investigating karst aquifers using pseudo 3 d electrical resistivity tomography to identify major karst features abstract this work presents the electrical resistivity imaging of the hydrogeological experimental site hes karst aquifer of poitiers france from pseudo three dimensional 3 d electrical resistivity tomography ert i e a three dimensional model obtained from the joint inversion of resistivity data collected along parallel profiles the inverse resistivity model provided a fairly reliable definition of the main hydrogeological units the survey also allowed the recognition of possible shallow dissolution enlarged fractures that do not show any ground expression at present but have been revealed at depth by vertical flowmeter data and high resolution video footage from wells these features seem to connect with middle depth sub vertical features down to a depth of 25 m which are likely to correlate with soil mantled incipient sinkhole formation features that do not show any ground expression at present as well as karst conduits at greater depth the resistivity model allowed the recognition of the first two main karst intervals 35 40 m and 85 87 m deep associated with water productive layers as revealed by well logs the opportunity to cross validate geophysical results with extensive ground truth provided by the hes allowed an assessment of the error the pseudo 3 d ert model makes in estimating the depth of the karst intervals synthetic dataset modelling provided the detectability of the pseudo 3 d ert model in identifying karst intervals synthetic dataset modelling also allowed an estimation of the response of the experimental and inversion setup to a variable degree of heterogeneity of the aquifer using well log data as geological a priori information

magnetic characterization of synthetic titanomagnetites quantifying the recording fidelity of ideal synthetic analogs 1 a series of four synthetic basalts comprising titanomagnetite fe3 xtixo4 grains of varied size and titanium content have been produced by a glass ceramic method complementary characterization techniques of x ray diffractometry secondary electron microscopy and transmission electron microscopy tem demonstrate the reaction product composition consisted of mainly fe3 xtixo4 pyroxene hedenbergite fayalite and sio2 the samples exhibit bimodal distributions of larger 2 m and smaller fe3 xtixo4 particles 50 nm in diameter the latter found inside pyroxene crystals as well as the sporadic occurance of dendritic fe3 xtixo4 structures magnetic measurements show their bulk characteristics fall into two groups ti rich titanomagnetite samples with varying ti content and near stoichiometric magnetite the tem technique of off axis electron holography allowed for visualization of the magnetic behavior of the synthetic fe3 xtixo4 grains energy dispersive x ray analysis and off axis electron holography confirmed the small fe3 xtixo4 grains 50 nm confined within glassy pyroxene regions to be fe rich and single domain carrying strong magnetic signals compared to the relatively magnetically weak larger fe3 xtixo4 grains x 0 6 the large grains in the pure magnetite sample are shown to be pseudo single domain in nature the quenching process involved in synthesis is considered similar to that of pillow basalts found at mid ocean ridges and hence the reaction products are thought ideal in terms of characterization and understanding for the purpose of studying natural systems

stability of equidimensional pseudo single domain magnetite over billion year timescales interpretations of paleomagnetic observations assume that naturally occurring magnetic particles can retain their primary magnetic recording over billions of years the ability to retain a magnetic recording is inferred from laboratory measurements where heating causes demagnetization on the order of seconds the theoretical basis for this inference comes from previous models that assume only the existence of small uniformly magnetized particles whereas the carriers of paleomagnetic signals in rocks are usually larger nonuniformly magnetized particles for which there is no empirically complete thermally activated model this study has developed a thermally activated numerical micromagnetic model that can quantitatively determine the energy barriers between stable states in nonuniform magnetic particles on geological timescales we examine in detail the thermal stability characteristics of equidimensional cuboctahedral magnetite and find that contrary to previously published theories such nonuniformly magnetized particles provide greater magnetic stability than their uniformly magnetized counterparts hence nonuniformly magnetized grains which are commonly the main remanence carrier in meteorites and rocks can record and retain high fidelity magnetic recordings over billions of years

direct observation of ferrimagnetic ferroelastic domain interactions in magnetite below the verwey transition abstract the magnetic behaviour of magnetite at low temperatures is dominated by its transformation to a monoclinic crystal structure that is simultaneously ferrimagnetic ferroelastic and ferroelectric below 125 k the verwey transition here we use electron microscopy to reveal the relationship between ferrimagnetic and ferroelastic domain structures in monoclinic magnetite we present dynamic observations of magnetite during heating and cooling across the verwey transition revealing a diversity of unexpected interaction phenomena between crystallographic twins and magnetic domain walls this study provides a new understanding of the low temperature magnetic properties of magnetite that will affect a broad range of rock magnetic studies from the interpretation of magnetic remanence in terrestrial rocks and sediments to the search for biogenic magnetite in extraterrestrial materials

coastal evolution in south west england united kingdom an enhanced reconstruction using geophysical surveys abstract the coastline of south devon south west england is believed to be subsiding faster than any area in the united kingdom uk current estimates are based however on very limited holocene relative sea level rsl and lithostratigraphic data there is therefore an urgent need for more information to improve our understanding of coastal evolution in the region sediment coring from slapton sands and blackpool sands in south east devon provides material for interpreting land and sea level changes further stratigraphic mapping was carried out using 2d electrical resistivity tomography ert of the near surface this method of geophysical survey ground truthed with borehole data has rarely been used for palaeoenvironmental reconstruction but provided useful results here models of holocene coastline evolution based on those from the eastern usa show that sea level in start bay was 17 m below present rsl ca 9000 cal yr bp a barrier lagoon system was forced landward by seas rising at 5 m ka across substrates comprised of weathered slate and shale thick deposits of minerogenic fines 10 m at slapton sands were identified in cores and mapped using the ert survey method barrier lagoons became choked by sediment when rsl was 5 m below present at ca 4400 cal yr bp and reached their current configuration during the late holocene ert results show that the slapton sands modern day barrier complex is a uniform 9 m thick for a longshore distance of at least 1 5 km

improvement to resistivity pseudosection modelling by removal of near surface inhomogeneity effects application to a soil system in south cameroon near surface inhomogeneities nsis can lead to severe problems in the interpretation of apparent resistivity pseudosections because their effects significantly complicate the image aspect in order to carry out a more efficient and reliable interpretation process these problematic features should be removed from field data we describe a filtering scheme using two sided half schlumberger array data the scheme was tested on synthetic data generated from a simple 2d resistivity model contaminated by nsis and is shown to be suitable for eliminating such contaminations from apparent resistivity data furthermore the original model without nsis can be recovered satisfactorily from the inversion of filtered apparent resistivity data the algorithm is also applied efficiently to a real data set collected at nsimi in southern cameroon along a 200 m shallow depth profile crossing a complex transitional zone for this case the filtering scheme provides accurate structural and behavioural interpretations of both the geometry of the major soil constituents and the groundwater partitioning

paleomagnetic recording fidelity of nonideal magnetic systems a suite of near identical magnetite nanodot samples produced by electron beam lithography have been used to test the thermomagnetic recording fidelity of particles in the 74 333 nm size range the grain size range most commonly found in rocks in addition to controlled grain size the samples had identical particle spacings meaning that intergrain magnetostatic interactions could be controlled their magnetic hysteresis parameters were indicative of particles thought not to be ideal magnetic recorders however the samples were found to be excellent thermomagnetic recorders of the magnetic field direction they were also found to be relatively good recorders of the field intensity in a standard paleointensity experiment the samples intensities were all within 15 of the expected answer and the mean of the samples within 3 of the actual field these nonideal magnetic systems have been shown to be reliable records of the geomagnetic field in terms of both direction and intensity even though their magnetic hysteresis characteristics indicate less than ideal magnetic grains

direct imaging of nanoscale magnetic interactions in minerals the magnetic microstructure of a natural finely exsolved intergrowth of submicron magnetite blocks in an ulvospinel matrix is characterized by using off axis electron holography in the transmission electron microscope single domain and vortex states in individual blocks as well as magnetostatic interaction fields between them are imaged at a spatial resolution approaching the nanometer scale the images reveal an extremely complicated magnetic structure dominated by the shapes of the blocks and magnetostatic interactions magnetic superstates in which clusters of magnetite blocks act collectively to form vortex and multidomain states that have zero net magnetization are observed directly

critical single domain grain sizes in elongated iron particles implications for meteoritic and lunar magnetism summary kamacite particles fe ni ni 5 per cent are very common in extra terrestrial materials such as meteorites it is normally assumed that for kamacite particles to be reliable recorders of magnetic fields they need to be magnetically uniform single domain sd and thermally stable largerparticlessubdivideintonon uniformmultidomain md magneticstructuresthat produce weaker magnetic signals while small sd particles become magnetically unstable due tothermalfluctuationsandexhibitsuperparamagneticbehaviour inthispaperwedeterminethe firstmicromagnetic calculation ofthestablesdrangedomain statephasediagram formetallic iron previous calculations were analytical there is a significant increase in the critical size for the sd md threshold size for example for cube shaped iron particles the critical sd md threshold has now been estimated to be 25 nm compared to 17 nm for previous estimates the larger critical sd md threshold size for iron agrees better with previously published nanometric observations of domain state for feni particles then early analytical models

observing thermomagnetic stability of nonideal magnetite particles good paleomagnetic recorders the thermomagnetic behavior of remanence induced magnetite fe3o4 particles in the pseudo single domain psd size range 0 1 10 m which dominate the magnetic signature of many rock lithologies is investigated using off axis electron holography construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual fe3o4 grain 200 nm in diameter as a function of temperature acquisition of a series of electron holograms at 100 c intervals during in situ heating up to 700 c demonstrates the vortex state of the fe3o4 grain in this instance remains thermally stable close to its unblocking temperature and exhibits a similar in plane remanent state upon cooling i e the particle is effectively behaving like a uniaxial single domain particle to temperatures near tc such particles are thought to be robust magnetic recorders it is suggested that evidence for psd behavior should therefore not preclude paleomagnetic investigation

magnetic vortex effects on first order reversal curve forc diagrams for greigite dispersions abstract first order reversal curve forc diagrams are used increasingly in geophysics for magnetic domain state identification the domain state of a magnetic particle is highly sensitive to particle size about which forc diagrams provide valuable information however the forc signal of particles with nonuniform magnetisations which are the main carrier of natural remanent magnetisations in many systems is still poorly understood in this study the properties of non interacting randomly oriented dispersions of greigite fe3s4 in the uniform single domain sd to non uniform single vortex sv size range are investigated via micromagnetic calculations signals for sd particles 50 nm are found to be in excellent agreement with previous sd coherent rotation studies a transitional range from 50 nm to 80 nm is identified for which a mixture of sd and sv behaviour produces complex forc diagrams particles 80 nm have purely sv behaviour with the remanent state for all particles in the ensemble in the sv state it is found that for sv ensembles the forc diagram provides a map of vortex nucleation and annihilation fields and that the forc distribution peak should not be interpreted as the coercivity of the sample but as a vortex annihilation field on the path to saturation

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

geomagnetic paleointensity in historical pyroclastic density currents testing the effects of emplacement temperature and postemplacement alteration thellier type paleointensity experiments were conducted on welded ash matrix or pumice from the 1912 novarupta nv and 1980 mt st helens msh pyroclastic density currents pdcs with the intention of evaluating their suitability for geomagnetic paleointensity studies pdcs are common worldwide but can have complicated thermal and alteration histories we attempt to address the role that emplacement temperature and postemplacement hydrothermal alteration may play in nonideal paleointensity behavior of pdcs results demonstrate two types of nonideal behavior unstable remanence in multidomain md titanomagnetite and nonideal behavior linked to fumarolic and vapor phase alteration emplacement temperature indirectly influences msh results by controlling the fraction of homogenous md versus oxyexsolved pseudo single domain titanomagnetite nv samples are more directly influenced by vapor phase alteration the majority of nv samples show distinct two slope behavior in the natural remanent magnetization partial thermal remanent magnetization plots we interpret this to arise from a thermo chemical remanent magnetization associated with vapor phase alteration and samples with high water content 0 75 loss on ignition generate paleointensities that deviate most strongly from the true value we find that pdcs can be productively used for paleointensity but that as with all paleointensity studies care should be taken in identifying potential postemplacement alteration below the curie temperature and that large welded flows may be more alteration prone one advantage in using pdcs is that they typically have greater areal spatial exposure than a basalt flow allowing for more extensive sampling and better assessment of errors and uncertainty

corrections of surface fissure effect on apparent resistivity measurements electrical resistivity tomography ert is a useful tool to detect and track water flow paths in the subsoil however measurements are strongly affected by subsurface heterogeneities such as fissures of different sizes and genesis shrinking swelling macropores and deformation in this work we focus on surface fissures characterized by dimensions lower than the interelectrode spacing and correct their effect on apparent resistivity pseudo sections by incorporating fissure geometry in the topography we show that fissures with depths greater than 0 10 times the interelectrode spacing for a dipole dipole array and equal to 0 16 for the gradient array and the wenner schlumberger arrays create significant anomalies greater than 5 per cent in the pseudo section surface fissure widths and dip angles have little effect with respect to the fissure depths which can increase the apparent resistivity up to 200 per cent the clogging of the fissures with water or soil material decreases the anomaly effect linearly with the percentage of filling the correction of apparent resistivity values is possible for relatively simple fissure geometries and only requires a manual survey of the surface fissures it allows to improve the quality of the inverted resistivity section by mitigating the inversion artefacts and therefore a better interpretation

separating geometry from stress induced remanent magnetization in magnetite with ilmenite lamellae from the stardalur basalts iceland

direct observation of the thermal demagnetization of magnetic vortex structures in nonideal magnetite recorders the thermal demagnetization of pseudo single domain psd magnetite fe3o4 particles which govern the magnetic signal in many igneous rocks is examined using off axis electron holography visualization of a vortex structure held by an individual fe3o4 particle 250 nm in diameter during in situ heating is achieved through the construction and examination of magnetic induction maps stepwise demagnetization of the remanence induced fe3o4 particle upon heating to above the curie temperature performed in a similar fashion to bulk thermal demagnetization measurements revealed that its vortex state remains stable under heating close to its unblocking temperature and is recovered upon cooling with the same or reversed vorticity hence the psd fe3o4 particle exhibits thermomagnetic behavior comparable to a single domain carrier and thus vortex states are considered reliable magnetic recorders for paleomagnetic investigations

ultra high precision 40ar 39ar ages for fish canyon tuff and alder creek rhyolite sanidine new dating standards required abstract the 40 ar 39 ar dating technique is a high precision 40 ar 39 ar standards include sanidine from the ca 28 ma fish canyon tuff fct and the ca 1 2 ma alder creek rhyolite acr despite common usage the ages of fct and acr sanidine have proven contentious with reported values varying by 2 well outside the 0 1 aspiration of earthtime www earth time org the current study presents ultra high precision multi collector 40 ar 39 ar results for fct and acr sanidine using a new generation argusvi mass spectrometer these analyses demonstrate the significantly higher by a factor of 10 level of precision achievable using the argusvi system compared to most previous studies significantly 40 ar 39 ar step heating analyses resolve distinct age gradients for both fct and acr sanidine possible explanations for these gradients include combinations of recoil loss of 39 ar instrumental bias isotopic fractionation during step heating thermally induced argon loss and or extraneous argon contamination minor recoil loss of 39 ar and partial retention of inherited argon during extended magma residence are deemed the most plausible causes of the age discordance given this assumption we calculate revised maximum eruption ages of 28 01 0 04 ma 2 for fct and 1 178 0 002 ma 2 for acr relative to the astronomically calibrated age of a1 tephra sanidine crete rivera et al 2011 earth planet sci lett 311 420 426 nonetheless the argusvi data demonstrate that fct and acr sanidine are non ideal as high precision 40 ar 39 ar standards with different heating protocols likely to induce inter laboratory bias the current findings account for at least some of the scatter in inter calibration ages reported previously for various 40 ar 39 ar standards in broader terms the results mandate a re evaluation of the astronomically calibrated ages for these and other sanidine samples while the new generation of multi collector mass spectrometers provides the means to further evaluate 40 ar 39 ar ages used to define new decay constants and standard ages

an exceptionally weak devonian geomagnetic field recorded by the viluy traps siberia abstract the detection of anomalous time averaged geomagnetic behaviour is crucial for understanding past magnetospheric shielding and inferring deep earth evolution links have been suggested between geomagnetic field variation over timescales of tens to hundreds of millions of years and processes near the core mantle boundary cmb however this becomes difficult to establish prior to the permo carboniferous reversed superchron pcrs 267 319 ma due to a lack of reliable data to improve the record prior to the pcrs we present multi method produced paleointensity results from nines dykes and lava flows from the viluy traps siberia emplaced during the upper devonian between 376 7 1 7 ma and 364 4 1 7 ma these sites have previously been published as part of two paleodirectional studies one of which produced the accepted 360 ma pole for siberia q factor 6 all of the sites produced very weak field values ranging from 4 3 14 9 z a m2 in close agreement with other recent results from mid lower devonian siberian samples q p i criteria have been used to illustrate the reliability of these new low paleointensities confirming the period of weak field suggested by other recent siberian work and the period of implied increased incidence of solar wind radiation extended into the upper devonian along with evidence for moderate high reversal frequencies and a potentially significant multipolar component during the devonian these weak field values also suggest a significantly different pattern of heat flow across the cmb relative to more recent times

present weathering rates in a humid tropical watershed nsimi south cameroon the study of biogeochemical and hydrological cycles in small experimental watersheds on silicate rocks common for the temperate zone has not yet been widely applied to the tropics especially humid areas this paper presents an updated database for a six year period for the small experimental watershed of the mengong brook in the humid tropics nsimi south cameroon this watershed is developed on precambrian granitoids north congo shield and consists of two convexo concave lateritic hills surrounding a large flat swamp covered by hydromorphic soils rich in upward organic matter mineralogical and geochemical investigations were carried out in the protolith the saprolite the hillside lateritic soils and the swamp hydromorphic soils biomass chemical analyses were done for the representative species of the swamp vegetation the groundwater was analysed from the parent rock saprolite weathering front to the upper fringe in the hillside and swamp system the chemistry of the wet atmospheric and throughfall deposits and the mengong waters was monitored in the nsimi watershed the carbon transfer occurs primarily in an organic form and essentially as colloids produced by the slow biodegradation of the swamp organic matter these organic colloids contribute significantly to the mobilization and transfer of fe al zr ti and th in the uppermost first meter of the swamp regolith when the organic colloid content is low i e in the hillside groundwater th and zr concentrations are extremely low 3 pmol l icp ms detection limits strongly insoluble secondary thorianite tho 2 and primary zircon zrsio 4 crystals control their mobilization respectively this finding thus justifies the potential use of both these elements as inert elements for isoelement mass balance calculations pertaining to the hillside regolith chloride can not be used as a conservative tracer of hydrological processes and chemical weathering in this watershed biogenic recycling significantly influences the low cl input fluxes sodium is a good tracer of chemical weathering in the watershed the sodium solute flux corrected from cyclic salt input was used to assess the chemical weathering rate even though low 2 8 mm kyr the chemical weathering rate predominates over the mechanical weathering rate 1 9 mm kyr compared to the rio icacos watershed the most studied tropical site the chemical weathering fluxes of silica and sodium in the mengong are 16 and 40 times lower respectively this is not only related to the protective role of the regolith thick in both cases but also to differences in the hydrological functioning this is to be taken into account in the calculations of the carbon cycle balance for large surfaces like that of the tropical forest ecosystems on a stable shield at the global level

multi scale three dimensional characterization of iron particles in dusty olivine implications for paleomagnetism of chondritic meteorites dusty olivine olivine containing multiple sub micrometer inclusions of metallic iron in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence capable of maintaining a faithful record of pre accretionary magnetization acquired during chondrule formation here we show how the magnetic architecture of a single dusty olivine grain from the semarkona ll3 0 ordinary chondrite meteorite can be fully characterized in three dimensions using a combination of focused ion beam nanotomography fib nt electron tomography and finite element micromagnetic modeling we present a three dimensional 3d volume reconstruction of a dusty olivine grain obtained by selective milling through a region of interest in a series of sequential 20 nm slices which are then imaged using scanning electron microscopy the data provide a quantitative description of the iron particle ensemble including the distribution of particle sizes shapes interparticle spacings and orientations iron particles are predominantly oblate ellipsoids with average radii 242 94 199 80 123 58 nm using analytical tem we observe that the particles nucleate on sub grain boundaries and are loosely arranged in a series of sheets parallel to 001 of the olivine host this is in agreement with the orientation data collected using the fib nt and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host the shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets individual particle geometries are converted to a finite element mesh and used to perform micromagnetic simulations the majority of particles adopt a single vortex state with bulk spins that rotate around a central vortex core we observed no particles that are in a true single domain state the results of the micromagnetic simulations challenge some preconceived ideas about the remanence carrying properties of vortex states there is often not a simple predictive relationship between the major intermediate and minor axes of the particles and the remanence vector imparted in different fields although the orientation of the vortex core is determined largely by the ellipsoidal geometry i e parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids the core and remanence vectors can sometimes lie at very large tens of degrees angles to the principal axes the subtle details of the morphology can control the overall remanence state leading in some cases to a dominant contribution from the bulk spins to the net remanence with profound implications for predicting the anisotropy of the sample the particles have very high switching fields several hundred millitesla demonstrating their high stability and suitability for paleointensity studies

40ar 39ar geochronology of terrestrial pyroxene abstract geochronological techniques such as u pb in zircon and baddeleyite and 40ar 39ar on a vast range of minerals including sanidine plagioclase and biotite provide means to date an array of different geologic processes many of these minerals however are not always present in a given rock or can be altered by secondary processes e g plagioclase in mafic rocks limiting our ability to derive an isotopic age pyroxene is a primary rock forming mineral for both mafic and ultramafic rocks and is resistant to alteration process but attempts to date this phase with 40ar 39ar has been met with little success so far in this study we analyzed pyroxene crystals from two different large igneous provinces using a multi collector noble gas mass spectrometer argus vi since those machines have been shown to significantly improve analytical precision compared to the previous single collector instruments we obtain geologically meaningful and relatively precise 40ar 39ar plateau ages ranging from 184 6 3 9 to 182 4 0 8 ma 2 uncertainties of 1 8 0 4 and 506 3 3 4 ma for tasmanian and kalkarindji dolerites respectively those data are indistinguishable from new and or published u pb and 40ar 39ar plagioclase ages showing that 40ar 39ar dating of pyroxene is a suitable geochronological tool scrutinizing the analytical results of the pyroxene analyses as well as comparing them to the analytical result from plagioclase of the same samples indicate pure pyroxene was dated numerical models of argon diffusion in plagioclase and pyroxene support these observations however we found that the viability of 40ar 39ar dating approach of pyroxene can be affected by irradiation induced recoil redistribution between thin pyroxene exsolution lamellae and the main pyroxene crystal hence requiring careful petrographic observations before analysis finally diffusion modeling show that 40ar 39ar of pyroxene can be used as a powerful tool to date the formation age of mafic rocks affected by greenschist metamorphism and will likely play an important role in high temperature thermochronology

a synthetic trm induction curve for fine particles generated from domain observations a synthetic thermoremanent magnetization trm induction curve is produced from domain observations of an ensemble of pseudosingle domain psd titanomagnetite particles in oceanic basalts the observations were made after the samples were given a trm in fields of 0 1 2 4 6 and 8mt an observation was also made of the domain state for saturation isothermal remanent magnetization irms the number and maximum size of grains which remain in a metastable single domain sd state increases with increasing field this in turn gives rise to a field dependence of the total moment carried by such particles in the ensemble by observing the number of metastable sd grains and estimating their volume one can construct a trm induction curve this curve approximates the known trm induction curve for fine particles demonstrating that the magnitude of trm in fine particles of titanomagnetites is controlled by nucleation this nucleation model also explains why weak field trm is more stable against alternating field af demagnetization than irms

first order reversal curve forc diagrams for pseudo single domain magnetites at high temperature abstract the recently developed first order reversal curve forc technique for rapidly examining magnetic domain state has great potential for paleomagnetic and environmental magnetic investigations however there are still some gaps in the basic understanding of forc diagrams in particular the behavior of pseudo single domain psd grains and the contribution of magnetostatic interactions in this paper we address some of these problems we report the first forc diagrams measurements on narrowly sized and well characterized synthetic psd through multidomain md magnetite samples the forc diagrams evolve with grain size from single domain sd like to md like through the psd grain size range since each sample contains grains of essentially a single size individual psd grains evidently contain contributions from both sd like and md like magnetic moments in proportions that vary with grain size the evolving forc diagrams cannot be due to physical mixtures of sd and md grains of widely different sizes the forc diagrams were all asymmetric small psd samples have forc diagrams with a distinctive closed contour structure the distributions of the larger md grains display no peak and lie closer to the interaction field axis to assess the effect of magnetostatic interactions we measured forc diagrams between room temperature and the curie temperature on heating the forc distributions contract without changing shape until 500 c above this temperature the diagrams become more md like and in addition become more symmetric the temperature dependence of the interaction field parameter is proportional to that of the saturation magnetization in accordance with neel s interpretation of the preisach diagram the decrease in asymmetry with heating suggests that the origin of the asymmetry lies in magnetostatic interactions the magnetic hysteresis parameters as a function of temperature were determined from the forc curves as the grain size decreased the normalized coercive force was found to decrease more rapidly with temperature

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well