kinematics of lava flows based on fold analysis a kinematic analysis of the mingling folding structures occurring in a lava flow from porri volcano southern tyrrhenian sea has been performed in order to estimate the flow kinematic parameters folds have resulted from the deformation of enclaves and banding structures and consist of a single layer of a crystal rich andesitic magma hosted in a less competent basaltic magma results of the analysis indicate that the flow kinematic vorticity increases with the distance from the vent whereas the ratio between pure shear and simple shear strain decreases following a power law quantitative estimates of the kinematic parameters provide an opportunity to examine the deformation behaviour of the lava flow near the vent the lava is a non ideal shear flow away from the vent the lava is an ideal shear flow gravity driven mechanisms control the relative contribution of pure and simple shear to the bulk deformation

jurassic penetrative deformation and cenozoic uplift in the central high atlas morocco a tectonic model structural and orogenic inversions the central high atlas is characterized by a relatively mild deformation with a local development of a more or less penetrative cleavage in the axial part of the belt locally this cleavage and the plutonic bodies which outcrop in the core of most of the north east trending anticlines ridges with intrusions are overlain by a disconformable sequence that comprises red clastic deposits which are capped by cenomano turonian limestones the age of these red deposits are bracketted between bathonian to mid cretaceous therefore the spatial relationship of the cleavage with mafic intrusions in the axial part of the central high atlas suggests that it developed contemporaneously with the emplacement of magmas probably during mid jurassic times during this period the structural inversion occurred from a transtensional regime to a transpressive regime there are few indications that an important shortening persisted within the axial part of the central high atlas after the end of the jurassic along the northern and the southern borders of the belt however cretaceous and cenozoic strata were deposited their sedimentary facies bear witness of successive stages of the atlas evolution especially the rapidly coarsening up of the clastic deposits since the oligocene in these marginal basins indicates the onset of the rising up of the belt i e the orogenic inversion

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

strain histories from the eastern central range of taiwan a record of advection through a collisional orogen abstract in the eastern central range of taiwan there is a regional variation in the orientation of maximum finite stretch across the slate belt with down dip maximum stretch found in the western central range and along strike maximum stretch in the eastern central range incremental strain histories from syntectonic fibers in pyrite pressure shadows indicate a progressive change in extension direction from down dip to along strike during deformation there is a corresponding temporal variation in stretching direction shown in samples from the eastern edge of the central range a pattern that mimics the regional west to east spatial variation these observed temporal and spatial strain distributions are used to evaluate the kinematics associated with slaty cleavage development during advection through the taiwan orogenic system the subduction zone beneath the island of taiwan is influenced by two types of obliquity that have the potential to generate the observed along strike stretching first the plate motion vector of the philippine sea plate relative to the eurasian plate is slightly oblique to the regional strike of the mountain range which could result in partitioning of strike slip shearing into the interior of the collision second the north south luzon volcanic arc on the philippine sea plate is obliquely oriented relative to the northeast southwest edge of the eurasian continental margin which could result in lateral extrusion of the ductile core of the range incremental strain histories in cleavage parallel samples represent a time for space equivalence where the stretching direction is fixed relative to the position within the mountain belt architecture e g the topographic divide and temporal variations in the eastern central range reflect lateral advection through the strain field in response to accretionary and erosional fluxes incremental strain histories in cleavage perpendicular samples show both clockwise and counter clockwise rotation of strain indicating the possibility of bulk coaxial strain and lateral extrusion

correlation between magnetic fabrics strain and biotite microstructure with increasing mylonitisation in the pretectonic wyangala granite australia abstract the wyangala granite is a foliated porphyritic silurian granite from the palaeozoic circum pacific type eastern lachlan orogen elo of australia it is a paramagnetic ilmenite bearing s marginal i type two mica to mainly biotite granite with different biotite contents and local chlorite alteration very highly strained quartz epidote bands are present in this contribution anisotropy of magnetic susceptibility ams is compared with independently measured intensity and 3d style of strain biotite microstructure and degree of mylonitisation for low strain granites with weak s foliations through medium strain protomylonitic granites with moderate s and c foliations to a high strain altered granite with a strong single foliation the samples are further analysed for possible contributions from sample heterogeneity magmatic flow and sub magmatic deformation a good correlation p ams 1 02 0 04 ln p e qtz is obtained between site average degree of ams p ams in the granite and degree of finite strain anisotropy p e qtz from aspect ratios of quartz aggregates in s foliations in hand specimen and outcrop p ams 1 03 1 14 p e qtz 1 4 19 the magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the march model the observed quartz strains however exceed the ams march strains and are near neutral plano linear character the geological factors that may have contributed to these differences include intra and inter crystalline deformation of biotite and bimodality in s and c magmatic fabric is not clearly evident in either the ams or the biotite data new data for synkinematic oligoclase low titanium biotite and low sodium k feldspar show that conditions during deformation were approximately transitional greenschist amphibolite facies i e well below solidus this agrees with published age data that put the granite emplacement in an extensional back arc setting in already deformed country rocks and before later convergent regional deformation in middle devonian tabberabberan event to early carboniferous kanimblan event time

reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

5 9 mw 18th june 2010 earthquake and fault segment linkage at andaman a study based on macroseismic survey gps geodesy and coulomb stress changes abstract 18th june 2010 5 9 mw earthquake at north andaman triggered along nw se pre existing fault with reverse fault mechanism macroseismic survey and gps geodesy reveal maximum damages following ne sw trend due to normal fault mechanism coulomb stress modeling for post and inter seismic earthquakes after the 2004 mega earthquake show different stages of fault segment linkage at north andaman the present earthquake has been explained as co shock due to asiesmic soft linkage of fault propagation

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

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

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

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

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

geometry and kinematics of the mosha fault south central alborz range iran an example of basement involved thrusting abstract field investigation of the western part of the mosha fault in several structural sections in the south central alborz range showed that the fault has a high angle of dip to the north and emplaces precambrian to cenozoic rocks over the eocene karaj formation study of the kinematics of the mosha fault in this area based on s c fabric and microstructures demonstrates that it is a deep seated semi ductile thrust strain analysis on rock samples from different sections across the mosha fault shows a flattening pattern of deformation in which the long axis of the strain ellipsoid is aligned in the fault shear sense the mosha fault is associated with a large hanging wall anticline cored by precambrian rocks and series of footwall synclines formed of late tertiary rocks this geometry together with several low angle short cut thrusts in the fault footwall implies that the mosha fault is an inverted normal fault which has been reactivated since the late tertiary in the study area the reverse fault mechanism was associated with the rapid uplift and igneous activity in the central alborz range during the late tertiary unlike in the eastern portion of the fault where the fault kinematics was replaced by a strike slip mechanism in the late miocene

deformation of the assegaai supracrustals and adjoining granitoids transvaal south africa abstract the structures in archaean quartzites of the assegaai greenstone belt in the transvaal of south africa can be interpreted in terms of three major deformation events earliest d1 involved thrusting along brittle ramp and flat crush zones rising temperatures then led to the mobilization of sio2 and the development of syn d1 stylolites and omnidirectional quartz veins in the quartzites increasingly ductile behaviour results in some of the early d1 crush zones being overprinted by late d1 mylonitic shear zones while eastward verging recumbent folds formed about n s axes in the layered quartzites the assegaai supracrustals were then separated from a contiguous basement of ancient gneiss complex agc by the intrusion of a granitoid sheet about 3 km thick along their sheared subhorizontal contact either late in d1 or in the interval between d1 and d2 the supracrustals were then refolded about steep nne trending axial surfaces by concentric f2 folds on a variety of scales such folds were the second major structures to affect the supracrustals but the first to deform the granitoid sheet the older of two suites of quartzo feldspathic veins in the agc were probably generated penecomtemporaneously with the syn d1 quartz veins in ther assegaai quartzites this interpretation can be tested by removing the intense d2 constriction and 30 volume increase recorded by a later network of syn granitoid quartzofeldspathic veins in the agc from the d1 d2 flattening recorded by the older veins this procedure can be carried out by geometric vector subtraction on a hsu diagram the result reveals that the d1 strains in the assegaai supracrustals and the then contiguous agc were identical penetrative subhorizontal flows prior to the intrusion of the intervening granitoid the last significant strain in the region is represented by a brittle nne trending strike slip fault and locally in the quartzites disharmonic conjugate folds

the use of microtomography in structural geology a new methodology to analyse fault faces abstract this paper describes a new methodology to kinematically analyze faults in microscale dimensions voxel size 40 m using images obtained by x ray computed microtomography ct the equipment used is a ge ms8x 130 scanner it was developed using rocks samples from santa catarina state brazil and constructing micro digital elevation models dems for the fault surface for analysing microscale brittle structures including striations roughness and steps shaded relief images were created for the dems which enabled the generation of profiles to classify the secondary structures associated with the main fault surface in the case of a sample with mineral growth that covers the fault surface it is possible to detect the kinematic geometry even with the mineral cover this technique proved to be useful for determining the sense of movement of faults especially when it is not possible to determine striations in macro or microscopic analysis when the sample has mineral deposit on the surface mineral cover this technique allows a relative chronology and geometric characterization between the faults with and without covering

mid crustal horizontal shear zone in the forearc region of the mid cretaceous sw japan arc inferred from strain analysis of rocks within the ryoke metamorphic belt abstract the strain geometry of a cretaceous low p high t metamorphosed accretionary complex in sw japan is one of the key geological constraints in understanding the cretaceous tectonics of the forearc region at the eastern margin of eurasia we studied the strain geometry of upper greenschist to lower amphibolite facies metamorphic rocks from the mid cretaceous low p high t ryoke metamorphic belt which during the mid cretaceous were located at mid crustal depths close to the volcanic front strain analysis focused on deformed radiolarian fossils in metachert and sandstone chert clasts within metapelite the maximum stretching direction x direction of the strain ellipsoid of the schistosity forming deformation at the peak metamorphism is oriented e w and the xy plane of the strain ellipsoid developed parallel to schistosity the metachert and metapelite exhibit plane strain to general flattening strain that probably largely resulted from the schistosity forming deformation based on the results of the previous strain analyses and this study it reveals that the schistosity forming deformation occurred under bedding normal shortening resulting in general flattening strain throughout the ryoke metamorphic belt the x direction of the strain ellipsoid of the schistosity forming deformation is oriented parallel to the length of the ryoke metamorphic belt throughout the sw japan arc the schistosity formed parallel to bedding planes that developed horizontally in non metamorphosed accretionary complexes of sw japan indicating horizontal xy plane of the strain ellipsoid these observations indicate the occurrence of horizontal shear deformation within the middle crust 15 km depth at the time of the low p high t metamorphism the deep seated horizontal shear zone and the shallower incipient median tectonic line mtl fault system could result in a crustal scale detachment fault in the forearc region of the mid cretaceous sw japan arc after the formation of the detachment the left lateral pull apart forearc basins onogawa izumi group distributed on the north side of the mtl and the southern marginal mylonite zone might be formed by the sinistral movement along the detachment fault

remanence stability and magnetic fabric development in synthetic shear zones deformed at 500 c shear experiments were performed on magnetite bearing calcite aggregates to examine magnetic fabric development and remanence stability in a deforming system using elevated temperature and pressure to encourage deformation by crystal plastic processes samples composed of 1 wt pseudo single domain magnetite 1 2 m in a calcite matrix were created with either strong or weak initial fabrics and deformed in coaxial simple shear to strains up to 1 5 at constant strain rates between 6 10 5 and 1 10 4 s 1 at 500 c and confining pressure of 300 mpa samples were given weak field thermal remanent magnetizations prior to deformation demagnetization of postdeformation remanence reveals that a primary remanent magnetization can withstand deformation at pressures and temperatures approximately equivalent to greenschist facies metamorphic conditions on laboratory time scales but this stability is found to depend on the character of the predeformation fabric the origin of secondary remanence components acquired during deformation is uncertain but is likely to partially result from thermal viscous remagnetization complete postdeformation remagnetization in initially anisotropic samples appears to involve a stress softening or piezoremanent magnetization mechanism postdeformation anisotropy measurements show progressive changes in magnetic fabric strength with strain in the absence of a strong initial magnetic anisotropy magnetic fabric intensity increases linearly as a function of strain however deformation that overprinted an existing fabric results in an apparent decrease of the initial anisotropy at low strains followed by rapid increases in magnetic fabric strength with increasing strain our results underscore the important role that initial fabric can play in determining the character of deformation fabrics

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

a theory for midlatitude forcing of tropical motions during winter monsoons abstract in order to understand the northeasterly monsoon surges and associated tropical motions over southeast asia during northern winter the dynamic response of the tropical atmosphere to midlatitude pressure surges is studied using the linearized shallow water equations on an equatorial plane the forcing is specified to have a gaussian spatial distribution with a zonal scale corresponding to approximately wavenumber 7 and a meridional scale of approximately 11 it rises rapidly from zero to maximum within one day or less and then decays slowly over 2 4 days the main results are as follows 1 after an initial period of gravity wave type motions with strong northerly winds the main tropical response takes the form of a rossby wave group 2 a pronounced northeast southwest tilt in this rossby wave group develops due to the faster westward group velocity of the lower meridional modes relative to the higher meridional modes 3 several conspicuous features of the rossby response closely resemble t

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

fold thrust belt evolution expressed in an internal thrust sheet sevier orogen the role of cataclastic flow large hinterland thrust sheets are the dominant structures in retroarc fold thrust belt ftb wedges these internal sheets remain active throughout the history of an ftb and strongly influence the kinematics of the external portions of the ftb and the overall behavior of the entire tectonic wedge their emplacement and deformation account for a significant portion of the total mechanical energy budget in ftb evolution based on estimates using deformation features preserved within such sheets moreover the deformation within dominant internal sheets can be used as a means to evaluate the tectonic history of the wedge as a whole the principal deformation mechanisms in different parts of an ftb wedge are strongly controlled by variations in the geothermal gradient retroarc ftbs typically show a steeper geothermal gradient in the hinterland than in the foreland resulting in a foreland ward slope of the brittl ductile transition therefore a change from plastic to elastico frictional ef mechanisms is expected not only with decreasing depth but also across strike as a dominant internal thrust sheet is transported toward the foreland and undergoes exhumation by synorogenic erosion however evidence for cataclasis overprinting early plastic deformation features is often not preserved in ancient ftbs because of extensive erosion of the wedge top even where evidence for lat stage cataclastic behavior exists in either ancient or modern i e active orogens it is often not recognized or studied our work in the canyon range central utah segment of the sevier ftb shows that unraveling the ef mechanisms such as lat stage cataclastic flow is critical to understanding the total deformation history of an internal thrust sheet after initial emplacement under plastic deformation conditions the cr thrust sheet was continuously reactivated under ef conditions thereby helping to maintain critical taper of the ftb wedge during its development structures preserved in the cr thrust sheet therefore record a significant portion of the deformation history of the ftb as a whole the canyon range cr syncline part of the cr sheet underwent fold tightening within the ef regime and the cataclasized rocks are well preserved the geometry and progressive deformation patterns of the cr syncline reveal four distinct to partly overlapping deformation stages the history of the rocks in the cr thrust sheet has been tracked by incrementally retro deforming the ftb and by unraveling details of the deformation within the cr syncline at various scales for each stage we use the cr syncline as a type example to show that unraveling ef mechanisms is critical to 1 understanding the state of a ftb wedge during its evolution 2 calculating the energy involved in ftb emplacement and 3 developing accurate restorations placing constraints on the depth of the rocks for successive stages of deformation is essential for developing retrodeformable balanced cross sections and in turn geometric and kinematic models for wedge evolution

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

strains and vorticity beneath a tabular batholith in the zambesi belt northeast zimbabwe structures on scales of cm to dm in formerly universally orientated quartz veins are used to analyse deformation in part of the pan african e w zambezi orogen by integrating their orientations over length scales of six orders of magnitude 2 cm to 20 km sixty two strain ellipsoids on locality scales 20 200 m and six on district scales 2 20 km demonstrate that each of the constituent lithologies together with the metasedimentary cover sequence as a whole strained as homogeneous materials after the quartz veins developed related to orogenic structures these homogeneous strains demonstrate that major folds in the cover initiated as buckles on e w axes before the quartz veins were inserted but tightened passively as the metamorphic grade rose from greenschist to upper amphibolite facies by contrast post vein f2 flow folds originally on ne axes amplified actively at the same time but without noticeable shortening such f2 folds are interpreted to have been driven by the gravitational stabilization of the relatively dense proterozoic cover and its less dense archaean basement the instability due to this primary density inversion was aided significantly by a secondary density inversion induced by the orogenic thermal gradient while the metamorphic gradient was below 30 c km the basement rose in conformable upright ridges on the same ne trends preserved in the archaean rocks in the kalahari craton to the south the early e w trending folds and later ne trending folds of the zambezi orogeny interfered to generate class ic patterns of elongate domes and basins throughout the cover sequence when the regional thermal gradient rose above 30 c km the basement rose diapirically into or through the cover as domes of migma migmatite or magma on centres 5 10 km apart melts of the deep basement eventually drained up the stems of earlier migma diapirs and presumably fed a tabular batholith in the epizone that has since been removed by erosion diapirs of basement or remobilized basement displaced the earlier class ic fold interference pattern in the cover in all directions this led to uniaxial radial flattening and vorticity down to scales of 100 m in the cover within about 2 km of the basement contact meanwhile away from the immediate influence of the diapirs the cover sequence continued to undergo vorticity about a nnw shortening axis on district scales but only spun on locality scales the mean post vein n s orogenic shortening of the cover sequence is found to be 60 on the locality scale linear strain fields for data from appropriate districts are interpreted in terms of plane strains with about 50 60 of the total shortening being due to uniaxial nnw volume loss of sio2 and water on both locality and district scales all the post vein shortening measured in the orogen can be attributed to lateral displacement of the cover by diapirs of a sialic basement which may not have shortened on the regional scale at any stage pre vein shortening of the cover by thrusts and ductile flow has not been quantified but n s shortening due to early buckles is calculated to have been about 17 the upward loss of sio2 in solution and either solid or molten basement from levels still exposed to others since eroded appears to be a far more characteristic aspect of the eastern part of the zambezi orogen than lateral shortening on the regional scale

synoptic disturbances over the equatorial south china sea and western maritime continent during boreal winter abstract during boreal winter the maritime continent is a region of deep cumulus convection and heavy precipitation systems that play a major role in several global and regional scale processes over the western part of this region the synoptic scale borneo vortex the northeast cold surge and the intraseasonal madden julian oscillation mjo contribute to the variability in deep convection this work studies the impact on deep convection due to interactions among these three different motion systems furthermore the role of the unique topography of the region is examined with respect to the variability in the synoptic scale cold surge and borneo vortex on the synoptic scale the interaction of northeast winds with local topography and the dynamic response to the change in latitude contribute to the turning of the winds and localized patterns of deep convection in days without a borneo vortex deep convection tends to be suppressed over the south china sea and borneo and enhanced downstream over th

strain ellipsoids from incompetent dykes application to volume loss during mylonitization in the singo gneiss zone central sweden we describe how to constrain bulk strain ellipsoids by distinguishing the attitudes of mullioned from planar contacts in incompetent dykes our method is demonstrated by using metabasaltic dykes to

change of direction of overthrust shear in the helvetic nappes of western switzerland abstract the lowest of the helvetic nappes in western switzerland the morcles and the doldenhorn nappes are large scale recumbent folds in equivalent tectonic positions in the alpine chain a comparison of the orientations of stretching lineations in both nappes shows that the lineations in the two stratigraphically normal sequences trend n s whereas those in the two stratigraphically inverted sequences trend nw se a similar geometrical relationship has been found from an analysis of the calcite c axis directions of these limestones the two normal sequences show nw se directed c axes whereas the two inverted sequences show w e directed c axes these observations lead to the following conclusions 1 regionally consistent shear movements occurred over a strike distance of more than 60 km and these gave rise to similar deformation patterns in both nappes 2 a progressive rotation of these shear movements from a northerly direction in the earlier formed limbs to northwesterly in the later formed inverted limbs can be deduced the finite strain stretching lineations lag behind the crystallographic fabric axes formed in the later part of the deformation history

typhoon vamei an equatorial tropical cyclone formation 1 due to the diminishing coriolis effect the belt 300 km either side of the equator has been considered tropical cyclone free typhoon vamei which developed near singapore on 27 december 2001 was the first recorded tropical cyclone formation within 1 5 degrees of the equator the development was the result of two interacting systems a weak borneo vortex that drifted into the southern tip of the south china sea and remained there for four days and a strong and persistent cold surge that created the large background cyclonic vorticity at the equator the probability of a similar equatorial development is estimated to be once every 100 400 years

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

climatic and hydrologic changes in the tien shan central asia abstract the authors analyze climatic and hydrologic data from 110 sites collected from the middle of the twentieth century to the present in the tien shan one of the largest mountain systems of central asia in spite of a few confounding interregional variations in the temporal changes of surface air temperature precipitation runoff glacier mass and snow thickness in the tien shan it has been possible to establish statistically significant long term trends in these key hydroclimatic variables the average rise in air temperature was 0 01 c yr 1 over the range with slightly lower values below 2000 m elevation the precipitation in the tien shan increased 1 2 mm yr 1 over the past half century the precipitation increase is larger at low altitudes in the northern and western regions than at altitudes above 2000 m a decrease in snow resources occurred almost everywhere in the tien shan the maximum snow thickness and snow duration have decreased on average 10 cm and 9 days respectively the annual

response of snow cover to climate change in the periphery mountains of tarim river basin china over the past four decades data of annual mean temperature annual total precipitation and snow cover area sca in the winter season from 1982 to 2001 have been analyzed to examine the response of sca to climate change in the tarim basin western china the results show that over the entire basin sca exhibits a slowly decreasing trend the responses of sca to temperature and precipitation in the northern western and southern parts of the basin show a stronger effect of precipitation change on sca than that of temperature sca has slowly increased below 2500 m a s l but has decreased at higher altitudes the lowest altitude zone was apt to be affected by precipitation while the highest altitude zone seems to have been influenced mainly by temperature the middle zone from 2500 to 5000 m was the most sensitive to climate change snowfall and melt rates were higher in the 1990s than in the 1980s in the winter season sca change was positively correlated with precipitation change but not with temperature change

some new aspects of kinematic vorticity analysis in naturally deformed quartzites abstract two vorticity methods have been proposed to estimate kinematic vorticity number in naturally deformed quartzites these combine the degree of quartz c axis fabric asymmetry either with the strain ratio in the xz plane of finite strain r xz or with the angle between the oblique grain shape fabric and the main foliation here it is suggested that the incorporation of r xz data with angle values can also serve as an additional method of vorticity analysis the use of a new nomogram that provides a rapid means of evaluating the consistency of vorticity estimates obtained by the three methods is also discussed a comparison of vorticity estimates from low grade test samples using all methods yields that three methods may record different parts of deformation history this hypothesis was then used to discuss the spatial and temporal variation of kinematic vorticity in a crustal scale shear zone this natural example showed that the new method is able to record late stage changes in the flow regime which are slightly or not detectable by previous methods also it is noteworthy that vertical vorticity profiles based on results of rigid porphyroclast analysis tend to average profiles obtained by the estimates of quartz based methods

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

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

a case study of the borneo vortex genesis and its interactions with the global circulation 1 during the east asian winter or the northeast monsoon november march cold surges associated with cold air outbreaks from the siberian high propagate equatorward and interact with the near equatorial trough in the southern south china sea usually in the later phase of the monsoon the so called borneo vortex develops over the sea and is the main driver for the formation of deep convection and heavy rainfall in east malaysia we present a case study of a cold surge induced event during january 2010 we diagnose a substantial export of potential energy from the borneo vortex strengthening the subtropical jet at 200 hpa the velocity potential maximum related to the established hadley circulation is shifted eastward from 140 e toward the dateline from presurge to postsurge periods this modifies the general circulation patterns in the southern hemisphere with possible consequences for trace gas distributions in addition we explore implications for vertical transport by deep convection occurring in association with the borneo vortex by diagnosing potential vorticity changes in the vicinity of the vortex

heterogeneous shear zone evolution the role of shear strain hardening softening mathematical models are proposed to describe heterogeneous shear zones characterized by variation thickness with time these models take into account several combinations of deformation type regime simultaneous simple shear pure shear and volume change and degree of strain localization increasing or decreasing shear zone thickness results respectively from strain hardening where deformation progressively diffuses into the host rock and strain softening where deformation gradually localizes within a narrow zone shear zone models are made of a series of layers each characterized by homogenous strain a quantitative evaluation of displacement thickness relationship and finite strain development may be obtained from each model temporal evolution depends on the following parameters i rate of shear strain hardening softening ii initial shear strain increment imposed to the system and iii thickness of homogenously deformed units within a layered shear zone based on data coming from natural shear zones displacement rates may be obtained independently of shear zone thickness

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

structural geology meets micromechanics a self consistent model for the multiscale deformation and fabric development in earth s ductile lithosphere abstract earth s lithosphere is made of rheologically heterogeneous elements of a wide range of characteristic lengths a micromechanics based self consistent multiorder power law approach is presented to account for lithospheric deformations and the accompanying multiscale fabric development the approach is principally based on the extended eshelby theory for the motion of a power law viscous ellipsoid in a power law viscous matrix and the idea of embedding inhomogeneities within inhomogeneities the extended theory provides a general means for investigating deformation partitioning in heterogeneous rocks the inhomogeneities within inhomogeneities method allows multi hierarchical levels of flow field partitioning and hence multiscale deformations to be investigated partitioned flow fields are used to investigate fabric development being based fully on micromechanics the approach generates model predictions of both kinematic quantities strain strain rates and vorticity and stress histories the former can be directly compared with field and laboratory structural observations while the latter can help to understand the physics of natural deformations the self consistent and multiscale approach is applied to a natural example of the cascade lake shear zone in the east sierra nevada of california the modeling shows that the fabrics are most consistent with a steeply dipping transpression zone with a convergence angle of 20 and a strike slip displacement about 26 km further the strength evolution of the model zone confirms that a transpression zone is a weakening system with respect to the simple shearing component and a hardening one for the pure shearing component this is consistent with slip partitioning in obliquely convergent plate boundaries boundary normal convergence tends to spread over a broad area whereas boundary parallel shear tends to localize in major strike slip zones

microstructures in a banded iron formation gua mine india this paper provides a detailed documentation of microstructures developed in the banded iron formation bif of gua mine located in the bonai synclinorium eastern india where the rocks have been subjected to three deformations d 1 to d 3 folded iron ores quartz strain fringes around rigid core objects and folded iron ore layers and refracted quartz veins are described from samples taken from d 2 folds in the banded iron formation orientations of microstructures are compared with mesoscopic structures to interpret the generations of ore minerals planar structures and the time relationship between deformation and development of different microstructures the mechanism of d 2 folding is worked out and its bearing on microstructure development is discussed the d 2 folds are inferred to have developed by a combination of tangential longitudinal strain in the competent layer flexural flow in the incompetent layers and flexural slip at the interface between layers of differing competence homogeneous flattening strain superposed the earlier strain which led to modification of the folds in the competent layer from class 1b to 1c this strain is quantified and is found to be higher in the limb than the hinge of a fold diffusive mass transfer by solution and bulging dynamic recrystallization in quartz are inferred as the dominant deformation processes during folding moreover based on comparison with published deformation microstructure maps the microstructures of the present study are estimated to have developed between 300 and 350 c temperatures at a strain rate of 10 14 10 12 s 1 which are geologically realistic conditions for naturally deformed rocks

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

subaerial salt extrusions in iran as analogues of ice sheets streams and glaciers abstract ice h20 and salt halite nacl share many physical properties and resemble each other in hand specimens and subaerial gravity driven flows however while most significant bodies of ice accumulate in cold highlands and gravity spread where and soon after they form most significant bodies of salt accumulate in tropical marine basins and have to be buried by 1 km of other rocks before they flow buried salt is driven by differential loading into various categories of piercing structures known as diapirs many diapirs extrude onto the surface as sheets of allochthonous out of place salt thousands of sheets of allochthonous salt have been interpreted in over 35 basins worldwide in the last 25 years mainly in the toes of passive continental margins and in orogenic belts where some are 103 km2 in area most former salt sheets are now submarine or subsurface but several active examples are beautifully exposed in iran these were compared to ice glaciers soon after they were introduced to western science a comparison that has been neglected since here we update this analogy and use modern understanding of flowing ice and salt to examine the similarities and differences that might be mutually beneficial to both fields of study as well as to extraterrestrial scientists the profiles internal structures and fabrics in flowing bodies of ice and salt are sensitive gauges of the histories of their budgets of supply and loss however whereas snow merely compacts where it accumulates salt sheets are fed from below by already deformed salt when salt diapirs first emerge on land they extrude domes that mature to the profiles of viscous fountains that often feed glacier like flows known as namakiers after locally exhausting their deep source layers salt fountains spread to the profiles of viscous droplets normal for ice caps ice typically deforms at 80 usually 90 of its absolute melting temperature while most salt deforms at

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

growth of the central andean plateau by tectonic segmentation is controlled by the gradient in crustal shortening abstract crustal deformation orocline formation and growth of the central andean plateau as well as the mutual relations of these processes with climate are a matter of international debate earthquake focal mechanism fault kinematic paleomagnetic and cross section balancing data are paramount for understanding the morphotectonic evolution of this noncollisional orogen but collectively await an explanation in terms of a comprehensive kinematic model we offer such a model that approximates simple shear in plan view and that predicts the kinematics of first order fault zones in the southern central andes the model indicates that segmentation of the upper crust into rhomb shaped domains confined by transpressive ranges resulted from the decrease in crustal shortening with distance to the central bend of the andes an anastomosing network of kinematically coupled reactivated orogen parallel and newly formed ne trending deformation zones encompassing components of sinistral and dextral strike slip res

strain localisation in an orthogneiss laccolith the pinet massif aveyron southern france abstract sheared granitoids of the pinet laccolith southern france display strain gradients from undeformed protolith to s c mylonites and ultramylonites that formed at amphibolite facies of metamorphism we study shear strain distribution at a regional scale and use image processing techniques to measure strain across continuous shear gradients local perturbations of strain intensity seem to represent early stages of shear strain localisation parallel to the main mylonitic foliation our study suggests that localisation of shear strain shows a periodicity at regional and outcrop scales

on the roles of the northeast cold surge the borneo vortex the madden julian oscillation and the indian ocean dipole during the extreme 2006 2007 flood in southern peninsular malaysia the mid december 2006 to late january 2007 flood in southern peninsular malaysia was the worst flood in a century and was caused by three extreme precipitation episodes these extreme precipitation events were mainly associated with strong northeasterly winds over the south china sea in all cases the northeasterlies penetrated anomalously far south and followed almost a straight trajectory the elevated terrain over sumatra and southern peninsular malaysia caused low level convergence the strong easterly winds near java associated with the rossby wave type response to madden julian oscillation mjo inhibited the counter clockwise turning of the northeasterlies and the formation of the borneo vortex which in turn enhanced the low level convergence over the region the abrupt termination of the indian ocean dipole iod in december 2006 played a secondary role as warmer equatorial indian ocean helped in the mjo formation

differences between magnetic and mineral fabrics in low grade cleaved siliciclastic pelites a case study from the anglo brabant deformation belt belgium abstract theoretically within a given pelitic rock in which the main paramagnetic carriers are white mica and chlorite and in which judging from the ams parameters ams is controlled by the paramagnetic carriers the results of x ray pole figure goniometry should show a qualitative relationship with ams this idea is tested on single phase deformed low grade pelites of the lower palaeozoic brabant massif belgium representing the southeastern part of the anglo brabant deformation belt for the vast majority of the samples investigated the different lf ams parameters suggest a paramagnetic control on lf ams different parameters of lf ams measured at 77 k low t lf ams and a comparison of these with the lf ams parameters indicate that lf ams is controlled virtually entirely by paramagnetic carriers high field torque magnetometry hf ams indicates further that ams is controlled entirely by paramagnetic carriers for the vast majority of the samples two apparent discrepancies are observed however these are 1 a frequent mismatch between the lf ams fabric on the one hand and the paramagnetic fabric indicated by low t lf ams and hf ams on the other hand and 2 a rather common mismatch between the preferred orientation of chlorite and white mica suggested by x ray pole figure goniometry on the one hand and the lf ams fabric low t lf ams fabric and hf ams paramagnetic fabric on the other hand these apparent discrepancies may partly be attributed to the composite nature of both the lf ams fabric and the paramagnetic susceptibility fabric the presence of different populations of paramagnetic carriers possibly in combination with minor traces of ferromagnetic s l carriers which are not picked up by the methods applied may explain some of the mismatches observed and are compatible with the basin evolution history of the brabant massif in addition it is possible that the low temperatures low t lf ams and high fields hf ams are capable of enhancing one of the paramagnetic phases thus leading to discrepancies between methods that define the mineral and the magnetic fabrics the results of this study show that even when the lf ams data suggest that the lf ams of a given pelitic rock in which phyllosilicates form the main paramagnetic carriers is controlled entirely by paramagnetic carriers alternative methods such as phyllosilicate x ray pole figure goniometry will not necessarily reflect the paramagnetic carrier orientation although a number of cases have successfully correlated lf ams with mineral fabric and occasionally even strain this study serves as an example for how methods to define mineral and magnetic fabrics can be sensitive in detecting different paramagnetic phases

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