timing of natural remanent magnetization in ferriferous limestones from the swiss jura mountains abstract goethite and hematite are the main magnetic phases contained in two ferriferous middle jurassic beds which are exposed within the mandach structure the major tectonic structure of the eastern tabular jura of northern switzerland the iron oxidic phases in a reddish brown sparry limestone known as spatkalk were formed diagenetically whereas these phases are weathering products in a stratigraphically slightly younger oolitic bed the hematite in the oolitic bed was magnetized after the jura main tectonic event in the miocene whereas the hematite in the spatkalk was magnetized before the miocene the goethites in the oolitic bed carry a pretectonic and in the spatkalk a syntectonic magnetization physical and chemical data show that the goethite which was resistant to remagnetization contains an al substitution of 3 4 mol resulting in a neel temperature of 90 c the remagnetized goethite has an al content of 10 7 mol and a neel temperature of 70 c the different goethite properties indicate that the tectonic formation of the mandach structure occurred under low temperature conditions below 90 c

magnetic fabrics and fluid flow directions in hydrothermal systems a case study in the chaillac ba f fe deposits france this study presents a possible use of anisotropy of magnetic susceptibility ams to describe the mineralizing process in hydrothermal systems ba f fe rich deposits within the chaillac basin are on the southern border of the paris basin in these deposits hydrothermal textures and tectonic structures have been described in veins sinters and sandstone cemented by hydrothermal goethite 278 oriented cores from 24 sites have been collected in these formations in addition a lateritic duricrust superimposed on the hydrothermal formation has been sampled rock magnetic investigations show that the principal magnetic carrier is goethite for the hydrothermal mineralization and for the laterite level the ams measurements show distinguishable behaviors in the different mineralogical and geological contexts the k1 magnetic lineation maximum axis is strongly inclined for the vertical veins for the horizontally mineralized sinters the magnetic lineation is almost horizontal with an azimuth similar to the sedimentary flow direction the ams of goethite rich sandstone close to the veins shows strongly inclined k1 as they are probably influenced by the vertical veins however when the distance from the vein is larger than 1 m the ams presents rather horizontal k1 directions parallel to the sedimentary flow the laterite has a foliation dominance of ams with vertically well grouped k3 axes and scattered k1 and k2 axes field structural observations suggest that the ore deposit is mainly controlled by ew extension tectonics associated with ns trending normal faults combining the ams results on the deposit with vein textures and field data a model is proposed in which ams results are interpreted in terms of hydrothermal fluid flow this work opens a new investigation field to constrain hydrodynamic models using the ams method textural study combined with efficient ams fabric measurements should be used for systematic investigation to trace flow direction in fissures and in sand porosity

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

emplacement of the early miocene pinto peak intrusion southwest utah usa 1 in this contribution we report rock magnetic petrographic and anisotropy of magnetic susceptibility ams data from the pinto peak intrusion all of which bear on volcanic construction rock magnetic data indicate that the dominant magnetic mineral phase is low ti titanomagnetite of multidomain grain size the composition of which varies spatially across the intrusion the intrusion is a porphyritic andesite dominated by ca rich plagioclase 60 as well as biotite amphibole olivine and opaque minerals reflected light petrography reveals mostly euhedral subhedral titano magnetite crystals that often form clustered glomerocrysts and stringers of equant crystals without exhibiting a consistent mineral alignment fabric moderate to shallow plunging prolate magnetic susceptibility ellipsoids dominate the northern part of the intrusion while steeply dipping plunging magnetic susceptibility ellipsoids are generally restricted to the southern part of the intrusion the vent facies rocks yield moderate to steep oblate susceptibility ellipsoids we interpret the flow pattern in the north to reflect subhorizontal flow of magma filling a tabular sheet like body associated with propagation of the intrusion to the north we argue that the southern part of the intrusion represents the ascent site of the magma rising to shallow crustal levels along a steep feeder system the oblate magnetic fabrics in the vent area plausibly represent flattening against the conduit walls as evidenced by a weak planar flow foliation observed in the vent conduit rocks on reaching shallow crustal levels the magma deformed and uplifted the roof rocks leading to gravitational instability as the slide mass released from the roof an explosive eruption ensued resulting in the emplacement of the rocks of paradise tuff and associated effusive lava flows following eruption magma pressure decreased and the magma drained northward forming the northern intrusive phase

trm arm and isr of two natural magnetites of md and psd grain size summary trm arm and isr stabilities with respect to alternating fields and high and low temperature treatment are compared for a set of artificial rock specimens the specimens contain grain size fractions of a homogeneous natural magnetite and a natural magnetite showing exsolution lamellae the grain size fractions are in the psd md range and vary between 5 and 250 m for large md grains the coercivity spectra of arm are similar to those of isr but differ from those of trm particularly in the lower part of the spectrum for small 5 m grains the coercivity spectrum of arm is similar to that of trm and both spectra are different from the coercivity spectrum of isr the use of arm instead of trm to determine palaeo intensities is discussed in relation to the results obtained during high and low temperature treatment arm behaves similarly to isr but unlike trm for all grain sizes studied the results of this study are discussed in terms of a remanence composed of psd surface moments and md and psd bulk moments

a comparative study of the arm and isr of some natural magnetites of md and psd grain size summary arm and isr stability with respect to alternating field and low temperature treatment were measured for a set of artificial rock specimens each of the specimens contained a known amount of a natural magnetic mineral of a known grain size the following minerals were used a homogeneous natural magnetite a natural titanomagnetite with submicroscopic fe rich inclusions and a natural titanomagnetite and a natural titano maghemite that both show exsolution phenomena the grain size of the fractions varied from 5 to 250 m it is found that the stability of arm and irs of multi domain grains with respect to alternating fields and low temperature treatment is similar whereas for the smallest grains studied 5 m arm is more stable than isr multi domain arm data from this study are in agreement with current multi domain arm theory low temperature behaviour of arm and isr can be explained either in terms of a model in which stable moments in the bulk of the grains are screened by the surrounding matrix or in terms of a model in which regeneration of the bulk remanence plays a role and in which stable moments are situated on the surfaces of the grains

the effects of annealing and concentration on the hysteresis properties of magnetite around the psd md transition abstract hysteresis parameters h cr h c j rs j s and their ratios h cr h c j rs j s have been measured for a large number of accurately prepared grain size fractions of magnetite in the range between 5 and 150 m for several grain size fractions three different concentrations of magnetite are used 100 0 1 and 0 002 vol most of the measurements were repeated after annealing the specimens to 600 c for some specimens in the pseudo single psd and multidomain md range h c and h cr have been measured as functions of temperature plots of the results from h c h cr h c and j rs j s versus the grain size reveal curves with a convex and a concave part concentration and annealing affects the values of the hysteresis parameters especially for grains coarser than 25 m but the shape of the curves remains the same the inflection point from convex to concave for all curves occurs at 25 m and it appears to be independent of concentration and annealing it is therefore proposed to define the transition from psd to md as the inflection point of these curves

magnetic behavior of natural goethite during thermal demagnetization goethite maximum blocking temperatures 60 105 c are governed by the amount of isomorphous substitution in the goethite lattice the goethite dehydration reaction 250 350 c is attended with a concurrent remanence decrease in finely intergrown hematite due to a change of the original hematite structure promoted by the liberated water vapor this remanence decrease leads to a bending point in the thermal decay curve which could be easily mistaken for the presence of another magnetic constituent the magnetic properties of the minerals formed through goethite dehydration hematite and traces magnetite strongly depend on their growth history

influence of observed mantle anisotropy on isotropic tomographic models there is a potential for isotropic tomographic models to be biased by ignored anisotropy anisotropy could be mapped as artificial isotropic velocity perturbations we investigate the distribution and strength of this potential bias for three tomographic s velocity models based on regional s and rayleigh waveforms we use observed sks delay times and fast axis orientations to compute equivalent s velocity perturbations for each wave path used for the tomographic models these synthetic perturbations are then combined into a three dimensional isotropic model which reflects the potential bias in the actual tomographic model we quantify anisotropic bias and find that it indeed exists in the isotropic tomographic models investigated here this bias gets weaker with increasing depth of the anisotropic material and compared to the isotropic velocity anomalies typically interpreted by tomographers the bias from anisotropy is small

palaeomagnetism and rock magnetism of the tortonian messinian boundary stratotype at falconara sicily langereis c g and dekkers mj 1992 palaeomagnetism and rock magnetism of the tortonian messinian boundary stratotype at falconara sicily phys earth planet inter 71 100 111 the tortonian messinian boundary stratotype at stazione falconara sicily yields normal polarity remanent magnetizations of post tilting age implying that the entire section is sub recently remagnetized the absence of direct time control on the biostratigraphic datum levels in the section makes it therefore less suited as a boundary stratotype section existing age estimates for the tortonian messinian boundary are discussed it is concluded that an age of 5 6 ma is at present the best estimate assessment of the magnetic mineralogy in the falconara section shows that rock magnetic parameters are for a large part lithologically controlled a second important controlling factor is the numerous joints which could have acted as channels for circulating groundwater and from which predominantly sub recent finely crystalline haematite was precipitated possibly mediated by weathering processes this haematite has completely replaced an earlier and presumably magnetite dominated magnetic mineralogy

relationship between median destructive field and remanent coercive forces for dispersed natural magnetite titanomagnetite and hematite summary remanent acquisition curves remanent hysteresis curves and alternating field demagnetization curves were determined for a number of artificial rock specimens containing well defined grain size fractions between 5 and 250 m of natural magnetite titanomagnetite and hematite from these curves the remanent acquisition coercive force h cr the remanent coercive force hcr and the median destructive field of irm h i were determined theoretically these parameters should be the same for an assembly of non interacting homogeneously distributed randomly oriented single domain grains for a given hematite specimen h cr hcr and h i have about the same value in spite of the strong grain size dependence of these parameters for each specimen of magnetite and titanomagnetite the value of h cr is larger than hcr which again is larger than h i however the ratios h cr hcr and h i hcr appear to have a different constant value an interesting relationship which appears to hold for dispersed magnetite titanomagnetite or hematite grains between 5 and 250 m independently of grain size quantity and packing density of the magnetic material is

grain size dependence of initial susceptibility and saturation magnetization related parameters of four natural magnetites in the psd md range summary initial susceptibility coercive force and several types of remanent coercive forces were measured on a set of artificial rock specimens containing grain size fractions of a natural magnetite and titanomagnetite both of which are optically homogeneous and a natural titanomagnetite and titanomaghemite both of which show exsolution phenomena it was found subsequently that the optically homogeneous titanomagnetite contains some submicroscopic fe rich inclusions these inclusions are magnetically screened in coarse grains only for the lower grain sizes studied they have an appreciable influence on the data the size of the fractions varied from 5 to 250 m the parameters and several parameter ratios are plotted as a function of grain size several of these parameters can be used as mineralogical and grain size indicators the varying degree of exsolution of the minerals is reflected in the gradients of the plots from plots of initial susceptibility versus grain size it is concluded that the shape of the grains does not play a dominant role in determining the change of this parameter with grain size variation of the various parameters with grain size is explained in terms of a gradual transition from large psd grains to md grains without there being any sharp transition for titanomagnetite x 0 55 the transition takes place at grain sizes that are about 15 m larger than for magnetite

widespread occurrence of a novel high coercivity thermally stable low unblocking temperature magnetic phase in heated archeological material 1 the widespread occurrence of a novel high coercivity magnetic phase in well heated archeological material is reported its properties are defined when it represents the dominant magnetic phase although it is nearly always found as part of a mixture of magnetic phases they are as follows very high coercivity remanence coercivity 600 mt low unblocking temperatures 200 c and high degree of thermal stability this last property distinguishing it from goethite the phase shows striking similarities to magnetic phases produced by thermal decomposition of nontronite an fe rich clay where decomposition occurs after prolonged heating in air to high temperatures conditions suffered by well heated archeomagnetic material preliminary results of mossbauer and x ray diffraction spectroscopy suggest that the phase is more likely to be a substituted hematite rather than fe cristobalite or a variant of fe2o3

paleomagnetism of ca 2 3 ga mafic dyke swarms in the northeastern southern granulite terrain india constraints on the position and extent of dharwar craton in the paleoproterozoic abstract the pole positions reported for the mafic dykes occurring in the northeastern southern granulite terrain and easterly trending dykes of dharwar craton are alike while their ages differ by ca 700 ma confounding tectonic reconstruction to resolve the discordance and to constrain the position of the indian continent in the proterozoic paleomagnetic and geochronological studies have been carried out on the mafic dyke swam in the northeastern southern granulite terrain two distinct pole positions are obtained one from the group of tiruvannamalai dykes as 27 7 s 231 5 e dp dm 12 14 with corresponding mean declination dm and inclination im as 125 and 73 8 95 22 7 6 respectively and second from the east coast dykes as 2 32 s 188 2 e dp dm 5 8 with corresponding mean dm and im as 88 9 and 33 8 95 48 7 1 respectively the remanent efficiency of magnetization values between 0 01 and 0 08 suggest that the dykes have been cooled through curie temperature of magnetite which is the carrier of magnetization the baked contact test confirms that the characteristic remanent magnetization is the primary magnetization the sm nd mineral whole rock isochron from one of the tiruvannamalai dykes yielded an age of 2318 60 ma mswd 1 9 this age is the time of intrusion of the tiruvannamalai dykes and is similar within errors to the age of dykes in the dharwar craton thus the contiguity of dharwar craton with the northern block of southern granulite terrain as early as 2 3 ga ago is established the pole position thus obtained corresponds to a high latitudinal position of dharwar craton during early paleoproterozoic

two types of chemical remanent magnetization during the oxidation of magnetite abstract the chemical remanent magnetization crm m crm resulting from oxidation of equidimensional magnetite to a mixture of 90 hematite and 10 cation deficient magnetite is jointly controlled by the initial anhysteretic remanent magnetization m arm of the parent magnetite and the field h crm applied during oxidation m crm lies in the plane defined by h crm and m arm which were perpendicular in our experiments in an intermediate orientation determined by the relative strengths of h crm 0 05 0 1 and 0 2 mt and m arm 0 002 0 12 saturation remanence the crms are univectorial remanences that remain fixed in these stable intermediate directions throughout the course of stepwise alternating field and thermal demagnetization similar experiments in which acicular single domain cation deficient magnetite was oxidized to maghemite gave quite different results m crm was always parallel to m arm its direction was unaffected by field strengths as high as h crm 1 5 mt the essential factors controlling crm direction seem to be the number and crystallographic structure of oxidation products for single phase oxidation without change in crystal lattice crm remains parallel to the initial remanence of the parent mineral for multiphase oxidation to a mixture of rhombohedral and spinel phases both initial remanence and the field acting during oxidation influence the crm direction which therefore has an intermediate orientation that parallels neither m arm nor h crm

high temperature characteristics of a natural titanomagnetite summary continuous recordings were made of thermal demagnetizations of isr arm and trm induced in artificial rock specimens the artificial rock specimens contained well defined grain size fractions of a natural titanomagnetite which under an optical microscope was homogeneous using a transmission electron microscope it was shown that submicroscopic inclusions exist within the titanomagnetite screening of the remanence of these inclusions by the surrounding titanomagnetite is thought to be responsible for the occurrence of peaks in the continuous thermal decay curves of isr and arm higher peaks observed in the case of trm are thought to be caused by the combined effects of screening and an anti parallel remanence in the titanomagnetite further submicroscopic exsolution processes which occur in the titanomagnetite as a result of repeated heating can be deduced from the development of new peaks from changes in the temperature at which the peak s occur their shape and their relative height the use of stepwise demagnetization techniques on the titanomagnetite yielded erroneous directional results due to the screening in the titanomagnetite the biasing effects due to screening could be avoided by using continuous thermal demagnetization techniques

magnetic properties of natural goethite iii magnetic behaviour and properties of minerals originating from goethite dehydration during thermal demagnetization summary the magnetic behaviour during stepwise demagnetization of a set of artificial samples containing well defined natural goethite from five localities chemical composition crystallite size and grain size are known is reported differential scanning calorimetry measurements indicated that the goethites converted to haematite between 260 and 360 c in this temperature range a small decrease in initial susceptibility and an additional remanence decay leading toward an extra bending point in the thermal decay curve are observed because titanomagnetite or pyrrhotite are absent in the samples this extra bending point is tentatively interpreted as being due to recrystallization of the minor haematite already present in the original goethite concentrates facilitated by water made available through the goethite haematite conversion at much higher temperatures at some 600 c a self reversal of the remanence is observed in most specimens the haematite derived from the goethites between 260 and 360 c appeared to be prone to further alteration at successive higher demagnetization temperatures chemical alterations in the magnetic mineral suite starting at temperatures from 380 c upward depending on the grain size of the original goethite were inferred from an increase in initial susceptibility the susceptibility behaviour showed an appreciable variation due to the creation of varying trace amounts of magnetite which appeared to be already present after the 400 c step after the final 685 c demagnetization step the magnetic mineralogy was usually dominated by magnetite the observed variation is thought to be the result of local within specimen differences in availability of the amount and possibly also the composition of the vapour phase the vapour phase is due to chemical reactions between the matrix constituents waterglass and calcite leading to a c02 h20 vapour phase reducing capacity necessary for the magnetite formation is envisaged to be created by decomposition of trace amounts of organic matter at relatively low temperatures up to some 400 c at higher temperatures over 550 c decomposition of traces of ferrous iron bearing clayminerals presumably donates the ferrous iron differences in the magnetite haematite ratio as well as in the properties of both minerals were assessed in some detail with more or less routine rockmagnetic methods acquisition of the isothermal remanent magnetization at room temperature in fields up to 11 2mam or 14t af demagnetization and low temperature cycling of the saturation remanence this was done after the 400 c step to study the magnetic properties of the newly formed haematite and after the 685 c step to evaluate the properties of the magnetite and more evolved haematite after the 400 c step the haematite appeared to be very fine crystalline and magnetically extremely hard its saturation remanence is considerably lower than that of well crystalline haematite after the 685 c step its hardness has decreased and its saturation remanence slightly increased chemical differences between the

determination of domain structure in igneous rocks by alternating field and other methods abstract af alternating field demagnetization arm anhysteretic remanent magnetization and strong field hysteresis properties of a large collection of mostly continental igneous rocks are reported here the collection included rocks whose magnetic carriers were believed from previous work to be of one of three types md multidomain sd psd single domain pseudo single domain or a bimodal mixture of md grains e g discrete opaques and sd psd material e g silicate inclusions two series of subaerial basalts with a full range of deuteric oxidation classes included examples of all three classes of behaviour sd psd rocks have relatively hard inflected af decay curves decay rate initially increasing then decreasing md rocks have soft exponential like decay curves and bimodal rocks have a combination of these characteristics relative hardnesses of normalized decay curves of remanences acquired in weak intermediate and strong fields the lowrie fuller test are also distinctively different for the three classes and the results support the theory developed in an accompanying paper 1 that lowrie fuller characteristics are an expression of the shapes of decay curves the lowrie fuller test although its result can be expressed as a numerical parameter is not capable of fine scale classification of domain structure or grain size the shape of the arm induction curve does have a quasi continuous variation with grain size however the parameter ar j rs initial anhysteretic susceptibility normalized to saturation remanence which is easily measured with standard paleomagnetic instrumentation is potentially useful for magnetic granulometry although ar itself was not diagnostic of grain size

effects of weathering on single domain magnetite in early pliocene marine marls rock magnetic parameters are often used to recognize variations in the original magnetic mineralogy and for normalizing purposes in palaeointensity studies incipient weathering however is shown to have a profound but partly reversible influence on the rock magnetic properties of the marls of the early pliocene trubi formation in southern sicily italy the remanence in the marls resides in single domain sd magnetite grains but the remanent coercive force hcr shows a strong variation and most values observed are anomalously high hcr range 36 188 mt the enhanced coercivities are attributed to stress in the magnetite grains induced by surface oxidation at low temperature upon heating to 150 c a reduction of coercivities occurs that can be explained by a stress reduction as a result of a reduction of fe2 gradient due to a higher diffusion rate at elevated temperature after heating to 150 c coercivities are quite uniform throughout the outcrop and the values are characteristic of sd magnetite hcr range 30 38 mt the bulk susceptibility increases by 4 24 per cent and the isothermal remanent magnetization irm decreases by 5 11 per cent the increase in anhysteretic remanent magnetization arm is large 20 242 per cent the magnitude of the changes is related to the degree of weathering another effect of heating the marl samples to 150 c is a substantial reduction of the coercivities of the secondary overprint in the natural remanent magnetization after heating separation of the secondary and primary components by alternating field demagnetization is more efficient the usual difficulties of thermal demagnetization above 300 c may thus be avoided by a combination of moderate heating to 150 c and subsequent alternating field demagnetization

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

cross shelf and out of bay transport driven by an open ocean current abstractthis paper studies the interaction of an antarctic circumpolar current acc like wind driven channel flow with a continental slope and a flat bottomed bay shaped shelf near the channel s southern boundary interaction between the model acc and the topography in the second layer induces local changes of the potential vorticity pv flux which further causes the formation of a first layer pv front near the base of the topography located between the acc and the first layer slope the newly formed pv front is constantly perturbed by the acc and in turn forces the first layer slope with its own variability in an intermittent but persistent way the volume transport of the slope water across the first layer slope edge is mostly directly driven by eddies and meanders of the new front and its magnitude is similar to the maximum ekman transport in the channel near the bay s opening the effect of the topographic waves excited by offshore variability dominates the cross isobath exchange and induces a

crystallization in flow i palaeocirculation track by texture analysis and magnetic fabrics summary in order to better define the dependence of the mineral texture on flow anisotropy of magnetic susceptibility ams and microscopic observations have been performed on calcite rich precipitations occurring in a horizontal pipe where the flow direction is clearly defined a total of 65 cubes were cut from five slices magnetic studies identified pseudo single domain magnetite as the major ams carrier horizontal foliation characterizes the magnetic fabrics and the lineation is parallel to the pipe axis that is the flow direction the origin of this lineation is discussed and is interpreted to be mainly the consequence of elongated pseudo single domain magnetite to complete the magnetic fabric studies shape preferred orientation statistics were performed on 563 calcite sections in the 0001 calcite plane it shows elongated shapes with a general orientation parallel to the pipe axis the mean shape orientation is the average of two distinct subpopulations that deviated slightly from the pipe axis observation on calcite shapes and the direction of the magnetic lineation are coherent suggesting that it is possible to track hydrothermal palaeocirculation using magnetic lineation and petrographic fabrics