Strain Ellipsoids Research Articles

Application of strain analysis to estimate pressure solution processes in regional shear zones

This paper considers the basic principles of the strain analysis method based on the analysis of antitaxial regeneration fibrous fringes around linear rigid inclusions in a low-viscosity rock matrix. This method has been developed for pressure shadows composed of fibrous minerals, whose orientation is controlled by the major elongation direction rather than the orientation of rigid inclusions. This approach is applicable only for rocks exposed to uniform coaxial straining. The strain ellipse is calculated in two ways: for three variably oriented strain markers, it is calculated using Mohr’s circles, and for numerous strain markers by average body ellipse. The strain ellipsoid is calculated using the parameters of a few strain ellipses calculated with three and more non-parallel planes. This paper provides the data on the method testing in reference sites of Dora–Pil’ ore field in the Upper Indigirka district and Vangash area in the Yenisei Range. Regeneration fibrous fringes around fragments of fern fossils and linear rutile metacrystals were used as markers. The results of strain analysis obtained for the reference sites in the Upper Indigirka district made it possible to describe the signs of variable strain stages of developing strike-slip zones making up the Adycha–Taryn Fault Zone. Sublatitudinal ore-bearing strike-slip zones are characterized by a subvertical orientation of the elongation axes X of elongated strain ellipsoids, which are subperpendicular to quartz–carbonate veins and slope kink zones. NW-trending strike-slip zones are characterized by subhorizontal orientation of the Z shortening axes of flattened strain ellipsoids, which are subparallel to the normals of quartz–carbonate veins and veinlets. The results of strain analysis obtained for reference sites in the Vangash area made it possible to describe the thrust strain environment following the metamorphism stage and to reveal specific features in the formation of the strain textures of ore-bearing rocks based on their rheological properties.

Finite Strain Estimation in Baba Dome Using Fry Method (NE Iraq)

Literatures survey indicates that no such study carried out concerning strain measurement and analysis in the concerned area. The well-known field and laboratory work carried out. An accurate ellipse was determined for each ab, bc and ac planes for each formation exposed in Baba dome using Matlab program with a relatively new toolbox (Polylx). Then for each sample the mentioned ellipses was mathematically compiled to generate strain ellipsoid with long, intermediate and short axes with their orientations using Mathcad software. Then the long and short axes of strain ellipsoids projected on ab plane and delineated. Because Baba dome took the present form during last phase of Alpine Orogeny (Miocene -Pliocene) with contemporaneous deposition of Mio- Pliocene formations, the present study deduced that the strain is directly proportional to the stress i.e. elastic deformation. Therefore, the orientation of short axes of strain ellipsoids should coincide with orientation of maximum stress axes giving rise the orientation of maximum stress direction in sampled station.

Fry and Rf/ϕ strain methods constraints and fold transection mechanisms in the NW Iberian Variscides

Apúlia is a small Portuguese sector in NW of Central-Iberian Zone, that have been deformed in a non-coaxial sinistral transpressive regime during the first and main Variscan tectonic event (D1). This deformation give rise to a major NW–SE anticline, where the S1 N–S cleavage transect the inverted short NE limb; two and three-dimensional strains analysis have been done in the low metamorphic grade Ordovician quartzites of this limb using Fry and Rf/ϕ methods. The data show that most deformation was due to intergranular deformation mechanisms. The intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the D1 phase. The apparent plane strain ellipsoids (if no volume change is assumed) related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of Apúlia Quartzites. This constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the Central-Iberian Zone.

Structural geometry, microstructural and strain analyses of L-tectonites from Paleoproterozoic orthogneiss: Insights into local transport-parallel constrictional strain in the Sikkim Himalayan fold thrust belt

Paleoproterozoic Lingtse orthogneiss shows three dominant structural associations in the Sikkim Himalayan fold thrust belt (FTB): (a) these rocks locally define the Pelling thrust (PT) zone that lies in the footwall of the Main Central thrust (MCT), (b) they occur as linear, almost N–S trending imbricates within the PT sheet, and (c) they form a N–S trending ∼13.5km long, ∼2km wide discontinuous linear mylonitic klippen within the Daling Formation of the lower Lesser Himalayan Sequence (LHS) that lie east of the N–S trending Teesta valley. The klippe records N–S trending, strong L-tectonites that are spatially associated with LS and SL tectonites; the stretching lineations are oriented along the transport direction. These rocks are exposed along three mylonite zones. From north to south these are the Phodong mylonite zone, the Tumin Eingee mylonite zone and the Rumtek mylonite zone.All the three mylonite zones are overall folded along gently plunging, transport-parallel, N–S trending synform with the strongest L fabric developed along the hinge zone, and its dominance decreases progressively toward the eastern and western structural contacts of the klippen. The highest constrictional strain is recorded in Phodong and Tumin-Eingee mylonite zones and decreases south toward Rumtek mylonite zone. The long axes (X) of the quartz strain ellipsoids show ∼N–S trend and gentle plunge that agrees with the stretching lineations observed in the field. Additionally, the XY plane of the generated ellipsoids overall agree with the observed variation of the mylonitic foliation planes in the field from all the three locations.Microstructural analysis from the mylonite klippe suggests that quartz and feldspar have undergone ∼35% and ∼76% grain size reduction with respect to the protolith. Dislocation creep and microfracturing are the dominant deformation mechanisms in quartz and feldspar, respectively. The grain-size reduction is more prominent near the eastern and the western boundaries as they mark structural contacts between the L tectonites and the Daling phyllites. Strain is partitioned between quartz and feldspar in the mylonite zones with quartz recording constrictional strain while feldspar records flattening strain. We explain this variation due to their different deformation mechanisms. Shear-sense analysis of feldspar porphyroclasts suggest dominantly transport-parallel flow along with a component of transport-perpendicular flow in the mylonite zones.Existing models on mechanism of L tectonite formation and transport-parallel folds do not completely explain our observations. We propose the possible existence of a lateral ramp beneath the PT sheet to explain the generation of L tectonites and transport-parallel fold in the study area.

Strain analysis using structural elements and geometry of surfaces of no finite longitudinal strain

In this research, using structural elements and the geometry of surfaces of no finite longitudinal strain, crustal shortening and strain analyses have been carried out between two thrust faults in the Khon-Khoreh area in the north of Dehbid. The direction of the principal axes of the finite strain ellipsoid was defined using stereographic analyses of pole of foliation and lineation. With separation of shortening and longitudinal strain domains, the geometry of surfaces of no finite longitudinal strain was determined in 3D. The results of stereographic analyses and angular relations of surfaces of no finite longitudinal strain on the XZ and XY principal planes of strain ellipsoid show the amounts of 2Φ angle as: 48° < 2ΦXZ < 58° and 75° < 2ΦXY < 82°. Results show three axial prolate strain ellipsoids in the study area. Using calculated angles and R/2Φ nomogram, the amount of finite strain in the principal planes of strain ellipsoid (RXZ and RXY) and natural logarithmic strain (e) was determined in the study area. With application of kinematic vorticity analysis, the amount of crustal shortening was determined to be about 30 to 60 % in the study area. Finally, it reveals that the amounts of finite strain ratios, natural logarithmic strain, and increment in the prolate shapes of strain ellipsoid increased with decrease in distance from the thrust faults.

Comparison of Strain Ellipsoid Shape in the South of Ardabil Range (NW), Based on the Results of the Magnetic Susceptibility Anisotropy and Paleostress Methods

In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Magnetic Susceptibility (AMS) and paleostress have been used. Paleomagnetism is the characteristics of magnetic rocks. Some issues in associated with the past places of continental and oceanic plates can be solved. AMS is one of the paleomagnetism methods that pay to measurement of parameters (which are reflector of the magnetic fabrics rocks). It is presenting an ellipsoid with three-axis perpendicular to each other that defines magnetic ellipsoid. In this regard, the number of 12 stations in different rocks (Jurassic to Quaternary) in the southern region of Ardebil sampling was conducted. In this connection, the study of magnetic fabrics has shown an elliptical magnetic susceptibility with the prolate shape. For the separation of paleostress phases in the Khalkhal area using the analysis of the paleostress based on the study of heterogeneous fault-slip data and sliding lineaments. Firstly, data were picked from 10 stations, and after their analysis, the elliptical shape (prolate) has been determinated. The shape of the ellipsoid, based on AMS and paleostress methods and their results show that in both methods the shape of the stress field is prolate.

Magnetic fabrics induced by dynamic faulting reveal damage zone sizes in soft rocks, Dead Sea basin

SUMMARY The anisotropy of magnetic susceptibility (AMS) of soft rocks was measured in order to distinguish between the effect of remote and local strain fields, determine the size of the related inelastic damage zone and resolve the fault-plane solutions of past earthquakes. The AMS fabrics were explored next to late Pleistocene syndepositional normal faults (total displacement up to ∼3.5 m) that cross soft lacustrine rocks within the seismically active Dead Sea basin. ‘Deposition fabrics’ prevail meters away from the fault planes and are characterized by scattered maximum and intermediate principal AMS axes. ‘Deformation fabrics’ are detected up to tens of centimetres from the fault planes and are characterized by well-grouped AMS axes, in which one of the principal axes is parallel to the strike of the nearby fault. Variations in the AMS fabrics and magnetic lineations define the size of the inelastic damage zone around the faults. The results demonstrate that the deformation-driven magnetic fabrics and the associated inelastic damage zones are compatible with coseismic dynamic faulting and the effects of the local strain field during earthquakes. Most of the AMS fabrics show a conspicuous similarity to that of the fault-plane solutions, i.e., the principal AMS axes and instantaneous strain ellipsoids are coaxial. These results suggest a novel application of the AMS method for defining the shape and size of the damage zones surrounding dynamic faults and determining the full tensor of the local strain field.

Sinistral transpressional and extensional tectonics in Dronning Maud Land, East Antarctica, including the Sør Rondane Mountains

In this paper we clarify the history of deformation in the Sør Rondane Mountains (SRMs), eastern Dronning Maud Land (DML), East Antarctica, and construct a form-line contour map of the metamorphic and plutonic rocks in order to comprehend their structural features and provide constraints on the collisional tectonics of East and West Gondwana. We divide the deformational history in the SRMs into 13 stages (D1–D13). The tectonic regime varied frequently from extension (D3–D4) to layer-normal compression and layer-parallel extension (D5), to compression (D6), extension (D7), sinistral transtension and sinistral strike-slip (D8), compression (D9–D11), and finally extension related to dextral shearing (D12–D13). D7 and D8 indicate major extensional tectonic activity in the southern part of the East African and Antarctic Orogen (EAAO) before the Pan-African compressional event, and after the c. 600Ma peak of metamorphism. The Pan-African compressional event resulted in the formation of upright folds with horizontal axes that curve along the coastline in central to eastern DML during the D9 deformation that took place between 600 and 560Ma. The coastline-parallel fold axes and subvertical axial-planes correspond to the X-axes and the XY-planes, respectively, of strain ellipsoids that were progressively rotated counterclockwise toward the central parts of a sinistral shear zone. Therefore, the curved fold axes and axial-planes suggest the EAAO acted as a zone of sinistral transpression during the collision of parts of East and West Gondwana. Around 560–550Ma, during D12, parallel dyke swarms of granitic pegmatite were intruded along normal faults under a regime of NNE–SSW horizontal extensional stress. The extensional paleo-stress and its related structures suggest dextral rather than sinistral shearing took place along the north-trending EAAO during this late Pan-African event. There is the possibility of a reversal of trans-orogen asymmetry from sinistral to dextral in the southern part of the EAAO. The dyke swarms are considered to have been the heralds of the voluminous 530–500Ma A-type granite intrusions in DML. At the same time, the Lützow–Holm Complex was under a non-extensional tectonic regime, and may have been situated in a different orogen from the EAAO.

A computed tomography approach for understanding 3D deformation patterns in complex folds

Analog models are an important tool for understanding complexly folded and faulted geological structures. In this paper, we propose the use of X-ray computed tomography to accurately reconstruct the geometry of analog models using an orthogonal reference system and to completely characterize deformation patterns within the modeled structure in 3D. The rheology and radiological contrast of various different materials have been studied showing that EVA sheets are a good choice to model buckling layers. After considering various possibilities to define the reference system, we opted to screen-print two orthogonal sets of parallel lines on the surfaces using minium (lead tetroxide). The model was then built with gOcad using a series of CT slices that can be closely spaced. This kind of model allows us to reconstruct the volume distribution of strain ellipsoids and can be very accurate and useful to ascertain the orientation of folded lineations in complex structures as well as to characterize the expected deformation on the surfaces. We have built a simple analog model inspired in the Balzes Anticline (located in the External Sierras, Southern Pyrenees) to illustrate the potential of the technique and to analyze the deformation patterns of this complex curved fold that has accommodated significant magnitudes of vertical axis rotation during its formation.

Structural evolution of metamorphic rocks in the Talas Alatau, Tien Shan, Central Asia: Implication for early stages of the Talas-Ferghana Fault

The Talas Alatau Ridge consists of three tectonic units separated by thrusts. The central (Talas parautochthon) and northeastern (Kumyshtag sheet) parts consist mainly of unmetamorphosed terrigenous and carbonate deposits. The southwestern part of the Talas Alatau (Usunakhmat sheet) consists of greenschists and is bounded by the Central Talas Thrust (CTT) and Talas-Ferghana Fault (TFF). The latter is a major strike-slip fault with post-Permian dextral displacement estimated at as much as 200km. A structural study shows that elongation axes of strain ellipsoids, stretching lineation and map-scale fold axes, as well as the trend of major faults including the CTT and the TFF, are parallel to each other. The natural deviatoric strain value gradually increases from the CTT to the TFF. The shape of the strain ellipsoid gradually varies within the Usunakhmat sheet from oblate at the frontal thrust to prolate in internal parts of the unit. The magnitude of shortening increases towards the CTT, whereas natural deviatoric strain decreases towards the CTT implying structural thickening of internal parts of the Usunakhmat sheet. Strong parallelism of the TFF, CTF and other map- and outcrop-scale structures and their close connection with strain patterns show that they were formed during the same tectonic event. They were likely formed during Middle to Late Ordovician collision and built up Kyrgyzian microcontinent as a thrust fold belt whereas reactivation of the TFF as a strike-slip fault occurred later, in Late Paleozoic.

Thermal elastic behavior of CaSiO3-walstromite: A powder X-ray diffraction study up to 900 C

Walstromite-structured CaSiO 3 (Wal) was synthesized at 6 GPa and 1200 °C for 6 h using a cubic press, and its thermal elastic behavior was investigated at T up to 900 °C using a powder X-ray diffraction technique at ambient pressure. Within the investigated T range, all unit-cell parameters, j, of Wal varied almost linearly with T, so that we fitted the data with the equation α j = j -1 (∂j/∂T) and obtained α a = 0.92(2) × 10−5/°C, α b = 1.65(1) × 10−5/°C, α c = 0.83(1) × 10−5/°C, and α V = 3.24(3) × 10−5/°C for Wal. The magnitudes of the principal Lagrangian strain coefficients (ε 1 , ε 2 , and ε 3 ) and the orientation of the thermal strain ellipsoids, between ambient T and measured T, were calculated. The orientation of the strain ellipsoid appears constant with T variation, whereas the strain magnitudes vary significantly with T: ε 1 increases, but ε 2 and ε 3 decrease. For T &gt; 900 °C, primitive data were collected for “parawollastonite” (Wo-2M), which led to a much smaller volumetric thermal expansion coefficient than that of Wal.

Analysis of superposed strain: A case study from Barr Conglomerate in the South Delhi Fold Belt, Rajasthan, India

The structural geometry in the Barr conglomerate and the neighboring rocks in the western flank of the Meso- to Neoproterozoic South Delhi Fold Belt indicate superposed deformation, with structures developed by horizontal dextral simple shear deformation superimposed on earlier structures formed during approximately ESE-WNW compression and subvertical maximum elongation. The first deformation produced NNE-SSW trending subvertical schistosity, and associated steeply plunging isoclinal folds, mineral lineation and pebble elongation lineation having almost downdip alignment on the schistosity surface. The second deformation produced dextral folds both on bedding and schistosity surfaces and modified the shape of the pebbles already deformed by the first deformation. On vertical sections perpendicular to the schistosity trace the pebbles show sub-ellipsoidal shape with their mean elongation direction parallel to the schistosity trace. On the horizontal section the pebbles often show asymmetrical shape and asymmetrical deflection of the schistosity surface around the pebbles. The mean elongation direction makes a small angle (2°–8°) in the counter-clockwise sense with the schistosity surface. This obliquity is due to modification of post-first-deformation sub-ellipsoidal shape by later horizontal simple shear using the schistosity surface as the movement plane. Analytical expressions are derived for the modification of an original ellipse by simple shear parallel to the long axis of the ellipse. A family of curves has been generated to depict the change in axial ratio and orientation of long axis for different initial axial ratios, and for different values of shear strain ( γ). Using these curves it has been possible to factorize the total strain into two components representing the earlier compression and the later simple shear. It is noted that the computed earlier shortening strain ellipsoids are consistently in the flattening field close to the line of pure oblate ellipsoids in the Flinn plot. There is no systematic spatial control on the variation in the values of shear strain ( γ), strain ellipsoid shape parameter ( k), and intensity of distortion ( d) as one proceeds south to north along the strike of the conglomerate.

Three-dimensional strain analysis using Mathematica

A suite of geological computer programs written in Mathematica is currently available both within the online repository for the Journal of Structural Geology as well as on the first author’s website ( http://www.sonoma.edu/users/m/mookerje/ProgramPage.htm). The majority of these programs focus on three-dimensional strain analysis (e.g., determining best-fit strain ellipsoids, plotting elliptical data on either a Flinn or Hsu diagram, and determining error bounds for three-dimensional strain data). This program suite also includes a ternary diagram plotting program, a rose diagram program, an equal area and equal angle projections program, and an instructional program for creating two-dimensional strain path animations. The bulk of this paper focuses on a new method for determining a best-fit ellipsoid from arbitrarily oriented sectional ellipses and methods for determining appropriate error bounds for strain parameters and orientation data. This best-fit ellipsoid method utilizes a least-squares approach and minimizes the error associated with the two-dimensional data-ellipse matrix elements with the corresponding matrix elements from sectional ellipses through a general ellipsoid. Furthermore, a kernel density estimator is utilized to yield reliable error margins for the strain parameters, octahedral shear strain, Flinn’s k-value, and Lode’s ratio. By assuming a gamma distribution for the simulated principal axes orientations, more realistic error bounds can be estimated for these axes orientations.

Transtensional analyses of fault patterns and strain provinces of the Eastern California shear zone–Walker Lane on the eastern margin of the Sierra Nevada microplate, California and Nevada

Obliquity of the strain velocity field to the deformation zone boundary requires strain to be triaxial. At the plate boundary scale, fault geometries predicted by transtensional theory better explain observed fault patterns in the northern Eastern California shear zone–Walker Lane area than do 2D plane strain predictions. Structural provinces in the Eastern California shear zone–Walker Lane are defined by variations in the orientation of the eastern margin of the Sierra Nevada microplate, and include the Honey Lake–Pyramid Lake, Lake Tahoe, Mono Lake–Long Valley, Owens Valley, and Coso subprovinces. The local geometry of the transtensional zone boundary and the microplate transport direction determines orientations of the instantaneous strain axes for each province. Fault orientations predicted with respect to these axes are consistent with those observed in each structural province. The variation of zone geometry among predominantly coaxially dominated strain provinces over a consistent period of deformation does not result in dramatic changes in shape or orientation among finite strain ellipsoids. Although Quaternary faulting strongly reflects transtensional kinematics, the magnitude of estimated finite strain for each province suggests that present-day transtensional deformation has not accommodated large amounts of extension, vertical thinning, or strike-slip offset. K-values for all structural provinces plot in the k>1 constrictional field on the logarithmic Flinn (Ramsay) diagram, indicating non-plane, transtensional strain. Collectively, these theoretical applications and structural–tectonic observations have implications for evaluating kinematics and faulting during brittle non-plane strain deformation, and for the overall evolution of the transtensional Sierra Nevada–North America plate boundary.

Triclinic transpression zones with inclined extrusion

Data from natural transpressional shear zones reveal a large range of lineation orientations that can spread along complete girdles. One possible way to account for such a type of fabrics is variation in the extrusion direction. This work presents a new theoretical model of oblique transpression with inclined extrusion. The model is kinematic and the flow is considered as homogeneous and steady. The angle ζ between the simple shear direction and the extrusion direction is one of the main parameters controlling the final fabric. Low values of ζ (<40°) yield plane-strain ellipsoids, while high ζ values (>40°) can generate strain ellipsoids very close to the abscissa axis of the Flinn plot. Depending on the vorticity of the flow, the finite strain and the actual value of the ζ angle, the model predicts the generation of lineation fabrics ranging from point maxima to patterns with opposite plunge senses. These patterns can display monoclinic, nearly monoclinic or clearly triclinic symmetry. Lineation patterns spreading along complete girdles can be obtained by allowing the extrusion direction to deviate less than 30° about the vertical in either direction.

Heterogeneous strain behaviour in competent layers during folding in transpressive regimes

The understanding of folding processes in transpression is crucial in structural geology. However, the study of folding in multilayers where adjacent strata exhibit high competence contrast is impossible if the observations are only restricted to geometrical features. Nevertheless, using detailed three dimensional finite strain analyses it is possible to constrain the solutions. Strain data from the deformed northern Portugal Ordovician quartzites show that folding mechanisms in transpression are highly variable. For the more deformed materials found, not only in the short limbs, but also in the thinner layers of the long limbs, the strain ellipsoids orientations can be explained by a combination of flexural shear (related to the folding process) and sinistral wrench component parallel to the bedding plane (a pervasive regime in the southern branch of the Ibero-Armorican Arc). In the thicker layers of the long limbs, orthogonal flexure seems to be the dominant mechanism. Concerning the strain ellipsoid shape, the constrictional forms predominate mainly in the long limbs. Strain partitioning in transpressive regimes is important at the mesoscopic fold scale, especially in asymmetric folds. In the more deformed short limb, the data indicate that transpression tends to be always an active mechanism, while in the long limb the regional wrench component it's often less important.

Transtensional Deformation of the Brittle Crust: Field Observations and Theoretical Applications in the Coso-China Lake Region, Eastern Margin of the Sierra Nevada Microplate, Southeastern California

The focus of this work is the description of non-plane strain brittle deformation through field observations and theoretical applications. The seismically and volcanically active Coso—China Lake region in the transtensional Eastern California shear zone is an exemplary location for field observation of brittle structure. The region deforms in a constrictional strain field, well-described by earthquake focal mechanisms and GPS measurements, and further demonstrated by our field observations and outcrop-scale mapping. Fundamental geometric relationships in transtensional zones and tectonic reconstruction allows practical applications of theory using real transtension zone parameters, and expands our ability to describe triaxial strain in three dimensions. Theoretical instantaneous strain axes are constrictional and oriented xi WNW, yi NNE, zi vertical, similar to seismogenic and GPS derived instantaneous strain axes, and kinematic analysis of field data. Orientations of brittle structures in the field correspond reasonably well to theoretical predictions, with normal faults striking generally NNE, parallel to yi, dextral faults northwest to NNW, sinistral faults ENE, and fold axes and thrust faults WNW, parallel to xi. We calculate theoretical rates and amounts of shortening, elongation, and rotation for specific structures within the deformation zone; paleomagnetically-derived rotations in Pliocene volcanics fall within our predicted ranges. We subdivide the field area based on geometry and derive shapes and orientations of the instantaneous and finite strain ellipsoids and associated k-values (Northern Coso, k = 6.84; Southern Coso, k = 2.21). Our results indicate a less prolate, more coaxially-dominated, higher strain and strain rate in Southern Coso, and a more prolate, less coaxially dominated, lower strain and strain rate in Northern Coso, part of which is reflected by elevation and topography. We observe varying degrees of three-dimensional strain partitioning of brittle structures depending on scale, as is also seen in seismicity, and possible partitioning of rotations around vertical and horizontal axes. Multi-scale partitioning of strain and rotation, influenced by preexisting and reactivated structures, characterizes transtensional deformation at Coso, and is well described by kinematic analysis of structural field observations and regional theoretical applications and analyses.

Finite strain variation across the Mahabharat Thrust in central Nepal Himalaya

This paper deals with the three-dimensional strain across the Mahabharat Thrust (MT) in the Malekhu area in central Nepal. The MT served as a glide plane for the Kathmandu Nappe. Its footwall is made up of phyllites, quartzites, and amphibolites, whereas the hanging wall contains garnetiferous schists, biotite schists, and quartzites with a few lenses of augen gneiss. A three-dimensional strain analysis reveals that Nadai’s amount of strain intensity (€s ) ranges from 0.396 to 0.575 in the footwall indicating an increasing trend towards the proximity of the MT. In contrast, the hanging wall shows an increase in (€ s) magnitude away from the MT and its value varies between 0.556 (at the basal part) and 0.795 (upper part). Microtextures and structures revealed dynamic recrystallisation of the footwall and static recrystallisation of the hanging wall rocks. The shape of three dimensional strain ellipsoids, types of microstructures, and mechanisms of grainscale deformation indicated that the footwall was dominantly affected by simple shear deformation at lower temperatures while the hanging wall suffered from pure shear with minor sub-simple shear deformation at relatively higher temperatures.

Interstitial defects in 316L austenitic stainless steel containing “colossal” carbon concentrations: An internal friction study

Carburization of 316L austenitic stainless steel under paraequilibrium conditions results in extremely hard (∼1100 HV) single-phase cases containing surface carbon concentrations of ∼15 mol.% and very high residual compressive stresses (⩾2 GPa). Carburization produced an anelastic relaxation peak at 543 K (1.0 Hz), due to a carbon-containing defect with a highly anisotropic strain field. Interstitial solid-solution strengthening theories can explain the approximate three-fold increase in hardness, using reasonable parameters for the strain ellipsoids of these defects.

Determination of relative strain ellipsoids from sectional measurements of stretching lineation

A novel strain inversion method is developed in this communication to determine relative strain ellipsoid (namely, principal directions and relative magnitudes) from four or more independent measurements of stretching lineation or the longest elliptical axes on planar surfaces. A linear, five-variable equation is obtained to describe such kind of measurements. Equations for these measurements are solved under some auxiliary constraints for the relative strain ellipsoid. This is similar in formulation to stress inversion. We believe the method will provide for structural geologists a simple, useful and more applicable tool for estimating strain in deformed rock where no passive strain marker other than stretching lineation is commonly observed at outcrop.