deformation of ductile inclusions in a multiple inclusion system in pure shear this paper analyzes the deformational behavior of mutually interacting spherical inclusions in a multiple inclusion system considering two physical factors viscosity ratio between inclusion and matrix m and the ratio of inclusion diameter to mean inter inclusion distance a b for a given value of m the strain partitioning between a stiff inclusion and the bulk system i e ratio of their natural extension rates increases non linearly with increasing a b ratios and the gradient of increase becomes steeper when the inter inclusion distance is less than about twice their diameter i e a b about 0 5 the strain distribution within a deformed inclusion is homogeneous when the a b ratio is less than about 0 6 for larger values of a b the internal deformation becomes heterogeneous with the strain increasing or decreasing towards the core in the case of stiff m 1 and soft m 1 inclusions respectively the deformed shape of inclusions in section also shows departure from an ideal ellipse with an increase in the a b ratio stiff inclusions develop shapes similar to that of a super ellipse in contrast to soft inclusions that resemble a sub ellipse the heterogeneity of internal deformation is also reflected in the distortion of passive foliations initially at right angles to the bulk extension direction which become curved with convexity outward and inward respectively within stiff and soft inclusions

strain analysis of heterogeneous ductile shear zones based on the attitudes of planar markers using the simple measurement of the attitude of planar features such as foliation shear planes and displaced tabular markers such as veins or dykes fundamental information is obtained on deformation types and rheology in heterogeneous ductile shear zones the method outlined in this study is based on the subdivision of the shear zone in n deformed layers each of them being characterized by approximately homogenous deformation for each layer paired measurements of and are made where is the angle that the foliation forms with the shear plane and is the effective shear strain by means of suitable grids constructed according to strain boundary conditions values of stretch k shear strain strain ratio r and kinematic vorticity number wk are calculated the method has been tested on three ductile wrench zones exposed in a deformed granitoid pluton in the eastern alps italy the data indicate that the shear zones are of dominantly transtensional or transpressional type furthermore the finite shear strain and strain ratio peaked profiles suggest that in all instances shear zone evolution was characterized by strain softening analysis of the kinematic vorticity indicates that strain softening essentially affected the simple shear component of the deformation

non ellipsoidal inclusions as geological strain markers and competence indicators abstract geological objects that do not deform homogeneously with their matrix can be considered as inclusions with viscosity contrast such inclusions are generally treated as initially spherical or ellipsoidal theory shows that ellipsoidal inclusions deform homogeneously so they maintain an ellipsoidal shape regardless of the viscosity difference however non ellipsoidal inclusions deform inhomogeneously so will become irregular in shape geological objects such as porphyroblasts porphyroclasts and sedimentary clasts are likely to be of this kind with initially rectilinear prismatic or superelliptical section shapes we present two dimensional finite element models of deformed square inclusions in pure shear parallel or diagonal to the square as a preliminary investigation of the deformation of non ellipsoidal inclusions with viscosity contrast competent inclusions develop marked barrel shapes with horn like corners as described for natural ductile boudins or slightly wavy rhombs incompetent inclusions develop dumb bell or bone shapes with a surprising degree of bulging of the shortened edges or rhomb to sheath shapes the results lead to speculation for inclusions in the circle to square shape range and for asymmetric orientations anticipated shapes range from asymmetric barrels lemons or flags for competent inclusions to ribbon or fish shapes for incompetent inclusions we conclude that shapes of inclusions and clasts provide an important new type of strain marker and competence criterion

modelling the bulk viscosity of two phase mixtures in terms of clast shape abstract the rheological behaviour of many rock types will depend on how mixtures of different minerals and rock clasts behave together this paper develops two dimensional modelling of the bulk viscosity of two phase viscous mixtures with different shape fabrics in pure shearing based on self consistent mechanics and behaviour of inclusion matrix systems an equation is presented for the bulk viscosity in terms of the phase viscosity contrast phase fractions and clast shape results are given for idealised two dimensional mixtures of circles squares or ellipses with a variety of phase viscosity contrasts in pure shearing parallel perpendicular to the shape fabric the normalised bulk viscosities of all these mixtures fall between the theoretical upper and lower viscous bounds given by homogeneous strain rate and homogeneous stress respectively but nearer to the upper bound with increasing shape fabric mixtures with a particular geometry are shown to have a constant relative horizontal distance between these two bounds as proposed by p d bons using graphs for the normalised bulk viscosities of mixtures with variably elliptical aligned shape fabrics the results for fabrics orthogonal to pure shearing can be extrapolated to a diagonal fabrics in pure shearing and b orthogonal or diagonal fabrics in simple shearing these reveal the bulk viscous anisotropy of mixtures with shape fabric in two dimensions it is speculated that during a progressive finite deformation two phase mixtures might undergo changes in bulk viscosity over time with steady stiffening during pure shear and perhaps cyclic stiffening and softening during simple shear the two dimensional models provide an approximation to the three dimensional properties of mixtures with shape fabrics with potential applications to rocks including conglomerates

high strain deformation of conglomerates numerical modelling strain analysis and an example from the wutai mountains north china craton abstract conglomerates have been widely used to investigate deformation history and rheology strain vorticity and viscosity previous studies reveal that several factors such as pebble shapes and concentrations as well as material properties affect conglomerate deformation however how pebble concentration and interaction between pebbles affect deformation is not understood very well we use the 2d numerical modelling platform elle coupled to the full field crystal visco plasticity code vpfft to simulate the deformation of conglomerates with various viscosity contrasts between pebbles and matrix and different pebble concentrations with both linear stress exponent n 1 and power law n 3 viscous rheologies under simple shear conditions up to a shear strain of ten pebbles can behave as effectively passive deformable or effectively rigid an increase in pebble concentrations viscosity contrasts enhances pebble deformation but reduces their rotation a mean aspect ratio rf orientation plot is proposed to gain an estimate of pebble deformation behaviour and the amount of bulk strain closely spaced rigid or deformable pebbles can form clusters that mechanically act as single inclusions rigid clusters rotate and survive for only short strain increments whereas the more stable deformable ones keep on elongating with minor rotation we provide a natural example of deformed conglomerates from the wutai mountains north china craton these consist of banded iron formation bif pebbles embedded in a schistose matrix using the mean rf plot a finite strain of 6 under simple shear could be determined the viscosity of the pebbles is estimated at about 5 8 times that of the matrix for a linear rheology n 1 or 2 to 5 times if a power law rheology with n 3 is assumed

estimation of viscosity contrast and finite strain from deformed elliptical inclusions a method of strain analysis is described which takes into account a possible competence difference between the strain markers and the rest of the rock using data consisting of the sectional shapes and orientations of groups of inclusions from conglomerate like rocks limits are placed on the possible effective viscosity contrast between the inclusions and the rock as a whole as well as on the bulk finite strain suffered by the rock these results are calculated using a computer program based on the theory for the deformation of elliptical cylinders the method can be considered an extension of the rf method but provides more information and involves less restrictive assumptions

vertical stretching and crustal thickening at nanga parbat pakistan himalaya a model for distributed continental deformation during mountain building 1 the localization of strain in the continental crust during compressional tectonics is examined using the active structures at the nanga parbat massif an exhumed tract of indian continental crust in the pakistan himalaya this large scale 40 km wavelength structure is considered to involve the whole crust thrusting at the modern surface places gneisses of the indian continental crust onto holocene deposits at the raikhot transect the thrust zone carries a relatively narrow 2 km wide shear zone within which minor structures are asymmetric and the deformation apparently noncoaxial however modeling of foliation and augen preferred orientation ellipticity suggests that the bulk deformation is a combination of relatively small simple shear strains 1 with larger stretching strains heterogeneous stretching within the shear zone was accommodated by localized shearing on metabasic layers so that strain is partitioned outside this shear zone on the transect there is penetrative deformation throughout the nanga parbat massif this broadly distributed deformation shows no asymmetry or evidence of rotation rather this deformation is better described as near pure shear subvertical stretching augen ellipticities suggest subvertical stretches of greater than 200 consideration of plausible changes in crustal thickness during the amplification of the nanga parbat structure suggests the magnitude of vertical stretch decays with depth presumably these strains in the deep crust are more distributed but weaker than in the exposed middle crustal sections assuming conservation of horizontal shortening displacement with depth these studies suggest that penetrative vertical stretching through dominantly pure shear deformation is an effective mechanism for thickening the continental crust and that models which assume that simple shear zones penetrate the whole crust need not be of ubiquitous applicability

the behaviour of deformable ellipsoidal particles in three dimensional slow flows implications for geological strain analysis abstract eshelby s equations governing the motion of a viscous inclusion embedded in a matrix of contrasting viscosity are solved numerically for arbitrarily shaped and arbitrarily oriented ellipsoidal particles the theory has important implications for geological strains and strain analysis specifically it predicts that particles more competent than their matrix will have deformed shapes with larger k values than equivalently shaped and oriented passive markers the effect is significant even for viscosity ratios as low as r 1 5 and increases with increase in r for general applications numerical solutions must be sought nevertheless there are useful exceptions 1 1 the two dimensional deformed shape of viscous particles can be computed graphically provided the matrix strain is irrotational pure shear and the section ellipse is a principal plane of the particle ellipsoid for sections through a three dimensional system with arbitrarily oriented particles this method and those based on sections through an elliptic cylinder is inaccurate the reliability is further diminished for simple shear 2 2 irrotational deformations in three dimensions can be computed on transformed flinn plots if the particle or average particle axial orientations are parallel with the applied flow similar diagrams may be used to make independent estimates of viscosity contrasts in polymict conglomerates

sedimentation and tectonics of the sylhet trough bangladesh the sylhet trough a sub basin of the bengal basin in northeastern bangladesh contains a thick fill 12 to 16 km of late mesozoic and cenozoic strata that record its tectonic evolution stratigraphic sedimentologic and petrographic data collected from outcrops cores well logs and seismic lines are here used to reconstruct the history of this trough the sylhet trough occupied a slope basinal setting on a passive continental margin from late mesozoic through eocene time subsidence may have increased slightly in oligocene time when the trough was located in the distal part of a foreland basin paired to the indo burman ranges oligocene fluvial deltaic strata barail formation were derived from incipient uplifts in the eastern himalayas subsidence increased markedly in the miocene epoch in response to western encroachment of the indo burman ranges miocene to earliest pliocene sediments of the surma group were deposited in a large mud rich delta system that may have drained a significant proportion of the eastern himalayas subsidence rates in the sylhet trough increased dramatically 3 8 times from miocene to pliocene pleistocene time when the fluvial tipam sandstone and dupi tila formation were deposited this dramatic subsidence change is attributed to south directed overthrusting of the shillong plateau on the dauki fault for the following reasons 1 pliocene and pleistocene strata thin markedly away from the shillong plateau consistent with a crustal load emplaced on the northern basin margin 2 the shillong plateau is draped by mesozoic to miocene rocks but pliocene and younger strata are not represented suggesting that the massif was an uplifted block at this time 3 south directed overthrusting of the shillong plateau is consistent with gravity data and with recent seismotectonic observations sandstone in the tioam has a marked increase in sedimentary lithic fragments compared to older rocks reflecting uplift and erosion of the sedimentary cover of the shillong plateau if the dauki fault has a dip similar to that of other himalayan overthrusts then a few tens of kilometers of horizontal tectonic transport would be required to carry the shillong plateau to its present elevation uplift of the shillong plateau probably generated a major 300 km westward shift in the course of the brahmaputra river

strain localization during high temperature creep of marble the effect of inclusions abstract the deformation of rocks in the earth s middle and lower crust is often localized in ductile shear zones to better understand the initiation and propagation of high temperature shear zones induced by the presence of structural and material heterogeneities we performed deformation experiments in the dislocation creep regime on carrara marble samples containing weak limestone or strong novaculite second phase inclusions the samples were mostly deformed in torsion at a bulk shear strain rate of 1 9 10 4 s 1 to bulk shear strains between 0 02 and 2 9 using a paterson type gas deformation apparatus at 900 c temperature and 400 mpa confining pressure at low strain twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at 0 1 0 2 peak shear stress at the imposed conditions is about 20 mpa which is 8 lower than the strength of intact samples strain progressively localized within the matrix with increasing bulk strain but decayed rapidly with increasing distance from the inclusion tip microstructural analysis shows twinning and recrystallization within this process zone with a strong crystallographic preferred orientation dominated by r and c slip in recrystallization induced weakening starts at local shear strain of about 1 in the process zone corresponding to a bulk shear strain of about 0 1 in contrast torsion of a sample containing strong inclusions deformed at similar stress as inclusion free samples but do not show localization the experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips recrystallization induced grain size reduction may only locally promote grain boundary diffusion creep accordingly the bulk strength of the twisted aggregate is close to or slightly below the lower isostress strength bound determined from the flow strength and volume fraction of matrix and inclusions

use of boudinaged rigid objects as a strain gauge insights from analogue and numerical models abstract using analogue experiments we investigate how far the extensional strain estimated from an array of rigid boudins tracks the bulk extension of the host rock the quadratic elongations of boudinaged objects b were compared with the corresponding bulk quadratic elongations in physical models m both for pure and simple shear a noticeable difference occurs between the two which depends on the aspect ratios of initial object r o and boudins r b boudin types and the nature of bulk deformation for a given r o the difference is proportional to r b and tends to diminish with increasing r o when r b is constant the difference is normalized with the quadratic elongation measured from boudins b to define a departure factor m b b approaches a stable value with increasing b in pure shear the stable for torn symmetric boudins is larger 10 1 than that for asymmetric boudins among which the planar type shows the departure close to 0 boudins in pure shear show values smaller than that in simple shear in case of simple shear antithetic slip boudinage involves lower values compared to synthetic slip boudinage finite element models with elasto viscous rheology also corroborate the experimental findings

non steady homogeneous deformations computational techniques using lie theory and application to ellipsoidal markers in naturally deformed rocks abstract the dynamic theory of deformable ellipsoidal inclusions in slow viscous flows was worked out by j d eshelby in the 1950s and further developed and applied by various authors we describe three approaches to computing eshelby s ellipsoid dynamics and other homogeneous deformations the most sophisticated of our methods uses differential geometric techniques on lie groups this lie group method is faster and more precise than earlier methods and perfectly preserves certain geometric properties of the ellipsoids including volume we apply our method to the analysis of naturally deformed clasts from the gem lake shear zone in the sierra nevada mountains of california usa this application demonstrates how given three dimensional strain data we can solve simultaneously for best fit bulk kinematics of the shear zone as well as relative viscosities of clasts and matrix rocks

the bholghati howardite chemical study bholghati is homogeneous on a cm scale in major element composition but heterogeneous in trace elements such as the rare earth elements rees the rees are concentrated in accessory phosphates and their sampling can influence the ree patterns of eucritic clasts which in turn can govern the bulk ree patterns bholghati can be reasonably modeled with 56 eucritic 45 diogenitic and 3 dark clast components however an additional component feldspathic is required to match the bulk composition dark clasts represent carbonaceous cm type material that was admixed with other components during regolith formation on the eucrite parent body epb one eucritic clast fine grained is light ree lree depleted relative to heavy ree hree which is unusual in normal eucrites the lree depletion pattern cannot be modeled from one stage partial melting of a chondritic source however it can be modeled from a non chondritic source depleted in lrees or multi stage melting of a chondritic source provided that the lree depletion is not from undersampling of phosphates bholghati has a complex history that involved early multiple magmatic events later annealing and fragmentation and low temperature mixing of eucritic diogenitic and carbonaceous components on the howardite parent body

analysis of anisotropy of magnetic susceptibility in iron oolitic beds a potential tool for paleocurrent identification a combined sedimentological shape preferred orientation and anisotropy of magnetic susceptibility ams analysis has been performed at the arroyofrio bed callovian oxfordian boundary level in the locality of moneva iberian range ne spain the arroyofrio bed is a widespread iron ooid limestone interval forming a condensed sequence the present study has focused on the analysis of the potential presence of a preferred ooid orientation at the arroyofrio bed the obtained data show that ooids were originally ellipsoidal and had an imbricate disposition with respect to the bedding lamination surface the main ooid orientation within the bedding plane shows a nne ssw trend results of ams analyses show a magnetic foliation parallel or slightly imbricated with respect to bedding and magnetic lineation parallel to the main ooid orientation magnetic mineralogy of studied samples shows that ams is mainly controlled by magnetite with minor contributions of hematite and paramagnetic minerals that can reach contributions of 35 the analyzed ooids show axial ratios between 1 4 and 2 8 intrinsic anisotropy while the anisotropy of their distribution shows lower anisotropies e g rs 1 15 or very low values of the anisotropic magnetic parameters e g p 1 01 sedimentary texture matrix features bioturbation and fossil content influenced both ooid main orientation and the magnetic fabric magnetic lineation and main orientation of long ooid axes are transverse to the inferred coastline in the studied area and parallel to the expected paleocurrent direction with respect to the ejulve maestrazgo paleogeographic high the direct correlation between ams magnetic lineation and the ooid analysis permits to demonstrate that the paleocurrent imprint can be recorded by means of ams despite the highly ferromagnetic context fabric and at coarse deposits obtained results support the interest and reliability of ams to unravel paleocurrent imprints for paleogeographic reconstructions

geological strain analysis a manual for the rf φ technique by richard j lisle pergamon press oxford 1985 viii 99 pp 15 hard cover 8 95 soft cover

analysis of superposed strain a case study from barr conglomerate in the south delhi fold belt rajasthan india abstract 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 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 strain ellipsoid shape parameter k and intensity of distortion d as one proceeds south to north along the strike of the conglomerate

the effect of non passive clast behaviour in the estimation of finite strain in sedimentary rocks abstract existing methodologies that use ellipsoidal objects for the analysis of geological strain typically assume that these objects acted passively during deformation this assumption when not valid can lead to significant underestimates of strain in rocks deformed under low grade conditions in orogenic forelands this is especially true when clastic sedimentary rocks are utilized to measure strain the competency contrast between clasts and matrix possibly leading to marked non passive behaviour the systematic nature of this finite strain underestimation may allow for a correction of strain estimates when this type of behaviour is evident

a tale of two viscosities abstract we describe a series of 12 large strain two dimensional simple shear numerical experiments on two phase linear and non linear viscous materials the modal percentage of the two phases their relative viscosities and the stress exponent of the dependence of viscosity on stress were systematically varied allowing us to observe the effects of these parameters on the flow behaviour of the system all experiments exhibited localisation but the extent and type of localisation varied considerably and the range of parameters allows both classical sc as well as sc structures to form the inter granular finite strain geometries also varied systematically although there is a tradeoff between non linearity of viscosity and the viscosity contrast that results in similar geometries for quite different mechanical behaviour the finite rotation of the harder phases was similar within any one experiment originally parallel passive marker lines thus remain sub parallel after deformation and rotation which may be mistaken for non rotation the internal deformability and interaction between grains allows meta stable grain elongation orientations to form without any additional consideration of external slip surfaces the slight variability of initial grain geometry and subsequent grain interactions leads to a wide variability in final grain shapes for the same initial viscosities

studies of strain and rheology of conglomerates abstract conglomerates can show significant strain variations among their component rock types previous studies have exploited this feature as a method of quantifying the effective viscosity ratios among different rock types using inclusion matrix models that we review here we further investigate the rheology of conglomerates via models of multiphase mixtures of spherical clasts with varying phase fractions using idealised models with two to four phases we can quantify the influence of phase viscosities and volume fractions on the bulk viscosity and reveal how this controls the strain partitioning among the different phases we consider practical methods of analysing conglomerates and choose r f analysis for measuring clast strain and fry analysis for whole rock strain the methods are illustrated through case studies of two very different conglomerates the port askaig tillite scotland and cesson conglomerate brittany we define the important rock phases in each and assess their strain variations although providing strain measurements of regional interest our main purpose is to quantify the viscosity ratios among the component rocks we find that among the most common rock types semipelite quartzite psammite volcanics granite the viscosity ratios span about one order of magnitude agreeing with previous studies these small numerical values for viscosity ratios among many rock types in many conglomerates lead us to conclude that these rocks each deformed at approximately constant viscosity i e as linearly viscous rather than according to a power law

shape fabric development in rigid clast populations under pure shear the influence of no slip versus slip boundary conditions abstract shape fabrics of elliptical objects in rocks are usually assumed to develop by passive behavior of inclusions with respect to the surrounding material leading to shape based strain analysis methods belonging to the rf family a probability density function is derived for the orientational characteristics of populations of rigid ellipses deforming in a pure shear 2d deformation with both no slip and slip boundary conditions using maximum likelihood a numerical method is developed for estimating finite strain in natural populations deforming for both mechanisms application to a natural example indicates the importance of the slip mechanism in explaining clast shape fabrics in deformed sediments

strain accumulation and fluid rock interaction in a naturally deformed diamictite willard thrust system utah usa implications for crustal rheology and strain softening abstract structural and geochemical patterns of heterogeneously deformed diamictite in northern utah usa record interrelations between strain accumulation fluid rock interaction and softening processes across a major fault willard thrust different clast types in the diamictite have varying shape fabrics related to competence contrasts with estimated effective viscosity ratios relative to micaceous matrix of 6 and 8 for large quartzite clasts respectively in the willard hanging wall and footwall 5 and 2 for less altered and more altered granitic clasts respectively in the hanging wall and footwall and 1 for micaceous clasts that approximate matrix strain within the footwall matrix x z strain ratios increase from 2 to 8 westward along a distinct deformation gradient microstructures record widespread mass transfer alteration of feldspar to mica and dislocation creep of quartz within matrix and clasts fluid influx along microcracks and mesoscopic vein networks increased westward and led to reaction softening and hydrolytic weakening in conjunction with textural softening from alignment of muscovite aggregates consistent si al and ti concentrations between matrix granitic clasts and protoliths indicate limited volume change mg gain and na loss reflect alteration of feldspar to phengitic muscovite within the hanging wall strain is overall lower with matrix x z strain ratios of 2 to 4 microstructures record mass transfer and dislocation creep concentrated in the matrix greater al and ti concentrations and lower si concentrations in matrix indicate volume loss by quartz dissolution na gain in granitic clasts reflects albitization large granitic clasts have less mica alteration and greater competence compared to smaller clasts differences in strain and alteration patterns across the willard thrust fault suggest overall downward up temperature fluid flow in the hanging wall and upward down temperature fluid flow in the footwall

effects of object ellipticity on strain and implications for clast matrix rocks we examine the influence of object shape on strain taking the example of an elliptical object in a matrix of different viscosity the eshelby bilby equation for the cross sectional strain of circular cylindrical objects in a matrix of different viscosity is differentiated to express the relationship of developing sectional ellipticity on incremental strain this leads to an expression for the strain of initial elliptical objects whose axes are parallel or perpendicular to pure shearing graphs show that competent elliptical objects with axial ratios of ri 3 or more will strain significantly more than circular objects of the same viscosity less if the objects are incompetent while the effect is likely to be insignificant for competent objects with initial ellipticity of 2 which is indicated from statistics for undeformed pebbles in conglomerates any clast with greater ellipticity such as ri 5 to 10 could deform significantly more than an equant clast and thus appear to be materially less competent these principles have implications for geological strain studies and for competence contrasts in rocks

pure shear deformation of square objects and applications to geological strain analysis abstract geological objects that deform differently from the rock matrix such as pebbles or other clasts are unlikely to have been originally circular or elliptical in section and must therefore be expected to deform heterogeneously and change shape irregularly we investigate this process with finite element models of pure shear deformation of square objects in three orientations square skew and diagonal in a matrix with different viscosity modelling shows that squares deform irregularly with competent objects becoming barrel shaped and fish mouthed cf boudins whereas incompetent objects become bone shaped or elongate lobes the object aspect ratios r o are less different from the bulk strain ratio r s than for equivalent circular objects in contrast diagonal squares deform almost homogeneously into rhombs with aspect ratios closer to those for circles asymmetrically oriented skew squares behave intermediately developing skew flag and hooked shapes according to competence contrasts that might be misdiagnosed as shear criteria all these square objects and circles in theory show almost linear strain paths of object versus bulk r 1 with slope related to viscosity ratio object shape and orientation linear relationships are also found for concavity convexity shape factors for squares the results have implications for strain analysis and competence contrasts in rocks

are viscosity ratios of rocks measurable from cleavage refraction abstract in this questions contribution i consider some of the accepted methods of measuring viscosity ratios in rocks and pose a new one for a wide range of strain and orientations it can be shown that the bedding normal is immeasurably close to the xy plane and this has applications to the relationship between cleavage and strain i therefore propose that with some limitations cleavage refraction can provide a measure of effective viscosity ratios in layered rocks examples show that cleavage refraction across competence contrasts yields surprisingly small viscosity ratios this method might also provide a way of distinguishing newtonian from non newtonian behaviour of rocks over time and space

strain analysis and rheology contrasts in polymictic conglomerates an example from the seine metaconglomerates superior province canada deformed conglomerates typically display contrasting strains between different lithological clast populations and matrix which can be exploited to provide information about effective viscosity contrasts we analyzed three different clast populations granitoid mafic volcanic and felsic volcanic across a strain gradient in the seine metaconglomerates of ontario canada we calculated finite strain using the rf 4 method and bootstrap statistics granitoid clasts exhibited the least amount of strain while the mafic and felsic clasts had similar greater strains we assumed that the bulk finite strain was recorded by the mafic clasts given their large proportion of the rock and their similar composition to the matrix we calculated effective viscosity contrasts using the finite strain information assuming newtonian viscous rheology the two volcanic clast populations have similar effective viscosities regardless of strain magnitude with ratios of felsic mafic ranging from 0 27 to 2 12 and average ratio of 1 19 the granitoid clasts are significantly more competent than the mafic clasts with effective viscosity ratios ranging from 2 35 to 12 39 and average ratio of 5 61 the results are consistent with a qualitative

influence of object concentration on finite strain and effective viscosity contrast insights from naturally deformed packstones deformed conglomerates and ooidal oncoidal packstones are commonly used to evaluate finite strain in deformed sedimentary successions in order to obtain a correct estimate of finite strain it is necessary to consider not only the different behaviour of matrix and objects but also object concentration the analysis of two component rocks characterised by high values of packing commonly results in a substantial underestimate of bulk strain and of viscosity contrast between objects and matrix in this study the effects of the volumetric fraction of competent inclusions on both object and bulk measured finite strain as well as on apparent viscosity contrast have been investigated in naturally deformed packstones characterised by variable object concentration on the scale of the hand specimen and hence for homogenous viscosity contrast object finite strain has been obtained by rf f analysis whereas the fry method provides a measure of whole rock strain that is also a function of inclusion concentration therefore the finite strain measured by the fry method is better termed effective bulk strain in order to investigate the role of object concentration this parameter has been plotted against object and effective bulk strain and also against viscosity contrast these diagrams show that i for high values of packing measured object and effective bulk strain show values that are significantly lower with respect to the calculated maximum value that would result in the ideal case of no particle interaction and represents therefore the real bulk strain of the samples ii the viscosity contrast shows lower values with respect to the calculated maximum one that is equal for the three principal sections of the finite strain ellipsoid and as packing reaches the maximum value the viscosity contrast approaches a unit value empirical equations have also been found that link object concentration with both object and effective bulk finite strain q 2005 elsevier ltd all rights reserved

the relationship between tectonic strain and the three dimensional shape fabrics of pebbles in deformed conglomerates the bias associated with the use of the shape of deformed inclusions to estimate bulk strain from conglomerate systems is examined mechanical considerations based on eshelby9s theory for the deformation of ellipsoidal inclusions supported by data from naturally deformed conglomerates with more than one type of inclusion reveal a discrepancy between the degree of prolateness oblateness shown by the inclusion and the bulk rock strain ellipsoid this bias is most marked in situations where the difference of competence between the inclusion and matrix is high and the volume fraction of inclusions is low in these situations an inclusion which is more competent than the matrix will deform to a shape which is more prolate than the bulk strain ellipsoid this has important implications for strain analysis of conglomeratic rocks and the interpretation of pebble shape fabrics in the context of regional tectonics

magnetic fabric shape preferred orientation and regional strain in granitic rocks since granites do not preserve easily mappable foliations lineations and strain markers determining the degree of shape preferred orientation spo in them is challenging the aim of this paper is to present a methodology for determining variation in the degree of spo in granites and to test the feasibility of correlating the same with regional strain the case of the godhra granite located in the southern parts of aravalli mountain belt india is taken as an example degree of spo is determined using two different techniques a anisotropy of magnetic susceptibility ams and b strength of mineral lineation determined by calculating the concentration parameter k of von mises distribution by digital image analysis of biotite kbi and feldspar kf in thin sections prepared parallel to the magnetic foliation plane spo data obtained using the above two techniques from 20 samples distributed across the entire granite are analysed samples with a higher k also have a stronger magnetic fabric magnetic lineation l and degree of magnetic anisotropy p 0 also the degree of spo is greater for granites from the southern parts as compared to the northern parts it is argued that this variation in degree of spo cannot be attributed to rheological differences or strain resulting from difference in aspect ratios regional strain is inferred as the dominant factor since the emplacement of the godhra granite is synchronous with the tectonic rejuvenation along the central indian tectonic zone citz that lies to its south the higher degree of spo in the southern parts is attributed to its proximity to the citz whilst caution needs to be exercised to directly apply magnetic data as a measure of strain intensity on a regional scale it can be a useful guide to select samples for detailed spo analysis using some alternative technique especially for granites and other magmatic rocks that are devoid of mesoscopic strain markers 2006 elsevier ltd all rights reserved

an apparatus to experimentally model the dynamics of ductile shear zones abstract we present a ring shear apparatus designed to deform soft ductile rock analogues to arbitraily high shear strains in simple shear in experiments attempting to model processes that occur in natural ductile shear zones the sintered specimen is deformed between two unsupported cylinders by two rotating grips under a normal and shear stress up to 5 mpa and at temperatures up to 600 k first results of experiments with octachloropropane ocp c 3 cl 8 and camphor c 10 h 16 o are presented experiments with pure ocp samples show that a steady state strain rate is achieved at a shear strain of around 4 when a steady state grain shape and crystallographic preferred orientation is established mechanical properties compare well with those of cylindrical samples deformed in triaxial compression shear localisation is relatively minor samples of pure camphor on the other hand show very strong shear localisation behaviour and mechanical properties which do not compare well with those of cylindrical samples deformed in triaxial compression experiments with two phase samples ocp containing stronger camphor inclusions show an initial softening of the composite followed by hardening this is associated with the development of a foliation defined by camphor inclusions that stretched to lenses and layers and the subsequent folding of this foliation at shear strains above 50 a steady state strain rate is not reached even at strains of 100 the experiments produce results closely resembling the kinematics observed in natural shear zones and give a first look into the complex changes in mechanical properties which occur at very high shear strains they show how this technique in conjunction with transparent deformation cells can be used to study both microstructural and rheological development during long simple shear deformation histories

trench slope controlled deep sea clastics in the exposed lower surma group in the southeastern fold belt of the bengal basin bangladesh abstract deltaic to shallow marine neritic depositional settings have until now been the accepted interpretation for the neogene surma group of rocks exposed throughout the southeastern fold belt of the bengal basin the present study revises the earlier views and proposes some new insights on the basis of detailed field studies carried out in the sitapahar anticline rangamati area and in the mirinja anticline lama area it is here proposed that the surma group succession represents an overall basinward progradation from deep marine to coastal marine depositional settings sedimentological evidence strongly suggests that the lower part of the surma group represents a slope apron the growth of which is thought to have been governed by a westward migrating accretionary prism complex within the active margin setting of the indo burmese plate convergence thin packages of distinct turbidity current generated deposits together with some slump and debris flow deposits contained within thicker intervals of mudstone characterize the lowermost exposed unit of the surma group in the sitapahar anticline the overlying slope deposits are essentially mudstone dominated comparable deep sea clastics with thicker intervals of sandstone turbidites contained within a submarine canyon are present in the mirinja anticline this new model suggests that it may be timely to re evaluate the existing stratigraphic and tectonic framework of the eastern bengal basin