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

late quaternary halimeda bioherms and aragonitic faecal pellet dominated sediments on the carbonate platform of the western continental shelf of india abstract the fifty fathom flat is a drowned carbonate platform located on the outer continental shelf of western india it is unique because the carbonate depositional environment prevailed until early holocene in spite of its proximity to a major siliciclastic tidal embayment study of the bathymetry seismic and sonograph data together with the petrology mineralogy and geochemistry of the carbonate sediments and limestones recovered from the platform resulted in a the discovery of late quaternary halimeda bioherms and b aragonitic faecal pellet dominated sediments echograms reveal buried pinnacles between 62 and 38 m and exposed 2 to 14 m high pinnacles between 65 and 85 m on the platform these pinnacles occur as narrow to broad mounds bioherms in seismic profiles and as linear ridges and massive structures in sonographs seismic profiles also show a prominent reflector about 25 m below the sea bed identified by boreholes as a late pleistocene erosion surface the platform consists of relict carbonate sands and limestones rounded and ovoid to ellipsoidal aragonite grains are predominant in the sediments sem studies indicate elongated parallel canals and crescent to hook shaped canals corresponding to faecal pellets occur in some grains algal grains and pellets enclosing algal fragments are also present the grains in the limestones are similar to those in the sediments halimeda and crustacean faecal pellets are abundant components with minor echinoid mollusc and benthic foraminifera the limestones are characterised by abundant pores dissolution cavities relic aragonite needles meniscus cements and drusy calcite fill the pores produced by dissolution of aragonite needles these features indicate vadose diagenesis the stable isotopes of the carbonate sands and limestones are almost identical and similar to isotope values of beachrocks of the red sea the limestones ages 8400 9200 yr b p lie within the same age limits 10 400 8300 yr b p as the surficial sediments it appears that fluvial sediments largely accumulate in the inner shelf and did not hinder carbonate growth on the platform lying on the outer shelf we presume that arid climate and nutrients brought by river runoff and shelf edge currents favoured the growth of algal bioherms dominated by halimeda between 13 700 and 8300 yr b p the absence of late holocene and modern carbonates on the platform may be due to the combined influence of climatic change upwelling and neo tectonic activity at about 9000 yr b p the bioherms dominated by halimeda produced abundant aragonite muds deposit feeding crustaceans and other invertebrates subsequently excreted these muds as faecal pellets the platform thus contains faecal pellet dominated sediments

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

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

lateral transport of suevite inferred from 3d shape fabric analysis evidence from the ries impact crater germany the transport mechanism of suevite parti cles during impact cratering is poorly under stood and was studied at the 15 ma ries crater in southern germany two emplace ment modes of suevite deposits are generally discussed 1 fallback of plume material into the crater and its periphery upon collapse of an ejecta plume and 2 horizontal transport of ejected material akin to emplacement of pyroclastic deposits erupting from volcanic centers in order to differentiate between the two emplacement modes of suevite deposition we analyzed the shape fabrics of suevite components from two localities out side the ries crater by fishape fabric ellipsoids to measured shape fabric ellipses and by applying high resolution x ray computed tomography to analyze the three dimensional shape and orientation of the suevite particles we show that the preferred orientation of long axes of elongate particles is disposed either radially or concentrically with respect to the crater center our obser vations indicate that suevite material was not only derived from an ejecta plume but was transported by lateral fl ow under viscous conditions upon fallback this fl ow regime resembles that known from pyroclastic fl ows

reply to comment on magnetic fabrics crystallographic preferred orientation and strain of progressively deformed metamorphosed pelites in the helvetic zone of the central alps quartenschiefer formation by carl richter lothar ratschbacher and wolfgang frisch

heterogeneous deformation recorded by magnetic fabrics in the pyrenean axial zone abstract magnetic fabrics studies ams are a useful tool in order to describe the distribution of deformation in orogenic areas where conventional techniques are difficult to apply especially due to the lack of proper strain markers in the present study ams and structural analysis are used to define the distribution of deformation in the central axial and nogueres zones an area of strong structural changes i in the geometry of the antiformal stack defining the pyrenean axial zone and ii the distribution of alpine cleavage the studied rocks are lower middle triassic red beds that crop out in three different stacked thrust units bielsa nogueres and orri primary sedimentary fabrics are preserved in the uppermost thrust units nogueres zone but a high percentage of the sampling sites shows an overprint of alpine compression on magnetic fabrics with the magnetic lineation mostly parallel to the tectonic grain defined by compressional structures and the magnetic foliation showing different orientations between the poles to cleavage and bedding the development of compressional fabrics strongly depends on the structural position of the sites and two deformation gradients can be inferred the southern margin of the axial zone orri and bielsa units shows strong internal deformation increasing towards the north farther north in the restored cross section deformation is in general terms lower but increases towards the basal thrust of the nogueres zone the heterogeneous distribution of alpine internal deformation indicates a preferred development of cleavage in the variscan basement and overlying units of the southern margin of the axial zone mainly in the orri unit that could be partly controlled by the tectonic load resulting from the stacking of thrust sheets

magnetic mineralogy of some granites from the french massif central origin of their low field susceptibility abstract with a view to a better understanding of the origin of the low field susceptibility in the variscan granitoids of the french massif central for which extensive structural mapping using the anisotropy of magnetic susceptibility ams technique is currently applied a detailed study of magnetic carriers has been undertaken origin of the susceptibility has been studied using high field and low temperature measurements in a cryogenic magnetometer together with standard rock magnetic techniques additional determinations of the opaque phases have been performed with the metallographic microscope x ray microdiffraction and electron microprobe techniques in almost all the granite types the magnetic susceptibility is essentially carried by the paramagnetic biotite crystals minor amounts of ubiquitous oxides ilmenite rutile titano haematite do not contribute significantly to the susceptibility this is also the case for rare occurrences of magnetite in some granitoids mainly the cordierite bearing anatexites sulphides are found to give a large contribution magnetic mineralogy identifies a mixture of ferromagnetic pyrrhotite and antiferromagnetic fe9s10 hexagonal pyrrhotite hpo the latter species is identified as forming the larger unaltered pyrrhotite grains the ferromagnetic pyrrhotite is identified to be mainly smythite fe9s11 a species formed by supergenic alteration of monoclinic pyrrhotite located along the basal cleavage planes the microfractures and the grain boundaries of the hpo this study which constitutes the first report of the magnetic properties of smythite in rocks indicates that magnetic carriers derived from low temperature alteration have to be taken into account for purposes of structural studies using ams

control of magnetic rock fabrics by mica preferred orientation a quantitative approach magnetic anisotropy analysis represents a well established and frequently used method in structural geology several attempts were made to relate the anisotropy of magnetic susceptibility ams to rock fabrics and to discover the sources of the ams in gneissic rocks paramagnetic phyllosilicates with lattice dependent magnetic properties are assumed to control the whole rock ams i e it is dominated by mica lattice preferred orientation texture in this study ams was modelled on the basis of the mica texture the rock composition and compared to the experimentally determined ams the orientations of the modelled and experimental tensors agree quite well whereas all the other characteristic parameters shape anisotropy mean susceptibility display large differences it has been concluded that accessory high susceptible phases as well as the diamagnetic rock constituents may have significant influence on ams consequently mica pole figure measurements cannot be replaced by ams measurements without control of the sources of ams it was also concluded that the march model to evaluate strain from mica preferred orientations is not valid for highly strained rocks beside the fact that the obtained strains are too low the deformation is generally inhomogeneous which leads to an overprint of the mica texture since the microstructural fabric elements which originate in different strain regimes prolate or oblate may create similar modifications of the mica orientation patterns it is obvious that the relationship between ams and deformation is rather complex

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

magnetic fabrics crystallographic preferred orientation and strain of progressively metamorphosed pelites in the helvetic zone of the central alps quartenschiefer formation we investigate the relationships between the anisotropy of magnetic susceptibility ams mineral preferred orientation macroscopic structures and finite strain in a section of increasing metamorphism in the helvetic zone of the central alps switzerland the upper triassic quartenschiefer formation an initially hematite bearing red bed sedimentary rock can be traced from unmetamophosed shale to amphibolite facies schists the magnetic fabrics of 805 specimens agree well in orientation with the foliation normal to kmin kmax kint kmin are principal susceptibilities and the mineral stretching lineation parallel kmax in all metamorphic grades the maximum susceptibility axes are in an approximately n s orientation and were acquired during the miocene north directed nappe transport the effects of the tectonic position and the metamorphic grade on the ams ellipsoid suggests that deformation has a stronger influence on its shape than the metamorphic grade the identification and quantification of the sources of magnetic susceptibility was done with 1 a model calculation 2 the high field low field method and 3 low temperature heating curves the ams of low grade samples is dominated by the paramagnetic minerals mainly mica and the ams of higher susceptible medium grade samples by magnetite the paramagnetic dominated magnetic fabrics correlate well with mica 002 lattice preferred orientations obtained from x ray texture goniometry a one to one correlation between march strains and a magnetic parameter mi ln ki kmaxkintkmin is predicted by a numerical model and verified empirically the magnetic fabrics of well characterized samples can thus be used to quantify the degree of mica preferred orientation using relatively simple magnetic anisotropy equipment

interpretation quantitative de l anisotropie de susceptibilite magnetique abstract we propose a model in which the magnetic susceptibility anisotropy is considered as resulting from the distinct properties of two rock components this model suggests that differences in the susceptibility ellipsoid can be principally related to mineralogical variations thus some difficulties in the quantitative interpretation of anisotropy data may be explained this model is consistent with a detailed analysis carried on dalradian rocks from scotland a new methodology of anisotropy analysis is derived it is based on the fact that in specimens from a same sample the susceptibility ellipsoid often varies but relations nevertheless exist between values of the principal and mean susceptibilities for each sample measurements are made on 6 12 specimens the study of the relations between principal and mean susceptibilities permits separation of the anisotropies of the rock components the anisotropy determination appearing the best for the high susceptibility component

magnetic anisotropy and fabric of some progressively deformed ophiolitic gabbros the ophiolites considered remnants of oceanic seafloor provide a fruitful source of information on the physical and chemical behavior of the deeper uncored lithosphere a study of the gabbros in a rather well preserved ophiolite from the western alps montgenevre france shows strong evidence for intraoceanic plate deformation to characterize the different steps of deformation observed in the outcrops a magnetic fabric study was conducted using the anisotropy of initial magnetic susceptibility aims method the main conclusions are 1 the aims is controlled by the paramagnetic ferromagnesian minerals such as hornblende resulting from the ocean floor metamorphism close to the spreading ridge partial amphibolitization and 2 the magnetic lineation and foliation of the gabbros show a deformation path with increasing strain a good correspondence between petrofabric and magnetic anisotropies is observed both suggest that the deformation mechanism was simple shear

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

magnetic fabrics in archean granitoids northwestern ontario isolation of accessory and matrix contributions by inspection of ams data abstract pre tectonic and post tectonic granitoid plutons in the same area share similar orientations for their ams anisotropy of magnetic susceptibility foliation and lineation and these are similar in orientation to the l s fabrics of the country rock which bears a vertical ene wsw foliation the ams fabrics in the granitoids are composite blending contributions from accessory but highly susceptible magnetite with those from paramagnetic matrix silicates we isolate magnetic sub fabrics in the granitoids by a simple numerical approach that standardizes the mean tensor for susceptibility of specimens thereby suppressing the skewing effect of high susceptibility accessories i e magnetite this approach approximately separates the contributions of ferro magnetic and of paramagnetic minerals to ams though not as completely as technical laboratory experiments

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

a theoretical and experimental comparison of the anisotropies of magnetic susceptibility and remanence in rocks and minerals summary susceptibility thermo remanent magnetization trm and isothermal remanent magnetization irm anisotropy ellipsoids have been determined for several rock samples the results indicate that the ellipsoid of initial susceptibility is less anisotropic than the trm and low field irm ellipsoids which are found experimentally to be of identical shape this suggests that palaeomagnetic data for anisotropic rocks may be corrected by using the anisotropy ellipsoid determined from magnetically non destructive low field irm measurements such irm measurements can also be used to obtain anisotropy axes of samples which are inherently anisotropic but which have a susceptibility which is too weak to be accurately measured the results for a series of artificial anisotropic samples containing magnetite particles of different sizes in the range 0 2 90 m were very similar to those for the rocks in contrast a comparison of the susceptibility and irm ellipsoids for anisotropic samples containing particles from a magnetic tape gave very different results in accordance with theory such results imply that susceptibility and irm ellipsoids could be used to determine whether anisotropic rocks contain uniaxial single domain particles magnetization confined to the easy axis or whether the particles are essentially multidomain

trm deviations in anisotropic assemblages of multidomain magnetite anisotropic assemblages of multidomain magnetite particles develop an anisotropy of magnetic susceptibility ams which in turn induces deviations of thermo remanent magnetization trm from the field direction from the theories of multidomain trm acquisition it is shown that the trm anisotropy tensor has its eigenvalue ratios ti related to the principal weak field susceptibility ratios pi by the order of magnitude ti p2i this relation has been experimentally verified on two sets of highly anisotropic rock samples the exponent has been determined to be 1 94 in the samples from a peruvian gabbro and 1 81 in those from the granite of flamanville nw france accounting for experimental difficulties in determining the trm anisotropy tensors these exponents are judged to agree well with the expected one it is therefore stressed that ams measurements provide a good means of evaluating the magnetic field direction from deviated trm directions providing magnetic carriers are mainly multidomain magnetites

new aspects of the interpretation of the loess magnetic fabric cerna valley succession hungary abstract anisotropy of magnetic susceptibility ams is a frequently applied method in sedimentology especially in the determination of the orientation of transport processes we present an analysis of magnetic fabric mf studies on loess new aspects of fabric development reveal i the deposition of the aeolian sediments was controlled by gravity low energy transport and local geomorphology hence no clarified wind direction can be defined ii the influence of phyllosilicates is also significant among the magnetic components iii while the primary mf is relatively well defined the secondary mf is influenced by several processes the analysis of stereoplots combined with the q diagram and photostatistics showed encouraging results during the characterization of various secondary mf such as redeposited mf and pedogenic fabric iv changes in processes from aeolian to water lain deposition and the increasing transportation energy were reflected by the connection between ams and observed micro scale sedimentary features v a relationship was obvious between the degree of pedogenesis and the transformation of sedimentary mf into a vertical mf typical for paleosols vi the significant role of very fine grained magnetite on the formation of inverse mf could not be excluded

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

mesozoic extension in the basque cantabrian basin n spain contributions from ams and brittle mesostructures abstract in this work we analyse and check the results of anisotropy of magnetic susceptibility ams by means of a comparison with palaeostress orientations obtained from the analysis of brittle mesostructures in the cabuerniga cretaceous basin located in the western end of the basque cantabrian basin north spain the ams data refer to 23 sites including triassic red beds jurassic and lower cretaceous limestones sandstones and shales these deposits are weakly deformed and represent the syn rift sequence linked to basins formed during the mesozoic and later inverted during the pyrenean compression the observed magnetic fabrics are typical of early stages of deformation and show oblate triaxial and prolate magnetic ellipsoids the magnetic fabric seems to be related to a tectonic overprint of an original compaction sedimentary fabric most sites display a ne sw magnetic lineation that is interpreted to represent the stretching direction of the early cretaceous extensional stage of the basin without recording of the tertiary compressional events except for sites with compression related cleavage brittle mesostructures include normal faults calcite and quartz tension gashes and joints related to the extensional stage the results obtained from joints and tension gashes show a dominant n s to ne sw and secondary nw se extension direction paleostresses obtained from fault analysis right dihedra and stress inversion methods indicate nw se to e w and n s extension direction the results obtained from brittle mesostructures show a complex pattern resulting from the superposition of several tectonic processes during the mesozoic linked to the tectonic activity related to the opening of the bay of biscay during the early cretaceous this work shows the potential in using ams analysis in inverted basins to unravel its previous extensional history when the magnetic fabric is not expected to be modified by subsequent deformational events brittle mesostructure analysis seems to be more sensitive to far field stress conditions and record longer time spans whereas ams records deformation on the near distance during shorter intervals of time

study on finite strain and its relationship with magnetic fabric along ailao shan red river shear zone 1 the finite strain along ailao shan red river shear zone has been studied the axial ratios of strain markers and shear strains vary greatly arising principally from deformation intensity and from contrasting competencies ellipticity of chloritic amygdales in basalt ranges from 6 79 to 10 47 corresponding shear strain gamma xz 2 22 2 93 and ellipticity of garnets from 1 56 to 2 95 gamma xz 0 45 1 14 in core gneiss the s c angle of the sheared rocks varies from 2degrees to 28degrees gamma sc 1 35 28 60 mostly in a range 2degrees to 7degrees optical observation thermal demagnetization and hysteresis curves were conducted to determine the nature of minerals and the contribution of paramagnetic and ferromagnetic minerals to magnetic susceptibility the result shows that ferromagnetic minerals and hornblende dominate the magnetic fabric of samples with high to very high susceptibility and play an important role in the magnetic fabric of samples with low to intermediate susceptibility the ferromagnetic minerals are mainly pseudo single domain and multidomain ti poor magnetite most samples have their magnetic lineation lying between the c and s surfaces in the remaining samples deviations from this common alignment principally resulted from the magnetic minerals being deflected by porphyroclasts mineral cleavage and cracks the axial ratio correlation is very poor between the magnetic and actual or imaginary strain ellipsoid calculated from the s c fabric this poor correlation suggests that the shape of the finite strain ellipsoid cannot be evaluated using the magnetic fabric when the latter is a combined result from multiple minerals and especially when the shape effect of multidomain titanomagnetite is important

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

conversion of the magnetic susceptibility tensor into the orientation tensor in some rocks abstract the preferred orientation of minerals in a rock with a structural or sedimentary fabric can be referred to by the orientation tensor this paper describes the determination of the orientation tensor of the crystallographic c axes from the rock magnetic anisotropy and the mineral anisotropy degree in rocks in which the magnetic anisotropy is dominantly carried by one mineral with uniaxial magnetic anisotropy e g phyllosilicates pyrrhotite hematite the orientation tensor of biotite c axes in four samples of the bites orthogneiss determined in this way is similar to that determined independently through the universal stage measurement of biotite leaves in thin sections and is obtained much more rapidly by the magnetic method

from qualitative to quantitative magnetic anisotropy analysis the prospect of finite strain calibration abstract a method of separating low field susceptibility anisotropies due to ferrimagnetics and the matrix proposed hitherto in cases where the principal axis of these two components are merged is generalized in cases where the axes are distinct the method consists of analysing in specimens close in the same sample anisotropies the differences of which are due to the variation of respective percentages of the two components although the strain rate remains constant one thus uses the cause which itself renders global anisotropy unusable a first application is presented where a control using the anisotropy of isothermal remanent magnetization allows the validity of the method to be tested a discussion of the choice of the best ellipsoid relative either to the matrix or to the ferrimagnetics to give the best indication of relative finite strain rate is opened

constraints on deformation of the southern andes since the cretaceous from anisotropy of magnetic susceptibility the southernmost segment of the andean cordillera underwent a complex deformation history characterized by alternation of contractional extensional and strike slip tectonics key elements of southern andean deformation that remain poorly constrained include the origin of the orogenic bend known as the patagonian orocline here renamed as patagonian arc and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in cordillera darwin here we present results of anisotropy of magnetic susceptibility ams from 22 sites in upper cretaceous to upper eocene sedimentary rocks within the internal structural domain of the magallanes fold and thrust belt in tierra del fuego argentina ams parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric which was likely acquired upon layer parallel shortening soon after sedimentation magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous n s contraction our data combined with the existing ams database from adjacent areas show that the early cretaceous late oligocene tectonic phases in the southern andes yielded continuous contraction variable from e w in the patagonian andes to n s in the fuegian andes which defined a radial strain field a direct implication is that the exhumation of the cordillera darwin metamorphic complex occurred under compressive rather than extensional or strike slip tectonics as alternatively proposed if we agree with recent works considering the curved magallanes fold and thrust belt as a primary arc i e no relative vertical axis rotation of the limbs occurs during its formation then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field we tentatively propose a kinematic model in which reactivation of variably oriented jurassic faults at the south american continental margin controlled the late cretaceous to cenozoic evolution of the magallanes fold and thrust belt yielding the observed deformation pattern

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