multimodal investigation of thermally induced changes in magnetic fabric and magnetic mineralogy summary low field magnetic susceptibility and its anisotropy ams were measured for a suite of sandstone and siltstone samples ams orientations measured on two systems bartington and digico divered before thermal treatment of the samples but became the same after thermal demagnetization in air to 600 c six position measurement schemes for the bartington system do not eliminate the evects of specimen inhomogeneity and other errors whereas 12 and 24 position measurements give good agreement with the digico anisotropy meter and with the observed petrofabric thermal demagnetization from temperatures between 400 and 650 c had the evect of enhancing both the magnetic susceptibility and ams although the most profound mineralogical change due to heating was the conversion of kaolinite into metakaolin irm xrd

paleomagnetic evidence for a neogene two phase counterclockwise tectonic rotation in the northern apennines italy paleomagnetic directions have been determined for a new collection of early oligocene and late miocene pliocene epiligurian clastic sediments from the frontal portions of the northern apennines these results are combined with cenozoic data from the literature to evaluate whether rotations of units in this region are related to the oligomiocene corsica sardinia rotation and or to younger phases of deformation of the apennine chain when corsica sardinia moved counterclockwise ov the coast of france the ligurian units located at its front were presumably pushed eastward and rotated counterclockwise above a main boundary thrust onto the adria africa margin we propose that about 24 out of a total of 52 of rotation observed in the epiligurian units can be related to the oligo miocene motion of the corsica sardinia block in partial agreement with previous conclusions and the remaining 28 to the pliocene tectonic phase at the apennine chain front which may have re activated thrust planes in the adria africa succession below the ligurian wedge 2000 elsevier science b v all rights reserved

magnetostratigraphy of a long quaternary sediment core in the south yellow sea abstract continental shelves serve as a bridge between the continent and ocean and sediments in this region are sensitive to land sea interaction sea level variation and local subsidence in this study we present a comprehensive magnetic study of the longest sediment core csdp 1 300 1 m recovered from the south yellow sea the major magnetic minerals in the studied sediments are magnetite hematite and greigite greigite records a chemical remanent magnetization which can be removed effectively by thermal demagnetization the magnetostratigraphy defined in this study contains the matuyama brunhes boundary m b 781 ka at 73 68 m which is consistent with results from adjacent cores the base of the quaternary 2 6 ma in the yellow sea is recovered for the first time at a depth of 227 16 m the basal age of the core is estimated to be 3 50 ma it indicates that the first transgression of the yellow sea occurred no later than 1 7 ma succeeding large amplitude regressions occurred in some cold periods such as during mis 20 mis 18 and mis 10 our results provide the first chronology that brackets the entire quaternary and we reconstruct the sedimentary evolution of the yellow sea with robust age constraints which provides an important framework for further paleoenvironmental and tectonic studies

unusual vegetation stability in a lowland pine forest area doksy region czech republic although the holocene is characterized by prominent vegetation changes some vegetation types can reveal surprising stability we studied holocene woodland history in a sandstone pseudokarst area

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

are the iron carbonate minerals ankerite and ferroan dolomite like siderite important in paleomagnetism magnetic mossbauer effect and thermal properties have been evaluated for specimens of the mineral ankerite and are contrasted with similar measurements reported for the mineral siderite to determine if ankerite and ferroan dolomite like siderite may be important in paleomagnetism as a producer of secondary spurious remanent moments as the result of oxidation in air our data indicate that ankerite and siderite both have comparable thermal stabilities and that ankerite does break down to form iron oxides at temperatures as low as 250 c during thermal demagnetization we conclude from our data that any iron carbonate siderite ankerite or ferroan dolomite may readily oxidize in air to maghemite or hematite thus producing a spurious remanent moment rm that can dominate the magnetic properties of the specimen thermal demagnetization of ankerite or siderite at lower temperatures below 250 c does not appear to produce such a spurious rm as might be expected the quantity of secondary iron oxides produced by oxidation is limited by the iron content in the carbonate crystal lattice oxidized siderite produces significantly greater amounts of iron oxides than equivalent percentages of ankerite which in turn produces more iron oxides than equal amounts of ferroan dolomite in a given sample

geomagnetic paleointensity at 2 41 ga as recorded by the widgiemooltha dike swarm western australia abstract absolute geomagnetic paleointensity measurements were conducted on samples from six mafic dikes of the 2 41 ga widgiemooltha swarm western australia rock magnetic analyses indicate that the paleointensity signal is carried by nearly stoichiometric pseudosingle domain magnetite and or low ti titanomagnetite paleointensity values were determined using the thellier double heating method supplemented by low temperature demagnetizations the ltd thellier method in order to reduce the effect of magnetic remanence carried by large pseudosingle domain and multidomain magnetite grains thirty one samples from five dikes yielded successful paleointensity determinations with the mean value of 41 2 3 8 t which corresponds to a virtual dipole moment of 6 65 0 98 a m 2 the mean and range of paleofield strength values are similar to those of the recent earth s magnetic field and are consistent with a compositionally driven geodynamo established by the earliest paleoproterozoic era the existence of a stable dipolar geomagnetic field during the proterozoic indicated by paleointensity and paleodirectional data from this and prior studies seems incompatible with a young age of the inner core suggested by recent models of the earth s thermal evolution acquisition of reliable paleointensity estimates using the novel approaches such as the ltd thellier method is crucial in constraining the development of more realistic earth like models of long term geodynamo behavior

variation of magnetic properties in sedimentary rocks hosting the foum zguid dyke southern morocco combined effects of re crystallization and fe metasomatism the effects of dyke intrusion on the magnetic properties of host sedimentary rocks are still poorly understood therefore we have evaluated bulk magnetic parameters of standard palaeomagnetic samples collected along several sections across the sediments hosting the foum zguid dyke in southern morocco the study has been completed with the evaluation of the magnetic fabric after laboratory application of sequential heating experiments the present study shows that 1 close to foum zguid dykes the variations of the bulk magnetic parameters and of the magnetic fabric is strongly related with re crystallization and fe metasomatism intensity 2 the thermal experiments on ams of samples collected farther from the dyke and thus less affected by heating during dyke emplacement indicate that 300 400 c is the minimum experimental temperature necessary to trigger appreciable transformations of the pre existing magnetic fabrics for temperatures higher than ca 580 c the magnetic fabric transformations are fully realized with complete transposition of the initial fabric to a fabric similar to that of samples collected close to the dyke therefore measured variations of the magnetic fabric can be used to evaluate re crystallization temperatures experienced by the host sedimentary rock during dyke emplacement the distinct magnetic behaviour observed along the cross sections strongly suggests that samples collected farther from the dyke margins did not experience thermal episodes with temperatures higher than 300 c after dyke emplacement 3 ams data shows a gradual variation of the magnetic fabric with distance from the dyke margin from sub horizontal k3 away from the dyke to vertical k3 close to the dyke experimental heating shows that heat alone can be responsible for this strong variation therefore such orientation changes should not be unequivocally interpreted as the result of a stress field resulting from the emplacement of the dyke for instance 4 magnetic studies prove to be a very sensitive tool to assess rock magnetic transformations thermally and chemically induced by dyke intrusion in hosting sediments

magnetic properties of oolitic iron ore on bell island newfoundland abstract magnetic properties of samples from bell island sedimentary rocks have been studied x ray analysis indicates that the main magnetic mineral is hematite in all samples the other iron bearing minerals identified are siderite and chamosite microscope observations of thin sections suggest that the rocks consist of oolitic hematite in a matrix of siderite or calcite the intensity of natural remanent magnetization nrm varies in the range of 0 03 0 4 a m 1 depending on the percentage of hematite the thermal demagnetization curves of nrm show in some cases a sharp increase in magnetization at temperatures in the range 500 600 c the peaks that occur in these demagnetization curves are due to a chemical change of siderite during repeated laboratory heating x ray analysis confirmed that the newly formed material is magnetite since the original nrm has been masked by the new intergrown material this would result in a serious error in the determination of paleomagnetic pole positions the samples showing this behaviour were not considered for paleomagnetic study the samples containing oolitic hematite in a calcite matrix exhibit very high stability of nrm including directional stability until almost 670 c for these samples a virtual pole position based on n 6 samples 32 specimens demagnetized to 665 c is 34 n 114 e not far from published ordovician poles for the north american craton

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

inverse magnetic fabric in carbonate bearing rocks abstract the observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric pole of bedding or schistosity is referred to as an inverse magnetic fabric the investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates that c axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones a mineralogical model based on the property of single domain grains to have a zero susceptibility parallel to their long axis is proposed however more complex cases are also encountered

diagenesis of ferriferous phases in the northampton ironstone in the cowthick quarry near corby england berthierine siderite and pyrite are the major ferriferous phases in the northampton ironstone nis mineralogical and chemical data suggest a formation of these phases in a diagenetic marine environment changing from post oxic to sulphidic conditions berthierine was formed first when the fe 2 activity in the diagenetic system increased later this phase was partially replaced by siderite and or pyrite a second stage of the diagenetic development in the nis with increasing co 2 partial pressure p co 2 is documented by siderite the isotopic composition 18 o mean value 1 7 pdb 13 c mean value 8 6 pdb points to siderite precipitation from a marine porewater environment with a microbial co 2 source the shift from post oxic to sulphidic conditions is indicated by the occurrence of pyrite and can be considered as a final stage the diagenetic processes in the marine environment and the formation of the ferriferous phases were stopped by the influx of brackish or fresh water when the midland shelf turned estuarine

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

strain indicators and magnetic fabric in intraplate fault zones case study of daroca thrust iberian chain spain abstract anisotropy of magnetic susceptibility ams has been applied to the study of shallow fault zones although interpretation of the results requires establishing clear relationships between petrofabric and magnetic features magnetic behaviour of fault rocks and an extensive knowledge of p t conditions in this work we demonstrate that magnetic methods can be applied to the study of heterogeneous fault zones provided that a series of requisites are met a major fault zone within the iberian plate daroca thrust showing transpressional movements during cenozoic time was chosen for this purpose because of the exceptional outcrops of fault gouge and microbreccia and its relevance within the context of the northeastern iberian plate magnetic fabrics were analysed and the results were compared with foliation and s c structures measured within the fault zone clay mineral assemblages suggest maximum burial depths shallower than 2 km

anomalous magnetic properties in rocks containing the mineral siderite paleomagnetic implications sampling and magnetic measurement of a 1 m bed in a new road cut of the upper cretaceous austin chalk northeastern texas has yielded anomalous magnetic results initial measurement of the anisotropy of magnetic susceptibility ams indicated unusually high anisotropies and low bulk susceptibilities characteristic of a magnetocrystalline anisotropy which might be expected for siderite feco3 natural remanent moments nrm for these samples were low 1 10 4 a m2 and directions were typical for samples which had acquired a normal geomagnetic field overprint at the site periodic remeasurement of the nrm yielded an increase in moment for some samples and periodic reversals of rm in a direction parallel or antiparallel to the ambient field in the laboratory isothermal remanent moments of these samples saturates at low induction values 200 mt ams remeasurement over a period of weeks to months revealed a general decrease in the anisotropy magnitudes an increase in susceptibility and a change in principal axis orientations these data were compared with heating oxidation experiments on austin chalk siderite ore and clastic sediments with siderite cements all of these results are consistent with the x ray diffraction and mossbauer data which indicate the presence of siderite in the austin chalk samples the mossbauer spectra of the samples obtained at room temperature and 78 k indicate the presence of approximately 80 pyrite 10 siderite and 10 of a clay component possibly chlorite when only the iron bearing mineral components are considered after sampling exposure to the air and subsequent oxidation in the laboratory the siderite in austin chalk samples appears to have altered to fe2o3 maghemite or fe3o4 magnetite increasing the magnetic moment and changing the nrm and ams directions in the samples the continuing changes appear to reflect a conversion from the less stable fe2o3 to fe2o3 hematite or oxidation of fe3o4 to fe2o3 we infer from our study that oxidation of siderite bearing limestone e g during the formation of unconformities or due to low magnitude tectonic events may produce a very stable secondary magnetic moment in the rock such changes may be very important when interpreting paleomagnetic data from limestones

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

inverse magnetic fabric in deformed limestones of the morcles nappe switzerland anisotropy of magnetic susceptibility ams was measured at 15 sites in deformed helvetic limestones of the morcles nappe in western switzerland inverse magnetic fabrics characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage were observed at four sites in the root zone of the nappe acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite with various proportions of magnetite hematite and goethite the matrix minerals were studied in thin section with a staining technique to distinguish different carbonates by x ray texture goniometry and by microprobe analysis observations of ams at room and liquid nitrogen temperatures and of the temperature dependence of bulk susceptibility lead to the conclusion that the inverse fabrics result from a paramagnetic component due to fe2 ions in the calcite matrix

integrated rock magnetic and mineralogical study of the lower triassic sedimentary rocks from spitsbergen abstract a rock magnetic mineralogical and mossbauer spectroscopy study was undertaken on the lower triassic sediments from the west spitsbergen fold and thrust belt wsftb in svalbard as well as the foreland of this orogen for a thorough recognition of magnetic mineralogy necessary for a better constrained interpretation of paleomagnetic results sem and mossbauer spectroscopy indicate the presence of magnetite and pyrrhotite both most probably of secondary origin but altered clasts of volcanic origin and grains of ilmenite and detrital magnetite are also observed thermomagnetic curves of whole rock samples exhibit paramagnetic behavior whereas ferromagnetic separates indicate the presence of magnetite irm component analysis shows three major contributors magnetite hematite and pyrrhotite to the remanence with ferromagnetic iron oxides the most dominant identified ferromagnetic minerals display a wide range of grain size and magnetic behavior with the domination of psd particles rock magnetic characteristics of both areas are similar but sites in the fold belt were most likely remagnetized whereas those in the foreland carry the primary magnetization the age of remagnetization was estimated as pre eurekan related to rift controlled mesozoic extensional phases of the barents sea shelf clark et al 2014 and or cretaceous injections of dolerites in the svalbard archipelago nejbert et al 2011 as well as early stages of the wsftb formation however triassic remanence might persist in volcanic lithoclasts and detrital magnetite indicated along the wsftb the multicomponent nature of the nrm displaying a broad range of grain size might impede the paleomagnetic interpretation of triassic rocks in spitsbergen

single domain particles in rocks and magnetic fabric analysis magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes we have recently demonstrated however in laboratory produced samples that as theoretically expected susceptibility anisotropy is dependent on particle size multidomain particles of magnetite or similar strongly magnetic particles with shape anisotropy exhibit a maximum susceptibility parallel to their easy remanent magnetization axes whereas uniaxial single domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state by demonstrating uniaxial single domain anisotropy characteristics for the first time in a rock specimen we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro or ferrimagnetic particles in rocks in particular apparently foliated rocks can actually be lineated and vice versa moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment

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

the nanophase iron mineral s in mars soil a series of surface modified clays containing nanophase np iron oxide oxyhydroxides of extremely small particle sizes with total iron contents as high as found in mars soil were prepared by iron deposition on the clay surface from ferrous chloride solution comprehensive studies of the iron mineralogy in these mars soil analogs were conducted using chemical extractions solubility analyses ph and redox x ray and electron diffractometry electron microscopic imaging specific surface area and particle size determinations differential thermal analyses magnetic properties characterization spectral reflectance and viking biology simulation experiments the clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron which slowly converts to more stable fully oxidized iron minerals the clay acted as an effective matrix both chemically and sterically preventing the major part of the synthesized iron oxides from ripening i e growing and developing larger crystals the precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1 10 nm having large specific surface area the noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate lepidocrocite gamma feooh was detected by selected area electron diffraction it is formed from a double iron fe ii fe iii hydroxy mineral such as green rust or ferrosic hydroxide magnetic measurements suggested that lepidocrocite converted to the more stable maghemite gamma fe2o3 by mild heat treatment and then to nanophase hematite alpha fe2o3 by extensive heat treatment after mild heating the iron enriched clay became slightly magnetic to the extent that it adheres to a hand held magnet as was observed with mars soil the chemical reactivity of the iron enriched clays strongly resembles and offers a plausible mechanism for the somewhat puzzling observations of the viking biology experiments their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide oxyhydroxides and silicate phase surfaces the reflectance spectrum of the clay iron preparations in the visible range is generally similar to the reflectance curves of bright regions on mars this strengthens the evidence for the predominance of nanophase iron oxides oxyhydroxides in mars soil the mode of formation of these nanophase iron oxides on mars is still unknown it is puzzling that despite the long period of time since aqueous weathering took place on mars they have not developed from their transitory stage to well crystallized end members the possibility is suggested that these phases represent a continuously on going extremely slow weathering process

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

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite