magnetic fabric in the malanjkhand granite central india implications for regional tectonics and proterozoic suturing of the indian shield abstract in this paper field microstructural and anisotropy of magnetic susceptibility ams data are presented from the 2 48 ga malanjkhand granite and adjacent gneiss with an aim to evaluate the time relationship between fabric development in the granite and regional tectonics the central indian suture cis that demarcates the southern margin of the ne sw to ene wsw trending central indian tectonic zone citz and is a consequence of the accretion between the northern and southern indian shields lies to the north of the granite the northern margin of the granite that has proximity to the cis is mylonitized and shows a dextral top to the ne sense of shear field and magnetic foliation in the gneiss are parallel to each other as well as to the field foliation in the western and northwestern margin of the granite also the field fabrics in the granite and gneiss curve clockwise into the cis the magnetic foliation trajectories curve from a ns orientation in areas remote from the cis to a ne sw orientation in parts that are proximal to the cis in the north the granite shows synmagmatic deformation fabrics such as preferentially oriented zoned feldspar phenocrysts as well as evidence of high t solid state deformation fabric such as chessboard pattern in quartz magnetic anisotropy increases towards the cis which is inferred to support synmagmatic deformation it is concluded that the tectonic evolution of the citz and emplacement fabric development in the malanjkhand granite were synchronous phenomena wnw ese directed convergence led to transpression which is inferred to be responsible for the emplacement of the granite it is concluded that in the malanjkhand granite the development of syndeformational emplacement fabrics to syntectonic cooling was a continuum and the suturing of the northern and southern indian shields along the cis took place during the palaeoproterozoic period thus the study provides an insight into the amalgamation and stabilization of the indian shield during the late archaean palaeoproterozoic time

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

misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

magnetic fabric development in a highly anisotropic magnetite bearing ductile shear zone seve nappe complex scandinavian caledonides magnetite bearing mylonitic garnet micaschists close to the major suture between the baltica and iapetus terranes seve nappe complex scandinavian caledonides show very high anisotropy of magnetic susceptibility ams with corrected degree of anisotropy p up to 4 8 three different magnetic fabric types can be distinguished they correspond to protomylonite type i p 3 respectively the orientation of the ellipsoid axes from all applied magnetic fabric methods in this study is similar with shallow dips of the metamorphic foliation toward wsw and subhorizontal mostly nw se trending mineral lineation differences between subfabrics were minimized under high shear strain as all markers tend to align parallel with the shear plane the very high anisotropies and mostly oblate ellipsoid shapes of type iii correlate with high magnetic susceptibility kmean up to 55 10 3 si units and are related to the concentration of magnetite aggregates with shape preferred orientation they show a distinct field dependence of magnetic susceptibility of up to 10 in the kmax direction we attribute this field dependence to a memory of high strains in the domain walls of the crystals acquired during synkinematic magnetite growth during shear zone fabric development at temperatures of 550 570 c

shape anisotropy versus magnetic interactions of magnetite grains experiments and application to ams in granitic rocks the magnetic fabric of ferromagnetic granitic rocks results from both the shape preferred orientation of individual magnetite grains and their distribution anisotropy through magnetic interactions between neighbouring grains measurement of the low field magnetic anisotropy of single multi domain magnetite grains shows a linear correlation between their magnetic anisotropy degree and their aspect ratio interactions between two elongated grains were studied experimentally using two types of grain arrangement an aligned configuration and a side by side configuration for a distance between the grain centers equal to approximately twice the average grain size the magnetic susceptibility and its anisotropy are enhanced in both configurations and the direction of kmax the easiest magnetization axis is stable in the aligned configuration whereas it rotates toward an orthogonal direction in the side by side configuration depending on the distribution of the interacting magnetite grains magnetic interactions may therefore either increase the whole rock anisotropy magnitude or reduce it as in the given example of the granitic rocks from madagascar

magnetic susceptibility anisotropy a new petrofabric tool in migmatites 1 the rheological behavior of the lower to middle continental crust during orogenic deformation is poorly understood migmatite common at this crustal level remains difficult to analyze from a structural viewpoint because of pervasive recrystallization we present new anisotropy of magnetic susceptibility ams data from 217 specimens of migmatites of the superior province in minnesota with the aim of investigating its potential as a petrofabric tool quarry exposures provide the ideal sampling playground for such a study the migmatites are coarse grained are granitic to tonalitic in composition and display a centimeter scale compositional layering the layering and the regional foliation are subhorizontal to shallowly dipping to the ne mineral lineations are difficult to observe due to recrystallization but trend around 70 n with gentle plunges magnetic properties are carried mainly by multidomain md primary magnetite grains ranging in size from 20 to 200 m the magnetic susceptibilities are generally high around 5 10 10 3 si the degree of magnetic anisotropy is large between 1 2 and 1 3 the principal axes of the ams ellipsoids coincide with those of the finite strain and the degree of anisotropy broadly correlates with the mineral fabric intensity this study is the first detailed investigation of magnetic fabrics in migmatites these preliminary results suggest that the ams technique is an easy and powerful tool for the petrofabric analysis of migmatites

controls on lineation development in low to medium grade shear zones a study from the cap de creus peninsula ne spain lineations composed of similarly oriented elongate mineral aggregates or grains are a common feature in deformed rocks but it is unclear which factors control the development of such lineations field observations and microstructural analysis of samples which were taken from discrete greenschist to lower amphibolite facies shear zones of the easternmost variscan pyrenees show that strain is only one of several factors that control the strength and type of a lineation dynamic recrystallization metamorphic reactions and rigid body rotation are also important controlling factors for the development of lineations the most important of these is dynamic recrystallization the way in which dynamic recrystallization influences lineation development is largely a function of the initial fabric in a specific rock type different lithologies with different initial fabrics produce distinctly different types and strengths of lineations even if deformed to the same finite strain in the same shear zone an initial fine grain size and a monomineralic composition of the parent rock type commonly hinder the development of lineations in contrast in initially coarse grained polymineralic rocks well developed lineations commonly develop therefore the ratio of initial to dynamically recrystallized grain size determines to a large extend the development of such lineations

plastic deformation of metamorphic pyrite new evidence from electron backscatter diffraction and forescatter orientation contrast imaging application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods specifically use of forescatter solid state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images which map the distribution of deformation domains within grains use of electron backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images combination of these techniques shows that the pyrite studied deforms by slip on 100 and more rarely 110 systems slip is often associated with distributed rotation of up to 20 about and more rarely axes pyrites may have simple histories involving rotation about a single axis or more complex histories involving rotation about different axes and more rarely in different domains of the same pyrite grain or sequential rotations about quite different systems typically distributed rotation about followed by discrete rotation about a non crystallographic axis

emplacement mechanism of the main granite pluton of the lavras do sul intrusive complex south brazil determined by magnetic anisotropies abstract magnetic fabric and rock magnetism studies were performed on apparently isotropic granite facies from the main intrusion of the lavras do sul intrusive complex pluton lsic rio grande do sul south brazil this intrusion is roughly circular 12 13 5 km composed of alkali calcic and alkaline granitoids with the latter occupying the margin of the pluton magnetic fabrics were determined by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm the two fabrics are coaxial the parallelism between ams and aarm tensors excludes the presence of a single domain sd effect on the ams fabric of the granites several rock magnetism experiments performed in one specimen from each sampled site show that for all sites the magnetic susceptibility is dominantly carried by ferromagnetic minerals while mainly magnetite carries the magnetic fabrics lineations and foliations in the granite facies were successful determined by applying magnetic methods magnetic lineations are gently plunging and roughly parallel to the boundaries of the pluton facies except at the few sites in the central facies which have a radial orientation pattern in contrast the magnetic foliations tend to follow the contacts between the different granite facies they are gently outerward dipping inside the pluton and become either steeply southwesterly dipping or vertical towards its margin the lack of solid state and subsolidus deformations at outcrop scale and in thin sections precludes deformation after full crystallization of the pluton this evidence allows us to interpret the observed magnetic fabrics as primary in origin magmatic acquired when the rocks were solidified as a result of processes reflecting magma flow the foliation pattern displays a dome shaped form for the main lsic pluton however the alkaline granites which outcrop in the southern part of the studied area have an inward dipping foliation and the steeply plunging magnetic lineation suggests that this area could be part of a feeder zone the magma ascent probably occurred due to ring diking

reply to the discussion of deb 2013 on the paper of saha et al 2013 entitled tectono magmatic evolution of the mesoproterozoic singhora basin central india evidence for compressional tectonics from structural data ams study and geochemistry of basic rocks abstract we appreciate that our attempt to document deformation pattern within the mesoproterozoic singhora group india and to resolve some key stratigraphic issues in chhattisgarh geology patranabis deb and chaudhuri 2008 dhang and patranabis deb 2012 in recent times has attracted the attention of deb we whole heartedly welcome the keen interest shown by deb in our paper and discussions attempted by him on different aspects of the paper here we offer our strong rebuttal of his imaginative discussions principally because the claims made by deb are neither supported by outcrop based field data nor through any available subsurface geophysical data it appears that the key concern of deb 2013 was to force fit the structural grains of the sonakhan greenstone belt within the deformation pattern of singhora cover sediments upholding an unsubstantiated assumption that the sonakhan greenstones belt constitutes the basement for the singhora basin without citing any evidence outcrop geophysical or bore hole showing sonakhan metamorphics in the basement of the singhora basin he plotted the structural data of the sonakhan greenstone belt and attempted comparison of those with the bedding attitudes of the singhora cover sediments and claimed that the possible rejuvenation of basement faults triggered folding in the singhora cover sediments leaving aside the issues of lack of any field support available geophysical results 3 layer gravity survey by srinivas et al 2000 magnetic survey by srinivas et al 2004 and short borehole observations pers comm mukherjee a 2012 all clearly demonstrates unclassified archean paleoproterozoic granites and gneisses of the bastar craton as basement for the singhora basin not the sonakhan greenstones neither is the presence of any basin scale fault inferred from the basement of the singhora basin in any geophysical model the result of magnetic survey along the basna sohela transect carried out by srinivas et al 2004 which represents the singhora basement in particular clearly shows granites as immediate basement for the singhora as the very assumption of deb 2013 i e that the sonakhan represents the basement to the singhora basin does not stand either on his own field data or on any strong reasoning we refrain from any further discussion on this topic instead we frame our reply on the doubts raised by deb 2013 on the mapping field analysis and concepts used in our paper saha et al 2013

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

magnetic fabric of clay sediments from the external northern apennines italy abstract we report on the anisotropy of magnetic susceptibility ams analyses of fine grained sediments deposited during the messinian in foredeep basins at the front of the northern apenninic chain the data refer to 32 sampling sites mostly distributed in the fine grained intervals of the laga and colombacci formations extending along the belt for a total length of about 300 km rock magnetism analyses indicate that the magnetic susceptibility and its anisotropy are in most cases dominated by the paramagnetic minerals of the clay matrix in order to delineate the contribution of the ferrimagnetic fraction to the overall susceptibility fabric the anisotropy of the anhysteretic remanent magnetisation was investigated at some representative sites the magnetic fabric of the studied sediments mostly reflects the effects of compaction showing a predominant magnetic foliation parallel to the bedding plane at all the sites a well distinct magnetic lineation was also found which is parallel to the fold axes and thrust fronts both at local and regional scales this feature is maintained in sequences that differ for sedimentological character and age implying that the magnetic lineation was produced by a mild tectonic overprint of the primary sedimentary compactional fabric the relationship between the magnetic lineation trends and the vertical axis rotations detected by speranza et al speranza f sagnotti l mattei m 1997 j geophys res 102 3153 3166 indicates that the magnetic lineation formed during the compressive phases of the messinian early pliocene when the apenninic front was almost rectilinear and oriented n320

shape preferred orientation of object populations automatic analysis of digitized images abstract an automatic technique is presented for systematic shape preferred orientation spo analysis of crystal fabrics in rocks this technique is based on digitization of an image with a ccd camera and separation of an object population from its matrix the image is analysed globally using a rotating grid that is superimposed on the square pixel grid of the computer screen the parametric method is based on counting intercepts in all directions the interceps rose provides information on both the orientation and strength of the spo problems of hardware related counting noise anisotropy are avoided using an original method of filtering the intercept function with a linear sliding mask on the counting grid the technique was tested both on single objects of different shapes and on different populations of identical objects a very high degree of accuracy was obtained for orientation measurements fabric shape parameters are introduced which are specific to this intercept technique they compare favourably with shape parameters used in axial fabric analysis

plastic deformation and recrystallization of garnet a mechanism to facilitate diffusion creep elongate and deformed garnets from glenelg nw scotland occur within a thin shear zone transecting an eclogite body that has undergone partial retrogression to amphibolite facies at circa 700 c optical microscopy back scattered electron imaging electron probe microanalysis and electron back scatter diffraction reveal garnet sub structures that are developed as a function of strain subgrains with low angle misorientation boundaries occur at low strain and garnet orientations are dispersed around rational crystallographic axes across these boundaries towards high strain areas boundary misorientations increase and there is a loss of crystallographic control on misorientations which tend towards random in high strain areas a polygonal garnet microstructure is developed the garnet orientations are randomly dispersed around the original single crystal orientation some garnet grains are elongate and ca rich garnet occurs on the faces of elongate grains oriented normal to the foliation commonly the garnet grains are admixed with matrix minerals and where in contact with other phases garnet is well faceted we suggest that individual garnet porphyroclasts record an evolution from low strain conditions where dislocation creep and recovery accommodated deformation through increasing strain where dynamic recrystallization occurred by subgrain rotation to highest strains where recrystallized grains were able to deform by diffusion creep assisted grain boundary sliding with associated rotations

kinematic evolution of the mbakop pan african granitoids western cameroon domain an integrated ams and ebsd approach abstract this study integrates anisotropy of magnetic susceptibility microstructural and crystallographic preferred orientation cpo data from the mbakop granitic pluton mgp pan african age in order to decipher its kinematic evolution the mgp lies close to ne sw branch of central cameroon shear zone ccsz and is emplaced in gneissic basement high mean magnetic susceptibility and presence of multi domain magnetite are recorded quartz cpo measured using electron backscatter diffraction reveals dominance of rhomb prism and prism slip in different samples which is consistent with microstructures developed under upper greenschist amphibolite facies conditions quartz cpo along with other kinematic indicators feldspar porphyroclasts mineral fish indicate non coaxial deformation was important during tectonic evolution of the mgp contrasting sense of shear is recorded implying multi stage mylonitization in the western cameroon domain top towards south sense of shear is related to regional d 2 deformation 613 585 ma while top towards north is related to d 3 585 540 ma the magnetic fabric in mgp records d 3 the obliquity between mean orientation of magnetic foliation n12 e and the ne sw ccsz branch n48 e gives kinematic vorticity number of 0 95 this indicates dominantly simple shear with a minor pure shear component it is concluded that regional transpression was important during mgp emplacement

titanohematite lattice preferred orientation and magnetic anisotropy in high temperature mylonites magnetic and crystallographic fabric studies were performed in mylonitic granulites from a km wide strike slip shear zone in the ribeira belt southeastern brazil in these mylonites a strong compositional layering underlines the tectonic foliation and the elongation of titanohematite amphibole and orthopyroxene crystals defines a mineral stretching lineation magnetic fabric deduced from anisotropy of magnetic susceptibility ams measurements and tectonic fabric compare favorably rock magnetic studies show that both paramagnetic and ferromagnetic minerals can be carriers of ams the anisotropy of isothermal remanent magnetization which is due to the shape preferred orientation of magnetite grains is coaxial with ams lattice preferred orientation lpo measurements using the electron backscattered diffraction technique show that orthopyroxene amphibole biotite and titanohematite have a strong lpo tightly related to the tectonic fabric among these four minerals titanohematite is the only mineral present in relatively large proportions s 1 5 in all studied samples titanohematite lpo is characterized by a strong concentration of 0001 poles c axes sub perpendicular to the foliation and by a distribution of the poles of the 2110 and 1010 prism planes within the foliation with a maximum close to the lineation this characteristic lpo is interpreted as resulting from dislocation creep during the mylonitization magnetic fabrics and titanohematite lpo fit well the axis of minimum susceptibility is aligned with the c axis maximum and the axis of maximum susceptibility coincides with the maximum concentration of poles of the prism planes titanohematite lpo may provide a valuable constraint for the kinematic interpretation of the magnetic fabrics fl 2002 elsevier science b v all rights reserved

magnetic versus crystallographic fabrics in a basaltic lava flow combined anisotropy of magnetic susceptibility ams and crystallographic studies were performed within a quaternary lava flow for which we have a thorough knowledge of the flow direction microscope examinations microprobe analyses and studies of rock magnetic properties show that ams is carried by homogeneous multidomain ti rich titanomagnetite xc0 6 this mineral forming either subhedral isolate individuals or grouped in various elongated aggregates represents a late crystallized interstitial phase ams determined from samples collected in the lower the middle and the upper part of the flow is characterized by a well defined magnetic foliation whereas magnetic lineation is generally poorly grouped and therefore meaningless the foliation plane of the lower and upper part of the flow show an obliquity which is interpreted as an opposite imbrication indicating a westward flow in agreements with the known flow direction in the lower part of the lava flow the tight correlation between ams and plagioclase lattice preferred orientation suggests that a silicate framework control the titanomagnetite crystallization and thus the orientation of the ams ellipsoid d 2005 elsevier b v all rights reserved

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

magnetic properties of the high himalayan leucogranites structural implications the magnetic properties of the high himalayan leucogranites have been investigated on 527 specimens in three plutons everest makalu 6 sites and manaslu 40 sites in nepal and gangotri 43 sites in india susceptibility varies between 2 and 100 10 6 si with an anisotropy ratio up to 1 16 high field and low temperature magnetic measurements together with comparison with weight percent iron demonstrate that anisotropy of magnetic susceptibility is carried by paramagnetic biotite and tourmaline the latter produces an inverse fabric i e with the minimum axis parallel to mineral lineation the magnetic fabric demonstrates complex patterns of stretching lineations during magmatic emplacement and its usefulness in semi quantitatively estimating petrofabric intensity is demonstrated for the biotite bearing facies natural remanent magnetization was measurable at only two sites in everest makalu where there are well defined reverse directions carried by titanomagnetite and pyrrhotite comparison of these preliminary results with predicted directions for stable india suggests northward tilting of about 10 and a small clockwise rotation of this massif

crystal plasticity of natural garnet new microstructural evidence scanning electron microscope sem orientation contrast images of mantle nodules show that garnets contain cellular domains of different crystallographic orientation electron backscatter diffraction shows small crystallographic mismatches

process of magnetite fabric development during granite deformation this study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development anisotropy of anhysteretic re

granite tectonics revisited insights from comparison of k feldspar shape fabric anisotropy of magnetic susceptibility ams and brittle fractures in the jizera granite bohemian massif in the jizera granite of the krkonose jizera plutonic complex northern bohemian massif contrasting patterns of magmatic k feldspar fabrics and brittle fractures characterize different structural levels of the pluton the uppermost exposed level at 800 1 100 m above sea level is dominated by flat foliation that overprints two steep foliations in contrast k feldspar shape fabric in an underground tunnel 660 m above sea level shows complex variations in orientation and intensity magnetic fabric carried by coaxial contributions of biotite magnetite and maghemite is homogeneous along the examined section of the tunnel and is decoupled from the k feldspar fabric the jizera granite is crosscut by two regional sets of subvertical fractures ne sw and nw se and by near surface exfoliation joints the multiple fabrics are inferred to reflect a complex magmatic strain history at different structural levels of the pluton bearing little or no relationship to the fracture network in contrast to the original concept of hans cloos granite tectonics we conclude that no simple genetic relationship exists between fabrics and fractures in plutons an alternative classification of fractures in plutons thus should avoid relationships to magmatic fabrics and should instead consist of cooling syntectonic uplift and post uplift fractures

magnetic fabrics and rock magnetism of archaean and proterozoic dike swarms in the southern sao francisco craton brazil abstract magnetic fabric and rock magnetism studies were performed on three mafic dike swarms total of 38 dikes from the southernmost part of the sao francisco craton sfc minas gerais state se brazil they cut archaean granite gneiss migmatite and paleoprototerozoic terranes these swarms are classified as basic noritic sm nd age 2 65 ga basic rb sr age 1 87 ga and metamorphic rb sr age 1 87 ga suites in which the second is the most important magnetic fabrics were determined by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm in most sites magnetic susceptibility is dominantly carried by ferromagnetic minerals however in some sites the paramagnetic contribution exceeds 70 of bulk susceptibility mainly coarse to fine grained ti poor titanomagnetite up to pure magnetite carry the magnetic fabrics three primary ams fabrics are recognized which are all coaxial with the aarm fabric normal ams fabric is dominant in the basic suite 16 of 20 analyzed dikes and occurs in 4 and 3 dikes from the basic noritic and metamorphic suites respectively this fabric is interpreted as a result of magma flow in which the analysis of k max inclination permitted to infer that the majority of dikes were fed by inclined flows 30 k max k max intermediate ams fabric was found in 50 of dikes from the basic noritic and metamorphic suites but in only 2 dikes from the basic suite it is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike inverse ams fabric is a minority 2 dikes from each suite the parallelism between ams and aarm tensors for dikes with abnormal fabrics suggests a primary origin for them gyroremanent magnetization grm effect was negligible for the majority of dikes but it was found in two dikes from the basic suite with normal ams fabric magnetic fabrics recognized for the three studied swarms do not depend on magnetic mineralogy geochemical composition dike strikes nor the age of the swarms since the same magnetic minerals and magnetic fabric types are found in dikes from all suites inclined and horizontal flows allow us to infer the relative position of at least three magma sources or magma chambers from which the dikes were fed

anisotropy of magnetic remanence a brief review of mineralogical sources physical origins and geological applications and comparison with susceptibility anisotropy the magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low field magnetic susceptibility ams however alternative methods based on remanent magnetization measured in the absence of a magnetic field rather than induced magnetization measured in the applied field have distinct advantages for certain geological applications this is particularly true for 1 adjunct studies in paleomagnetism in order to assess the fidelity with which a natural remanence records the paleofield orientation 2 studies of weakly magnetic or weakly deformed rocks for which susceptibility anisotropy is very difficult to measure precisely and 3 quantitative applications such as strain estimation the fundamental differences between susceptibility and remanence and their respective anisotropies are due to several factors 1 susceptibility arises from all of the minerals present in a sample whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals 2 ferromagnetic minerals are generally more anisotropic than para and diamagnetic minerals 3 for ferromagnetic minerals remanence is inevitably more anisotropic than susceptibility and 4 a number of common minerals including single domain magnetites possess an inverse anisotropy of susceptibility i e they tend to have minimum susceptibility parallel to the long axis of an individual particle remanence is immune to this phenomenon as a consequence of all these factors remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample

degree of magnetic anisotropy as a strain intensity gauge in ferromagnetic granites anisotropy of magnetic susceptibility data for a ferromagnetic granite godhra granite nw india are presented and it is shown that the degree of magnetic anisotropy p is not controlled by the mean susceptibility k m analyses carried out across a high strain zone lying between granite and adjacent gneiss show that p values are highest in samples that lie close to the contact and decrease away from it based on these results it is concluded that if p is not controlled by k m then the former can be used to gauge strain intensity variations in ferromagnetic granites

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

the use of the anisotropy of magnetic remanence in the resolution of the anisotropy of magnetic susceptibility into its ferromagnetic and paramagnetic components abstract the anisotropy of magnetic susceptibility ams is often controlled by both ferromagnetic sensu lato and paramagnetic minerals the anisotropy of magnetic remanence amr is solely controlled by ferromagnetic minerals jelinek trav geophys 37 1993 introduced a tensor derived from the isothermal amr whose normalized form equals the normalized susceptibility tensor provided that the ferromagnetic fraction is represented by multi domain magnetite the present paper shows the close correlation between these tensors for a collection of strongly magnetic specimens containing multi domain magnetite in addition acceptable correlation between the tensors was also found for a collection of specimens containing single domain magnetite a new method is developed for the ams resolution into ferromagnetic and paramagnetic components using the amr some examples are presented of this resolution in mafic microgranular enclaves in granodiorite and in gneisses of the ktb borehole

anisotropies of partial anhysteretic remanence and susceptibility in compacted black shales grainsize and composition dependent magnetic fabric we have quantified the magnetic fabric of the highly compacted heebner shale pennsylvanian of kansas in terms of the anisotropies of partial anhysteretic remanent magnetization parm and low field susceptibility hysteresis loops exhibit almost purely paramagnetic behavior and the ratio of high field linear susceptibility to low field susceptibility is very close to one the susceptibility anisotropy therefore reflects the fabric of the paramagnetic matrix while the remanent anisotropies are due to the preferred orientations of ferrimagnetic grains both the paramagnetic and ferrimagnetic fabrics are dominated by a horizontal foliation with a weak northeasterly lineation but the parm anisotropies are generally much larger than the susceptibility anisotropy the degree of foliation measured with parm s decreases markedly with increasing coercivities indicating stronger foliation in the coarser grainsize fraction in contrast the parm mean lineations are grainsize independent suggesting a post compactional origin related to tectonic compression the susceptibility lineation appears to have a slightly different azimuth and may therefore be due to paleocurrents

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

emplacement of dike swarms from the island of ilhabela se brazil and its relationship with the south atlantic ocean opening revealed by magnetic fabrics abstract magnetic fabric and rock magnetism studies were performed on 153 dikes from diabase lamprophyre and alkaline dike swarms that outcrop on the island of ilhabela ne sao paulo state the dikes crosscut archean and proterozoic polymetamorphic rocks their thicknesses range from a few centimeters to 4 or 5 m they trend predominantly n30 60e with a very steep 60 to vertical dip magnetic fabrics were determined using anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm rock magnetism measurements reveal that the magnetic mineral of the three swarms is magnetite mainly with grains in the range of 2 5 m for a few dikes these grains are the carriers of bulk magnetic susceptibility but are not responsible for the ams which is due to fe bearing minerals as shown by aarm the main ams fabric recognized in the swarms is due to magma flow in which the kmax kint plane is parallel to the dike s plane and the magnetic foliation pole kmin is perpendicular to it the analysis of the kmax inclination showed that the dikes were fed by horizontal to vertical flows however for the minority of the dikes the ams and aarm tensors are not coaxial the aarmmax is oriented n30 60 w approximately perpendicular to the kmax the aarmmax orientation is similar to the direction of a fault system located mainly in the santos marginal basin which was formed in the cretaceous rifting during the south atlantic opening the aarm fabric is tectonic in origin and is parallel with the extensional paleostress responsible for the gondwana break up the comparison of ams and aarm fabrics suggests that diabase and lamprophyre dikes were emplaced in three distinct events in the earliest stages of the south atlantic opening later the alkaline dikes were emplaced in the final stages of the atlantic opening

factors affecting the relative importance of shape and distribution anisotropy in rocks theory and experiments abstract the effect of magnetic interactions has been commonly neglected in the interpretation of the anisotropy of magnetic susceptibility ams of igneous rocks despite the likely occurrence of magnetic interactions due to their relatively high content of ferromagnetic minerals current models of magnetic interactions apply to highly simplified systems and are not directly applicable to natural rocks on this work a model that includes variables previously neglected is used to assess the relative importance of magnetically interactive and non interactive fractions in a rock results of the model show that a variable proportion of magnetically interactive grains the relative values of the bulk susceptibility degree of anisotropy and orientation of the anisotropies characteristic for each fraction all play an important role in controlling the rock ams experimental evidence illustrating the importance of the distribution of the ferromagnetic grains within a specimen is also reported and supports the model predictions both theory and experiments indicate that if a rock has unequant magnetic grains and clusters of magnetic grains the contribution to the ams of the rock will depend on the relative values of all the model variables and not only on the occurrence of magnetic interactions as previously presumed

the effect of magnetic anisotropy on paleomagnetic directions in high grade metamorphic rocks from the juiz de fora complex se brazil the juiz de fora complex is mainly composed of granulites and granodioritic migmatite gneisses and is a cratonic basement of the ribeira fold belt which was formed during the last stage of brasiliano orogeny samples widely distributed over the studied region se brazil rio de janeiro state were collected for paleomagnetic and magnetic anisotropy determinations after measurement of anisotropy of low field magnetic susceptibility ams the same specimens were submitted to both alternating field for anisotropy of remanent magnetization arm determinations and thermal demagnetization for paleomagnetic analyses demagnetization processes allowed isolating an eastern steep positive inclination characteristic remanent magnetization chrm direction from the rocks the studied specimens are strongly heterogeneous at sample scale regarding the amount of magnetic minerals even for specimens from the same core rock magnetism indicates that there is a complex mixture of magnetic minerals with both low and high coercivity which are associated with coarse grained titano magnetite and either fine grained titano magnetite or titanohematite grains respectively these magnetic minerals are responsible for both remanent direction and magnetic anisotropies even though for some specimens paramagnetic minerals are the carriers of ams fabric the chrm direction found for the rocks should represent the cooling phase of the brasiliano event in the area and it was acquired after the magnetic fabric was formed the ams and arm fabrics are coaxial and tectonic in origin and compare favorably with the mesoscopic scale fabrics in the adjacent areas however arm measurements have reached only low coercivity grains and it could be determined in few specimens then only an estimate of arm effect on chrms correction is shown the rocks are strongly magnetically anisotropic 50 and foliated the paleomagnetic directions from each specimen within a site tend to approach its ams or arm foliation kmax kint or armmax armmin plane these directions were corrected specimen by specimen from the sites taking into account the pole of ams or arm foliation kmin or armmin and the value of the degree of anisotropy p results show that even for specimens with high p the angular difference between corrected and uncorrected magnetization direction may be insignificant if the geomagnetic field at the time of acquired magnetization was approximately parallel to the magnetic foliation of the specimens our data set suggests that ams is a powerful tool to correct the chrm deviation from paleofields in rocks with complex magnetic mineralogy such as those from the juiz de fora complex

conflicting structural and geochronological data from the ibituruna quartz syenite se brazil effect of protracted hot orogeny and slow cooling rate the ibituruna quartz syenite was emplaced as a sill in the ribeira aracuai neoproterozoic belt southeastern brazil during the last stages of the gondwana supercontinent amalgamation we have measured the anisotropy of magnetic susceptibility ams in samples from the ibituruna sill to unravel its magnetic fabric that is regarded as a proxy for its magmatic fabric a large magnetic anisotropy dominantly due to magnetite and a consistent magnetic fabric have been determined over the entire ibituruna massif the magmatic foliation and lineation are strikingly parallel to the solid state mylonitic foliation and lineation measured in the country rock altogether these observations suggest that the ibituruna sill was emplaced during the high temperature similar to 750 degrees c regional deformation and was deformed before full solidification coherently with its country rock unexpectedly geochronological data suggest a rather different conclusion la icp ms and shrimp ages of zircons from the ibituruna quartz syenite are in the range 530 535 ma and la icp ms ages of zircons and monazites from synkinematic leucocratic veins in the country rocks suggest a crystallization at similar to 570 580 ma i e an ht deformation 35my older than the emplacement of the ibituruna quartz syenite conclusions from the structural and the geochronological studies are therefore conflicting a possible explanation arises from ar 40 ar 39 thermochronology we have dated amphiboles from the quartz syenite and amphiboles and biotites from the country rock together with the ages of monazites and zircons in the country rock ar 40 ar 39 mineral ages suggest a very low cooling rate 3 degrees c my between 570 and similar to 500 ma and similar to 5 degrees c my between 500 and 460 ma assuming a protracted regional deformation consistent over tens of my under such stable thermal conditions the fabric and microstructure of deformed rocks may remain almost unchanged even if they underwent and recorded strain pulses separated by long periods of time this may be a characteristic of slow cooling hot orogens that rocks deformed at significantly different periods during the orogeny but under roughly unchanged temperature conditions may display almost indiscernible microstructure and fabric

kinematic analysis using ams data from a deformed granitoid abstract this study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis a vis shear zone data are presented from the chakradharpur granitoid ckpg that lies to the north of the northerly dipping ene wsw striking singhbhum shear zone ssz eastern india whilst the foliation recorded in the field in some parts of the granitoid is parallel to the ssz the magnetic foliation is n54 e 90 mean orientation it is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing thrusting event the evidence of which is preserved on the mesoscopic scale it is envisaged that during the initial stages of deformation there was simple shear along the evolving ssz that resulted in sinistral strike slip movement the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise space was generated in a direction n25 e perpendicular to maximum instantaneous stretching axis into which ckpg emplaced synchronously with regional deformation and evolving ssz with continued deformation there was thrusting along the ssz the vorticity axis flipped to a sub horizontal orientation thus leading to the development of down dip stretching lineations and sheath folds within the ssz however at the same time the vorticity axis responsible for fabric evolution within the syntectonically crystallizing cooling ckpg was steeply plunging with clockwise rotation the magnetic foliation mean orientation n54 e 90 developed during the final stage of syntectonic crystallization however deformation in the region and thrusting along the ssz continued even after the ckpg had fully crystallized and solidified which led to the development of the ene wsw striking mesoscopic foliation that is parallel with the ssz we propose that the angle between the magnetic foliation and the ssz foliation recorded in the field enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the ckpg it is concluded that transpression was an important mechanism and during regional deformation whilst the ssz developed structures by dominantly simple shear the ckpg underwent dominantly pure shear

magnetic anisotropy in the trenton limestone results of a new technique anisotropy of anhysteretic susceptibility a new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described the magnetic fabric of a collection of trenton limestone specimens has been determined using this method as well as by conventional anisotropy of magnetic susceptibility the results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the trenton in which the bulk magnetic susceptibilities are low a model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses the original fabric is inferred to have been isotropic the anisotropy resides in secondary magnetite of late paleozoic age it is argued that the observed magnetic fabric must therefore be alleghenian or younger in age our method has the potential to determine paleostress directions in carbonates elsewhere provided our assumptions are correct

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

tectonic rotations and internal structure of eocene plutons in chuquicamata northern chile abstract a paleomagnetic and ams study on eocene plutonic complexes in the calama area northern chile reveals high temperature high coercivity magnetizations of dominantly thermoremanent origin and magnetic fabrics controlled by magnetite the paleomagnetic results indicate that 43 ma plutons underwent clockwise tectonic rotation whereas adjacent 39 ma plutons did not undergo discernible rotation this points to a middle eocene age for the younger tectonic rotations associated with the central andean rotation pattern in the chuquicamata calama area the petrofabric in these rocks formed under conditions ranging from purely magmatic i e before full crystallization to low temperature solid state deformation ams and paleomagnetism suggest that the plutonic bodies were formed by progressive amalgamation of subvertical magma sheets spanning multiple magnetic polarity chrons the parallelism between magmatic and tectonic foliations suggests that regional tectonic stress controlled ascent emplacement and rock deformation during cooling in this context we suggest that magma ascent and emplacement in the upper crust likely exploited mesozoic structures which were locally reactivated in the eocene

composite magmatic magnetic fabrics evidences late ams in syn tectonic dikes in the monteiro sume plutonic volcanic complex ne brazil abstract interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility ams are based on the orientation of the magnetic fabric recorded next to the dike walls however uncertainties remain when ams is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma we study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks the dikes have magnetic susceptibilities mostly between 10 3 and 10 2 si carried by fe ti oxides ams shows fabrics that would be consistent with a lateral movement of the magma however the anisotropy of anhysteretic remanence aar and silicate shape preferred orientation spo indicate that the melt moved upward based on the steeply plunging lineations detected by aar and spo furthermore the obliquity of the aar foliations in the dike margins indicates a component of transtension resolved in the dike walls as there is no evidence for internal deformation of titanomagnetite ams would record its late growth in the tectonic extension direction the magnetic subfabric concealed by late ams therefore documents an earlier tectonic episode and evidence the limits of using just ams directions to constrain the emplacement of syntectonic magmas

the effect of dauphine twinning on plastic strain in quartz we present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies t 300 400 c granitoid protomylonite from the arolla unit of the nw alps mechanical dauphine twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane z almost orthogonal to the compression direction z twin orientation twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb r nearly parallel to the compression direction r twin orientation in contrast we report the lack of twinning in two porphyroclasts already oriented with one of the r planes orthogonal to the compression direction one twinned porphyroclast has been investigated with more detail it shows the localization of much of the plastic strain into discrete r twins as a consequence of the higher amount of elastic strain energy stored by r twins in comparison to z twins the presence of dauphine twins induced a switch in the dominant active slip systems during plastic deformation from basal regions without twinning to and pervasively twinned regions dynamic recrystallization is localized along an r twin and occurred dominantly by progressive subgrain rotation with a local component of bulging recrystallization part of the recrystallized grains underwent rigid body rotation approximately about the bulk vorticity axis which accounts for the development of large misorientation angles the recrystallized grain size piezometer for quartz yields differential stress of 100 mpa the comparison of this palaeostress estimate with literature data suggests that mechanical dauphine twinning could have a potential use as palaeopiezometer in quartz bearing rocks

granite emplacement and its relation with regional deformation in the aravalli mountain belt india inferences from magnetic fabric abstract this contribution presents field microstructural and anisotropy of magnetic susceptibility ams data from the godhra granite a ca 1 ga pluton at the southern margin of the aravalli mountain belt western india that lies near the central indian tectonic zone citz the northern and southern margins of the granite are high strain zones with north dipping e w striking foliations and nw plunging stretching lineations the presence of preferentially oriented feldspars suggests that the granite was subjected to magmatic deformation during its emplacement high temperature solid state deformation fabrics are recorded from microstructural studies which imply that the granite is deformed ams data show magnetic foliations and magnetic lineations in the granite with orientations similar to the field data the magnetic foliation in the granite is parallel to the d 3 foliation in the gneissic host rock both the stretching lineations and the magnetic lineations at the granite margin high strain zones are parallel with the axes of d 3 reclined folds in the gneiss therefore the emplacement of the godhra granite is inferred to have taken place syntectonically while the gneiss was undergoing the d 3 phase of deformation the orientation and character of these lineations and the vergence of the d 3 folds imply oblique simple shear which is inferred to have controlled the emplacement of the granite the magnetic fabric data are compared with the regional structural trends of the metasedimentary rocks of the southern aravalli region and the available geochronological data from rocks of the southern aravalli region are summarised based on this information it is suggested that the emplacement of godhra granite deformation of the southern parts of aravalli mountain belt and tectonothermal events along the citz and rodinia supercontinent assembly were related events

plastic behavior of magnetite and high strains obtained from magnetic fabrics in the parry sound shear zone ontario grenville province abstract magnetic anisotropy and quantitative petrology of a transition from relatively undeformed metaanorthosite protolith to highly deformed ultramylonite in the parry sound shear zone provide information on magnetite as a kinematic indicator rock magnetic experiments show that anisotropy of magnetic susceptibility ams is controlled by magnetite in the mylonites and ultramylonites and by paramagnetic minerals hornblende biotite ilmenite in the protolith geothermometry in the ultramylonite indicates a temperature of 630 50 c during deformation a deformation mechanism map calculated from published experimental work for 630 c indicates that magnetite in the parry sound shear zone deformed plastically rather than via rigid body rotation the ams orientations accurately track a foliation trajectory in a portion of the shear zone which allows the utilization of orientation based strain models to determine shear strains shear strains of 1 9 were obtained and an empirical correlation of strain with the ellipsoid shape resulted in the logarithmic relationships mmax 0 15 ln x and mmin 0 13 ln z where mi ki kmean describes the principal ams axes or k max k min x z 0 14 these ams strain correlations were subsequently applied to mylonites and ultramylonites elsewhere in the shear zone predicting shear strains as high as 13 these observations also reveal that ams fabrics do not saturate at high strains as would be expected for rigid body rotation due to the plastic behavior of magnetite during deformation

composite ferromagnetic fabrics magnetite greigite measured by ams and partial aarm in weakly strained sandstones from western makran iran summary we present examples of composite magnetic fabrics ams and partial aarm in five sites from the western makran accretionnary prism these rocks are weakly strained sandstones of mio pliocene age rock magnetic investigations show a large occurrence of magnetite and also some greigite at two sites partial anhysteretic remanent magnetization coercivity spectra reveal that grain size is not homogeneous suggesting several grain fractions ams foliations are close to bedding except at one greigite bearing site where ams foliation is almost perpendicular to bedding soft aarm 0 50 mt foliations are slightly oblique both to bedding and ams foliation surprisingly hard aarm 50 100 mt foliations are perpendicular to bedding comparison of two limbs of one fold suggests that ams foliations are pre tilting while hardaarm foliations are post tilting corrected degree of anisotropy parameters display similar trends for all sites p 1 04 p 1 11 p hardaarm 1 19 we suggest that ams soft aarm and hard aarm reflect distinct magnetic grain populations however a possible relationship between hard aarm and a component of natural remanent magnetization is possible our study shows that two orthogonal fabrics exist in these weakly strained rocks coarse grains are parallel to bedding while fine grains are aligned perpendicular to bedding

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

correlation between magnetic anisotropy and fabric for devonian shales on the appalachian plateau the magnetic anisotropy of devonian black shale samples was measured from two cores drilled in the appalachian plateau the mineralogy of the shales is predominantly clay with small quantities of quartz and minor amounts of opaques and chlorite magnetite is the predominant ferromagnetic mineral present in the samples the magnetic fabric was measured at both room temperature and liquid nitrogen temperature and is dominated by a well defined bedding vertical compaction and a lesser defined magnetic lineation measurements of the anisotropy of magnetic susceptibility ams at liquid nitrogen temperature which enhances the paramagnetic contribution in the rock showed a strong increase in both the bulk susceptibility and susceptibility differences this increase suggests that the ams is controlled by the paramagnetic minerals particularly the clays and chlorite strain was measured from the orientation of basal planes of the chlorite crystals by texture goniometry good correlations have been found 1 between the orientation of the magnetic lineation and the long axes of the chlorite crystals and 2 between the degree of magnetic foliation and the amount of vertical compaction the magnetic lineation also agrees well with the direction of seismic anisotropy over the plateau the anisotropy of the anhysteretic remanence which expresses the anisotropy due to the ferromagnetic component in the rocks shows a weaker correlation with the amount of vertical compaction a weak magnetic lineation suggests that the magnetite grains were aligned during a deformation phase which post dates the main alleghanian orogeny the magnetic anisotropy of the devonian shales mirrors the compaction and tectonic fabric on the appalachian plateau

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

magnetic susceptibility and partial anhysteretic remanence anisotropies in the magnetite bearing granite pluton of tourao ne brazil abstract rock magnetism and magnetic fabric studies were performed in the tourao granite western part of serido belt ne brazil this pluton 350 km2 is composed of k rich calc alkalic monzogranites and was emplaced between a set of ne and e trending dextral strike slip shear zones electronic and optical microscopy thermomagnetic curves hysteresis data and coercivity spectra revealed that magnetite fine and coarse grained is the unique ferromagnetic mineral in these rocks anisotropy of low field magnetic susceptibility ams was measured in 83 sites and for many sites from central and southern parts of the intrusive body a large scatter was noticed anisotropy of partial anhysteretic remanence paar was determined for 29 sites in the 0 50 mt paar0 50 and 19 sites in the 50 90 mt paar50 90 windows to isolate the fabric contribution of the remanence bearing grains magnetite in most sites ams is dominantly carried by magnetite whereas in some sites the paramagnetic contribution exceeds 60 of the bulk susceptibility the paar0 50 is assumed to be related to coarse grained early crystallized magnetites while the paar50 90 is interpreted as due to fine needle shaped magnetites hosted in biotites the combined analysis of these magnetic techniques permits interpretation in terms of fabric formation in the tourao granite and the inference that at least two successive kinematic events were recorded in this intrusive body devoid of any solid state deformation overprint the ams and paar0 50 fabrics for most of the sites correlate with the early nne trending magmatic fabric whereas paar50 90 reveals a different fabric probably related to late partitioning of magmatic straining along the e trending shear zones in the southern part of the body a completely different paar0 50 fabric is correlated with the late intrusion of charnockite stocks

a statistical approach to determination of a mineral lineation abstract a statistical model of the bipolar von mises type was applied to the analysis of mineral lineation defined by the preferred dimensional orientation of inequant grains on a foliation surface orientation data of 203 258 grains from each of four rock specimens fit the model well suggesting a useful analytical technique with three advantages 1 confidence in whether a metamorphic tectonite has a mineral lineation can be determined using a 2 test 2 the orientation of the mineral lineation can be represented by the mean direction with a specified confidence interval and 3 the degree of preferred dimensional orientation of grains can be quantified by the concentration parameter

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