sources of magnetic susceptibility in a slate abstract magnetic susceptibility and its anisotropy in the borrowdale volcanic slates at kentmere in the english lake district are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite ripidolite composition in units of 10 6 cgs g the principal susceptibilities for the slates are 9 61 9 42 8 69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11 57 11 22 and 9 15 because the magnetic susceptibility is carried by a tightly packed matrix forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility

ultrahigh pressure texture inheritance during retrogression evidence from magnetofabrics in eclogites and ultramafic rocks chinese continental scientific drilling project abstract in order to contribute to a better understanding of exhumation related retrogression processes ultrahigh pressure uhp mafic and ultramafic rocks from the chinese continental scientific drilling ccsd in the maobei eclogite body of the sulu ultrahigh pressure metamorphic belt in eastern china were studied for their magnetofabrics variably retrogressed eclogites and serpentinized ultramafic rocks were retrieved from the depth interval of 100 to 1000 m of the borehole a vein network of irregular shaped veins with a retrograde metamorphic assemblage cuts across the eclogite foliation at both low and high angles sem imaging of the eclogites documents that magnetite associated with retrograde pargasitic amphiboles developed around shape preferred garnet sem imaging of the serpentinized ultramafic rocks documents that magnetite rims grew around shape preferred garnet and that magnetite formed within a mesh texture related to serpentinization syn serpentinization magnetite growth increased bulk susceptibilities but reduced anisotropy maximum susceptibility axes from both eclogites and serpentinized garnet peridotites trend n s i e parallel with the stretching lineation as defined by olivine and omphacite grains this implies that the magnetic fabric mimics the uhp fabric and survived retrogression and that the fabric is inherited from the uhp stage as a consequence retrogression was not associated with substantial ductile deformation and the mafic ultramafic maobei body behaved as a rigid body within a ductile deforming quartzo feldspathic matrix during exhumation internal strain is restricted to brittle fracturing associated fluid circulation and vein formation facilitating retrograde reactions in the mafic ultramafic rocks

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

determination of field independent and field dependent components of anisotropy of susceptibility through standard ams measurement in variable low fields ii an example from the ultramafic body and host granulitic rocks at bory in the moldanubian zone of western moravia czech republic abstract a large ultramafic body garnet clinopyroxenite and garnet peridotite embedded in felsic granulite at bory moldanubian zone of western moravia czech republic contains multiple carrier of susceptibility low field variation of anisotropy of magnetic susceptibility ams enables the separation of the field independent and low field dependent ams components to be made in granulite the former is carried by paramagnetic minerals and a subordinate admixture of magnetite while the latter is due to pyrrhotite in the ultramafite the field independent component is carried by pure magnetite formed by serpentinization while the field dependent component is due to pyrrhotite and subordinate paramagnetic minerals despite small differences all ams components are roughly coaxial both within granulite and within ultramafite but very different between granulite and ultramafite the difference indicates that the forces that imposed the later granulite fabric were not strong enough to obliterate the original magnetic fabric of the ultramafites

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

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

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

anisotropy of magnetic susceptibility in alkali feldspar and plagioclase feldspars are the most abundant rock forming minerals in the earth s crust but their magnetic properties have not been rigorously studied this work focuses on the intrinsic magnetic anisotropy of 31 feldspar samples with various chemical compositions because feldspar is often twinned or shows exsolution textures measurements were performed on twinned and exsolved samples as well as single crystals the anisotropy is controlled by the diamagnetic susceptibility and displays a consistent orientation of principal susceptibility axes the most negative or minimum susceptibility is parallel to 010 and the maximum least negative is close to the crystallographic 001 axis however the magnetic anisotropy is weak when compared to other rock forming minerals 1 53 10 9 m3 kg 1 at maximum therefore lower abundance minerals such as augite hornblende or biotite often dominate the bulk paramagnetic anisotropy of a rock ferromagnetic anisotropy is not significant in most samples in the few samples that do show ferromagnetic anisotropy the principal susceptibility directions of the ferromagnetic subfabric do not display a systematic orientation with respect to the feldspar lattice these results suggest that palaeointensity estimates of the geomagnetic field made on single crystals of feldspar will not be affected by a systematic orientation of the ferromagnetic inclusions within the feldspar lattice

magnetic fabric and deformation in the navia alto sil slate belt northwestern spain abstract ries and schackleton ries a c schackleton r m 1976 patterns of strain variation in arcuate fold belts philos trans r soc london a 283 281 288 discussed the distribution of finite strain in the ibero armorican arc and suggested that the arc was produced by tectonic bending of a straight or gently curved fold belt later investigations by others revealed different strain patterns in the fold thrust belt and so its evolution continues to be controversial this study focuses on the strain pattern in the navia alto sil slate belt the low field anisotropy of magnetic susceptibility ams was measured in ordovician black slates and cambrian to lower ordovician quartzites sampled around the arcuate belt the magnetic fabric is controlled primarily by the slaty cleavage in both lithologies the ams was also measured with a high field torsion magnetometer and the results indicate that paramagnetic minerals are responsible for the magnetic fabric in the slates and diamagnetic and paramagnetic minerals in the quartzites strain markers i e pressure shadows around pyrite grains and rutile distribution are found in the slates and the orientation of the principal axes of strain ellipsoids agrees with those of the ams ellipsoid a systematic variation in the orientation of the strain ellipsoid and anisotropy ellipsoid suggests that there is strain heterogeneity along the slate belt and that the arc did not form by tectonic bending

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

inversion tectonics and magnetic fabrics in mesozoic basins of the western tethys a review abstract positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics since tectonic markers for the extensional episodes are not commonly well developed anisotropy of magnetic susceptibility ams has provided recently a tool for analyzing early stages in the evolution of sedimentary basins even in the absence of other outcrop scale mesostructures here we expose and discuss the applicability of magnetic fabrics by means of ams to different types of intra plate sedimentary basins in the western tethys region formed under extensional or transtensional regimes and which underwent different inversion styles total or partial inversion with or without cleavage development forming part of compressional thrust sheets etc owing to specific particular p t conditions and structural controls factors such as lithology magnetic mineralogy position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution a basin classification is proposed according to inversion styles and magnetic fabrics where inversion did not involve cleavage development magnetic lineation is parallel to the stretching direction corresponding to the extensional stage the transition between non cleaved to inversion related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding these relationships are enhanced when extension and compression are roughly coaxial then favoring the clustering of axes of the magnetic ellipsoid even when extreme inversion occurs and the early extensional fabric is obliterated magnetic fabrics provide information about the interaction between preferred deformation directions associated with the main stages in basin evolution

evidence for the permo triassic transtensional rifting in the iberian range ne spain according to magnetic fabrics results abstract anisotropy of magnetic susceptibility ams techniques are applied to permo triassic red beds from the castilian branch iberian range ne spain that were deposited in an extensional basin inverted during cenozoic times the main goal of this work is to characterize the tectonic evolution of the basinal stage by differentiating synsedimentary to early diagenetic magnetic fabrics from the secondary tectonic fabrics related to compression which are scarcely developed because no penetrative structures related to compression have been recognized oblate magnetic fabrics with kmin axes perpendicular to bedding are observed in most cases magnetic lineations are variable showing a dominant ene wsw maximum which fits with a dextral transtensional regime acting on nw se master faults during the triassic we propose that variations in the orientation of the magnetic lineation are associated with transfer faults which fragment the basin and trigger strain partitioning in different areas magnetic fabrics are locally modified by cenozoic compression with intermediate and minimum axes distributed along girdles perpendicular to fold axes comparing all these results with macrostructures and mesostructural kinematic indicators we conclude that the fine grained hematite bearing rocks carry a consistent magnetic fabric which can be used to reconstruct the basin history

magnetic fabrics in the bjerkreim sokndal layered intrusion rogaland southern norway mineral sources and geological significance abstract magnetic anisotropy can provide important information about mineral fabrics and thus magmatic processes particularly when it is known how multiple mineral species contribute to the anisotropy it may also affect the direction of induced or remanent magnetization with important consequences for paleomagnetic studies or the interpretation of magnetic anomalies here we aim at describing the magnetic fabrics in the bjerkreim sokndal layered intrusion and identifying their carriers anisotropies of magnetic susceptibility and remanence were measured on samples covering different geographic locations and stratigraphic units within the bjerkreim sokndal layered intrusion the intrusion is characterized by magmatic layering and has a synform structure with strong foliation on the limbs detailed comparison between magnetic and mineral fabric shows that they are not necessarily coaxial but the minimum susceptibility and minimum anhysteretic remanence are generally normal to the foliation or the magmatic layering the minimum susceptibility and anhysteretic remanence are associated with pyroxene 100 axes and the maximum susceptibility and anhysteretic remanence are sub parallel to the pyroxene 001 axes in layers mcu ivc and mcu ive for which electron backscatter data are available however the paramagnetic anisotropy of pyroxene is too weak to explain the observed anisotropy we propose that the magnetic anisotropy of magnetite free specimens is carried by hemo ilmenite exsolutions within pyroxene in addition to pyroxene itself when present multi domain magnetite dominates both the anisotropy of magnetic susceptibility and anhysteretic remanence due to shape preferred orientation and distribution anisotropy the orientation of the magnetic fabric appears independent of carrier due to their common deformation history but the degree of anisotropy is stronger for magnetite bearing specimens the results of this study will facilitate future structural interpretations and may be used to correct for magnetization deflection

magnetic fabric arising from paramagnetic phyllosilicate minerals in mudrocks the magnetic fabric of mudrock samples from the westbury member of the penarth group rhaetian the blue lias formation hettangian to sinemurian and the oxford clay callovian to oxfordian has been measured using a high field torque magnetometer the magnetic susceptibility anisotropy of these mudrocks originates from paramagnetic phyllosilicate minerals of which the most important is considered to be detrital chlorite the magnetic fabric preserves both a lineation and a foliation which are of a primary style this magnetic fabric is sensitive to the effects of recent weathering due to the ease with which chlorite is oxidized during weathering a model is proposed utilizing compaction to explain the acquisition of this magnetic fabric this model infers that the magnetic fabric represents in both degree and direction a measure of the preferred crystallographic orientation of the paramagnetic phyllosilicate minerals the magnetic fabric data suggest that the kmax direction corresponds with the quartz grain long axis preferred orientation and therefore may be used as a palaeocurrent indicator as in titanomagnetite bearing sediments evidence is presented to suggest that paramagnetic susceptibility anisotropy may be common in other mudrocks

crystallographic and magnetic preferred orientation of hematite in banded iron ores abstract the crystallographic preferred orientation of hematite in banded iron ores and the orientation of both the measured and the calculated principal susceptibility axes are strongly related the maximum susceptibility is aligned with the lineation and the pole of the foliation coincides with the minimum susceptibility although there are often distinct differences between the measured and calculated values of the susceptibilities a wide variety of configurations of c axis pole figures modeled by varying the parameters of the bingham distribution and bingham mardia distribution reveal that quite different c axis patterns of hematite ores may have the same anisotropy of the magnetic susceptibility ams parameters large deviations between calculated and experimental ams data should initiate further investigations to resolve a probably unnoticed heterogeneity of the fabric the present investigations show that the structural analysis of the preferred orientation of hematite ores by means of the rather inexpensive and fast magnetic method must be accompanied by the more expensive but unambiguous determination of preferred orientation by x ray and neutron diffraction experiments in order to accomplish a complete and sound interpretation

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

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

a paleomagnetic study of tectonically deformed red beds of the lower glarus nappe complex eastern switzerland a paleomagnetic study at 15 sites 315 samples in permo triassic red beds of the helvetic nappes of eastern switzerland isolated stable characteristic and secondary remanent directions thermal demagnetization and isothermal remanent magnetization experiments suggest pigmentary hematite carries the characteristic direction secondary directions are scattered but may have been acquired during the alpine deformation in the oligocene and miocene the characteristic directions also show large between site scatter anisotropy of magnetic susceptibility indicates that the hematite grains are flattened within the slaty cleavage and that there is a north south lineation this anisotropy pattern implies that the magnetic grains were realigned by the alpine deformation it is not possible to explain the characteristic remanent magnetization deviations on a site by site basis but the site mean directions are streaked along a great circle the down dip direction of which is approximately parallel to the regional fold axes 60 20 this spread could be explained by a penetrative simple shear deformation associated with the nappe internal deformation

paramagnetic metamorphic mineral assemblages controlling ams in low grade deformed metasediments and the implications with respect to the use of ams as a strain marker a regional analysis of the anisotropy of magnetic susceptibility ams has been performed on low grade metamorphic deformed homogeneous siltstone beds hsbs of the plougastel formation in the central armorican domain together with exhaustive compositional analyses of the studied specimens despite sampling a single horizon different paramagnetic minerals are controlling the ams in the crozon peninsula sites white mica and chlorite and in the inland sites of the central armorican domain white mica chloritoid and some chlorite both the crozon peninsula and inland datasets show a hockey stick shaped pattern on a plot of the shape parameter t versus the corrected degree of anisotropy p j although the whole pattern is shifted to higher p j values for the inland dataset high field ams indicates that the low field p j and t values from two inland sites are slightly enhanced by a small ferromagnetic sensu lato contribution furthermore variation in p j and t values within single sites can be attributed to an effect of the observed quartz white mica ratio as quartz grains disrupt the petrofabric intensity our findings clearly demonstrate that the ams of the hsbs in the central armorican domain is strongly influenced by compositional variations and does not merely indicate tectonic strain even in very similar tectonostratigraphic settings supplementary material outcrop coordinates with information on the hsbs and samples and the summarized low field room temperature ams data are available at www geolsoc org uk sup18578

evidence for non coaxiality of ferrimagnetic and paramagnetic fabrics developed during magma flow and cooling in a thick mafic dyke abstract a detailed analysis of fabrics of the chilled margin of a thick dolerite dyke foum zguid dyke southern morocco was performed in order to better understand the development of sub fabrics during dyke emplacement and cooling ams data were complemented with measurements of paramagnetic and ferrimagnetic fabrics measured with high field torque magnetometer neutron texture and microstructural analyses the ferrimagnetic and ams fabrics are similar indicating that the ferrimagnetic minerals dominate the ams signal the paramagnetic fabric is different from the previous ones based on the crystallization timing of the different mineralogical phases the paramagnetic fabric appears related to the upward flow while the ferrimagnetic fabric rather reflects the late stage of dyke emplacement and cooling stresses

spatiotemporal variation in cross shelf exchange across the inner shelf of monterey bay california abstractcross shelf exchange resulting from wind and wave driven flows across the inner shelf has been the focus of a considerable body of work this contribution extends recent analyses to the central california coastline using 5 yr of moored current observations acoustic doppler current profiler adcp data from stations across the monterey bay two in the northern bay and one in the southern bay in water depths of 20 m showed net offshore transport throughout the year for the northern bay sites cross shelf exchange was dominated by ekman transport driven by along shelf diurnal sea breezes during the upwelling season intense stratification in the northern bay leads to very shallow observed ekman layers 5 8 m and consequently no overlap between bottom and surface ekman layers within a few hundred meters of the coast the total transport is less than predicted by theory consistent with models of shallow water ekman transport the observed transport 42 of full ekman transport is shown to b

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

resolution of ferrimagnetic and paramagnetic anisotropies in rocks using combined low field and high field measurements summary a method of separation of ferrimagnetic and paramagnetic components of magnetic anisotropy from the total anisotropy is developed from the anisotropy measurement of a specimen in a low field susceptibility anisotropy and from measurement in two high fields stronger than the saturation field of the ferrimagnetic fraction present the following anisotropy components can be calculated susceptibility anisotropy field independent of the paramagnetic fraction low field susceptibility anisotropy of the ferrimagnetic fraction and high field anisotropy of the ferrimagnetic fraction errors possibly arising from imperfect saturation of the ferrimagnetic fraction in the field practically available are analysed

understanding the mesozoic kinematic evolution in the cameros basin iberian range ne spain from magnetic subfabrics and mesostructures abstract analysis of anisotropy of magnetic susceptibility ams and brittle mesostructures hydroplastic synsedimentary faults and tension gashes is applied in this study in order to characterize the mesozoic tectonic events in the cameros basin nw iberian range formed between tithonian and albian times low field ams at room and low temperature lf ams at rt and lf ams at lt respectively together with high field ams hf ams measurements allow separating ferro and paramagnetic fabrics the combination of lf ams at lt and hf ams torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the ams magnetic fabric results combined with the analyses of synsedimentary faults indicate a nw se extension direction during aptian and probably barremian times this extension direction is perpendicular to the main extension direction ne sw prevailing during early and late stages of basin evolution it is also consistent with extension direction deduced from large scale bending folds and tension gashes developed after partial lithification cleavage development during albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression

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

preferred mineral orientation of a chloritoid bearing slate in relation to its magnetic fabric 2014 elsevier ltd a regional analysis of the anisotropy of the magnetic susceptibility on low grade metamorphic chloritoid bearing slates of the paleozoic in central armorica brittany france revealed very high values for the degree of anisotropy up to 1 43 nonetheless high field torque magnetometry indicates that the magnetic fabric is dominantly paramagnetic chloritoid s intrinsic degree of anisotropy of 1 47 0 06 suggests that chloritoid bearing slates can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic s l minerals to validate this assumption we performed a texture analysis on a representative sample of the chloritoid bearing slates using hard x ray synchrotron diffraction the preferred orientation patterns of both muscovite and chloritoid are extremely strong 38 6m r d for muscovite 20 9m r d for chloritoid and display roughly axial symmetry about the minimum magnetic susceptibility axis indeed suggesting that chloritoid may have a profound impact on the magnetic fabric of chloritoid bearing rocks however modeling the anisotropy of magnetic susceptibility by averaging single crystal properties indicates that the cpo of chloritoid only partially explains the slate s anisotropy

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

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

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

identification of multicomponent anisotropies in rocks using various field and temperature values in a cryogenic magnetometer abstract a new technique involving magnetization measurements on a rotating sample in a cryogenic magnetometer with variable field from 0 to 4 t and variable temperature is presented it can be used to separate and identify multi component anisotropy in rocks the results obtained for anisotropy due to magnetite haematite pyrrhotite or phyllosilicates are interpreted according to different magnetization models

inversion of polyphase calcite twin data for deviatoric stress tensors 1 a novel numerical approach abstract a new inversion method is developed in this paper to estimate deviatoric stress tensors from a certain population of polyphase calcite twins it is both to minimize the number of the common incompatible twinned and untwinned e planes and to maximize the sum of the resolved shear stresses along the compatible twinned e planes under each reduced stress the genetic algorithm is employed to resolve this optimization problem a series of two phase equally mixed artificial datasets generated under the prescribed stresses were taken to demonstrate the feasibility of this method results indicate a strong tendency to have an increasing accuracy of reduced stress with the ascent of the prescribed maximum differential stress the difference between the prescribed stresses and the number of twinned calcite crystals respectively what is more the maximum differential stress becomes sufficiently large to permit an accurate estimate of reduced stress even though the prescribed stresses are intermediately similar to each other however the method assumes a constant critical resolved shear stress value to rescale the stress tensors and does not consider the influence on the critical resolved shear stress value of strain hardening grain size and temperature it takes an enormous amount of time in calculation