a new geological map of the brabant massif belgium a new geological map mostly subcrop of the brabant massif is presented based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area new interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes a structural model of the western northern and southern parts of the brabant massif is presented the main anticlinal axis plunges towards the west northwest its core comprising upper precambrian to lower cambrian terrigenous rocks which outcrop in the southeast to the north of the main axis younger rocks appear in regular succession but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc

magnetic susceptibility anisotropy strain and progressive deformation in permian sediments from the maritime alps france abstract the relationships among magnetic susceptibility anisotropy finite strain and progressive deformation have been studied in permian red shales and slates of the maritime alps southeastern france these rocks contain deformed reduction spots which serve as finite strain indicators the magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements the magnetic fabric changes progressively from oblate to prolate and back to oblate as deformation increases the quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined they differ between the less and more deformed areas perhaps due to a change in deformation mechanism accompanying an increase in metamorphism the relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

cleavage fold relationships in the lower cambrian tubize group southeast anglo brabant fold belt lembeek belgium little is known about the cleavage fold relationships in the lower palaeozoic brabant massif primarily because of the scarcity of suitable exposures moreover to date folds have only been described in the ordovician and silurian sequences along the southern extremity of the basement however excavation works for the construction of the tgv railway track south of brussels created an opportunity to study cleavage fold relationships in the lower cambrian terrigenous series tubize group in a more central part of the brabant massif the structural features observed seemed inconsistent with the suspected regional trends primarily a divergent cleavage fan was observed in a region thought to have a regular cleavage attitude the symmetrical but divergent disposition of the cleavage with regard to the fold hinges is explained by flexural folding of a pre existing bedding parallel compaction fabric cleavage development and folding are considered synchronous the divergent cleavage fan reflects local strain variations also the steeply plunging hinge lines of the open subangular folds are seemingly inconsistent with the regional trend characterized by subhorizontal fold hinges taking into account the structural position of the fold assemblage in the subvertical limb of a large scale upright isoclinal fold structure the fold assemblage is interpreted as an incongruous parasitic feature the steeply plunging hinge lines are considered to be caused by fold hinge rotation during progressive coaxial deformation although this incongruous fold assemblage with its divergent cleavage fan is localized it provides important information on both local and regional deformation circumstances in this part of the anglo brabant fold belt

the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

magnetic fabrics and strain in pencil structures of the knobs formation valley and ridge province us appalachians pencil structures which are found in weakly deformed mudrocks reflect the bedding cleavage intersection in weak to moderatelycleaved rocks their presence indicates conditions where bedding and cleavage fabrics are approximately equal in intensity we have determined the anisotropy of magnetic susceptibility ams in pencil structures from a sequence of mudstones of the ordovician knobs formation in the valley and ridge province of the us appalachians magnetic mineralogy was determined by x ray analysis and lowtemperature susceptibility measurements distribution of the magnetic ellipsoid axes is consistent with the incipient tectonic fabric of the pencil mudstones the maximum susceptibility axes parallel the pencils long axes while the minimum axes of susceptibility are normal to the primary sedimentary fabric independent strain quantification permits a correlation between magnetic fabric and tectonic strain an exponential relationship between the ams shape parameter t and tectonic shortening has been found for the interval of 10 25 shortening shortening 17 p exp t this relationship appears to be supported by tectonic strains up to 40 the t parameter t lnf 2 lnl lnl lnf where l lineation is kmax kint and f foliation is kint kmin describes the shape of the magnetic susceptibility ellipsoid which appears more sensitive to strain than past correlation attempts with the magnetic intensity parameter p or p 0 whereas this correlation between strain and ams is only valid within a restricted window of strain 10 40 shortening it establishes the magnitude and directions of tectonic strain in weakly deformed clay rich rocks where strain indicators are otherwise lacking or are poorly developed q 2003 published by elsevier science ltd

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

phyllosilicate fabric characterization by low temperature anisotropy of magnetic susceptibility lt ams 1 this paper examines the use and applicability of anisotropy of magnetic susceptibility at low temperature 77 k called lt ams paramagnetic susceptibility increases significantly with low temperature which permits high precision determination of the anisotropy of paramagnetic susceptibility of a rock from measurements at liquid nitrogen temperature we describe a new procedure that measures directional susceptibility in an oriented rock specimen while immersed in liquid nitrogen our procedure overcomes the problem of temperature heterogeneity within a rock sample while its susceptibility is being measured offering the opportunity to measure low temperature susceptibility in multiple orientations this non destructive method provides a way of characterizing the principal paramagnetic minerals present in a rock based on temperature induced changes of the anisotropy degree moreover the method offers a better resolved relationship between anisotropy degree and grain alignment which is used to quantify rock fabrics

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

multidisciplinary approach to constrain kinematics of fault zones at shallow depths a case study from the cameros demanda thrust north spain thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts e g mylonites sheath folds shear bands in this paper a combination of techniques including structural analysis magnetic methods as anisotropy of magnetic susceptibility and paleomagnetism and paleothermometry is used to define thrusting conditions deformation and transport directions in the cameros demanda thrust north spain three outcrops were analyzed along this intraplate large scale major structure having 150 km of outcropping length 30 km of maximum horizontal displacement and 5 km of vertical throw results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis mixed layer illite smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust kinematic indicators foliation s c structures and slickenside striations indicate altogether a dominant nnw movement of the hanging wall in the western zone and ne in the eastern zone of the thrust thus implying strain partitioning between different branches of the main thrust the study of ams in fault rocks nearly 400 samples of fault gouge breccia and microbreccia indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k max k int plane in sites with strong shear deformation paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting in spite of the shallow depth for deformation and a strong deformation or scattering of the magnetic remanence vectors in the fault zone the application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels

preferred orientation of phyllosilicates effects of composition and stress on resedimented mudstone microfabrics abstract development of a preferred orientation of clay minerals is investigated in response to changes in vertical effective stress and composition in resedimented material boston blue clay boston blue clay bbc an illitic glacio marine clay composed of 57 clay sized particles

spatial and temporal variations of model derived diurnal amplitude of sea surface temperature in the western pacific ocean 1 the diurnal amplitude of sea surface temperature sst at 1 m depth is estimated with a simple empirical model in the region of 80 e 160 w 60 s 60 n covering the western pacific ocean using 4 years of satellite derived wind speed solar radiation and latent heat flux data the advantage of this indirect method is that the diurnal amplitude of sst sst can be obtained even in cloudy areas sst is large in the tropics through the year summer sst in the middle and high latitudes of the northern hemisphere especially around japan is larger than that of the southern hemisphere however sst in the kuroshio and its extension regions is smaller compared with that in its surrounding ones because of higher wind speed in the bay of bengal the south china sea and the timor sea sst becomes largest in spring when the surface wind becomes weak in the transition of the monsoon the period of about 35 50 days is clearly seen in the temporal variation of sst in the tropics this reflects the madden julian oscillation furthermore there are some differences in sst between el nino and la nina periods the authors then investigate how clouds affect the detection of sst if sampling is limited to clear areas only the areas of strong solar radiation and weak wind are selectively picked up and the probability that larger sst is sampled increases the mean of the sst sampled from clear areas only is greater by 0 2 0 3 k compared with the actual mean

late folding related magnetic foliation in the active ferdows northeastern iran thrust fold system abstract in this work we present new ams and structural results from the ferdows active fold thrust system lut block central iran ams analyses show that the miocene units of the upper red formation have a well defined magnetic fabric of tectonic origin with both magnetic lineation and magnetic foliation oriented parallel to the regional fold axes in most of the cases the magnetic fabric acquired when the bedding was still horizontal is related to different degrees of lps shortening in some other cases the magnetic foliation is vertical and oblique to the bedding suggesting that in the ferdows thrust fold structure a cleavage system not visible at the outcrop scale has been developed as a consequence of later shortening related to the activity of the thrust system responsible of the recent earthquakes in the area results from this study establish a relationships between the recent tectonics of the area and the evolution of the magnetic fabric and demonstrate that a well defined magnetic fabric of pure tectonic origin can also develop in poorly deformed rocks lacking field evidence of pervasive internal deformation

timing of magmatism foreland basin development metamorphism and inversion in the anglo brabant fold belt new data implying crustal activation of eastern avalonia along the anglo brabant fold belt are presented late ordovician subduction related magmatism in east anglia and the brabant massif coupled with accelerated subsidence in the anglia basin and in the brabant massif during silurian time indicate a foreland basin development final collision resulted in folding cleavage development and thrusting during the mid lochkovian to mid eifelian in the southeast of the anglo brabant fold belt acadian deformation produced basin inversion and the regional antiformal structure of the brabant massif the uplift inferred from the sedimentology petrography and reworked palynomorphs in the lower devonian of the dinant synclinorium is confirmed by illite crystallinity studies the tectonic model discussed implies the presence of two subduction zones in the eastern part of eastern avalonia one along the anglo brabant fold belt and another under the north sea in the prolongation of the north german polish caledonides

distinct magnetic fabric in weakly deformed sediments from extensional basins and fold and thrust structures in the northern apennine orogenic belt italy we report on results from anisotropy of magnetic susceptibility ams analyses carried out on weakly deformed fine grained sediments from the northern apennine orogenic system italy we sampled 63 sites from preorogenic synorogenic and postorogenic sequences which differ in age composition depositional environment degrees of deformation and tectonic regimes the magnetic fabric is typical of weakly deformed sediments with a magnetic foliation subparallel to the bedding plane and a magnetic lineation well defined in this plane northern apennine chain deposits are characterized by strongly oblate magnetic susceptibility ellipsoids indicating that the magnetic fabric is the result of both compaction process and tectonic load experienced by the sediments during diagenesis and orogenic events the orientation of magnetic lineation is significantly different depending whether the studied sites underwent extensional or compressional tectonic regimes in the northern apennine chain the magnetic lineation is mostly oriented nnw sse parallel to the main compressional structures it suggests a tectonic origin of the magnetic lineation with an acquisition related to the apennines compressional phases in the extensional tuscan tyrrhenian margin magnetic lineation is oriented ene wsw almost perpendicular to the main extensional faults which represent the main deformation elements of the area our results demonstrate a close relationship between the shape and orientation of magnetic fabric and the tectonic history of rocks confirming that ams represents a valuable tool to investigate the tectonic history of weakly deformed sedimentary rocks

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

the origin of tectonic lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays abstract in extensional sedimentary basins fine grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern the origin of the magnetic lineation which is often found in extensional basins is not yet well understood in clays from extensional basins in southern italy the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults a combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings low field high field and low temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy the magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite lying parallel to the common axis of differently oriented basal planes a quantitative correlation between the magnetic and rock fabric was made comparing the low and high field magnetic anisotropy ams hfa to the theoretical anisotropy calculated from the chlorite preferred orientation a good linear correlation is found between the degree of theoretical anisotropy and the ams and hfa results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins where macroscopic evidence of deformation is often not visible

lidar monitoring of mass wasting processes the radicofani landslide province of siena central italy abstract the radicofani basin stretching about 30 km nw se is an intra central apennine basin connected to pliocene pleistocene extensional tectonics it consists of an early to middle pliocene succession including essentially shelf pelites in the radicofani area province of siena tuscany region morphodynamic processes are very frequent with widespread badlands and rapidly evolving mudflows in order to evaluate the general instability of the radicofani area geological and geomorphological surveys were carried out the 1954 1990 and 2003 aerial surveys allowed a comparison of the changes in the various morphological aspects of the study area which suggested an increase in slope instability with time a new complex translational landslide evolving into mudflows activated during the winter of 2003 was monitored using an experimental system based on terrestrial lidar light detection and ranging and gps global positioning system technologies this system allowed the monitoring of the morphologic and volumetric evolution of the landslide a comparison of the monitoring data of october 2004 june 2005 may 2006 and may 2007 points out that the evolution is characterised by the sliding of displaced materials a volume of about 1300 m 3 of materials was removed during the period 2004 2005 300 m 3 for 2005 2006 and 400 m 3 for 2006 2007 the greater initial mass movement probably reflects a greater static imbalance during the early period of landslide movement and increased rainfall therefore the proposed monitoring system methodology allows the numerical evaluation of the landslide morphological evolution and to validate the landslide evolution model based on geological and geomorphological field surveys

phyllosilicate preferred orientation as a control of magnetic fabric evidence from neutron texture goniometry and low and high field magnetic anisotropy se rhenohercynian zone of bohemian massif

phyllosilicate preferred orientation in relation to strain path determination in the lower paleozoic stavelot venn massif ardennes belgium abstract phyllosilicate preferred orientation measured by means of an x ray pole figure goniometer allows a quantitative exploration of the slaty cleavage development the relationship between phyllosilicate preferred orientation and strain as demonstrated in the march model furthermore enables the application of phyllosilicate pole figures in a strain determination in slate belts both applications are illustrated in this paper in which the results are presented of a crystallographic fabric analysis of argillites in the southern domain of the lower paleozoic stavelot venn massif belgium in these argillites the development of a phyllosilicate preferred orientation is primarily defined by the low grade metamorphism and the deformation history the metamorphism causing recrystallisation to be active during cleavage development assures the development of a high degree of preferred orientation on the other hand the deformation history defines the type of phyllosilicate pole figure pattern based on the distinction of different pole figure patterns a possible strain path for the argillites in the southern domain of the stavelot venn massif is proposed an axially symmetric pole figure pattern indicates a caledonian cleavage development in a pure flattening regime the variscan cleavage development on the other hand is characterised by an additional extensional component in the cleavage plane if the primary phyllosilicate fabric due to a pre deformational compaction or a caledonian cleavage development underwent a complete reorientation caused by syntectonic recrystallisation a typical orthorhombic pole figure pattern is formed otherwise a transition pole figure pattern develops reflecting the superposition of the variscan cleavage development on a pre existing caledonian cleavage fabric the general deformation history of the southern domain of the stavelot venn massif differs substantially from that described for the northern domain contrary to the northern domain the southern domain seems to have undergone considerable variscan deformation

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

a tectonic origin of magnetic fabric in the shemshak group from alborz mts northern iran abstract the magnetic lineation observed in undeformed sedimentary units has been interpreted either as an indication of paleoflow direction or as a result of tectonic overprint which progressively modifies the original sedimentary fabric related to compactional processes distinguishing between the two processes is not always easy in fact most studies of the anistropy of magnetic susceptibility ams of undeformed sequences have been carried out in fine grained sediments from foredeep sequences which are characterized by sedimentary flow directions which are almost parallel to the main deformation structures like thrust faults and folds in the alborz mts the upper triassic lower jurassic shemshak group was deposited in a foreland to molassic basin of the eo cimmerian orogen and now outcrops in several folds which are oriented parallel to the curved chain paleoflow directions are generally oblique to the main tectonic structures being directed ssw to sse and showing negligible changes in their orientation along the alborz mountains we have therefore the opportunity to distinguish between tectonic or sedimentary related origins of the magnetic lineation the ams results show that magnetic lineations of the shemshak group are oriented almost parallel to the main fold axes and thrust structures which follow the alborz mts curved trend suggesting that magnetic lineation is of tectonic origin in fine to medium grained mostly massive sandstones and confirming that ams is a valuable tool to study deformation processes in sedimentary rocks

effect of progressive deformation on remanent magnetization of permian redbeds from the alpes maritimes france abstract the relationships among the anisotropy of magnetic susceptibility the finite strain and the characteristic remanent magnetization chrm have been investigated in deformed red sediments from the alpes maritimes in southeast france the magnetic properties of these rocks are due to hematite the finite strain is known from field studies of the shapes and orientations of green reduction spots and from optical microscopy and x ray texture goniometry studies of chlorite and illite the strain data permit a classification of the magnetic results according to four main stages of progressive deformation in the compaction stage magnetic anisotropy is flattened in the bedding due to compactional loading the chrm directions approximate to a fisherian distribution about a mean value close to the known permian direction for the region as deformation proceeds pencil structure first develops and the anisotropy is characterized by a prolate pattern with maximum axis parallel to the subhorizontal azimuth of the pencil structure and fold axes with increasing deformation the magnetic susceptibility ellipsoid becomes oblate and finally triaxial at these stages of high deformation the anisotropy patterns show that the hematite grain orientations are strongly influenced by the cleavage the remanence directions in deformed rocks do not correspond to a fisher distribution and eventually deviate strongly from permian directions these results show that paleomagnetic vectors are affected by the distortional strains which accomodate shape change in the rock simple tilt correction without compensation for the strain would yield incorrect paleopole positions an attempt has been made to compensate for the effects of deformation by regarding the remanent vector as a passive marker march 1932 equations for strain removal were applied to the remanence in two ways 1 a using strain data directly obtained in the field for each site and 2 b by converting the magnetic susceptibility anisotropy of each sample to a corresponding finite strain value correcting for the finite strain by both methods improves the within site grouping of paleomagnetic vectors in strongly deformed rocks strain removal assuming the march model results in overcorrection of the remanent magnetization data in low strain regions distortion may produce mechanical rotation of the hematite particles but recrystallization may alter the deformation mechanism in regions of high strain the limits of applicability of the passive marker treatment could not be tested adequately in the deformed red sediments of the alpes maritimes

the anisotropy of magnetic susceptibility ams in low grade cleaved pelitic rocks influence of cleavage bedding angle and type and relative orientation of magnetic carriers

strain removal applied to paleomagnetic directions in an orogenic belt the permian red slates of the alpes maritimes france abstract detailed investigations of relationships between strain and directions of characteristic remanent magnetization chrm have been conducted on the permian red series of the alpes maritimes france the analysis of the results obtained by structural and paleomagnetic studies on 14 sites leads to the following observations in most sites the mean direction of the strain shortening axis is close to the expected permian paleomagnetic direction in this case we observe a large scatter of the chrm directions within each site which is interpreted as an increase of an initial dispersion due to strain moreover this dispersion more or less increases with strain intensity in other cases where the angle between the shortening axis and the paleomagnetic direction is high the whole population is deflected towards the cleavage xy plane these observations lead us to assume a material line like behaviour of the chrm vectors and consequently an attempt has been made to recalculate these directions by strain removal these calculations give positive results at two levels 1 a statistically significant improvement in the clustering of the within site distributions and 2 after tilt correction using unstrained bedding planes a significant improvement in the clustering of the between site distribution the formation mean direction after strain removal is in good agreement with known permian results for stable europe

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

arcuate fold and cleavage patterns in the southeastern part of the anglo brabant fold belt belgium tectonic implications abstract the brabant massif belgium is situated at the southeastern extremity of the anglo brabant fold belt the predominantly concealed eastern branch of the british belgian caledonides in contrast to the other parts of this caledonian slate belt the deformation history in the brabant massif has to date never been constrained properly in this paper a synthesis is presented of the structural observations in the limited outcrop area of the brabant massif in particular with respect to cleavage and fold trajectories and mutual cleavage fold relationships arcuate fold and cleavage patterns as well as the presence of cleavage transected folds are demonstrated similar to the other parts of the belt moreover the arcuate trajectories are considered to reflect the trace of the caledonian deformation front once obscured by the variscan ardenne allochthon combined with interpretations of the aeromagnetic and bouguer anomaly maps an overall kinematic model is proposed for the acadian deformation event in the brabant massif with the proposed model calling upon processes of indentation by promontories and lateral escape of lithostructural domains as well as on the control exerted by rigid granitoid basement blocks the strong similarities with the other parts of the british belgian caledonides become apparent by defining an overall shortening direction and proposing a trace for the caledonian deformation front in this southeastern extremity of the anglo brabant fold belt an integrated tectonic image is obtained for the entire british belgian caledonides

magnetic anisotropy rock fabrics and finite strain in deformed sediments of sw sardinia italy abstract although some empirical relationships have been established between the anisotropy of magnetic susceptibility ams and the state of finite strain in studies from specific geologic areas the mechanisms governing correlations are not well understood a comparative study has been made in order to elucidate the ams strain relationship by investigating mineral preferred orientations and the responsible microstructural deformation processes detailed analyses are presented from low grade metamorphic slates of a palaeozoic sequence exposed in the variscan of sw sardinia rock magnetic experiments suggest that paramagnetic minerals dominate the ams in these rocks excellent agreement was found between magnetic fabrics and lattice preferred orientations 001 of mica and chlorite determined from x ray texture goniometry measurements depending on the oblate or prolate ellipsoidal shape of anisotropy the minimum principal axes of ams and x ray textures can coincide with the poles to slaty cleavage or the maximum principal axes can coincide with the bedding cleavage intersection respectively the measured ams and x ray textures only partially reflect the finite strain determined from deformed micro pebbles and reduction spots axial orientations of magnetic fabrics mica and chlorite preferred orientations and finite strain ellipsoids are generally in good agreement depending on development of oblate or prolate fabric ellipsoidal shapes linear correlations can be established for magnitudes of minimum and intermediate axes of the ams and finite strain ellipsoids but shape comparisons are complex microstructural studies by scanning electron microscopy sem indicate that the preferred orientation of the phyllosilicates is caused by different grain scale deformation mechanisms such as kinking micro folding and preferential growth thus magnetic fabrics and mineral preferred orientations evidently result from different deformation mechanisms than the finite strain they reflect the heterogeneous deformation due to micro mechanical reorientation processes of mineral grains while finite strain reflects the homogeneous deformation accommodated cumulatively by the strain markers

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

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics 1 the anisotropy of magnetic susceptibility ams is an integral measure of the preferred orientation of all minerals present in a rock when the ams is carried by paramagnetic minerals alone the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals the relationship between the ams and deformation depends on several factors which control the development of lattice preferred orientation lpo in a rock a mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase measurements of the ams are compared with fabric based anisotropy models for black slates from the navia alto sil slate belt in northern spain the ams is carried by paramagnetic minerals as has been confirmed by high field torque magnetometry low temperature ams and magnetization curves the lpo of mica and chlorite has been determined by x ray texture goniometry pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates the models have been tested in samples displaying three types of pole figures a high intensity point maximum a medium intensity elliptical maximum and a girdle shaped distribution at one site displaying kink bands the lpo shows variations between these types at the outcrop scale the case studies illustrate the success in modeling different lpo types

deformation in rocks from itajai basin southern brazil revealed by magnetic fabrics magnetic measurements were performed on sedimentary and volcanic rocks from the itajai basin rock magnetism analyses reveal that magnetite and hematite and paramagnetic minerals show different contributions to magnetic susceptibility magnetic fabrics were determined in 19 sites by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence magnetization aarm the analysis at the individual site scale defines three ams fabric types the first type shows kmin perpendicular to the bedding plane while kmax and kint are scattered within the bedding plane itself this fabric is usually interpreted as primary the second type 77 of the sites shows the three well clustered ams axes with kmin still perpendicular to the bedding plane the third type is characterized by well clustered kmax in the bedding plane while kmin and kint are distributed along a girdle perpendicular to kmax the second and third fabric types are interpreted as combinations of sedimentary compactional and tectonic contributions at the earliest and at a slightly later stage of deformation respectively ams represents the contribution of all the rock forming minerals while aarm isolates the contribution of remanence bearing minerals with coercivity 100 mt for some sites the ams and aarm fabrics are non coaxial mainly with respect to the lineation orientations the comparison of magnetic lineations and the regional structural data indicates that the rocks with no mesoscopic or macroscopic deformation were affected by the two deformation phases that occurred in the region one of them results from compressional tectonics related to the collisional orogen d1 and the other is extensional related to post collisional orogen d2 after the former tectonic event the volcanic rocks were emplaced at the top of the stratigraphic sequence and after that the itajai basin as a whole was deformed by the extensional tectonic d2 that occurred after 560 ma which is the age of the intrusion

a method for the separation of paramagnetic ferrimagnetic and haematite magnetic subfabrics using high field torque magnetometry summary in this study the contribution of the paramagnetic ferrimagnetic and haematite components to the magnetic anisotropy is separated by means of high field torque magnetometry torque measurements at different fields which are high enough to saturate the ferrimagnetic minerals however still low enough that the torque resulting from the haematite is linear with field allow for the separation of the three magnetic anisotropy components the method has been applied to haematite single crystals in which no paramagnetic or ferrimagnetic components have been found contribute to the torque signal the mean direction of the poles to the crystallographic basal plane in the haematite single crystals is subparallel to the minimum susceptibility direction measured in low field the separation analysis has also been applied to highly deformed red beds from the lower glarus nappe complex switzerland no ferrimagnetic phases are present in the rocks and therefore they cannot contribute to the anisotropy of magnetic susceptibility the magnetic fabric arises from a paramagnetic subfabric carried by the phyllosilicate minerals and haematite in which the basal planes of both phases are in the cleavage plane the measured magnetic lineation seen in low field anisotropy of magnetic susceptibility appears to be an apparent lineation that arises from a weak girdling of haematite and the paramagnetic minerals conforming the rock

kinematics and strain distribution in an orogen scale shear zone insights from structural analyses and magnetic fabrics in the gavarnie thrust pyrenees abstract this work aims to characterize the gavarnie thrust one of the large scale thrusts that define the alpine structure of the west central sector of the pyrenees a detailed comparison of structural analysis and magnetic fabrics is carried out for the paleozoic phyllonites of the gavarnie thrust in order to decipher strain distribution and transport direction the ams at room rt ams and low lt ams temperature and the airm can be correlated with the structural patterns kmin axes are mainly parallel to the pole of the s c or c planes and kmax axes are parallel to the transport direction and related to ductile s c structures furthermore the pj t changes across the shear zone characterize strain variations larger pj and t are found in the basal most deformed part of the shear zone and lower values are found where the interaction between alpine and variscan related petrofabrics is stronger we also interpret the reactivation of variscan inherited fabrics within the alpine shear zone in spite of the heterogeneous strain markers indicate a common top to the south n190e alpine transport direction which contrasts with the strong obliquity of the genetically related structures developed in the southern mesozoic sedimentary cover in this sense our data suggest a complete decoupling between basement and cover units during the alpine compression

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

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

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible