the orientation diagrams, the deformation proceeds mainly by twin gliding. In most of the tests reported here the symmetry of the external loading (coaxial or orthorhombic) can be correlated with the symmetry of the orientation diagrams. Real triaxial deformation (P1Nep2Nep3) produces two sets of planes ± perpendicular to each other as B ⊥ B′. In the tests with the strong anisotropic material the strain was measured in the three main directions and plotted as strain-time curves. When the foliation is oriented perpendicularly or even obliquely to p1 compression dominates at the beginning in the direction of the intermediate loading p2 producing preferred orientation of the twin lamellae. Later on there is compression in p1 and extension in p2 and p3. This phase of deformation is characterized by brittle fracture and increase of volume.

Mechanical Twinning in Naturally and Experimentally Deformed Diopside

Lamellar twinning on (100) and to a lesser extent on (001) are present in clinopyroxenes of deformed mafic and ultramafic rocks. Both sets of twins are mechanical in origin and form where the resolved shear stress on the twin-glide system is high. Statistically, compression axes most favorably oriented for twin gliding in each of a large number of grains are aligned sub-parallel to the direction of maximum compression in experiments. In some deformed diopside-bearing calc-silicate rocks from South Australia, compression and tension axes deduced from twinning are consistent with principal stresses deduced from faulting. It is concluded that lamellar twinning in clinopyroxenes may be used for determination of the direction of principal stresses in natural deformations of rocks.

Mechanical twinning in naturally and experimentally deformed diopside

Lamellar twinning on (100) and to a lesser extent on (001) are present in clinopyroxenes of deformed mafic and ultramafic rocks. Both sets of twins are mechanical in origin and form where the resolved shear stress on the twin-glide system is high. Statistically, compression axes most favorably oriented for twin gliding in each of a large number of grains are aligned sub-parallel to the direction of maximum compression in experiments. In some deformed diopside-bearing calc-silicate rocks from South Australia, compression and tension axes deduced from twinning are consistent with principal stresses deduced from faulting. It is concluded that lamellar twinning in clinopyroxenes may be used for determination of the direction of principal stresses in natural deformations of rocks.

Microscopic Structure and Fabric of Yule Marble Experimentally Deformed at Different Strain Rates

Specimens of Yule marble deformed in extension by Dr. H. C. Heard at 400°-500° C., 5,000 bars, and strain rates between and . have been used for analysis of microscopic structure and fabric. The effect of lowering the strain rate a million-fold at 500° C. is broadly analogous to raising the temperature by 100° C. at constant rapid rate of strain. In all specimens the concept of statistically homogeneous stress in the strained material is supported by general correlation between the spacing index for e-twin lamellae and the resolved shear stress on the system of twin gliding. Turner's earlier dynamic interpretation of e-twinning in marble in terms of "compression" and "tension" axes is found valid if due account is taken of initial preferred oritentation of c-axes. Symmetry of c-axis orientation and of strain is consistently related to the combined symmetry of stress and initial fabric.

Petrofabric Analysis of Experimentally Deformed Calcite-Cemented Sandstones

Cylinders of sand crystals, composed of single crystals of calcite that poikilitically enclose detrital grains, and calcite-cemented sandstones from the Tensleep (Pennsylvanian, Wyoming) and Supai (Permian, Nevada) formations were experimentally deformed dry at confining pressures of 1-5 kilobars and temperatures of 150°-300° C. Thin sections of the undeformed and deformed specimens were studied microscopically to gain a better understanding of the behavior of sandstones in simulated tectonic environments. The calcite and the detrital grains (quartz, feldspar, and others), which have radically different physical and mechanical properties, are shown statistically to have deformed with respect to the principal stresses across the boundaries of the whole specimens rather than with regard to local stress concentrations at grain contacts. The deformation mechanisms of calcite and quartz are the same in the sandstones as in monomineralic aggregates, such as marbles and quartz sands. Statistically, twin lamellae are developed in those calcite grains that are favorably oriented for twin gliding with respect to the load axes. The resolved shear-stress coefficient for these twin planes averages 0.27. Compression and extension axes deduced from the best developed set of twin lamellae in each calcite grain yield derived positions for the principal stress axes that are in excellent agreement with those known from the experiments. In addition, the number of lamellae per millimeter increases with increased strain of the specimens. Quartz, feldspar, rock fragments, and garnet grains comprise the bulk of the detrital material. These deform primarily by fracturing. The microfractures in the grains are nearly planar features which, because of their geometric relationship to the known principal stress directions, are recognized as extension and shear fractures. They develop independently of thegrain mineralogy and, in quartz grains, greatly overshadow a slight tendency for fractures to parallel r{} and z{}. The degree of fracturing in a specimen, expressed as a fracture index, tends to increase with increased strain of the specimen. In sand crystals loaded unfavorably for twin gliding in the calcite crystal, extension fracturing in the detrital grains causes local reorientation of the stresses and produces twin lamellae in the adjacent calcite. Twin lamellae in calcite and fractures in detrital grains are shown to be criteria for simulated tectonism. The development of lamellae and microfractures is directly related to the orientations of the principal stresses in heterogeneous, sedimentary rocks at the time of deformation.

EXPERIMENTAL DEFORMATION OF DOLOMITE SINGLE CRYSTALS

Research Article| March 01, 1959 EXPERIMENTAL DEFORMATION OF DOLOMITE SINGLE CRYSTALS DONALD V HIGGS; DONALD V HIGGS SHELL DEVELOPMENT Co., 3737 BELLAIRE BLVD., HOUSTON 25, TEXAS Search for other works by this author on: GSW Google Scholar JOHN HANDIN JOHN HANDIN SHELL DEVELOPMENT Co., 3737 BELLAIRE BLVD., HOUSTON 25, TEXAS Search for other works by this author on: GSW Google Scholar Author and Article Information DONALD V HIGGS SHELL DEVELOPMENT Co., 3737 BELLAIRE BLVD., HOUSTON 25, TEXAS JOHN HANDIN SHELL DEVELOPMENT Co., 3737 BELLAIRE BLVD., HOUSTON 25, TEXAS Publisher: Geological Society of America Received: 23 Jun 1958 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1959, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1959) 70 (3): 245–278. https://doi.org/10.1130/0016-7606(1959)70[245:EDODSC]2.0.CO;2 Article history Received: 23 Jun 1958 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DONALD V HIGGS, JOHN HANDIN; EXPERIMENTAL DEFORMATION OF DOLOMITE SINGLE CRYSTALS. GSA Bulletin 1959;; 70 (3): 245–278. doi: https://doi.org/10.1130/0016-7606(1959)70[245:EDODSC]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 Jacketed cylindrical specimens of dolomite single crystals were deformed dry under a constant confining pressure of 5000 bars at a strain rate of 1 per cent per minute at temperatures from 24°C. to 500°C. Uniaxial compression and extension experiments were carried out with the load oriented (1) parallel to the optic axis Cv, (2) parallel to a horizontal axis a, (3) perpendicular to a cleavage r, and (4) parallel to an edge [f:f].In orientations (1) and (2), unfavorable for basal translation, crystals loaded at temperatures below 400°C, are brittle and fail on shear fractures inclined at about 30° to the direction of greatest principal pressure. At 400°C, and above, specimens of orientations (1) and (2) flow in compression and extension, respectively. Large permanent deformations are achieved in orientations (3) and (4), favorable for translation gliding, at all temperatures.Petrographic studies by the techniques developed by Turner in his investigation of calcite crystals (Turner et al., 1954a) reveal that translation gliding on c{0001} along the gliding line parallel to an a axis is the flow mechanism for orientations (3) and (4) below 400°C. This confirms Johnsen's (1902) first discovery and the results of the later work of Turner et al. (1954b) on dolomite rock. The intracrystalline slip mechanism for orientations (1) and (2) is twin gliding on in a negative direction sense (in contrast to the positive sense of twinning in calcite), which, however, occurs only at about 400°C. and above. This confirms the hypothesis of Fairbairn and Hawkes (1941) and the data of Turner et al. (1954b) and Handin and Fairbairn (1955) for dolomite rocks. In orientations (3) and (4) twinning occurs to the exclusion of translation at 500°C., and both mechanisms are operative at 400°C.The critical resolved shear stress for translation increases with temperature up to 400°C. at least, a most unusual behavior. The critical stress for twinning decreases at least in the range of 400°C. to 500°C., and the two critical stresses are equal at about 400°C.A few magnesite crystals were deformed parallel to Cv, under similar conditions. Basal translation cannot occur in this orientation, but translation on along the line does occur. No twinning was detected. 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.

EFFECTS OF GAMMA RADIATION ON THE EXPERIMENTAL DEFORMATION OF CALCITE AND CERTAIN ROCKS

Calcite single crystals, Yule marble, and certain other rocks were deformed dry at room temperature under constant confining pressures of 2000 or 2750 bars at a strain rate of 1 per cent per minute. Uniaxial compression and extension experiments were made; for the marble, parallel and normal to c v fabric maximum; for the single crystals, parallel to c v and normal to m {1010}. Yule marble exposed to 17 megaroentgens of gamma radiation before deformation turned from white to bright blue when deformed. Intensity of color varied with orientation and amount of strain. Irradiated single crystals changed from amber to ultramarine blue when the greatest principal stress paralleled c v . No color change occurred when the least principal stress paralleled c v . Irradiation resulted in small reductions in yield stress of most of the rocks, but not of the single crystals. Petrographic studies of the single crystals revealed that established principal deformation mechanisms, twin gliding on e {0112} and translation gliding on r {1011}, were still operative and confirmed that blue color was associated with translation gliding only. In Yule marble blue grains had deformed by translation, clear grains by twinning. Thermoluminescence studies indicated that compression along c v yielded a new peak in the glow curves (at 280°), not present in undeformed irradiated calcite. Extension along c v increased the magnitude of the glow curve at about 240° but gave rise to no new peaks.

DEFORMATION OF YULE MARBLE. PART VII: DEVELOPMENT OF ORIENTED FABRICS AT 300°C–500°C

Yule marble has been deformed at 400° and 500° C and a confining pressure of 5000 atmospheres. Its strength, relative to that at room temperature, is 47 per cent at 400° C and 41 per cent at 500° C, measured in all cases at 3 per cent strain. Textures of the deformed rock are similar to those of marble comparably deformed at 300° C. Sander's method of “axial-distribution analysis” has been used to test homogeneity of fabric in the original marble and in a specimen shortened 19 per cent at 300° C. In both cases aggregates of a few tens of grains show local very strong preferred orientation of the lattice. In this respect there is no effect that can be correlated with deformation. Petrofabric analysis of specimens shortened 40 per cent or elongated 90–120 per cent demonstrates strong preferred orientation of the c axis at 10°–30° to the axis of compression or at 60°–80° to the axis of extension. The symmetry of the deformed fabrics corresponds with the symmetry of strain, which is determined by the orientation of the axis of extension or compression in relation to the preferred orientation pattern of the original fabric. Behavior of grains is predicted on the basis of a hypothesis of approximately homogeneous deformation, involving twin gliding on ![Graphic][1] and translation gliding on ![Graphic][2] . Behavior of individual grains is also reconstructed from evidence of observed internal rotation of early e lamellae, interpreted in the light of previous observations on single crystals of calcite. The same data are used to compute shortening or elongation of individual grains parallel to the axis of applied force. The behavior and strain so deduced and the details of observed preferred-orientation patterns agree with prediction. It should prove possible to compute strain in geologically deformed rocks on the basis of petrographically measured effects of internal rotation. However, at present this can be attempted only for those few minerals, such as calcite and dolomite, whose glide systems have been ascertained experimentally. Possible analogy between a natural marble fabric and a fabric resulting from experimental compression is noted. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif