orogen parallel flow during continental convergence numerical experiments and archean field examples using triaxial numerical experiments we investigated the evolution of the state of stress and that of the bulk instantaneous and fi nite strain during ongoing convergence and subsequent progressive tectonic unloading of a warm and buoyant continental lithosphere various unloading histories of the driving tectonic force were considered as the tectonic force progressively declines the instantaneous strain evolves from plane strain to horizontal constriction in a direction perpendicular to that of convergence and fi nally to horizontal fl attening during the progressive unloading of the tectonic force driving convergence bulk constrictional strain accommodates the release of accumulated gravitational stress the decline of the triaxial strain rates to low values reduces the potential for the orogen parallel linear fabric to be erased by horizontal fl attening this is confi rmed by the fi nite strain ellipsoid that evolves toward plane strain with a long axis parallel to the orogen in the ca 2 5 ga gawler and terre adelie cratons we have identifi ed a well preserved and widespread horizontal linear fabric as suggested by our numerical experiments we associate the development of this linear fabric with the waning stages of late archean convergence

re evaluation of polyphase kinematic and 40 ar 39 ar cooling history of moldanubian hot nappe at the eastern margin of the bohemian massif a structural and geochronological 40ar 39ar study was performed in kilometre scale middle and lower crustal lens shaped domains dominated by a preserved subvertical foliation surrounded by horizontally foliated migmatites these domains occur within the moldanubian nappe overlying the brunia microcontinent at the eastern margin of the european variscides three main deformation phases were recognized subvertical s2 fabric trending nw se in lower crustal rocks and ne sw in mid crustal rocks it is reworked by ht mt horizontal fabric s3 along margins of crustal domains and in surrounding migmatites s3 bears a prolate ne lineation parallel to the s2 s3 intersection in the lower crustal domain in the middle crustal units l3 is weak connected to oblate strain and trends ne sw parallel to the s2 s3 intersection d4 non coaxial shear deformation is mainly localized at the boundary between the moldanubian nappe and brunia and bears strong top to the nne shear criteria in order to constrain kinematics of the d3 deformation strain modelling was performed to show that the moldanubian hot nappe was frontally thrust over the brunia indentor the renewed d4 tangential movement only heterogeneously reactivates the horizontal s3 this evolution is recorded in 40ar 39ar amphibole cooling ages which show two statistically significant carboniferous peaks at 342 and 332 ma which are also reflected by published detrital muscovite 40ar 39ar ages in the adjacent foreland basin this geochronological record is correlated with progressive erosion of the topographically elevated upper crustal part of the moldanubian nappe during d3 frontal thrusting followed by greenschist facies d4 transpressive reactivation and subsequent erosion of high grade parts of the nappe

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

interactions between plutonism and detachments during metamorphic core complex formation serifos island cyclades greece in order to better understand the interactions between plutonic activity and strain localization during metamorphic core complexes formation the miocene granodioritic pluton of serifos cyclades greece is studied this pluton 11 6 9 5 ma intruded the cycladic blueschists during thinning of the aegean domain along a system of low angle normal faults belonging to the south dipping west cycladic detachment system wcds based on structural fieldwork together with microstructural observations and anisotropy of magnetic susceptibility ams we recognize a continuum of deformation from magmatic to brittle conditions within the magmatic body this succession of deformation events is kinematically compatible with the development of the wcds the architecture of the pluton shows a marked asymmetry resulting from its interaction with the detachments we propose a tectonic scenario for the emplacement of serifos pluton and its subsequent cooling during the aegean extension 1 a first stage corresponds to the metamorphic core complex initiation and associated southwestward shearing along the meghalo livadhi detachment 2 in a second stage the serifos pluton has intruded the dome at shallow crustal level piercing through the ductile brittle meghalo livadhi detachment southwest directed extensional deformation was contemporaneously transferred upward in the crust along the more localized kavos kiklopas detachment 3 a third stage was marked by syn magmatic extensional deformation and strain localization at the contact between the pluton and the host rocks resulting in narrow shear zones nucleation which 4 continued to develop after the pluton solidification

ocean contribution to co seismic crustal deformation and geoid anomalies application to the 2004 december 26 sumatra andaman earthquake large earthquakes do not only heavily deform the crust in the vicinity of the fault they also change the gravity field of the area affected by the earthquake due to mass redistribution in the upper layers of the earth besides that for sub oceanic earthquakes deformation of the ocean floor causes relative sea level changes and mass redistribution of water that have again a significant effect on the gravity field to model these deformations sea level changes and gravity field perturbations self consistently we use an adapted version of the sea level equation sle that has been used for glacial isostatic adjustment studies the sea level equation next to our normal mode model for seismic solid earth modeling allows us to compute a gravitationally self consistent solution for the co seismic relative sea level surface deformation and geoid height changes we apply our geographically detailed models to the case of the 2004 december 26 sumatra andaman earthquake recent studies that have modeled the ocean mass effect on co seismic gravity change for this specific earthquake show model results that indicate a broad negative change in geoid height around the fault due to ocean water redistribution de linage et al 2009 melini et al 2010 our model results for the ocean contribution to geoid height differ from these studies in the sense that we find a pattern similar to the elongated dipole pattern of the solid earth model outputs for gravity and vertical deformation together with a relatively small broad negative geoid height change we explain the relation between outcomes for geoid height relative sea level and vertical deformation of the ocean floor and we confront our model results with a least squares estimation of the co seismic discontinuity in grace derived gravity field time series we show that taking into account the contribution of ocean water redistribution to the co seismic geoid height change next to a compressible solid earth model is essential to explain the predominant negative co seismic geoid anomalies from the grace gravity field solutions besides we introduce a detailed approach to modeling an earthquake in a normal mode model that better approximates realistic continuous slip on the fault plane than models that do not distribute slip with depth to demonstrate the importance of the slip distribution we show the differences in outcomes for modeled geoid height and vertical deformation

internal structure and emplacement of the papoose flat pluton an integrated structural petrographic and magnetic susceptibility study the papoose flat pluton of eastern california is commonly cited in the geologic literature as a classic example of a forcibly emplaced pluton although the relative importance attributed to magmatic versus tectonic processes in controlling the structural evolution of the pluton has been controversial reexamination of this late cretaceous 83 ma pluton using a combination of new structural petrographic microstructural and anisotropy of magnetic susceptibility ams data on the pluton wall rock system has shown that the pluton is an inclined and internally zoned tabular structure assembled by forcible intrusion of successive pulses of magma at a crustal depth of 12 15 km initial pluton formation involved magma ascent in a vertical west northwest striking feeder dike which was arrested at a stratigraphically controlled mechanical discontinuity in the overlying cambrian metasedimentary rocks leading to formation of a southwest dipping sill subsequent sill inflation accompanied by horizontal infilling from the feeder dike at the base of the sill resulted in deformation and vertical translation of previously emplaced magma pulses and local raising of the sill roof facilitated by thermal weakening as the wall rock temperatures progressively rose during emplacement of successive magma pulses cooling from the roof of the pluton downward resulted in cessation of vertical inflation on the west side of the pluton and promoted lateral expansion toward the northeast and floor depression below the eastern part of the pluton we have been unable to document any regional scale structures e g of equivalence to similar age synplutonic strike slip shear zones in the sierra nevada batholith to the west that may have controlled emplacement of the papoose flat pluton however this fact does not preclude the likelihood that the country rocks were subjected to a regional deviatoric stress field at this time indeed tectonic overpressuring was probably essential for producing sufficiently high magma pressures for laccolith formation at this midcrustal level simple thermal modeling using microstructural and thermobarometric data indicates that the total duration of emplacement of the pluton did not exceed 30 000 yr this rapid emplacement rate may explain why the pluton appears to be anorogenic even though it was emplaced during a period of regional scale deformation

the mechanism of flow and fabric development in mechanically anisotropic trachyte lava anisotropy of magnetic susceptibility ams and electron back scattered diffraction ebsd of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in tertiary volcanic province of the nw czech republic revealed two fabric types the high degree of ams fabric is associated with sanidine textural domains similar to normal kink bands type i fabric and occupies the whole body except the sw margin folded fabric and low anisotropy of ams also in the sw margin reveals sanidine alignment domains resembling reverse kink bands type ii fabric the flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their 010 planes and also by readjustment of the textural domain boundaries according to the fibre slip theory this microfabric study suggests that the type ii fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit type i fabric is interpreted to originate from type ii fabrics by further stretching of highly attenuated fold limbs asymmetric type i fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow the trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

sm nd dating and cooling history of scourian granulites sutherland the scourian gneisses of the lewisian complex of north west scotland have been the subject of many geochronological investigations sm nd whole rock measurements suggest that the protoliths of the lewisian complex differentiated 2 92 0 05 gyr ago from an approximately chrondritic mantle1 rb sr and pb pb whole rock ages between 2 8 and 2 6 gyr reflect subsequent depletion in rb and u refs 2 3 which has generally been associated with granulite facies metamorphism zircons which are thought to have crystallized during this metamorphism have also given u pb ages of 2 66 gyr ref 4 this granulite facies metamorphism involving pressures in excess of 10 kbar and peak temperatures estimated between 820 50 c ref 5 and 1 250 c refs 6 7 affects a terrain including supracrustal rocks7 and thus implies a major tectonic event we report here the first geochronological data measured on mineral assemblages that have also provided estimates of the conditions of metamorphism such measurements are possible because the major minerals of granulite facies assemblages show an unusually favourable spread in sm nd ratios garnet especially is strongly enriched in sm ref 8 data for three garnetiferous basic gneiss assemblages suggest that closure of the sm nd system occurred significantly later than the peak of the metamorphism

magnetic fabric transposition in folded granite sills in variscan orogenic wedge abstract new approach involving evaluation of anisotropy of magnetic susceptibility ams data in stereoplots and jelinek s p j t space vollmer s eigenvalue and microstructural analyses is proposed to discriminate between homogeneous and superposed deformation in granites this method is used to decipher the internal ams fabric and microstructural evolution of a folded array of granitic sills the studied major sill shows a fabric and microstructural zonality marked by submagmatic and high temperature type i planar linear fabric developed at sill margins and the transpositional type ii subsolidus fabrics that formed at high to medium temperature deformation in the sill core while type i fabric is associated with dip slip magnetic lineations type ii subsolidus fabrics are marked by subhorizontal magnetic lineations striking parallel to the long axis of the sill the structural reconstruction of the fabrics in the granite and the host rocks as well as new u pb zircon ages suggest coeval emplacement of horizontal and vertical sills accounting for significant weakening of the host rock magma multilayer the model of folding of such multilayer and extrusion of residual magma parallel to axial planes is discussed with respect to structural record in other syn contractional granite sill arrays forming sheeted plutons worldwide

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

multiple magmatic fabrics in the sazava pluton bohemian massif czech republic a result of superposition of wrench dominated regional transpression on final emplacement abstract the sazava pluton 354 ma of the central bohemian plutonic complex was emplaced syntectonically into the upper crustal neo proterozoic and lower paleozoic host rock along the se margin of the tepla barrandian zone bohemian massif czech republic the host rock is characterized by transpressional fabric dominated by steep se nw dipping foliations and subhorizontal ne sw stretching lineations associated with flattening to a plane strain ellipsoid the strain intensity degree of oblateness and temperature conditions of deformation increase in the host rock towards the pluton margin in the pluton quartz microfabric indicates progressive cooling of the syntectonically emplaced magma the ams method revealed multiple magmatic fabrics and lateral variations in the shapes of the ams ellipsoid and the magnetic fabric intensity in the pluton the central part of the pluton yields prolate shapes of the ams ellipsoid and a low degree of anisotropy with preserved steep magnetic lineations whereas along the pluton margins oblate ams ellipsoids are associated with a high degree of anisotropy we interpret the multiple fabrics and the partially decoupled fabric pattern between the host rock and the pluton as being a result of superposition of regional tectonic strain during highly oblique transpression on emplacement related intrusive strain where outer solidified and more rigid edges of the pluton enabled preservation of older steep fabrics in its interior

some remarks on fabric overprints and constrictional ams fabrics in igneous rocks during the ascent emplacement and post emplacement deformation of igneous rocks two or more phases of deformation that overprint each other are often depicted these overprints when magnetic minerals are present are recorded in magnetic fabric in this contribution overprints are studied by means of numerical modeling following several basic scenarios common to igneous rocks biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic susceptibility modeling shows that 1 a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic rocks may result from a deformation overprint and not necessarily from an extensional transtensional regime and 2 that the constrictional ams fabrics originates from orthogonal superimposition of a deformation event on an ams fabric inherited from earlier magma emplacement history therefore the interpretation of a constrictional fabric must be performed with caution numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data

strain distribution and fabric development modeled in active and ancient transpressive zones 1 a model based on kinematics of transpression allows the measurable internal parameters simultaneous strain fabric and vertical elevation to be simulated in relation to the macroscopically determined external parameters of transpressive zones i e zone width velocity angle of convergence and zone depth we present a diagram of convergence angle against time for homogeneous transpression where isolines of strain intensity d strain symmetry k and vertical elevation of rock samples are superposed however the distribution of internal strain parameters is sensitive to three types of strain partitioning 1 discrete partitioning results in general decrease of finite strain accumulations and in increase of pure shear component 2 ductile partitioning splits the transpressional domain into a pure shear zone where strain accumulations decreases and in a wrench dominated zone where strain accumulations increases and 3 viscosity partitioning is marked by different strain rates in zones of different viscosity and therefore by different strain parameters

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

influence of melt induced mechanical anisotropy on the magnetic fabrics and rheology of deforming migmatites central vosges france in the central vosges france we describe and model the structural relationships existing between orthogneiss domains and their surrounding viscous migmatites these domains show a structural and anisotropy of magnetic susceptibility ams zonation associated with an increasing amount of melt from the core to their margins a pre extension oblate to plane strain fabric is preserved in the core of the orthogneiss domains where the granite veins were emplaced along a dilated mechanical anisotropy the internal margin of the orthogneiss bodies exhibits development of a prolate fabric and active buckling of an orthogneiss granite multilayer the external margin of the orthogneiss bodies is characterized by oblate fabrics resulting from a layer perpendicular shortening of a melt orthogneiss multilayer pinch and swell structures and extensional kink bands along which granite veins have been injected the surrounding metasedimentary migmatites show a similar structural history but the degree of fabric resetting is significantly higher this systematic fabric and structural succession is due to contrasting rheological evolution between orthogneiss and metasedimentary migmatites during progressive melting and continuously evolving degree of mechanical anisotropy in the stronger orthogneiss numerical modeling confirms the role of the relationship between initial mechanical anisotropy and superimposed deformation overprints on finite ams fabrics in migmatites

ams record of brittle dilation viscous stretching and gravity driven magma ascent in area of magma rich crustal extension vosges mts ne france orogenic compression related fabrics 340 335 ma were reworked during regional extensional deformation 328 325 ma in a large anatectic crustal domain of the central vosges ne france the extension was first accommodated by brittle dilation affecting vertically anisotropic high grade rocks associated with emplacement of subvertical granitic sheets the ams fabric of granitoids is consistent with highly partitioned transtensional deformation marked by alternations of flat and steep foliations and development of orthogonal lineations this deformation passes to top to the southwest ductile shearing expressed in southerly migmatitic middle crust the ams fabric revealed moderately west dipping foliations bearing subhorizontal nnw sse trending lineations and predominantly plane strain to prolate shapes this fabric pattern is interpreted as a viscous response of stretched partially molten crust during continuous ductile extension vertical ascent of voluminous granites and stoping of the upper crust occurs further south this gravity ascent triggered by extension leads to development of south dipping ams foliations south plunging lineations and oblate fabrics in various crustal granites vertical shortening related to ascent of these 325 ma granitoids and persistent n s stretching is responsible for reworking and remelting of originally vertical compression related fabric in roof supracrustal granites 340 ma and development of highly prolate fabrics in these rocks this work shows that the finite shape of ams fabric ellipsoid is highly sensitive to both strain regime and superpositions of orthogonal deformation events

non scaled analogue modelling of ams development during viscous flow a simulation on diapir like structures development of magnetic fabric within a diapirically ascending columnar body was investigated using non scaled analogue model made of plaster of paris containing small amount of fine grained homogeneously mixed magnetite the apparatus for the modelling consists of a manual squeezer with calibrated spring and a perspex container set of weak coloured layers at the bottom of the container was forced to intrude overlying fine grained sand through a hole in a board attached to the squeezer the development of ams fabric is correlated with complex flow pattern indicated by coloured and originally horizontal plaster layers strongly constrictional and vertical fabric in the base and in the lower domain of the diapir resulting from convergent and upwards flows is overprinted by subhorizontal oblate fabrics due to vertical flattening and initial divergent flow in the apical parts the measured ams fabrics are compared with natural examples of magmatic stocks and dykes

rb sr and sm nd dating of different metamorphic events from the sausar mobile belt central india implications for proterozoic crustal evolution abstract sr and nd isotopic studies of various rock suites and their mineral separates in and around the sausar mobile belt central india have revealed that 1 the last amphibolite facies metamorphism main sausar metamorphism occurred during 800 900 ma and has more or less reset the rb sr isotopic clock in this whole terrain whereas older sm nd isotopic signatures were mostly unaffected 2 the main sausar group of rocks is bounded both in the north and the south by two granulite belts of different crustal histories at least up to 1100 ma 3 the northern granulite belt experienced peak metamorphism during pre 1100 ma followed by steep decompression and subsequent cooling around 1100 ma 4 peak metamorphism in the southern granulite belt occurred at 2672 ma this was followed by emplacement of a vast basic igneous body represented as metagabbro and subsequent cooling around 1400 ma these two granulite belts were juxtaposed with each other during the neo mesoproterozoic which is correlatable with high pressure metamorphism in the northern granulite belt this tectonic movement might have been triggered by mesoproterozoic rifting of the southern bastar craton resulting in basic magmatism in the southern granulite belt mafic dykes were emplaced during subsequent readjustment of the crust and amphibolite facies reactivation main sausar event of granulites in the whole terrain lithological and tectonic arrangements metamorphic history along with the present geochronological data from citz point towards an evolutionary history similar to the grenville province of canada

multiple cmt source analysis of the 2004 sumatra earthquake while it is agreed that the great sumatra earthquake of december 26 2004 was among the largest earthquakes of the past century there has been disagreement on how large it was which part of the fault ruptured and how the rupture took place we present a centroid moment tensor cmt analysis of the earthquake in which multiple point sources are used in the inversion to mimic a propagating slip pulse the final model consists of five point sources with the southernmost sources accounting for the majority of the moment release the presumed fault planes of the southern sources strike northwest while those in the north strike northeast consistent with the geometry of the subduction trench slip on the fault is found to be more oblique in the north than in the south the inversion with five sources leads to a moment magnitude for the sumatra earthquake of m w 9 3 consistent with estimates from long period normal mode amplitudes

constriction due to subduction evidence for slab pull in the marianske lazně complex central european variscides pervasive l and l s tectonites of the marianske lazn eclogites include pencil fabrics constrictional folds and mullions that result from the first deformation increment observed petrological and microstructural data suggest that these structures formed by constrictional flow at deep subduction levels after or even during the eclogite facies stage and before the subsequent high pressure granulite facies overprint constriction at mantle depths is explained by taking into account the geometry and seismic properties of recent subduction zones here constrictional strain and associated l s tectonites should be expected below the rheologycontrolled slab bend at about 40 km depth where dip parallel extension and a reduced viscosity of the downgoing slab are compatible with a coaxial flow regime

multiple magmatic fabrics in plutons an overlooked tool for exploring interactions between magmatic processes and regional deformation this paper elaborates on the concept of multiple magmatic fabrics in plutons after a general overview of various types of multiple fabrics that may develop in magmatic rocks two case examples of porphyritic granite and melasyenite plutons in the bohemian massif are examined in the jizera granite complex variations in k feldspar phenocryst shape fabric revealed by image analysis of a 200 m long section of an underground tunnel are in contrast with homogeneously oriented magnetic ams fabric carried by coaxial contributions of biotite magnetite and maghemite in the kni eci stolec melasyenite pluton emplacement related margin parallel feldspar foliation was overprinted by flat lying foliation the latter is interpreted to record regional tectonic strain at the two stations examined in detail the crystallographic preferred orientation of biotite and amphibole in the inter phenocryst matrix measured using electron back scatter diffraction ebsd differed from both feldspar fabric and also from the ams principal directions multiple magmatic fabrics in these two plutons are interpreted in terms of fabric superposition where late weak strain is superposed onto a high strength phenocryst framework but is accommodated preferentially by small mineral grains biotite magnetite in the melt bearing matrix this mechanism may explain the discrepancy between mesoscopic feldspar fabric and ams we conclude that multiple magmatic fabrics in plutons may thus result from accumulated strain caused by different processes during final crystallization and as such may serve as a sensitive indicator of the evolving interactions between magmatic and tectonic processes in the earth s crust

structure age and mode of emplacement of the hercynian borderes louron pluton central pyrenees france the hercynian borderes louron pluton 20 km2 in the central pyrenees intrudes devonian and carboniferous metasediments it shows a concentric zoning and consists of a significant proportion of quartz gabbros in its periphery and of granodiorites biotite monzogranites and biotite muscovite monzogranites in its core ams study shows that the pluton corresponds to an elongated dome with a n100 e trending axis the anisotropy intensity ppara is high in the south and in the core of the pluton whereas it is low in the north the shape parameter t indicates that the fabric is strongly planar in a large central band oriented nw se whereas it is strongly linear in the western and eastern tips of the pluton these characteristics suggest that the borderes louron pluton emplaced in two episodes 1 intrusion of mafic magmas along a n100 e sill parallel to the regional foliation of the host metasediments and 2 injection of three successive silicic batches granodiorite biotite monzogranite two micas monzogranite which pushed aside the early mafic injections in situ u pb dating of zircon grains indicates that the emplacement age of the biotite monzogranite is 309 4 ma synchronous with the d 2 dextral transpressive event and close to the ages of the eastern pyrenean plutons may be slightly older

fabric evolution of rigid inclusions during mixed coaxial and simple shear flows abstract in a slowly moving viscous fluid a population of non interacting rigid inclusions evolves in an oscillatory fashion or creates a stable fabric depending on the flow geometry and the shape of the inclusions using jeffery s equations for the motion of a rigid ellipsoidal inclusion a mixed coaxial and simple shear flow was investigated both analytically and by numerical modeling exact results were obtained for spheroidal inclusions depending on the axial ratio of the inclusion and the amount of the coaxial component of flow individual inclusions can move cyclically or rotate to a stable orientation in one of two mutually orthogonal directions equations were found which allow us to distinguish between these types of motion and to determine the stable inclusion orientation the relative motions of individual inclusions determine the preferred orientation in a population of inclusions in a heterogeneous population with diverse axial ratios the fabric evolves as the superposition of subfabrics corresponding to subsets with different axial ratios the orientations of stable subfabrics depend on axial ratios and could thus be used as kinematic indicators in cases of a sufficiently large coaxial component of flow the fabric created by a heterogeneous population may comprise two stable mutually orthogonal subfabrics no exact results are available for general i e non spheroidal ellipsoidal inclusions and numerical modeling must be used if the coaxial component of flow is sufficiently strong the non spheroidal inclusions move much like the spheroidal ones orthogonal subfabrics may appear as transient features in the evolution of a homogeneous population of non spheroidal ellipsoidal inclusions

constriction during exhumation evidence from eclogite microstructures the eclogite zone tauern window eastern alps austria represents one of only a few examples of high pressure units providing both the prograde and the retrograde metamorphic evolution the eclogites are associated with rocks originating from continental and transitional crust that also have been affected by high pressure metamorphism eclogites that formed along the prograde path indicate metamorphic conditions of 17 20 kbar 1700 2000 mpa at 550 580 c the peak assemblages formed at 21 25 kbar 2100 2500 mpa at 600 620 c omphacite microstructures in particular shape fabrics and crystallographic preferred orientations indicate that the final phases of the prograde evolution were characterized by flattening strain the evolution at the pressure peak and along the exhumation path shows a constrictional strain geometry this change is interpreted to have been controlled by the force balance between slab pull related to an oceanic slab and the buoyancy of subducted adjacent continental crustal material including the eclogites at a certain lithospheric level where the subducted continental rocks were entirely surrounded by high density lower crustal and upper mantle material the buoyancy forces exceeded the slab pull forces this force change resulted in the buoyancy driven extrusion of continental material between two lithospheric plates the part of the subducted slab that remained in buoyant equilibrium was therefore affected by constriction moreover this process may have resulted in breakoff of the subducted oceanic slab if so the cessation of slab pull resulted in accelerated buoyancy driven extrusion of the continental material extrusion of these high pressure sheets would have been accompanied by constriction subparallel to the subduction channel as well

structural and anisotropy of magnetic susceptibility records of granitoid sheets emplacement during growth of a continental gneiss dome central sudetes european variscan belt 1 granitoid magmatic sheets emplaced syntectonically during growth of the orlica nieznik mantled gneiss dome central sudetes european variscan belt were examined by means of structural geology quartz and anisotropy of magnetic susceptibility ams fabric studies magmatic emplacement was localized along the eastern transpressive margin of the high metamorphic core and below the low grade detached mantle rimming the southern margin of the dome in the first area the magmatic sheets were emplaced parallel to the dilated subhorizontal foliation of an anisotropic pre orogenic block the resulting melt host rock multilayer localized the transpressive zone along which the bulk of magma was emplaced the ams study shows an across strike fabric zonation underlying a strongly transpressive solid state deformation in the hanging wall magmatic subhorizontal fabric in the foot wall and a transitional fabric in the center of the intrusion in contrast along the southern dome margin magmatic sheets intruded along steep foliations of weakly metamorphic mantle rocks and are affected by recumbent folding and subhorizontal shearing the bulk of the sheets present a shallow dipping magmatic foliation and an along strike magmatic lineation the variations of the quartz and magnetic fabrics are attributed to superimposition of pure shear dominated ductile thinning followed by simple shear dominated detachment onto the original steep fabric ams modeling confirms the role of variation of orientation of pre intrusive anisotropy during progressive deformation on the resulting fabric pattern and helps explaining observed variations in fabric orientations and symmetries this study highlights contrasting mechanical behavior of syntectonically emplaced magmas in different parts of a growing crustal scale mantled gneiss dome

loss of isotopic nd o and chemical ree memory during metamorphism of komatiites new evidence from eastern finland komatiites are often considered to depict the chemical and isotopic composition of their source rocks in the archean mantle however a weakness of these rocks in tracking the initial compositional heterogeneity of the earth s mantle is the ubiquitous presence of metamorphic recrystallization which casts some doubt about the preservation of primary chemical and isotopic characteristics two spinifex textured komatiite flows from the 2 75 ga old kuhmo greenstone belt siivikkovaara area of eastern finland document this weakness both flows have experienced low to medium grade metamorphism t 450 50 c and now consist entirely of secondary metamorphic assemblages of amphibole chlorite plagioclase with minor proportions of magnetite and ilmenite mgo contents range from 25 to 8 which suggests that low pressure differentiation was likely controlled by olivine and clinopyroxene fractional crystallization however neither major nor trace elements fall on olivine and or clinopyroxene control lines this is particularly well illustrated by the ree as there is an overall 60 variation of ce sm n ratios 0 38 to 0 91 which far exceeds that expected from olivine and clinopyroxene fractionation alone in fact careful evaluation of petrographic including mineral composition data and chemical characteristics shows that most elements of geological interest including the reputedly immobile ree were mobile on a whole rock scale during metamorphic recrystallization of these two flows this view is fully supported by sm nd isotopic data since both whole rock and mineral amphibole and plagioclase samples lie on a single isochron relationship at t 1800 ma an age which corresponds to the time of regional metamorphism thus the meta komatiite flows from siivikkovaara document a case of komatiite flow units in which metamorphism has induced whole rock scale resetting of primary ree patterns and sm nd isotope systematics as regards the nature of the mechanism responsible for this resetting it is suggested here that the secondary mineralogy played an important role as there are correlations between whole rock 147sm 144nd ratios major and trace element chemistry oxygen isotopic ratios and modal proportions of secondary minerals consideration of oxygen isotopic data as well as previous results from a komatiite flow from the nearby tipasjarvi belt further enable us to propose that the ree carrier was likely a co2 rich fluid the process of secondary ree redistribution prevents estimation of the true initial nd isotopic compositions of the two flows taken as a whole the results presented in this paper show that great care should be be exercised in the use of meta komatiites as probes of archean mantle composition

mechanical anisotropies and mechanisms of mafic magma ascent in the middle continental crust the sondalo magmatic system n italy

overprinting of magnetic fabrics in granites by small strains numerical modelling abstract the anisotropy of magnetic susceptibility ams is used to determine weakly defined mineral preferred orientation fabrics in granites however the effects of small strains superimposed on the low intensity ams fabrics typical of these rocks is not well understood numerical simulations are presented which investigate the effects of small superimposed strains on the shapes magnitudes and orientations of pre existing ams fabrics which are similar to those reported in the literature for undeformed granites a computer generated biotite petrofabric is subjected to progressive strain using march s strain response model for pure shear plane strain axially symmetric shortening and simple shear regimes results indicate that a pre existing ams fabric might be significantly modified or overprinted by small strains 10 15 strain in the pure shear and axially symmetric shortening regimes 0 5 1 0 for simple shear a new ams fabric may develop with an orientation similar to that expected for shearing of an initially isotropic petrofabric at low strains the evolution of the shape of the ams ellipsoid depends strongly on the orientation of the initial petrofabric with respect to the strain framework the ams ellipsoid may evolve towards either oblate or prolate shapes and the evolution in the ellipsoid shape may be reversed during progressive strain this modelling suggests that small strains affecting a pluton following its emplacement could mask ams fabrics developed earlier the results also suggest that in simple shear the orientation of the ams ellipsoid may serve as a shear sense indicator for small strains even if the earlier fabric is not isotropic

four magmatic fabrics in the tuolumne batholith central sierra nevada california usa implications for interpreting fabric patterns in plutons and evolution of magma chambers in the upper crust for the first time four distinct magmatic fabrics are documented in a composite plutonic body the tuolumne batholith central sierra nevada california usa one type of fabric was formed by strain caused by highly localized magma flow type 1 whereas the other three chamber wide fabrics recorded strain increments during boundary processes along batholith margins type 2 superimposed by increments of heterogeneous regional tectonic strain types 3 and 4 our present work indicates that in contrast to studies that consider magmatic fabrics to be simple structures formed by a single process magmatic lineations and foliations in plutons may reflect accumulated finite strain and form as composite structures recording multiple strain increments in relatively static actively deforming and rheologically complex crystal mushes at lower melt percentages we demonstrate that multiple magmatic fabrics in a single batholith may record remarkably different processes and thus preserve a temporal record of strain in the batholith from strain during internal chamber processes to postem placement regional tectonic strain however it may be commonly very problematic to infer the exact nature of flow or even fabric forming process from the preserved rock record our study also exemplifies how examination of magmatic fabric patterns in plutons complemented with geochronology may provide crucial constraints on the interplay among successive magma emplacement fabric preservation temporal evolution of strain fields in a crystallizing magma chamber and the development of crystal mush zones

fabric evidence for granodiorite emplacement with extensional shear zones in the variscan gredos massif spanish central system abstract three granitoid bodies in the central part of the gredos massif spanish central system batholith are tabular around 1 km in thickness and intruded into a migmatitic middle crust during the d3 deformation phase of the variscan orogeny petrologically they are composed of bt granodiorite and crd monzogranite and they show varying abundance of large cm scale feldspar megacrysts a detailed study of the shape preferred orientation spo magmatic fabric defined by these megacrysts together with a kinematic analysis of the structures due to interactions between them and the measurement of quartz c axis fabrics in migmatites and granitoids suggests that granitic magma and country rocks were mechanically coupled during deformation the emplacement took place along large scale extensional shear zones active during the first stages of the d3 phase the shape of the spo ellipsoids varies from constrictional at the centre of the granitic bodies to flattening or even oblate at their external contacts with the migmatitic host rocks the favoured interpretation of this spatial fabric variation is the overprinting of the emplacement fabrics by a constrictional tectonic regime associated with the growth of tabular magma chambers along extensional detachments followed by shear zone development commonly at the top of the granitic bodies the entire structure was later folded during the last stages of the d3 phase

tonalite sill emplacement at an oblique plate boundary northeastern margin of the bohemian massif abstract a tonalitic sill has been examined at the variscan transpressive boundary of the lugian and silesian plates at the ne margin of the bohemian massif a structural petrological and geochronological study reveals that it was emplaced syn tectonically with major ductile shearing in lower crustal rocks magmatic and pre rheological critical melt percentage rcmp fabrics are concordant with the hanging wall structures but discordant with those of the footwall the ams study shows the predominance of flattening strain at the margins and plane strain fabrics in the core numerical modelling of ams fabrics is in good agreement with the hypothesis of magma flow and deformation in oblique transpression a tectonic model was developed explaining emplacement and syn tectonic deformation of progressively cooled tonalitic intrusion

magnetic fabric methods and applications fabric is a ubiquitous and significant feature of geological materials the processes involved in the formation and deformation of rocks and sediments leave their mark on the orientations of the constituent mineral grains petrofabrics thus provide essential keys to understanding the history of geological materials magnetic anisotropy is directly related to petrofabric and has become one of the most rapid sensitive and widely used tools for its characterization the relationship between magnetic fabric and petrofabric is complex and depends on various factors including the composition concentration and grain size of mineral grains ongoing research in geological applications is paralleled by studies of the fundamental mineral magnetic phenomena involved the papers in this book represent the current state of investigations in magnetic anisotropy studies as a discipline that integrates geological interpretations mineral fabric development technical advances and rock magnetic properties

temperature time paths in the high p manicouagan imbricate zone eastern grenville province abstract the manicouagan imbricate zone miz eastern grenville province is a series of lithotectonic units assembled from different crustal levels during the grenvillian orogeny structural evidence along with u pb dating suggests that two separate stages of metamorphism occurred at ca 1050 and 1020 ma respectively the first stage is characterised by high pressure and temperature high pt metamorphism up to eclogite facies with a range of maximum recorded pressures between 14 and 20 kbar consistent with variations in burial depth maximum t conditions recorded from apparently different structural levels are rather similar 800 900 c suggesting high heat flow during eclogite facies metamorphism evidence of high temperatures 700 800 c recorded during the early stage of tectonic exhumation indicate near isothermal decompression the second stage is a high t event coeval with the emplacement of syn metamorphic granite and is recorded by rocks in the upper most tectonic slice boundary zone in the south east miz this event may also be responsible for amphibolite facies overprinting across the rest of the miz using the u pb and pt data sets along with published diffusion rates for pb in monazite titanite and rutile tt paths have been modelled for several of the lithotectonic units in most of the units suggested cooling rates appear to have been relatively fast during initial exhuamtion but show a prolonged period of slower cooling 5 10 c ma for 30 40 ma apparently at odds with the steep near isothermal pt paths preservation of eclogitic textures and preservation of garnet zoning in the highest grade rocks on the other hand in the boundary zone the recorded cooling rates are much faster 20 c ma indicative of tectonic exhumation this phase of rapid cooling in the boundary zone corresponds in time with the slow cooling rates at 1030 1000 ma in the rest of the miz thus thrusting of the boundary zone over the rest of the miz appears to have caused a thermal overprint which was superimposed on the tt paths taken as a whole the tt paths for the miz are interpreted as representing two separate metamorphic events which were both relatively short in duration

tectonic strain recorded by magnetic fabrics ams in plutons including mt kinabalu borneo a tool to explore past tectonic regimes and syn magmatic deformation tectonic strain commonly overprints magmatic fabrics in ams anisotropy of magnetic susceptibility data for plutonic rocks produced by both compressional and extensional regimes mt kinabalu borneo is a composite pluton with an exceptional vertical range of exposure and clearly defined internal contacts we show that tectonic fabrics are recorded pervasively throughout the intrusion even near contacts and present a workflow distinguishing compressive and extensional syn magmatic deformation at mt kinabalu this reveals a pervasive tectonic fabric indicating nw se miocene extension in borneo at 7 9 7 3 ma later than previously recognised oriented nw se at 319 13 1 comparing data from mt kinabalu with data from globally distributed studies shows that tectonic strain is commonly recorded by plutons therefore ams fabric can be used to identify the syn magmatic tectonic setting and combined with both geochronology and evidence for paleomagnetic rotation to provide a powerful tool for accurate determination of syn magmatic tectonic regimes and strain orientations within temporal frameworks

variscan magnetic fabric overprinting in sedimentary and crystalline thrust sheets in the ne bohemian massif the magnetic fabric of pre cambrian and devonian crystalline rocks of the hrub jesenik mountains and of lower carboniferous sedimentary rocks of the nizk jesenik mountains is predominantly deformational in origin the orientations of the tectonic magnetic fabric elements are similar in all rocks and geological units investigated at least one strong deformation phase affected both the sedimentary and crystalline complexes overprinting the original depositional magnetic fabric in sedimentary rocks as well as earlier deformational magnetic fabrics in crystalline rocks the overprinted magnetic fabric is probably of variscan origin

detecting geophysical signals in gravity satellite missions summary geophysical events implying a large mass displacement especially in the vertical direction can produce a localized change of the earth gravity field the sumatra earthquake of 2004 december is an example of this kind of geophysical phenomena the aim of this work is to investigate the possibility of detecting such gravimetric changes by exploiting the information coming from gravity space missions proper testing procedures to be directly applied into the observation space have been set up they require to propagate the effect of the geophysical event to the satellite observables and then to compare their track wise spectra with the instrument noise level these testing procedures have been applied to a realistic simulation of the gravimetric signal generated by the sumatra earthquake considering three different geodetic missions the forthcoming goce mission recovering a full gravity gradient tensor the presently flying grace mission collecting low low satellite to satellite tracking sst observations and a possible future gravimetric mission based on the same principle of grace but with an improved accuracy thanks to the use of laser doppler interferometry the results of the simulations confirm the higher capability of the sst missions of detecting gravity variations due to geophysical phenomena like the sumatra earthquake however this signal could be seen also by a gradiometric mission like goce on condition that a considerable amount of observations is collected over the study area after the event

magnetic anisotropy in natural amphibole crystals anisotropy of magnetic susceptibility ams is often used as a proxy for mineral fabric in deformed rocks to do so quantitatively it is necessary to quantify the intrinsic magnetic anisotropy of single crystals of rock forming minerals amphiboles are common in mafic igneous and metamorphic rocks and often define rock texture due to their general prismatic crystal habits amphiboles may dominate the magnetic anisotropy in intermediate to felsic igneous rocks and in some metamorphic rock types because they have a high fe concentration and they can develop a strong crystallographic preferred orientation in this study the ams is characterized in 28 single crystals and 1 crystal aggregate of compositionally diverse clino and ortho amphiboles high field methods were used to isolate the paramagnetic component of the anisotropy which is unaffected by ferromagnetic inclusions that often occur in amphibole crystals laue imaging laser ablation inductively coupled plasma mass spectrometry and mossbauer spectroscopy were performed to relate the magnetic anisotropy to crystal structure and fe concentration the minimum susceptibility is parallel to the crystallographic a axis and the maximum susceptibility is generally parallel to the crystallographic b axis in tremolite actinolite and hornblende gedrite has its minimum susceptibility along the a axis and maximum susceptibility aligned with c in richterite however the intermediate susceptibility is parallel to the b axis and the minimum and maximum susceptibility directions are distributed in the a c plane the degree of anisotropy k increases generally with fe concentration following a linear trend k 1 61 10 9 fe 1 17 10 9 m3 kg additionally it may depend on the fe2 fe3 ratio for most samples the degree of anisotropy increases by a factor of approximately 8 upon cooling from room temperature to 77 k ferroactinolite one pargasite crystal and riebeckite show a larger increase which is related to the onset of local ferromagnetic s l interactions below about 100 k this comprehensive data set increases our understanding of the magnetic structure of amphiboles and it is central to interpreting magnetic fabrics of rocks whose ams is controlled by amphibole minerals

remanence rotation due to rock strain during folding and the stepwise application of the fold test numerical modeling was conducted to determine the effects of simple models of folding strain on prefolding fisherian distributions of magnetization i found that the constant volume simple shear associated with flexural slip flexural flow folding can rotate a prefolding magnetization to have a maximum precision parameter k value at partial unfolding and thus appear to be synfolding in age if the magnetization is treated as a passive line marker this behavior only occurs for steep initial magnetizations the initial homogeneity of the fisherian precision parameters from each limb is degraded by this type of deformation and may be used to detect a strain modified remanence if the magnetization is carried by rigid mechanically active ellipsoidal or spherical particles a maximum k value at partial unfolding will occur for any initial inclination with the special case that rigid spheres will be rotated to cause a maximum k value at 50 unfolding for any initial inclination homogeneity of limb precisions is not affected in this case a discontinuous model of strain during folding in which pressure solution removes material at an axial planar spaced cleavage and causes limb dips steeper than bedding dips could also produce a maximum k value at partial unfolding strain and remanence studies of flexural slip folding in the allentown formation dolomite and the bloomsburg formation red sandstones and mudstones suggest that 1 the rigid grain model may be a more realistic model of magnetic particle behavior during shear strain and 2 about one quarter to one third of the theoretically predicted simple shear strain occurs in these rocks this amount of strain cannot explain the synfolding behavior observed in the allentown formation but could explain the maximum k values at 80 90 unfolding seen in the bloomsburg formation and perhaps other appalachian clastic rocks

modified jeffery model influence of particle concentration on mineral fabric in moderately concentrated suspensions 1 a modified jeffery model involving particle interactions allows the simulation of preferred orientation of crystals and the anisotropy of magnetic susceptibility in magmatic flow with up to 40 of rigid particle fraction numerical simulations are compared to analogue and natural fabrics a study of the role of particle concentration shows that the increasing percentage of crystal fraction in dilute suspensions leads to progressive attenuation of the fabric intensity and cyclicity at high strains in simple shear flow the lineation converges to a constant value close to the shear plane with increasing particle concentration the fabric diverges from the shear direction reflecting the effect of increased crystal tiling the model can be applied to quantify mineral preferred orientations of crystal mushes in magmatic fabric studies

possible cryptic tectono magnetic fabrics in post tectonic granitoid plutons of the canadian shield two late archean granitic plutons forcefully intruded and thermally metamorphosed archean schists feldspar magacrysts aligned concentrically with the margins during inflation substantial tectonic deformation never affected the plutons nevertheless both plutons show the same consistently oriented cryptic magnetic fabric revealed by anisotropy of low field susceptibility ams from 134 samples they have an ne sw vertical magnetic foliation and a magnetic lineation trending 060 15 eigenvalues of the orientation distribution of principal susceptibilities show that the magnetic fabrics have almost identical strengths orientations and symmetry in both plutons we propose a post magmatic reactivation of the earlier regional tectonic shortening this imparted a cryptic tectonic magnetic fabric on the plutons that overprinted the magmatic ams fabric in most outcrops the plutons ams fabrics are subparallel to the much older schistosity of the country rocks because multidomain magnetite provides 99 of the low field susceptibility of the rocks it controls the ams however we see no alignment of the magnetite grains thus magnetic anisotropy may be due to stress alignment of intragranular domain walls and not controlled by grain shape as usually assumed for magnetite

model of successive granite sheet emplacement in transtensional setting integrated microstructural and anisotropy of magnetic susceptibility study 1 this study presents a model of successive emplacement of three granite plutons in transtensional deformation regime controlled by the preextensional synconvergent history of the lower and middle crust in the central vosges mountains france the complex compressional orogenic structure recorded a vertical exhumation related fabric in midcrustal levels which was overprinted by the regional extension three successively emplaced granite sheets exploited the inherited vertical anisotropy obliquely oriented with respect to the applied tensile stress this progressive opening of original steep fabric leads to the sequential generation of free spaces toward the south and emplacement and deformation of granite sheets repeated granite intrusions are responsible for reheating of southern margins of the already partially solidified granites which became reactivated under lower ambient thermal conditions related to overall 6 ma cooling of rapidly exhumed crust the results of anisotropy of magnetic susceptibility ams fabric modeling suggest a highly partitioned oblique extension divided into pure shear dominated deformation close to the central and northern margins of intrusions and wrench dominated shear along the southern margins the ams modeling suggests the importance of overprinting of the intrusive fabrics by the transtensional deformation

quantitative comparison of microfabric and magnetic fabric in black shales from the appalachian plateau western pennsylvania u s a abstract anisotropy of magnetic susceptibility ams has been shown to be a good proxy for crystallographic preferred orientation texture however it is not clear in detail how different factors e g modal composition and preferred orientation define the total ams in a rock black shale samples from a drill core on the appalachian plateau in western pennsylvania were analyzed with respect to their microfabric as determined by texture and microstructure and ams low and high field ams which was measured at room temperature reveals that the ams of the samples is dominated by the para and diamagnetic phases synchrotron diffraction was applied to determine the texture of all relevant mineral phases incorporated in the samples muscovite and chlorite pole figures show single maxima perpendicular to the foliation reflecting dominant flattening strain from these textures and the modal compositions ams models were calculated using the intrinsic magnetic anisotropy of the single crystals the modeled and measured ams are comparable in terms of their principal directions and shapes of the anisotropy ellipsoid for the dominantly paramagnetic samples with the maximum susceptibility axes oriented subhorizontal to the ne sw both textures and ams indicate that the samples have undergone largely bedding compaction with a weak tectonic overprint linked to the alleghenian orogeny our results suggest that the microfabric and the magnetic fabrics on the plateau 200 km away from the allegheny front detect the tectonic shortening the ams modeling demonstrates how the contribution of the intrinsic ams of each mineral controls the ams of the whole rock

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

controls on the sr and nd isotopic compositions of hydrothermally altered rocks from the pindos ophiolite greece abstract the sr and nd isotopic behaviour of hydrothermally altered basaltic rocks from the pindos ophiolite nw greece has been investigated samples were obtained mainly from rocks affected by intense hydrothermal alteration in field areas believed to represent hydrothermal discharge zones formed at a mesozoic seafloor spreading centre 87 sr 86 sr ratios in the altered rocks show a narrow range of values intermediate between those of seawater and fresh rock regardless of the degree of alteration this has been interpreted as the result of high overall water rock ratios which were sufficient to produce a homogeneous overprint throughout most of the hydrothermal cell a sr shift index which uses the sr isotopic composition and sr concentration of both rock and fluid has been derived to express the degree of sr exchange between rock and seawater it has been used to investigate the variations in water rock interaction between known hydrothermal systems and to compare ophiolite hosted with modern oceanic systems the results indicate that even when compared on such a uniform basis all the known present day hydrothermal systems are generally more rock dominated than those of pindos and other ophiolites 143 nd 14 nd ratios in the altered rocks are much less markedly affected but may show a shift from original magmatic values the results presented here suggest that this effect cannot simply be attributed to exchange with seawater nd these shifts must result from seawater transporting basaltic nd of a different isotopic composition from elsewhere in the volcanic pile into the zones of intense alteration this study has shown that sr and nd isotopes vary independently as a result of their different original distribution as well as their contrasting geochemical mobility

magnetic fabric and rheology of co mingled magmas in the nasavrky plutonic complex e bohemia implications for intrusive strain regime and emplacement mechanism abstract the fabrics of mafic microgranular enclaves mme and of the host granodiorite of the old granodiorite intrusion of the nasavrky plutonic complex e bohemia were investigated by means of magnetic anisotropy the magnetic fabric in mme is oriented coaxially with the magnetic fabric of the host granodiorite which is undoubtedly magmatic intrusive in origin consequently the magnetic fabric in mme originated during the same process as the magnetic fabric in granodiorite i e during the granodiorite emplacement in addition also the degree of anisotropy and the shapes of susceptibility ellipsoids are very similar in mme and in granodiorite which probably indicates that the mme had probably a similar viscosity to that of granodiorite and behaved as passive markers whose shapes resembled those of the intrusive strain ellipsoids petrological and geochemical approaches coupled with rheological modelling allow the prediction of the physical states of magmas and of the development of their internal fabrics observed fabrics were compared to the results of numerical modelling of multiparticle systems slowly moving in viscous fluid the steep magnetic foliations and almost vertical magnetic lineations suggest that today s erosion level represents a relatively deep intrusive level where magma flowed vertically and its intrusion was controlled by the shape of the feeder zone used for magma ascension

combined lu hf and sm nd geochronology of the marianske lazně complex new constraints on the timing of eclogite and granulite facies metamorphism abstract lu hf and sm nd garnet whole rock geochronology combined with petrographic observations minero chemical variations thermodynamic modelling and structural data was used to constrain the p t t d evolution of eclogites from the marianske lazn complex bohemian massif boudins of mostly isotropic eclogite with relict steep eclogite facies fabric are affected by steep migmatitic foliation which is followed on a regional scale by the development of almost pervasive predominantly se dipping extensional foliation the structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite a least retrogressed sample of eclogite shows clusters of fine grained inclusion poor garnet omphacite relicts surrounded by a fine grained clinopyroxene plagioclase symplectite with minor amphibole biotite plagioclase intergrowths after white mica kyanite with plagioclase spinel coronas and accessory rutile rare potassic white mica occurs as inclusions in omphacite a more retrogressed eclogite with no omphacite or kyanite relicts contains inclusion poor garnet surrounded by amphibole plagioclase corona in a matrix dominated by plagioclase amphibole symplectite with minor clinopyroxene in places the symplectite is overgrown by coarse grained amphibole peak p t conditions inferred from combined conventional thermobarometry and phase equilibria modelling and based on inclusions of white mica up to 3 33 si p f u matrix omphacite jd33 36 and garnet core alm33 38prp38 42grs22 25sps1 compositions are 25 kbar at 650 750 c a ht overprint occurred at 14 18 kbar and 800 c based on coexisting clinopyroxene jd18 24 plagioclase an18 35 and amphibole na b lu hf and sm nd garnet geochronology has been applied to both samples an older age c 390 ma obtained by the lu hf method is interpreted as the timing of hp metamorphism while c 15 ma younger ages were obtained by the sm nd method as temperatures for the ht overprint exceed the empirically and experimentally determined closure temperature of the sm nd system the sm nd ages are interpreted to date cooling following the ht overprint combined together contrasting eclogite and amphibolite facies migmatite fabrics the mineral textures calculated p t conditions and distinct lu hf and sm nd ages provide a complete p t t d path characterised by rapid 15 ma transition from hp subduction crustal thickening to extensional ht shearing this unconventional exhumation path does not fit to models of monocyclic exhumation in a subduction channel proposed for the munchberg and zev devonian hp units to the west in contrast the post peak extensional low angle shearing shortly after subduction and collision resembles more the geodynamic model typical for the iberian subduction system both in time scales and sequence of tectonic events

interpreting magnetic fabrics in amphibole bearing rocks abstract if amphibole is a major constituent in a rock its magnetic fabric can be largely controlled by the crystallographic preferred orientation of amphibole this study describes the para magnetic anisotropy in two amphibolites both containing ca 70 hornblende with rather strong crystallographic preferred orientation both amphibolites display a significant and well defined anisotropy of magnetic susceptibility with the minimum susceptibility approximately normal to foliation however in one amphibolite the maximum susceptibility is parallel to the lineation whereas in the other it is not this seemingly inconsistent observation can be explained by the intrinsic susceptibility anisotropy of single crystals of hornblende and their texture in the rocks numerical models show how the principal susceptibility axes relate to macroscopic foliation and lineation for point and fiber textures this study underlines the potential of using magnetic anisotropy to obtain information about mineral fabrics in mafic rocks at the same time it highlights the necessity for taking into account single crystal properties of the mineral s responsible for the anisotropy and their crystallographic preferred orientation when interpreting magnetic fabrics

mechanics microstructure and ams evolution of a synthetic porphyritic calcite aggregate deformed in torsion in order to investigate the mechanical microstructural and ams evolution of porphyritic mylonites we made a synthetic aggregate composed of 70 fine calcite 3 mm in length defined a conspicuous

a new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method a growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized rigid sponge magma this paper demonstrates that such magma could be idealized as a rheological solid and that the development of non coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics using the finite element method fem we modeled two strain regimes of small magnitudes plane strain horizontal simple shear with the shear strain of up to 0 30 and plane strain pure shear of up to 15 shortening superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix in the simple shear regime the phenocrysts slightly rotate toward the shear plane while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45 or less to the phenocryst fabric simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics by contrast the vertical phenocryst fabric is maintained in the pure shear regime and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening 5 shortening after 10 ky in our model we conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span first thousands of years is required to develop magmatic fabric in a pluton for normal rates 10 15 to 10 13 s 1 of tectonic deformation

40ar 39ar ages of precambrian manganese ore minerals from sweden india and morocco in order to test their chronometric potential 40ar 39ar stepheating and 4he analyses have been carried out on five manganese ore minerals of the hollandite cryptomelane series from three precambrian manganese deposits ultevis sweden sitapar india bachkoun morocco samples from the metamorphic occurrences ultevis and sitapar yielded ar ages of 1 8 ga and 0 95 ga interpreted as the age of postmetamorphic cooling hollandites ultevis and of an early k introducing alteration process subsequent to amphibolite facies metamorphism cryptomelanes sitapar both data are consistent with known chronologies of the svecokarelian and satpura orogenic cycles a date of 670 ma obtained for a hollandite from a volcanogenic vein deposit bachkoun however contrasts with published extrusion ages of 580 560 ma for the volcanic host rocks ouarzazate series probably due to incorporation of excess argon the use of the 40ar 39ar technique together with multiple isotope systematics made it nevertheless possible to establish a reasonable estimate of a mineralization age close to 580 ma measurement of fractional ar losses during vacuum step heating 500 1600 c although indicating good ar retentivities failed to define model diffusion parameters because of non linear arrhenius arrays helium diffusion results 200 1200 c indicated retention of radiogenic 4he by the samples corroborated by u he mineral dates between 0 96 and 0 31 ga potassium bearing manganese oxides are therefore able to retain argon possibly also 4he through geological times and may thus provide ages of ore forming processes and perhaps later cooling and alteration stages

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

patterns of nd and sr isotopic ratios produced by magmatic and post magmatic processes in the shiant isles main sill scotland the shiant isles main sill of the british tertiary igneous province is a classic example of a differentiated alkaline basic sill four separate intrusions each emplaced internally in rapid succession form a 165 m thick sill hosted by lower jurassic sedimentary rocks extensive nd and sr isotopic studies were conducted on samples from a vertical section through the sill where the relationships of samples to one another are well defined the results illuminate patterns of modification of isotopic ratios and clarify the petrogenesis magma sources crustal contamination magmatic processes bulk mixing interstitial liquid mixing and post magmatic alteration hydrothermal effects on sr and nd overall the whole rock initial 87sr 86sr ratios range from 0 7037 to 0 7061 while initial 143nd 144nd ratios vary from 0 51243 to 0 51286 nd 0 7 to 5 7 values that contrast markedly with those of the country rock acid leaching hcl of the whole rock samples that removes analcime indicates that most of the scatter in the 87sr 86sr is caused by the ubiquitous sub solidus aqueous alteration during which more radiogenic sr was introduced into the sill especially along the margins and also reveals magmatic isotopic ratios in contrast nd was immobile during fluid interaction so that the sill 143nd 144nd ratios were not affected even 1 m from the country rock contact using leached rock values 87sr 86sr and 143nd 144nd ratios are inversely correlated from magmatic processes magmas with two distinct isotopic compositions were involved a more primitive one with 143nd 144nd 0 51285 and 87sr 86sr 0 7035 that produced the first two intrusions and a more evolved one with 0 51252 and 0 7048 that produced the third intrusion mixing of the two magmas was very limited restricted to near contacts between units and apparently occurred by interstitial melt migration the more evolved crinanitic magma was probably produced from a batch of the more primitive picritic melt by a small degree of crustal contamination and crystal fractionation during a short crustal residence prior to ascent and emplacement

strain and magnetic remanence abstract experimental data may be compatible with the hypothesis that a single direction of magnetic remanence rotates as a rigid marker with strains up to 40 shortening in coaxial perfect flattening x y z detailed agreement with the passive line model is relatively poor for the specimens in which remanance is carried by magnetite however for this range of strains the differences with the passive line model wettstein s equation are so slight that the latter model may be more easily employed to de strain or restore deformed remanance to its original attitude in the case of hematite bearing remanences the differences between the passive line and rigid marker model are even smaller because of the higher aspect ratios of grains of hematite therefore it is suggested that wettstein s equation may be safely used to restore remanence after even higher strains where the remanence is carried by hematite

noncoaxial k feldspar and ams subfabrics in the land s end granite cornwall evidence of magmatic fabric decoupling during late deformation and matrix crystallization 1 a comparative study of the anisotropy of magnetic susceptibility ams and k feldspar phenocryst fabrics in the land s end granite demonstrates that the ams fabric predominantly reflects late magmatic deformation tensor analysis of the k feldspar fabric shows a complex pattern characterized by meter scale variations in orientation symmetry and intensity mainly related to heterogeneous flow of the phenocryst rich magma during emplacement in contrast the ams fabric is predominantly homogenous subhorizontal and oblate and is stable at the pluton scale quantitative microstructural analysis suggests that the ams fabric is controlled by deformation of the partially crystallized matrix resulting from the combined effects of late internal adjustment within the pluton and regional deformation a general model of fabric development associated with a vertical pure shear overprint on a variable vertical fabric is evaluated by numerical modeling the study demonstrates how the memory of different fabric elements may be dependent upon their grain size crystallization sequence and recorded previous strain

multistage magma emplacement and progressive strain accumulation in the shallow level krkonose jizera plutonic complex bohemian massif 1 field relationships combined with new u pb zircon geochronology suggest that the shallow level krkonose jizera plutonic complex northern bohemian massif was assembled successively from bottom to top starting with emplacement of the separately evolved s type tanvald granite 317 3 2 1 ma followed by at least two voluminous batches of the i type porphyritic liberec 319 5 2 3 ma and jizera 320 1 3 0 ma and 319 3 3 7 ma granites the intrusive sequence was completed by uppermost minor intrusions of the equigranular harrachov 315 0 2 7 ma and krkonose granites the i type granites exhibit an unusually complex pattern of superposed feldspar phenocryst and magnetic fabrics as revealed from the anisotropy of magnetic susceptibility ams the outer liberec granite preserves margin parallel foliations and lineations interpreted to record emplacement related strain captured by cooling from the pluton floor and walls in contrast the inner jizera harrachov and krkonose granites were overprinted by synmagmatic strain resulting from dextral movements along regional strike slip faults cutting the opposite ends of the plutonic complex late stage felsic dikes in the liberec and jizera granites reorient from horizontal to vertical lineation perpendicular attitude in response to changing the least principal stress direction whereas mafic schlieren do not do so representing only randomly oriented small scale thermal mechanical instabilities in the phenocryst framework in general this case example challenges the common approach of inferring pluton wide magma flow from interpolated foliation lineation and schlieren patterns more likely magmatic fabrics in large plutons record complex temporal succession of superposed strains resulting from diverse processes at multiple scales