are we studying deformed rocks in the right sections best practices in the kinematic analysis of 3d deformation zones abstract a standard procedure in kinematic analyses of deformed rocks is studying samples only on the foliation perpendicular lineation parallel section based on the assumption that the rotational component of deformation is restricted to that plane the theoretical background for this procedure is that deformation is plane strain which is often useful but fails to account for all relevant features observed in many natural cases more general 3d kinematic models reproduce several of these features and help to better understand 3d deformation likely predominant in nature so they are a more appropriate starting point for deformation zone analysis theoretical and natural 3d deformation examples suggest that the section with highest degree of asymmetry the vorticity normal section vns and the corresponding vorticity vector are independent from the finite strain fabric and thus may present varied orientations with respect to the tectonic foliation and lineation the vns orientation depends on the kinematics resulting from boundary conditions whereas the strain fabric orientation also depends on accumulated strain the orientation of the vns is itself an essential element of shear zone kinematics hence it cannot be pre assumed but must be determined independently

quantitative finite strain and kinematic flow analyses along the zagros transpression zone iran abstract the ghouri area in southwest iran exposes a cross section through the zagros orogenic belt the area provides an opportunity to investigate quantitative finite strain rs kinematic vorticity number wk proportions of pure shear and simple shear components sense of shear indicators steeply plunging lineations and other moderate to steeply plunging stretching lineations in a transpressional zone based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape the zagros orogenic belt is classified as a pure shear dominated zone of transpression but asymmetry of shear sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries the long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone the stretching lineations have a steep to moderate plunge but a constant strain magnitude characteristics of dextral inclined transpressional kinematics in the zagros continental collision zone were quantified and indicate an estimated k value

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

a miner s perspective on pb isotope provenances in the western and central mediterranean the conventional approach to ore provenance studies of ancient silver coins and artifacts has been to first analyze and then try to match them to published data about mining districts a difficult task given our incomplete knowledge of these while literary sources are useful to identify possible provenances they potentially bias interpretations proper because of a variety of limitations of their time archeological evidence in the form of mining shafts galleries spoil heaps and tools also provides a tangible and reliable record of mining but dating such activity can be problematic and the record is inconsistent here we propose a new approach driven by pb isotopic data rather than numismatic groups statistical analysis of pb isotopic data is used to identify ore defined isotopic clusters this new method is based on an algorithm that predicts the number of isotopic clusters necessary to fulfill the simple condition that variance within isotopic clusters is minimized whereas inter cluster variance is maximized since each cluster reflects a discrete geological episode within a particular environment broadly datable to a specific pb model age it can be identified as a potential source exploited by ancient miners we explore the potential of this method in two examples using data from coins and ores respectively in the first example roman republican silver coins form three end member clusters sourced in mining districts with cenozoic mesozoic and paleozoic pb model ages the example demonstrates how sources of silver used to mint coinage of the roman republic shifted within 50 years of the end of the second punic war in 201 bce in the second example using aegean galena samples pb isotopes distinguish components with model ages datable to the hercynian basement the recent aegean tectonic province and cyprus noting that significant silver mining districts may remain unidentified in either spain or the aegean world we further clarify a number of potential analytical issues and advocate that users of pb isotopes for tracing archeological artifacts measure all four lead isotopes and inspect the 12 proposed isotope combinations in order to select those that provide the best representation of the data we also emphasize that full advantage should be taken of the geologically informed parameters model age and th u pb relationships to identify the geological context of metal sources

strain and vorticity analysis in the zagros suture zone w iran implications for neo tethys post collision events abstract shear zone development in the zagros orogenic belt is a result of the oblique collision of the arabian plate with the iranian plateau to distinguish areas deformed during the collisional phase from those deformed by post collisional events the coaxiality of deformation and the shape of the strain ellipsoid ses have been analyzed the variation of strain intensity in each shear zone has been evaluated by calculating the strain ratio in the principal strain planes the angle and the kinematic vorticity number wk in the post collisional shear zones wk varies from 0 80 to 0 99 and from 16 7 to 44 01 the strain component is mostly simple shear though in some shear zones it is sub simple shear outside of the shear zones wk is extremely low varying from 0 00 to 0 26 and values are under 5 a coaxial deformation regime is dominant and the strain component is pure shear in most of the shear zones ses is constricted and prolate indicating that deformation occurred under transtensional conditions however in some regions ses is flattened and oblate as is common in transpressional zones shear zones that have evolved under dual deformation conditions suggest that transtensional events can be superimposed on transpressional structures

extraction of pb and zn from crude oil for high precision isotopic analysis by mc icp ms abstract radiogenic and stable isotopic tracing of crude oils has not so far been undertaken largely because of the difficulties of dealing with the low trace element contents of oil samples for high precision isotopic measurements here we present a novel analytical protocol that allows for precise and accurate determination of radiogenic pb and stable zn isotopic compositions on as little as 5 ml of crude oil from a variety of geographically geologically and environmentally diverse settings the 41 pb and zn samples measured to validate the new protocol were separated from their respective crude oils by liquid liquid extraction into an aqueous phase readily handled in a clean laboratory for subsequent purification of pb and zn by standard anion exchange column chromatography lead and zn isotopic compositions on the same 5 ml sample of crude oil were obtained by mc icp ms on 95 of the total extracted pb and zn while elemental concentrations were measured by q icp ms on 5 aliquots to the best of our knowledge the present technique is the first efficient procedure for pb and zn isotopic analysis of crude oil which owing to the elimination of the organic fraction at the liquid liquid extraction stage does not require any specialized equipment neither for the wet chemistry nor for the mass spectrometry the high extraction yields of the method and the low detection limits and high sensitivity of respectively q icp ms and mc icp ms permit analysis of very small sample quantities down to 2 ng and 100 ng respectively of pb and zn for isotopic analysis and a few hundred pg for abundance measurements reproducibility is on a par with routine state of the art pb and zn isotopic measurements of other types of geological materials while total procedural blanks for both elements are negligible relative to the amounts of pb and zn typically separated from crude oil

stable lead isotope studies of central taurus ore sources and related artifacts from eastern mediterranean chalcolithic and bronze age sites abstract this is the first paper in a series presenting stable lead isotope studies of geological and archaelogical specimens obtained in 7 years of archaeometallurgical surveys in turkey the geological specimens presented here are ore and slag samples taken from ancient mining sites in the central taurus mountain range the archaelogical specimens are metal objects dating to the chalcolithic and bronze ages from anatolia syria mesopotamia greece and the aegean the isotopic measurements on these specimens have been made and statistically analysed as part of a collaborative effort between the smithsonian institution conservation analytical laboratory and the united states national institute of standards and technology nist a comprehensive data base of approximately 1000 stable lead isotope measurements on such eastern mediterranean specimens has been formed by combining the accumulated measurements at nist with analyses published in the literature the overlap between specimens in the overall data bank and the central taurus source specimens provides a realistic evaluations of the effectiveness of the use of stable lead isotope measurements for metallic ore source characterization and for the recognition of exchange patterns of metal and metal artifacts in the formative periods of metallurgy

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

active strike slip faulting in the zagros mountains geological and geomorphological evidence of the pull apart zaribar lake basin zagros nw iran abstract the zaribar lake is situated along the main recent fault a dextral major strike slip active fault system in the zagros collision zone the formation of the zaribar lake in late pleistocene is associated with the activities of the main zagros reverse fault initiated in late oligocene and with the main recent fault whose inception occurred about 5 ma ago metamorphic intrusive and ophiolitic rocks in the zagros suture zone are affected by a normal fault system in the zaribar area geometry and kinematics of these normal faults indicate that the zaribar lake is generated in a releasing zone the strike of the main recent fault varies from 300 to 330 along the marivan fault segment the releasing bend of the marivan fault around the zaribar lake has resulted in the extensional deformation by which the lake has been downdropped between two strike slip faults besides the extensional mechanism of the main right lateral strike slip faults that has resulted in the formation of the zaribar as a large scale pull apart basin minor strike slip faults have also produced specific landforms around the lake small scale normal faults and large scale grabens developed around the lake are geological indicators of extensional areas geomorphological evidence also support the pull apart origin for the zaribar lake beheaded rivers numerous offsets in drainage system half broom shaped drainage pattern sag ponds with different scales linear and strike parallel valleys and alluvial fan with high sweep angle and width length ratio confirm the movements along right lateral strike slip faults around the zaribar

finite strains in transpression zones with no boundary slip abstract a mathematical model describing finite strains has been developed for transpression zones where no slip is allowed in any direction at the zone boundaries this has been adapted to model transpression zones where the boundaries are inclined the model can also be used to describe finite strain patterns where material is incorporated into the deforming zone from one or both sides after the initiation of deformation so that the deforming zone remains at a constant width thus allowing large transpressional strains to be accommodated without the deforming zone closing to zero thickness this model of steady state transpression can be used to explain some of the features of the south mayo trough a late silurian transpression zone in the west of ireland

testing the utility of the porphyroclast hyperbolic distribution method of kinematic vorticity analysis kinematic vorticity wk is a dimensionless measure of rotation relative to finite stretching and is essential for complete understanding of flow in ductile shear zones the porphyroclast hyperbolic distribution phd method is a widely used technique for estimating wk based on the acute angle between the flow eigenvectors determined from the orientations of back rotated s porphyroclasts the utility of the phd was tested with tertiary ultramylonites from the santa catalina mountains arizona proterozoic ultramylonites from the virgin mountains nevada and a paleozoic ultramylonite from the hylas zone in the virginia piedmont bootstrapping statistics and a computational sieving process were used to analyze the phd data set average standard deviations of the bootstrapped data sets yield a 1s standard error of 9 for a wk value measured as a simple shear sieving results imply that back rotated porphyroclasts may not orient parallel to the extensional eigenvector the phd method is useful for discerning between deformations that are pure shear dominated general shear or simple shear dominated but is not accurate enough to report precise wk values when performed on multiple sections the phd method can identify zones of monoclinic versus triclinic shear 2007 elsevier ltd all rights reserved

implications of strain and vorticity of flow analyses to interpret the kinematics of an oblique convergence event zagros mountains iran abstract finite strain and vorticity of flow analyses were carried out within the deh vazir deformed conglomerates in the sanandaj sirjan metamorphic belt zagros mountains iran this belt is in a sequence of tectono metamorphic complexes made of low to high grade metamorphic rocks affected by a polyphase deformation history using rf technique for two dimensional strain analysis showed that the finite strain of xz plane is rs 3 7 0 70 the calculation of the harmonic mean from the axial ratios of the extracted pebbles and plotting these data in the flinn diagram resulted in k 0 7 0 38 i e oblate strain ellipsoid kinematic vorticity analysis of deformed pebbles showed that wk parameter is 0 59 0 10 i e pure shear dominated non coaxial flow the results quantitatively support the recognition of a partitioned dextral inclined transpressive regime with bulk triclinic symmetry along the sanandaj sirjan metamorphic belt resulted from the oblique collision between the african arabian continent and the iranian microcontinents

impact of co2 geological sequestration on the nucleation of earthquakes 1 can co2 storage cause earthquakes what is the maximum possible earthquake magnitude resulting from co2 injection here as a theoretical case study we investigate these questions using coupled hydromechanical modeling with multiphase flow and seismological variables for quantifying earthquake magnitude and energy our simulations consider transient fluid flow and stress coupling and the evolution of fault properties we simulate co2 injection into a reservoir caprock system bounded by a subvertical normal fault subjected to different extensional stress regimes and over a range of initial fault permeability values for our assumed system and injection rate the simulation results show that sudden stress drop and fault slip primarily initiated along the fault portion intersecting the storage reservoir after a few months of injection when a sufficiently high reservoir pressure has been reached the size of the rupture area and consequently the earthquake magnitude and energy depends on initial horizontal to vertical stress ratio and fault permeability which strongly influences the size of the pressurized area and subsequent stress variations

kinematic vorticity flow analysis and 40ar 39ar geochronology related to inclined extrusion of the hp lt metamorphic rocks along the zagros accretionary prism iran abstract the zagros accretionary prism in southwestern iran is exposed along the nw se trending of the zagros thrust system and inclined zagros transpression zone this accretionary prism consists of two units the upper sedimentary melange unit on top and the high pressure metamorphic melange unit at the bottom both units show characteristics of a tectonic wedge the upper unit consists of type i ii and iii melanges which display s c and c type shear band cleavages quartz ribbons and rectangular or fish head boudins the lower unit fabrics display and type porphyroclasts and quartz ribbon mylonites these fabrics formed from a combination of 60 5 simple shear and 39 5 pure shear both components were involved in a lateral exhumation of the high pressure low temperature metamorphic rocks in an inclined transpression wedge shaped geometry the estimated kinematic vorticity number wk was calculated from quartz c axis patterns rotation of porphyroclasts and orientation of finite strain with respect to shear zone boundaries using the mean estimated wm value of 0 84 the inclination angle for the thrust wedge on top of the ne subducting neo tethyan oceanic lithosphere is 18 the 40ar 39ar plateau ages of early generations of biotite from the lower metamorphic melange are 119 95 0 88 ma and 112 58 0 66 ma this late aptian age is related to early thrusting and formation of hp lt metamorphic rocks the dating of two amphibole samples from the amphibolite yields a weighted mean age of 91 23 0 89 ma this turonian cenomanian age suggests a later metamorphic event associated with subduction and obduction of the neyriz ophiolite and later lateral extrusion of hp lt metamorphic rocks along the inclined zagros accretionary prism

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

provenance of tin in the late bronze age balkans based on probabilistic and spatial analysis of sn isotopes abstract we report the largest published dataset to date of sn isotopic compositions of bronze age artifacts 338 along with 150 cassiterite samples 75 new from six potential tin ore sources from which the tin in these artifacts were thought to have likely originated the artifacts are from a broad area central europe through the central balkans and the six tin sources are cornwall three sites in the erzgebirge and two sites in serbia a clustering analysis on mean site level isotopic values of 124sn identifies regional variation that can be attributed to the use of different tin ore sources in different regions therefore geographically meaningful regions were identified to group the bronze age artifact assemblages and a probabilistic bayesian analysis was performed to determine the proportional contribution of each tin source to each regional assemblage artifacts enriched in heavy isotopes 124sn 0 7 that cluster in west central serbia are likely associated with the ores from mt cer in west serbia mixed artifact assemblages high and low 124sn in this region are attributed to the use of cassiterite from the two serbian sites mt cer and mt bukulja moderate composition artifacts that occur north of the middle danube in vojvodina transylvania and central europe are likely associated primarily with ores from the west pluton of the erzgebirge compositionally light bronzes 124sn

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

test of the frictional reactivation theory for faults and validity of fault slip analysis the notion that slip on faults is controlled by the balance between resolved shear stress and the magnitude of frictional resistance is examined in the light of the published orientations of ancient faults and slip lineations by compiling data from more than 1500 faults used in 228 stress analyses we observe that natural fault planes as well as lineations formed by fault slip display characteristic patterns of preferred orientation when rotated into the reference frame defined by the principal stress axes these patterns vary systematically according to the relative magnitudes of principal stresses determined by fault slip analysis furthermore these patterns are strikingly similar to those predicted by a frictional model for fault reactivation in which the potential for slip is equated to the ratio of the components of shear stress and normal stress on the fault plane our findings therefore make a compelling case for the concept of frictional slip tendency for the prediction of fault reactivation and lend support to the validity of fault slip methods for paleostress analysis

fabric attractors in general triclinic flow systems and their application to high strain shear zones a dynamical system approach high strain zones may deform by flow with a triclinic symmetry this paper describes triclinic flow in a reference frame where instantaneous stretching axes isa are fixed the operation of triclinic flow is described in two ways first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain in monoclinic flow at least one of the eigenvectors of the flow coincides with one of the isa and one or two of the eigenvectors act as attractors of foliation or lineation elements in triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues controlling the flow are imaginary imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20 from one of the isa strong deviation from monoclinic flow is therefore possible but this will not produce permanent foliations or lineations for triclinic flow that does produce permanent fabrics the angle between isa and the fabric is so small that it is unlikely that it can be recognised in nature a discussion of the potential application of such results within real shear zones is presented

strain partitioning in transpression zones abstract transprcssional strain acting upon structurally anisotropic rocks can be partitioned into separate deformational domains of pure shear and simple shear this contrasts with homogeneous transpression in which both the pure shear and the simple shear strain components are uniformly distributed across the zone of deformation structural weaknesses capable of partially or fully accommodating one component of deformation include lithological contacts rheological heterogeneities and faults or shear zones situated within the deformation zone or lying along its boundaries partitioning of transprcssional strain can occur when stress is applied oblique to pre existing structural weaknesses or can occur during later stages of progressive strain when the early deformation of isotropic rocks imparts sufficient anisotropy to allow subsequent strain to be partitioned partitioning of transpressional strain into domains lying parallel to the deformation zone boundaries can be distinguished from fault stepped transpression in which strain is partitioned along the length of a segmented fault zone mesofracture analysis of rocks affected by mid devonian deformation on both sides of the highland boundary fault zone hbfz in central scotland shows that strain was not homogeneous the mesofracture data suggest that regional north south compression orientated oblique to the pre existing ne sw trending hbfz was partitioned into separate deformational domains the hbfz accommodated most of the simple shear component whilst the rocks flanking the zone were deformed predominantly by pure shear a contemporary example is the san andreas fault in central california where analyses of neo tectonic stresses show that the direction of principal compression is perpendicular to the fault zone many examples of the partitioning of transpressional strain have also been recognised at destructive plate margins where the direction of plate motion is oblique to the edge of the over riding plate

intracrystalline deformation of garnet wollastonite and pectolite grains during development of a crenulation cleavage in the sheared skarn abstract this study focuses on a mylonitic skarn at the margins of a harzburgite of the neyriz mantle diapir iran the studied sample contained garnet porphyroclasts in a wollastonite and pectolite matrix the microstructures of porphyroclasts and matrix are analyzed using electron backscatter diffraction ebsd detailed analysis of garnet porphyroclast distortions and subgrain boundary trace analysis suggests that 110 110 dislocation control intracrystalline deformation of garnet grains wollastonite and pectolite crystallographic preferred orientations cpos are dominated by 100 parallel to foliation plane and 010 parallel to lineation however a dominance of low angle misorientation axes parallel to 010 precludes 010 dislocations from significant involvement in intracrystalline deformation schmid factor analysis also shows this slip system does not have high integrated schmid factor these observations suggest that oriented grain growth may be responsible for wollastonite and pectolite cpo development schmid factor analysis suggests 001 100 and 100 001 slip systems in the wollastonite and pectolite were involved in intracrystalline deformation and are linked kinematically to s 2 and reactivated s 1 planes

kinematics of rock flow in a crustal scale shear zone implication for the orogenic evolution of the southwestern hellenides combined shear sense criteria finite strain data and vorticity analyses were used to study the deformation path in a curved crustal scale shear zone phyllite quartzite series of the southwestern hellenides the results are combined with data on the structural evolution of a cover nappe pindos thrust belt to provide new insights into the orogenic evolution of this region ductile deformation within the phyllite quartzite series was associated with a top to the west southwest shearing and was partitioned into two structural domains a root zone and a frontal domain the root zone is characterized by vertical coaxial stretching high strain and upward movement of the material while the frontal domain comprises simple shear deformation at the base and pure shear at the top this pattern suggests superposition of pure shear on simple shear deformation and implies tectonic extrusion of the material from the root zone the initiation of brittle deformation in the pindos thrust belt was associated with westward translation above the sub horizontal pindos thrust later as the mountain range elevated normal faulting at high altitudes and migration of thrusting to the west occurred while east directed folding and thrusting in the belt started to the east according to the proposed model crustal thickening was taking place throughout the oligocene and early miocene including the subduction of the apulian beneath the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite series during the lower miocene vertical buoyancy forces led to the successive steepening of the shear zone and the simultaneous duplexing of its basement facilitating tectonic extrusion of the material from its root zone finally an indentation process caused vertical expulsion of the orogenic wedge and gravity collapse in the brittle crust

a mohr circle method for 3d strain measurement using the geometry of no finite longitudinal strain and the rxz strain ratio abstract this paper proposes a new method for 3d finite strain analysis this method utilizes a mohr circle construction combined with stereographic projection of the geometry of no finite longitudinal strain and with the strain ratio on the xz plane of the finite strain ellipsoid the method is described using numerical examples and then it is tested by applying it to the deformed deh vazir conglomerate in the southwestern part of the sanandaj sirjan hp lt metamorphic belt within the zagros orogenic belt in iran the results of this method compare well with previous finite strain measurements using strain ratios on three principal planes of finite strain calculation of finite strain from strain ratios on the xy and yz principal planes is advantageous when preparation of 3 perpendicular sections is difficult or impossible

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

structural evidence for superposition of transtension on transpression in the zagros collision zone main recent fault piranshahr area nw iran abstract the main recent fault of the zagros orogen is an active major dextral strike slip fault along the zagros collision zone generated by oblique continent continent collision of the arabian plate with iranian micro continent two different fault styles are observed along the piranshahr fault segment of the main recent fault in nw iran the first style is a sw dipping oblique reverse fault with dextral strike slip displacement and the second style consists of cross cutting ne dipping oblique normal fault dipping to the ne with the same dextral strike slip displacement a fault propagation anticline is generated sw of the oblique reverse fault an active pull apart basin has been produced to the ne of the piranshahr oblique normal fault and is associated with other sub parallel ne dipping normal faults cutting the reverse oblique fault another cross cutting set of ne sw trending normal faults are also exist in the pull apart area we conclude that the ne verging major dextral oblique reverse fault initiated as a sw verging thrust system due to dextral transpression tectonic of the zagros collision zone and later it has been overprinted by the ne dipping oblique normal fault producing dextral strike slip displacement reflecting progressive change of transpression into transtension in the collision zone the active piranshahr pull apart basin has been generated due to a releasing damage zone along the nw segment of the main recent fault in this area at an overlap of piranshahr oblique normal fault segment of the main recent fault and the serow fault the continuation of the main recent fault to the n

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

the pb isotope geochemistry of granitoids from the himalaya tibet collision zone implications for crustal evolution abstract pb isotopic data on 80 k feldspars from six individual granitoid belts of the himalaya tibet collision zone are reported the isotopic trends observed in the trans himalayan complex which outcrops along the indus zangpo suture zone are best explained by a mixture of mantle derived pb component s with crustal derived pb these confirm that the batholith was built upon sialic continental crust as a result of the northward subduction of mesozoic oceanic crust beneath southern tibet the pb isotopic compositions of k feldspars from the three granitoid belts located within the lhasa block to the north of the indus zangpo suture zone are all radiogenic and indistinguishable from those of k feldspars extracted from basement rocks no pristine mantle derived component was identified and the granitoids are interpreted as being wholly derived from the partial melting of the continental crust furthermore the isotopic compositions of the granitoids are remarkably similar over the entire lhasa block implying that they were equilibrated by fluid remobilization during granulite facies metamorphism in the lower crust to the south of the indus zangpo suture zone and within the indian shield the lead isotopic composition of k feldspars from two granitoid belts although significantly more radiogenic than those of the lhasa block are identical to that of the basement gneisses indicating also that the granitic melts are the products of the anatexis of the continental crust in both the lhasa block and the indian shield the generation of granitic melts occurred as a consequence of large scale intracontinental thrusting events that created crustal repetition and induced the development of thermal anomalies at depths due to the burial of meta sedimentary rocks rich in water and radioactive heat producing elements the lhasa block and the indian shield define two distinct pb isotopic provinces which have undergone complex episodes of u th pb fractionation and are largely composed of precambrian material furthermore the correspondence between distinct pb isotopic provinces and discrete continental segments might indicate that the blocks originated from different sectors of the gondwanian continent

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

sm nd constraints on the growth rate of continental crust abstract the time constants are calculated which rule the evolution of nd isotopes in a model earth composed of the continental crust a depleted upper mantle and a pristine lower mantle and in which the upper mantle is not constrained to grow or not to grow at the expense of the lower mantle the growth rate of the continental crust is calculated to be 1 8 0 7 km3 yr with 2 5 0 5 km3 yr of new crust addition from the mantle and 0 8 0 5 km3 yr of sediment entrainment at subduction zones the characteristic times for nd evolution in the depleted mantle and continental crust imply that the sm nd system evolves far from steady state

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

deformation path in high strain zones with reference to slip partitioning in transpressional plate boundary regions abstract the current status of the kinematics and strain geometry of high strain zone studies is briefly summarized a general high strain zone has a triclinic deformation path and monoclinic shear zones are special end member cases fabrics observed in natural shear zones and theoretical considerations based on continuum mechanics are compatible with this conclusion non steady deformation paths remain difficult to deal with and may ultimately rely on a realistic mechanical treatment of high strain zones which may be possible when our knowledge of the mechanical behavior of rocks under natural deformation conditions is improved an examination of the phenomenon of slip partitioning in transpressional plate boundary regions shows that the bulk deformation path in the forearc area trench parallel high strain zone is generally triclinic the alpine fault in the south island of new zealand provides an example of a currently active triclinic shear zone the southern knee lake shear zone of manitoba canada provides an archean example of a triclinic shear zone

strain pattern and vorticity analysis of deformed conglomerates in the heneshk area within the sanandaj sirjan metamorphic belt zagros mountains iran strain measurements have been carried out using the rf method on a jurassic deformed conglomerate in the sanandaj sirjan metamorphic belt zagros mountain of iran estimated finite strain ellipsoids range from general flattening to near plane strain flinn parameter k 0 6 0 9 with strain ratios in the x z plane with rxz 5 4 quantitative kinematic analyses were performed on the conglomerates using the rigid clast method estimated kinematic vorticity numbers wk varied between 0 43 and 0 63 implying a general shear flow 30 simple shear 42 and 58 pure shear 70 i e pure shear dominated non coaxial flow combining strain and vorticity data we estimated a horizontal shortening of 42 55 measured normal to the walls of the deformation zone we discuss this pure shear dominated deformation in terms of convergence between the afro arabian continent and the central iranian microcontinents

iridium to provenance ancient silver trace levels of iridium in ancient silver artefacts can provide information on the sources of silver bearing ores as well as the technologies used to extract silver a geographically and chronologically disparate legacy dataset comprised of near eastern objects from the sasanian and byzantine empires 1st millennium ad and coins circulating around the mediterranean in the mid 1st millennium bc shows that ag au ir log ratio plots can help identify silver derived from the same mining areas as well as broadly differentiating between the ore types exploited combining trace element and lead isotope analyses through the pb crustal age of the ore further delimits interpretations on the compositions and locations of silver ore sources furthermore it is shown that silver artefacts of near eastern origin have exceptionally high iridium levels suggesting a unique silver bearing ore source potentially in the taurus mountain range of southern anatolia the wide range of crustal ages identified for ancient greek coins and near eastern objects suggest that the addition of exogenous lead as a silver collector during smelting was common practice in the near east as early as 475bce the practice of mixing silver from different sources has also been identified by triangulating the log ratio subcomposition plots pb crustal ages of the ore from which the silver derived and absolute values of trace levels of gold and iridium in silver artefacts

why mohr circle analyses may underestimate the risk of fault reactivation in depleting reservoirs abstract fault reactivation may lead to induced seismicity damage to wells and loss of containment of potentially harmful and economically valuable fluids or gas in the subsurface for this reason fault reactivation is assessed in hydrocarbon development projects in particular when injecting water gas or steam but also when disposing of contaminated water or co2 in depleted oil or gas reservoirs in this paper we compare the results obtained by a mohr circle evaluation and two dimensional finite element fe analysis that are commonly used to assess the likelihood of fault reactivation it is found that mohr circle evaluations provide a non conservative estimate of the allowable reservoir pressure in cases where the reservoir is offset by a fault in practice this may comprise virtually all imageable faults as the limited seismic resolution does not allow interpretation of faults with no or small throws furthermore we demonstrate that the maximum vertical element size for capturing the onset of fault slip with sufficient accuracy is about 2 of the reservoir thickness finite element models with larger vertical element size increasingly over estimate the depletion pressure required to cause fault reactivation or won t predict fault reactivation at all thereby under estimating the hazard associated with fault reactivation this paper concludes with recommendations for evaluating onset of fault slip using mohr circles and two and three dimensional finite element analysis

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

kinematics of rock flow and fabric development associated with shear deformation within the zagros transpression zone iran this paper presents quantitative data on the finite strain quartz crystal fabric geometry of flow and deformation temperatures in deformed quartzite samples to characterize the ductile deformation along the thrust sheets constituting the sanandaj sirjan metamorphic belt within the zagros mountains of iran the results of this study emphasize the heterogeneous nature of deformation in this belt showing a spatial variation in strain magnitude and in degree of non coaxiality a dominant top to the se sense of shear is indicated by the asymmetry of microstructures and quartz c axis fabrics quartz c axis opening angles suggest deformation temperatures range between 435 50 c and 510 50 c which yield greenschist to amphibolite facies conditions during the ductile deformation mean kinematic vorticity number w m measured in the quartzite samples ranges between 0 6 and 0 9 with an average of 0 76 which indicates that extrusion of the metamorphic rocks of the region was facilitated by a significant component of pure shear strain traced towards the basal thrust of the zagros thrust system from northeast to southwest the quartz grain fabrics change from asymmetric cross girdle fabrics in the internal part of the deformation zone to an asymmetric single girdle fabric at distances close to the basal thrust this variation may depend on the structural depth and on the geometry of the ductile deformation zone the observed increase in strain and vorticity within the study area is comparable with patterns recorded within metamorphic rock extrusions within other orogens in the world

physical experiments of vertical transpression with localized nonvertical extrusion abstract previously proposed models of vertical walled transpression implicitly assume that material extrudes upwards during deformation this assumption is not necessarily valid at all scales given that a in areas of diverse lithologies local zones of relatively rigid materials may cause extruding material to deflect around those zones and b ductile strain often forms anastomosing geometries of shear zones therefore it is possible that a local extension direction in otherwise classic transpression may be nonvertical for rocks deforming at depth using an analogue experiment we have modeled a transpression zone with localized nonvertical extrusion this extrusion is accomplished by the addition of a side leak that allows sideways extrusion in addition to vertical extrusion the net extension direction depends on the material s position within the deforming zone resulting in a significant range of lineation orientations with deformation the strain patterns produced by transpression with localized nonvertical extrusion may explain the wide array of lineation orientations found in some natural ductile transpression zones

pb isotopic geochemistry of granitoids and gneisses from the late archean pontiac and abitibi subprovinces of canada abstract initial pb isotopic compositions were determined on k feldspars for thirty granitoid plutons and gneiss complexes in the abitibi and the pontiac subprovinces of canada the gneisses cover a wide spectrum of initial pb isotopic compositions and undoubtedly demonstrate that very radiogenic reservoirs were present in the pontiac subprovince and along its southern boundary with the grenville province in the late archean the gra nitoid rocks also define a large spectrum covering 0 3 unit of the 207 pb 204 pb ratio ranging from compositions typical of mafic mantle melts to those of sedimentary banded iron formations the older intrusives emplaced between 2 72 and 2 68 ga were principally derived from juvenile mantle sources they may have been formed in a volcanic arc environment but they still frequently record the signature of crustal precursors which may have been represented by subducted sediments or by older assimilated crustal components a sharp change in the provenance of the granitoid magmas occurred close to 2 68 ga an age that also corresponds to an episode of alkaline activity and fault related sedimentation for the following 40 ma magmatism chiefly resulted from melting of crustal precursors in a thickened crustal lithosphere the pb isotopic compositions of these crustal melts demonstrate that the basement of the pontiac subprovince contains a major component of rocks older than 3 0 ga in comparison the abitibi subprovince may not contain basement components older than 2 9 ga or else they represent a negligible fraction of the crust this supports the concept that the abitibi and pontiac subprovinces formed as discrete crustal segments tectonically juxtaposed finally the grenville front tectonic zone was metamorphosed and partially melted in the late archean and is probably the deep crustal equivalent of the pontiac subprovince

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

tectonic evolution of the hinterland of the zagros orogen revealed from the deformation of the golpaygan metamorphic complex iran in the southwestern part of the central iran zone the golpaygan metamorphic complex gmc was evolved during the zagros orogeny this complex is composed of different metamorphic rocks including schist marble slate gneiss and amphibolite the metamorphic complex is overlain by a cover sequence including permian carbonates jurassic clastic rocks cretaceous carbonates and eocene clastic rocks the internal structure of the gmc is characterized by four deformational stages the first stage d1 developed contemporaneously with the prograde regional metamorphism and resulted in formation of the first generation folds and prevailing axial plane foliation the second stage of deformation d2 was accompanied by deformation partitioning and formation of contractional shear zones these structures were overprinted by different scale folds of the third stage d3 the fourth stage of deformation d4 is characterized by generation of the extensional shear zones which gradually transformed into normal faults d1 and accompanied metamorphism may have resulted from steep subduction of the neotethys ocean beneath the active margin of the central iran zone during jurassic times d2 d3 structures and retrograde metamorphism may have been formed by a regional shortening and transpression deformation event which resulted in exposure of the metamorphic rocks in shallower levels during cretaceous flat slab subduction this condition lasted until paleocene time when the slab roll back caused extension and thinning of the overriding central iran plate the subsequent decompression and regional extension resulted in intrusion of magmatic rocks and generation of d4 which formed the gmc and related magmatism in paleocene eocene time

strain partitioning in ductile shear zones an example from a lower pennine nappe of switzerland abstract the rocks of the maggia nappe a lower pennine nappe of the swiss alps were deformed in at least three phases during alpine orogeny hercynian granites in the core of the nappe developed ductile shear zones during the early phases of deformation but between shear zones they remained almost undeformed both heterogeneous simple shear and heterogeneous volume change played an important role in the formation of the ductile shear zones partitioning of different strain components indicates a volume loss of nearly 80 90 towards the centres of some of the shear zones such a large amount of volume loss is also corroborated by strain analysis of deformed xenoliths in other shear zones of the same region a comparative study of theoretical strain paths and the natural results indicates constant shear strain rate but changing dilation rate during deformation

poroelastic stressing and induced seismicity near the lacq gas field southwestern france o hundreds of shallow small to moderate earthquakes have occurred near the lacq deep gas field in southwestern france since 1969 these earthquakes are clearly separated from tectonic seismicity occurring in the pyrenees 25 km to the southwest the induced seismicity began when the reservoir pressure had declined by 30 mpa repeated levehng over the field shows localized subsidence reaching a maximum of 60 mm in 1989 segall 1989 suggested that poroelastic stressing associated with volumetric contraction of the reservoir rocks is responsible for induced seismicity associated with fluid extraction to test this model we compare the observed subsidence and hypocentral distributions with the predicted displacement and stress fields we find that the relationship between average reservoir pressure drop and subsidence is remarkably linear lending support to the linear poroelastic model displacements and stresses are computed based on a priori knowledge of the reservoir geometry materim properties and reservoir pressure changes the computed vertical displacements are found to be in excellent agreement with the subsidence observed from leveling stress perturbations accompanying gas extraction computed using the same parameters are found to be 0 2 mpa or less changes in coulomb failure stress are computed assuming that shp occurs on optimally oriented planes the predicted failure zones correlate very well with the spatial distribution of earthquakes if the perturbing stresses are small in comparison to the ambient regional deviatoric stresses and if the minimum regional compresslye stress axis is vertical accurate determination of focal mechanisms of the induced events would allow a more rigorous test of the poroelastic model and could lead to important inferences about the crustal stress state

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

constraints on deformation path from finite strain gradients we present a methodology for analyzing finite strain gradients in high strain zones in order to place constraints on the zone s possible deformation path to accomplish this the high strain zone is divided into several sub zones within each of which finite strain is described by a single ellipsoid based on knowledge of the spatial and temporal evolution of deformation strain observed in less deformed sub zones is then mathematically removed from more deformed sub zones to calculate incremental finite strains the mean kinematic vorticity number of each of these increments must be constant if deformation was steady state we use the methodology to analyze two natural examples of high strain zones at different scales both natural examples have non steady state likely deformation paths which may be a common characteristic of high strain zones although results of the methodology are not unique identification of likely paths considerably narrows the range of possible deformation paths consequently useful kinematic information can be extracted from finite strain data even in instances where the detailed spatial and temporal evolution of a high strain zone cannot be determined conclusively

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

kestel an early bronze age source of tin ore in the taurus mountains turkey an ancient mine located at kestel on the outskirts of nigde in the taurus mountains of south central turkey has been dated by radiocarbon and pottery type to the third millennium b c archeological soundings in the mine located cassiterite tin oxide in the detritus of ancient mining activity cassiterite is also present in veins and as placer deposits in streams nearby since tin is used with copper in order to form bronze but is thinly distributed in the earth s crust the presence of tin ore at kestel offers a source for the much sought after tin of the bronze age the discovery of an ancient mine containing cassiterite sheds light on this question but also greatly complicates the accepted picture of regional economic patterns in the highland resource areas of anatolia and of interregional metal exchange in the formative periods of urbanization and metal use in the eastern mediterranean

on the physics based processes behind production induced seismicity in natural gas fields author s zbinden d rinaldi ap urpi l wiemer s abstract 2017 american geophysical union all rights reserved induced seismicity due to natural gas production is observed at different sites worldwide common understanding states that the pressure drop caused by gas production leads to compaction which affects the stress field in the reservoir and the surrounding rock formations and hence reactivates preexisting faults and induces earthquakes in this study we show that the multiphase fluid flow involved in natural gas extraction activities should be included we use a fully coupled fluid flow and geomechanics simulator which accounts for stress dependent permeability and linear poroelasticity to better determine the conditions leading to fault reactivation in our model setup gas is produced from a porous reservoir divided into two compartments that are offset by a normal fault results show that fluid flow plays a major role in pore pressure and stress evolution within the fault fault strength is significantly reduced due to fluid flow into the fault zone from the neighboring reservoir compartment and other formations we also analyze scenarios for minimizing seismicity after a period of production such as i well shut in and ii gas reinjection in the case of well shut in a highly stressed fault zone can still be reactivated several decades after production has ceased although on average the shut in results in a reduction in seismicity in the case of gas reinjection fault reactivation can be avoided if gas is injected directly into the compartment under depletion however gas reinjection into a neighboring compartment does not stop the fault from being reactivated

inclined transpression in the neka valley eastern alborz iran three major nappes in the neka valley in the eastern alborz mountains of iran allow the cimmerian to present convergence following the oblique collision between iran and the southern margin of eurasia this work reports the identification of an inclined transpression zone recognized by field investigations and strain analyses of the geometries of formations and detailed mesoscopic structural analyses of multiple faults folds and a cleavage the main structures encountered include refolded recumbent asymmetric fold nappes highly curved fold hinges in a transpression zone that dips 37 to the nw between boundaries thrusts striking from n050 to n060 the angle the angle between the zone boundary and direction of horizontal far field shortening is about 80 the north west and south east boundaries of this zone coincide with the haji abad thrust and the shah kuh thrust respectively fold axes generally trend ne sw and step to both right and left as a result of strike slip components of fault displacements strain analyses using fry s method on macroscopic ooids and fusulina deformed into oblate ellipsoids indicate that the natural strain varies between 2 1 and 3 14 the estimated angle between the maximum instantaneous strain axis isamax and the transpression zone boundary is between 6 and 20 the estimated oblique convergence angle therefore ranges between 31 and 43 the average kinematic vorticity number wk is 0 6 in a zone of sinistral pure shear dominated inclined triclinic transpression these results support the applicability of kinematic models of triclinic transpression to natural brittle ductile shear zones

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

strain in ductile shear zones in the caledonides of northern sweden a three dimensional puzzle small scale ductile shear zones are well developed in amphibolites of caledonian nappes of the swedish lapland strain in the shear zones is recorded by the shapes of originally sub equant aggregates of plagioclase feldspar classical strain analysis on two dimensional xz profiles across the shear zones leads to results that indicate large volume losses associated with the shear strain large volume losses are however incompatible with geochemical analysis which shows little chemical variation across the shear zones by including data from xy and yz sections information on the three dimensional state of strain can be obtained these data indicate that deformation is not confined to a two dimensional plane particle extension within the shear zone parallel to the shear plane and perpendicular to the shear direction has also occurred the state of strain and strain path in the shear zone can be modeled in a general way by combining stretches in x y and z with simple shearing and volume loss end member models correspond to plane strain with volume loss kx ky 1 kz 1 transpression kx 1 ky 1 kz and pure shear kx 1 kz ky 1 these models produce identical strain ratios and orientations on the xz section but differ in stretch in y and in area of the strain ellipse on the xz section extension in y or x allows for reconciliation of the geometrical and geochemical data for part of an individual shear zone but poses a problem of strain compatibility at the edges and terminations of the shear zones the shear zones show a complex anastomosing pattern in three dimensions and their connectivity provides a way in which strain compatibility is maintained

nucleation and arrest of dynamic rupture induced by reservoir depletion seismic events induced by the depletion of hydrocarbon reservoirs can cause damage to housing and cause societal and economic unrest however the factors controlling the nucleation and size of production induced seismic events are not well understood here we used geomechanical modeling of production induced stresses and dynamic rupture modeling to assess the conditions controlling down dip rupture size a generic model of offset depleting reservoir compartments separated by a fault was modeled in 2 d using the finite element package diana fea linear slip weakening was used to control fault friction behavior fault reactivation was computed in a quasi static analysis simulating stresses during reservoir depletion followed by a fully dynamic analysis simulating seismic rupture the sensitivity of reactivation and rupture size to in situ stress dynamic friction critical slip distance and reservoir offset was evaluated after reactivation a critical fault length was required to slip before seismic instability could occur in a subsequent fully dynamic analysis the propagation and arrest of dynamic rupture was simulated rupture remained mostly confined to the reservoir interval but could also propagate into the overburden and underburden or sometimes transition into a run away rupture propagation outside the reservoir interval was promoted by a critical in situ stress a large stress drop a small fracture energy and no or little reservoir offset with increasing offset up to the reservoir thickness reactivation was promoted but dynamic rupture size decreased 2019 the authors

structural pattern and emplacement mechanism of the neka valley nappe complex eastern alborz iran the neka valley nappe complex is exposed in the south of gorgan county in the eastern alborz fold and thrust belt we use the results of a regional survey of the structural data and their patterns to interpret the mechanisms that emplaced the unmetamorphosed nappes in the foreland fold and thrust belt of the alborz mountains most of the strain magnitudes are low in the study area but increase slightly towards what are probably their proximal ends strain ellipsoid is dominantly oblate with xy aligned along and across the belt or the nappe complex the average kinematic vorticity number w k 0 6 which indicates most of the strain partitioning resulted in a general shear most of flinn s k values and the stretch along the shear plane values are lower than 1 structural indicators such as orthogonal extensional joints pinch and swell structures anastomosing cleavages and listric normal and growth faults developed by push from the rear large scale thrust complexes with opposed dips such as triangle zones as well as k and values 1 are compatible with the shear flow diverging distally and streamlines expected of the rear compression emplacement mechanism together with a later minor brittle deformation these major ductile strains appears to provide a general model suitable for the emplacement of the nappes studied in a thin skinned fold and thrust belt where the sedimentary cover strata shortened and imbricated in the upper crust

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

unscrambling the lead model ages abstract a linear relation is derived for the secular evolution of 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios that permits tests to be made for open system evolution on each system independently application of the method to conformable ore bodies of various geological age indicates that the available data do not demand an open system evolution for the last 3 8 b y 238 u 204 pb and 232 th 204 pb of 9 66 0 15 and 37 65 1 14 respectively fit best the data for this time interval a single stage evolution since 4 5 b y is unlikely however and the major events of continent formation postdate the earth accretion by at least 400 m y the larger scatter of 207 pb 204 pb data about the evolution line relative to the other isotopic ratios is also interpreted as resulting from a series of continental differentiation events taking place at 3 85 0 15 b y

tectono metamorphic evolution of the neyriz metamorphic complex quri kor e sefid area sanandaj sirjan zone sw iran abstract the neyriz region includes outcrops of metamorphic rocks that are thrust over the neotethyan ophiolites these rocks are affected by a major deformational event the result of which includes a shearing polyphase foliation present in gneissic core domes overprinted by a crenulation cleavage these fundamental structures developed contemporaneously with a medium pressure metamorphism which is characterized by the syn kinematic crystallization of kyanite and the beginning of anatexis followed by the development of retrometamorphic mineral parageneses the major deformation phase in the area occurred during the early cimmerian orogeny in the late triassic following the orogeny the gneiss domes started to rise into the upper levels of the crust from the geodynamic point of view after the mid permian the studied area was situated at southern passive margin of the iranian plate the central iranian microcontinent at that time was separated by the neotethys ocean from the gondwanian supercontinent after the late triassic the region became an active margin associated with an accretionary prism the margin was finally involved in an orogenic wedge after the closure of the neotethyan oceanic basin in the late mesozoic closure of the basin resulted in a major thrusting of the metamorphic rocks of the southern iranian margin over the neotethyan ophiolites

general shear deformation in the pinaleno mountains metamorphic core complex arizona abstract granitic mylonites from the pinaleno mountains metamorphic core complex in southeastern arizona record general shear deformation the mean kinematic vorticity number w m was estimated using 1 the strain ratio r s and the angle between the long axis of the strain ellipsoid with respect to the high strain zone boundary and 2 the porphyroclast hyperbolic distribution method w m for protomylonites and mylonites ranged from 0 6 to 0 9 ultramylonites record lower w m values 0 1 0 3 suggesting that the incremental vorticity changed during deformation three dimensional strain analysis indicates that deformation in protomylonites and mylonites approximates plane strain and has a monoclinic symmetry the vorticity path followed by rocks tectonically exhumed in the footwall of major extensional fault systems may evolve from a significant pure shear component early in the deformation towards simple shear as overburden load decreases during uplift

provenance and recycling of ancient silver a comment on iridium to provenance ancient silver by jonathan r wood michael f charlton mercedes murillo barroso marcos martinon torres j archaeol sci 81 1 12 it is argued that it is unlikely that iridium can be used as tracer for the provenance of ancient silver for geochemical reasons instead it is suggested that the observed low but measurable iridium concentrations may be due to silver produced from argentiferous gold by cementation it is furthermore argued that the calculation of geological model ages from lead isotope ratios does not provide any additional information compared with the use of conventional three isotope diagrams

mechanics of seismic instabilities induced by the recovery of hydrocarbons we review earthquake distributions associated with hydrocarbon fields in the context of pore pressure diffusion models poroelastic stress transfer and isostasy theory these three mechanisms trigger or induce seismic instabilities at both local scale d 5 km and at regional scale d 20 km the modeled changes in stress are small 1 mpa whatever the tectonic setting each mechanism corresponds to different production processes 1 local hydraulic fracturing due to fluid injection induces seismic slip on cracks ml 3 within the injected reservoir through decreasing the effective stress 2 pure fluid withdrawal causes pore pressure to decrease within the reservoir it triggers adjustments of the geological structure to perturbations related to the reservoir response to depletion poroelastic mechanisms transfer this stress change from the reservoir to the surrounding levels whereml 5 seismic instabilities occur either above or below the reservoir 3 massive hydrocarbon recovery induces crustal readjustments due to the removal of load from the upper crust it can induce larger earthquakes ml 6 at greater distance from the hydrocarbon fields than the two other mechanisms

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

3d evolution of fold and thrust belts formed by oblique convergence abstract this paper presents the results of a series of scaled analogue models designed to simulate thrust belt development formed by orthogonal and oblique convergence the models were constructed to produce doubly vergent orogenic wedges with a pro wedge and a retro wedge separated by an uplifted orogenic core models were constructed from homogeneous layered sandpacks in a 3 m 1 3 m deformation rig the progressive evolution of the models was recorded using digital photography and the photographs were animated for analysis the experiments investigated convergence obliquities from orthogonal 90 to as low as 15 obliquity orthogonal models produced long linear critically tapered pro wedge fold and thrust belts parallel to the convergence margin together with a narrow uplifted core and a steep retro wedge thrust system the taper angle of the pro wedge was typically 11 12 whereas the retro wedge maintained a steeper taper of 38 42 models where the convergence vector was oblique at angles of 60 and 45 to the margin produced doubly vergent thrust wedges with thrust faults trending parallel to the margin there was little evidence of linked penetrative strike slip faulting but en echelon riedel like shear systems developed in the 45 oblique model subordinate oblique slip motion was observed on some thrust faults in contrast for 30 and 15 oblique convergence models strong deformation partitioning developed with steeply sloping pro wedges that did not have critical tapers through going linked strike slip faulting was developed that cut the uplifted axial zones of these models analysis of the models by animation of the digital photographs shows how the thrust systems initiated and propagated in particular it is clear that at any one time several thrusts were moving simultaneously serial cross sections through the moderately oblique convergence models 60 45 are almost indistinguishable from the orthogonal model cross sections the results of orthogonal convergence experiments compare well to the map patterns of faults and folds in the salt range pakistan 60 and 45 oblique convergence models compare well to the zagros where some strain partitioning on strike slip faults occurs the highly oblique models show very strong strain partitioning with penetrative margin parallel strike slip faulting similar to that found in ne venezuela

different slip systems controlling crystallographic preferred orientation and intracrystalline deformation of amphibole in mylonites from the neyriz mantle diapir iran abstract a deformed layered gabbro and a mylonitic gabbro sample from the marginal shear zone of the neyriz mantle diapir in iran were analyzed using electron backscatter diffraction ebsd both samples have the common amphibole crystallographic preferred orientation cpo in which 100 lies perpendicular to foliation and parallel to lineation amphibole grains in the layered gabbro sample have little internal deformation whereas in the mylonitic gabbro sample the amphibole grains are strongly distorted and contain low angle grain boundaries there is a subtle change in cpo as a function of grain size in the mylonitic gabbro coarse grains porphyroclasts have a 100 cpo oriented with the main foliation reference frame whilst fine grains have a 100 cpo oriented with the c shear bands detailed analysis of porphyroclast distortions and subgrain boundary trace analysis suggests that hard slip systems most particularly 110 control intracrystalline deformation schmid factor analysis suggest that these slip systems are not involved in foliation formation but are linked kinematically to c shear bands it is unlikely that the slip systems that control intracrystalline deformation are important in cpo formation we interpret that subgrain rotation recrystallization lead to grain size reduction and the elongate recrystallized grains were rotated towards the c shear bands by grain boundary sliding this rigid body rotation possibly in combination with easy slip on 100 are considered the main cause of cpo formation amphibole zonation patterns in the layered gabbro sample suggest that oriented growth of amphibole may have contributed to cpo

vorticity analysis in the zagros orogen shiraz area iran quantitative vorticity analyses in orogenic belts are essential for studying the kinematics of deformation and can be performed using a range of methods the combination of microstructural analysis for vorticity with other methods creates a more rigorous analysis in order to determine the degree of non coaxiality and spatial pattern of vorticity during deformation in the zagros orogenic belt a study area containing the boundary of the zagros folded belt and the zagros fold and thrust belt is selected the study area is situated in the shiraz region of e zagros in iran the kinematic vorticity analysis is carried out using 4 methods based on 1 the degree of asymmetry of the calcite c axis fabric 2 the assumption that the orientation of the long axes of calcite within an oblique stylolite foliation delineates the direction of the instantaneous stretching axis 3 the assumption that the tension gash tips determine the direction of the instantaneous stretching axis and 4 stylolite teeth determine the direction of the instantaneous stretching axis c axis data from calcite give a kinematic vorticity number between 0 68 and 0 83 and the orientation of the long axes of calcite grains yields a range between 0 5 and 0 84 stylolites provide a kinematic vorticity number between 0 5 and 0 79 and tension gashes provide a kinematic vorticity number between 0 56 and 0 81 this range of vorticity numbers confirms the contributions of both simple 33 59 and pure shear 41 67 twining of calcite also reveals that the last stage of deformation occurred at a temperature of 170 200 c spatial analysis reveals an increase in the simple shear component from the sw of the zagros folded belt to the ne of the zagros fold and thrust belt

importance of differentiating ductile slickenside striations from stretching lineations and variation of shear direction across a high strain zone shear direction is an important parameter in the kinematic interpretation of high strain zones recent developments in the study of high strain zones show that there is no simple relationship between the orientation of stretching lineations and the shear direction and it is difficult to use the former to determine the latter in contrast striations on c surfaces a product of ductile deformation form parallel to the shear direction it is therefore important for the kinematic interpretation of high strain zones to differentiate such striations from stretching lineations ductile striations are much more common in natural high strain zones than reported in the literature we discuss how to differentiate the two types of lineations and describe a natural high strain zone example from the superior craton of canada the striation data show that the shear direction of the high strain zone varies from subhorizontal to moderately plunging across the strike of the zone we conclude that well developed ridgein groove type striations are a reliable indicator of the shear direction we also discuss situations where the orientation of stretching lineations can potentially be used as an indicator of shear direction 2007 elsevier ltd all rights reserved

testing models for obliquely plunging lineations in transpression a natural example and theoretical discussion theory predicts that stretching lineations in an ideal vertical transpressional zone should be either vertical or horizontal many field descriptions of transpressional zones however indicate a range of lineation orientations between these extremes several theoretical models have been developed to explain such departures from expected lineation orientation and we discuss these in the context of a field example from the archean superior province in the north american craton existing models are insufficient to explain obliquely plunging lineations in this example because 1 obliquely plunging lineations cannot be accounted for by shear zone boundary effects imposed by a no slip condition 2 foliations and lineations vary independently 3 the vorticity normal section is subhorizontal limiting possibilities for inclined simple shear 4 high vorticity is needed for finite strains and lineations to match previously proposed triclinic models but vorticity is relatively low and 5 juxtaposed east and west plunging lineations are unlikely in the previously proposed triclinic models because existing theoretical models are not applicable to our field example we contemplate a new model to explain obliquely plunging lineations within quasi homogeneous transpression

deformation path partitioning within the transpressional white mountain shear zone california and nevada most numerical simulations of transpression zones predict a change in finite stretching direction from subhorizontal to subvertical for simple shear dominated zones we provide a detailed description of a dextral transpression zone the white mountain shear zone wmsz with a range of lineation orientations and compare these natural data to numerical models the wmsz is characterized by steeply dipping foliations with dominant shallowly plunging lineations and coeval subordinate domains of steeply plunging lineations within shallowly lineated domains foliation geometry shear sense indicators and quartz c axis fabrics indicate a large component of simple shear while microstructural and quartz c axis fabric data from steeply lineated domains indicate a large component of pure shear geometric relationships between foliations and lineations and quartz c axis fabrics demonstrate that lineation orientation has remained constant during much of the deformation history comparison of numerical models with the data collected from wmsz shows that the shear zone geometry and the observed strain path partitioning do not match any of these models we propose a conceptual kinematic model for the wmsz involving stable segregated coeval kinematic domains of simple shear dominated fabrics and pure shear dominated fabrics that accommodate the transcurrent and contractional components of deformation respectively

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

slip partitioning and inclined dextral transpression along the zagros thrust system iran abstract flexural duplex structures and shear zones are well developed in the heneshk area in southwestern iran the zagros thrust system in this area consists of eight sheets of nw striking ne dipping dextral strike slip duplexes that are linked with imbricate fans and oblique slip thrusts the zagros thrust system is a portion of the internal zone of the zagros orogenic belt this internal zone is characterized by penetrative plastic deformation and metamorphism based on the kinematic vorticity number w k 0 73 0 02 calculated from quartz porphyroclasts of the goshti shear zones along the zagros thrust system the estimated angle between the maximum instantaneous strain axis isa and the transpressional zone boundary is 33 the estimated angle of the plate convergence or the flow apophysis of the displacement field is 25 the presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence the mean estimated finite deformation w m value indicates relative contributions of 47 pure shear and 53 simple shear for the deformation which involved both strike slip and oblique slip displacements in this inclined transpression about 40 strike slip partitioning was required to accommodate the finite strain and re orientation of instantaneous strain

strain and possible volume loss in a high grade ductile shear zone small scale ductile shear zones in high grade metagabbros from the caledonides of northern sweden provide a good opportunity for examining the development of fabric and strain in rocks undergoing progressive non coaxial deformation the rocks contain strain markers in the form of aggregates of plagioclase feldspar a selected shear zone is analyzed assuming monoclinic symmetry which requires for the zone as a whole variable simple shear variable volume change or variable simple shear and volume change plus a homogeneous deformation both size of the feldspar aggregates and aspect ratio of the aggregates plotted against orientation indicate significant volume decrease in excess of 50 and perhaps as much as 80 towards the centers of the zones the data are broadly consistent with a deformation path involving constant shear strain across the zone followed by variable volume change or by a path of progressive loss of volume with increasing shear strain followed by a homogeneous strain they are not consistent with a single path involving rates of shear strain and volume loss that are in constant proportions there is little difference in chemical composition between the shear zone and the surrounding rock an analysis of the concentrations of elements in the shear zone and wall rock suggests that volume changes were slight 15 the discrepancy between the values of volume change estimated from strain analysis and geochemical analysis may be resolved either by geochemical equilibration being attained after deformation or by a departure from the geometric constraints of the monoclinic band model for shear zones modification of marker particle size and shape during dynamic recrystallization may also partly account for the apparent volume loss