the effects of 10 to 160 gpa shock on the magnetic properties of basalt and diabase hypervelocity impacts within the solar system affect both the magnetic remanence and bulk magnetic properties of planetary materials spherical shock experiments are a novel way to simulate shock events that enable materials to reach high shock pressures with a variable pressure profile across a single sample ranging between 10 and 160 gpa here we present spherical shock experiments on basaltic lava flow and diabase dike samples from the osler volcanic group whose ferromagnetic mineralogy is dominated by pseudo single domain titano magnetite our experiments reveal shock induced changes in rock magnetic properties including a significant increase in remanent coercivity electron and magnetic force microscopy support the interpretation that this coercivity increase is the result of grain fracturing and associated domain wall pinning in multidomain grains we introduce a method to discriminate between mechanical and thermal effects of shock on magnetic properties our approach involves conducting vacuum heating experiments on untreated specimens and comparing the hysteresis properties of heated and shocked specimens first order reversal curve forc experiments on untreated heated and shocked specimens demonstrate that shock and heating effects are fundamentally different for these samples shock has a magnetic hardening effect that does not alter the intrinsic shape of forc distributions while heating alters the magnetic mineralogy as evident from significant changes in the shape of forc contours these experiments contextualize paleomagnetic and rock magnetic data of naturally shocked materials from terrestrial and extraterrestrial impact craters this article is protected by copyright all rights reserved

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

comparing a three dimensional and a dupuit forchheimer solution for a circular recharge area in a confined aquifer abstract an exact closed form analytic solution is presented for three dimensional steady state flow due to a source disc the solution is used to model a circular recharge area at the upper boundary of a confined aquifer streamlines and contour plots of equipotentials are compared with those obtained from a dupuit forchheimer solution the latter solution is approximate in that resistance to vertical flow is ignored as a further illustration a groundwater contamination problem is solved that of a leaching circular pond in a uniform flow field some streamlines and the shape of the downstream plume are plotted for both the three dimensional and the dupuit forchheimer solution it appears that when the recharge area is sufficiently large the dupuit forchheimer solution is quite adequate particularly when tracing streamlines the results therefore confirm the validity of the dupuit forchheimer assumption when modeling regional flow even under circumstances of areal recharge however when the size of the recharge area is in the order of the aquifer thickness a truly three dimensional solution is needed

the effect of cooling rate on the intensity of thermoremanent magnetization trm acquired by assemblages of pseudo single domain multidomain and interacting single domain grains summary experiments designed to measure the absolute palaeointensity of the geomagnetic field generally do so by comparing the ancient thermoremanent magnetization trm retained by an igneous rock with a new trm imparted in the laboratory one problem with this procedure is that the relative magnitudes of the ancient and laboratory trms may be influenced not only by the external field intensities at the time the two coolings took place but also by the rate at which the coolings themselves occurred here we present new measurements of this cooling rate effect obtained from treatments in the laboratory differing in cooling rate by a factor of 200 synthetic samples containing sized ferrimagnetic grains were used in the experiments theoretical considerations and previous experiments have indicated the cooling rate effect to be dependent on domain state increases in trm magnitude of more than 7percent per order of magnitude decrease in cooling rate have been reported for assemblages of non interacting single domain sd grains here we focus on magnetite grains in the less well studied pseudo single domain psd and multidomain md states using a range of applied field intensities to impart the trms for the first time we also measure the cooling rate effect in grains of titanomagnetite that have been oxyexsolved so that they contain strongly interacting sd lamellae in all cases the cooling rate effect measured was in the same sense as alreadyobservedinidealmagneticallynon interactingsdgrainsbutwasconsiderablyweaker on average the effect did not exceed 3percent increase in trm per order of magnitude decrease in cooling rate and did not show any systematic dependence on appliedfield intensity insomesamples containing coarsergrains thecoolingrateeffectwasnotdistinguishablefrom zero the sense and magnitude of the cooling rate effect remain uncertain in truly md grains as different studies have produced discrepant results for the more practically relevant case of psd and interacting sd grains which commonly dominate the trm in igneous rocks however it appears that we can be more confident in our assertions the cooling rate effect in such materials is in the same sense as in non interacting sd grains but smaller a consequence of long range ordering in lavas and small intrusions containing these it is unlikely to exceed 10percent although a correction should always be attempted the results of palaeointensity studies based upon such samples will generally not be severely biased

the henkel petrophysical plot mineralogy and lithology from physical properties the henkel plot logarithm of magnetic susceptibility versus density of rock samples reveals that most rocks fall on either a magnetite trend or a paramagnetic trend i

fe ti oxide micro inclusions in clinopyroxene of oceanic gabbro phase content orientation relations and petrogenetic implication abstract fe ti oxide micro inclusions in clinopyroxene of oceanic gabbro from the mid atlantic ridge have been studied using electron backscatter diffraction and electron probe microanalyses a first generation of fe ti oxide inclusions occurs as needles or elongated plates lying in the 010 plane of the clinopyroxene host the inclusions show distinct elongation directions following irrational planes either nearly parallel to the c or nearly parallel to the a axis of the clinopyroxene host the habit planes correspond to inclusion host interfaces where densely packed oxygen layers of the inclusion and host phases are coherent across the interface both inclusion types have distinct crystallographic orientation relations to the host which are determined by the nearly parallel alignment of densely packed oxygen layers in the inclusions and the clinopyroxene host based on the angle between the two elongation directions primary formation of the inclusion at 800 to 900 c was inferred initially homogeneous ti bearing magnetite was precipitated together with titanian pargasite lamellae due to reaction of early magmatic clinopyroxene with late magmatic fluid or melt after cooling below 600 c the ti magnetite decomposed into an oriented magnetite ulvospinel intergrowth late stage hydrothermal alteration leads to the corrosion of the magnetite ulvospinel inclusions and partial replacement by ilmenite as well as newly precipitated homogeneous ilmenite plates that are closely associated with actinolite lamellae lying in the 100 plane of the clinopyroxene host

characteristics and genesis of maghemite in chinese loess and paleosols mechanism for magnetic susceptibility enhancement in paleosols abstract morphological characteristics and microstructures of magnetic minerals extracted from chinese loess and paleosols were investigated using powder x ray diffraction xrd and high resolution transmission electron microscopy hrtem our results indicate that maghemite in loess paleosol sequences was transformed from magnetite through oxidation of magnetite maghemite transformed from eolian magnetite during chemical weathering has low angle grain boundaries among maghemite nano crystals some nano crystalline maghemites with nanoporous texture resulted from microbe induced precipitation of magnetite or transformation of poorly crystalline ferric fe oxy hydroxides in presence of fe reducing bacteria aggregates of euhedral maghemite nano crystals were transformed from magnetite magnetosomes both microbe induced nanoporous magnetite and microbe produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols it is proposed that the formation of nano crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility although the total amount weight percent of magnetic minerals in both paleosol and loess units is similar our results also show that nano crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi arid soil environments instead of hematite although hematite is a thermodynamically stable phase this result also indicates that a decrease in crystal size will increase stability of maghemite it is also inferred that surface energy of maghemite is lower than that of hematite

exsolved magnetite inclusions in silicates features determining their remanence behavior submicroscopic needle shaped titanomagnetite inclusions exsolved in silicate minerals commonly occur in mafic intrusive rocks and are protected from alteration by their silicate hosts making them excellent candidates for paleomagnetic studies a suite of samples containing clinopyroxene and plagioclase hosted magnetite inclusions from five geologically diverse sites was examined using magnetic force microscopy to image the inclusions magnetic domain state alternating field demagnetization experiments indicate that some inclusions are more stable recorders than others the two factors controlling the remanence behavior of the inclusions are internal microstructures and inclusion dimensions magnetite ulvospinel unmixing within an inclusion subdivides the original titanomagnetite solid solution into a boxwork structure composed of 103 105 magnetite prisms separated by thin ulvospinel lamellae the conversion of multidomain sized needles into assemblages of interacting single domains increases the coercivity and hence relaxation time of the inclusions and results in a thermochemical magnetic remanence in samples without this exsolution microstructure the inclusions diameters determine coercivity and their magnetization is thermoremanent both styles of high coercivity inclusions successfully record paleomagnetic directions in mesozoic rocks and their ubiquity within silicate minerals clinopyroxene and plagioclase of mafic intrusive rocks indicates their value as chemically and magnetically stable tools for elucidating the ancient magnetic field marine magnetic anomalies and crustal kinematics

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

dike intrusion as a possible cause of linear martian magnetic anomalies a model in which the ancient 100 200 km wide magnetic lineations in the southern hemisphere of mars are formed by repeated dike intrusion is proposed on the basis of magnetizations observed at terrestrial mid ocean ridges a likely upper bound on the martian crustal magnetization is about 15 a m 1 this upper bound gives a minimum magnetized layer thickness of 35 60 km because the magnetic material is likely to be magnetite the long term stability of the anomalies probably requires ilmenite lamellae to have exsolved from the magnetite this exsolution process provides an upper bound on the cooling time available of 102 105 yr these bounds can be satisfied if the magnetic anomalies are created by successive intrusion of dikes from 20 to 2000 m wide production of a martian crust 35 60 km thick by rifting requires either mantle potential temperatures in excess of 1430 c or stretching factors greater than 5

nanogeochemistry of hydrothermal magnetite magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million ppm of elements such as ti si v al ca mg na which tend to either structurally incorporate into growth and sector zones or form mineral micro to nano sized particles here we report micro to nano structural and chemical data of hydrothermal magnetite from the los colorados iron oxide apatite deposit in chile where magnetite displays both types of trace element incorporation three generations of magnetites x z were identified with concentrations of minor and trace elements that vary significantly sio2 from below detection limit bdl to 3 1 wt al2o3 0 3 2 3 wt cao bdl 0 9 wt mgo 0 02 2 5 wt tio2 0 1 0 4 wt mno 0 04 0 2 wt na2o bdl 0 4 wt and k2o bdl 0 4 wt an exception is v2o3 which is remarkably constant ranging from 0 3 to 0 4 wt six types of crystalline nanoparticles nps were identified by means of transmission electron microscopy in the trace element rich zones which are each a few micrometres wide 1 diopside 2 clinoenstatite 3 amphibole 4 mica 5 ulvospinel and 6 ti rich magnetite in addition al rich nanodomains which contain 2 3 wt of al occur within a single crystal of magnetite the accumulation of nps in the trace element rich zones suggest that they form owing to supersaturation from a hydrothermal fluid followed by entrapment during continuous growth of the magnetite surface it is also concluded that mineral nps promote exsolution of new phases from the mineral host otherwise preserved as structurally bound trace elements the presence of abundant mineral nps in magnetite points to a complex incorporation of trace elements during growth and provides a cautionary note on the interpretation of micron scale chemical data of magnetite

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

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 properties of ilmenite hematite single crystals from the ecstall pluton near prince rupert british columbia paleomagnetic studies of the 91 ma ecstall pluton and other cretaceous plutons of british columbia imply large northward tectonic movements 2000 km may have occurred during the tectonic evolution of western north america however more recent studies have shown that the eastern edge of the ecstall pluton experienced considerable mineralogical changes as younger eocene plutons such as the 58 ma quottoon pluton were emplaced along its margins we investigated changes in the rock magnetic properties associated with this reheating event by examining isolated grains of intergrown ilmenite and hematite the primary paleomagnetic recorder in the ecstall pluton measurements of hysteresis properties low temperature remanence and room temperature isothermal remanent magnetization acquisition and observations from magnetic force microscopy and off axis electron holography indicate that samples fall into three groups the groups are defined by the presence of mineral microstructures that are related to distance from the quotoon plutonic complex the two groups closest to the quottoon pluton contain magnetite within hematite and ilmenite lamellae reheating of the ecstall pluton led to an increase in coercivity and magnetization as well as to development of mixed phase hysteresis these results indicate that shallow paleomagnetic directions from the western ecstall pluton are not affected by reheating and are therefore likely to record original field conditions at the time of pluton emplacement in the absence of structural deformation these shallow inclinations are consistent with large scale northward translation suggested by the baja british columbia hypothesis

widespread occurrence of silicate hosted magnetic mineral inclusions in marine sediments and their contribution to paleomagnetic recording magnetic mineral inclusions occur commonly within other larger mineral phases in igneous rocks and have been demonstrated to preserve important paleomagnetic signals while the usefulness of magnetic inclusions in igneous rocks have been explored extensively their presence in sediments has only been speculated upon the contribution of magnetic inclusions to the magnetization of sediments therefore has been elusive in this study we use transmission electron microscope tem and magnetic methods to demonstrate the widespread preservation of silicate hosted magnetic inclusions in marine sedimentary settings tem analysis reveals detailed information about the microstructure chemical composition grain size and spatial arrangement of nanoscale magnetic mineral inclusions within larger silicate particles our results confirm the expectation that silicate minerals can protect magnetic mineral inclusions from sulfate reducing diagenesis and increase significantly the preservation potential of iron oxides in inclusions magnetic inclusions should therefore be considered as a potentially important source of fine grained magnetic mineral assemblages and represent a missing link in a wide range of sedimentary paleomagnetic and environmental magnetic studies in addition we present depositional remanent magnetization drm modeling results to assess the paleomagnetic recording capability of magnetic inclusions our simulation demonstrates that deposition of larger silicate particles with magnetic inclusions will be controlled by gravitational and hydrodynamic forces rather than by geomagnetic torques thus even though these large silicates may contain ideal single domain particles they can not contribute meaningfully to paleomagnetic recording however smaller silicate grains e g silt and clay sized silicates with unidirectionally magnetized magnetic inclusions can potentially record a reliable drm

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

the eight classical monteregian hills at depth and the mechanism of their intrusion the eight classical monteregian hills are monadnocks on the st lawrence lowlands and adjacent appalachian foothills in a swath that sweeps 80 km eastward from montreal gravity anomalies suggest t

effects of internal mineral structures on the magnetic remanence of silicate hosted titanomagnetite inclusions an electron holography study 1 titanomagnetite inclusions in pyroxene and plagioclase are carriers of stable magnetic remanence in some slowly cooled rocks such as gabbros anorthosites granulites and diorites needle shaped inclusions with average dimensions of 1 1 25 m form epitaxially by exsolution from their host silicate close examination of clinopyroxene hosted inclusions reveals an internal microstructure which consists of magnetite fe3o4 prisms and ulvospinel fe2tio4 lamellae that formed as a result of phase unmixing during initial cooling this internal structure exerts a profound influence on the magnetic remanence properties of each inclusion primarily by transforming it from a multidomain grain into an assemblage of magnetostatically interacting single domain prisms here we use off axis electron holography to image the magnetization states of individual prisms and the magnetostatic interactions between them we show that the inclusions exhibit both single domain and collective magnetic states that depend primarily on the shape anisotropies of individual magnetite prisms magnetostatic interactions between closely spaced prism stacks and the shape anisotropy of the needle itself prisms that are separated by thick ulvospinel lamellae show uniformly magnetized and or vortex states in contrast closely spaced magnetite prisms behave as multipart vortices or as long composite columns whose strong net magnetization may not be related directly to the orientation and shape of either the needle or the constituent prisms the overall remanence direction recorded by clinopyroxene crystals containing finely exsolved inclusions is a reflection of both the inclusions elongation directions and the prism arrangements within them

magnetic hysteresis of 0 6 110 μm magnetites across the verwey transition we report saturation magnetization ms saturation remanence mrs coercive force hc and remanence coercivity hcr as a function of grain size d and temperature t for 0 6 135 m magnetites