neoformed magnetic minerals as an indicator of moderate burial the key example of middle paleozoic sedimentary rocks west virginia in order to help unravel the thermal history of middle paleozoic sedimentary rocks in west virginia a rock magnetic study was conducted with a focus on the marcellus shale vitrinite reflectance fluid inclusions microthermometry and conodont alteration index data yield contradictory burial temperature within the range 150 250 c 302 482 f the characterization of magnetite and pyrrhotite may be used as an index to track burial temperature around 200 c 392 f low temperature and room temperature magnetic measurements were performed in order to determine the magnetic assemblage three magnetic assemblages were identified that were stratigraphically distributed the goethite and nanosized magnetite a1 assemblage is mainly found in the clinton group oriskany sandstone stratigraphic interval silurian lower devonian nanosized fraction of magnetite and probably pyrrhotite a3 assemblage essentially constitutes the marcellus shale chemung formation sequence devonian microsized pyrrhotite is the typical mineral for a2 that is only identified near the alleghenian structural front overall the rare occurrence of micron pyrrhotite in our samples suggests that the study area has not experienced burial temperatures higher than 200 c 392 f

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

new silurian and devonian palaeomagnetic results from the hexi corridor terrane northwest china and their tectonic implications summary a total of 239 orientated drill core samples from 23 sites were collected for palaeomagnetic study from silurian and devonian red beds marlaceous sandstone and limestone rocks in the eastern part of the hexi corridor southwest ningxia north china the characteristic high temperature component resides in both haematite and magnetite it clusters around a northwesterly and shallow to moderate downward direction and its antipode after tilt correction the primary origin of this characteristic remanent magnetization chrm is ascertained by positive fold and reversal tests at the 95 per cent confidence level the corresponding palaeopoles at 339 0 e 60 1 n with a 95 11 2 silurian and 336 0 e 56 0 n with a 95 9 2 devonian imply that the north china block ncb had a low palaeolatitude of around 15 n in the northern hemisphere during the silurian devonian period comparison with the early middle ordovician palaeopole of the ncb suggests that the ncb moved rapidly northwards by 30 8 10 9 to cross the palaeo equator during the early middle ordovician to silurian in combination with the palaeobiogeographical data from ningxia our palaeomagnetic results suggest that the ncb was located close to australia during the late devonian

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

an investigation of the magnetic carriers and demagnetization characteristics of the gulang loess section northwestern chinese loess plateau we report the results of a rock magnetic and paleomagnetic investigation of unit l9 of the gulang gl loess section in the northwestern chinese loess plateau clp we demonstrate that the dominant magnetic remanence carriers are coarse grained pseudo single domain multidomain magnetite particles and hematite the application of either thermal thd or alternating field demagnetization afd yielded several normal polarity intervals interbedded with intervals of reversed polarity but which cannot be correlated with standard geomagnetic polarity time scales a greater number of normal polarity intervals however were evident after thd than after afd we propose that the normal polarities are either the result of overprinting of a viscous remanent magnetization vrm carried by coarse magnetite particles on the original depositional remanent magnetization drm or that they represent genuine geomagnetic excursions such as the kamikatsura and santa rosa excursions which are difficult to identify in addition we propose that in the case of the gl loess section the effect of thermal demagnetization tails of a vrm is a possible reason why thd treatment yielded a greater number of normal polarity intervals than does afd however reversed polarities obtained by either thd or afd may be credible for sedimentary intervals with a relatively high content of hematite particles which preserve the primary drm although numerous studies have proposed that thd provides more reliable paleomagnetic directions for loess sediments from the clp our results suggest that careful attention needs to be paid to the type of demagnetization method chosen especially in the case of coarse grained loess deposits

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

complex polarity pattern at the former plio pleistocene global stratotype section at vrica italy remagnetization by magnetic iron sulphides the vrica section in calabria southern italy was the global stratotype for the pliocene pleistocene boundary until this boundary was redefined in 2009 several paleomagnetic investigations have been carried out at vrica to determine the age of the formerly defined pliocene pleistocene boundary which was a key calibration point for the astronomical polarity timescale apts each study has documented a complex polarity pattern at and above the top of the olduvai subchron and in relation to the existence of the so called vrica subchron when constructing the apts two alternative interpretations for the vrica section were proposed neither of which could be conclusively supported authigenic growth of magnetic iron sulphide minerals was proposed to explain the complex magnetic polarity record availability of a fresh 50 m sediment core enabled us to test this possibility our magnetostratigraphic record is similar to that of previous studies but it is also complex above the olduvai subchron we confirm abundant occurrences of authigenic greigite and pyrrhotite along with detrital titanomagnetite authigenic monoclinic pyrrhotite indicates growth significantly later than deposition and greigite can grow at any time during diagenesis depending on the availability of dissolved iron and sulphide the spatially variable magnetic polarity pattern at vrica is therefore interpreted to have resulted from post depositional magnetic iron sulphide formation at variable times tectonism along the calabrian arc provides a plausible mechanism for forcing reducing fluids through the sediments thereby supplying the dissolved ions needed to produce late diagenetic sulphide growth and remagnetization the complex magnetostratigraphic record at vrica was taken into account when the apts was developed and alternative interpretations result in a maximum age difference of 50 kyr for the upper olduvai reversal our results therefore do not undermine the apts rather they explain the complex magnetic polarity pattern at this globally important location and highlight the importance of remagnetization processes in such sediments

paleosecular variations of the geomagnetic field during the holocene from eastern asia abstract high resolution paleomagnetic secular variation psv records bear great information of dynamics processes of the earth s geomagnetic field and can be further used for inter profile correlation and for dating sediments however effects of changes in the depositional environment on psv records have not been fully determined this study constructed holocene psv records for the gravity piston core zsqd34 obtained from the northern south china sea rock magnetic and transmission electron microscope tem results indicate that single sd and psd domain magnetites are the main carrier of the natural remanent magnetization comparable to the records derived from the freshwater lakes and the modeling results we observed that direction curves from these two environments of contrasting salinity content are rather consistent the direction curves are independent of the constructed salinity however the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity furthermore on the centennial and millennial time scale the relative intensity and salinity show some positive relation suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes

assessing the ability of first order reversal curve forc diagrams to unravel complex magnetic signals 1 first order reversal curve forc diagrams for mixtures of different magnetic phases and bimodal distributions have been measured to examine the efficiency of the forc method at unraveling complex magnetic signals the forc distributions for various magnetic minerals including magnetite maghemite hematite and goethite and their linear additivity are assessed mixtures containing only hard magnetic minerals like hematite or goethite which have relatively small spontaneous magnetizations ms and large magnetocrystalline anisotropies can be adequately described by a linear addition of the two end members because there are virtually no magnetostatic interactions between the phases mixtures dominated by softer minerals like magnetite and maghemite are more susceptible to interactions and exhibit nonlinear behavior when a hard phase with low ms like hematite is mixed with a softer phase with high ms like magnetite it can still be identified using the forc technique whereas it is impossible to do so using standard magnetic hysteresis measurements when the weaker phase can be identified then weak strong mixes add linearly however beyond a certain critical concentration the mineral with high ms swamps the magnetic signal and linearity breaks down it is suggested that the forc method is highly suitable for identifying small traces of hard magnetic minerals like hematite and goethite in the presence of minerals with high ms such as magnetite

volcanic records of the laschamp geomagnetic excursion from mt ruapehu new zealand abstract we present palaeodirectional records of the laschamp geomagnetic excursion from lavas on mt ruapehu new zealand fourteen lava flows on the northwestern and southern flanks of mt ruapehu with 40ar 39ar weighted mean plateau ages that range from 46 3 2 0 to 39 9 1 4 ka were studied the youngest and older flows carry a normal polarity magnetization however six flows dated between 46 3 2 0 and 42 7 1 8 ka record excursional directions three of these flows record southerly palaeomagnetic declinations and negative inclinations that agree well with a published laschamp record from the auckland volcanic field avf together the avf and mt ruapehu lavas currently represent the only volcanic records of the laschamp excursion outside the chaine des puys region france thus they make an important contribution to the global set of laschamp excursion records virtual geomagnetic pole vgp groups for the new zealand and french records early in the excursion are compatible with a dipole dominated field that rotated to an equatorial orientation while simultaneously decaying in strength in contrast younger excursional flows from france and new zealand yield separate vgp groups which suggest either that the field had a nondipolar morphology in this later phase or that the vgp groups were not synchronous 40ar 39ar ages for the mt ruapehu record are on average slightly older than published northern hemisphere ages and from the relative palaeointensity minimum in the glopis sedimentary stack although few individual ages differ significantly at the 2 level the spread suggests an overall excursion duration that is longer than the currently accepted 1500 years this age spread may result from excess ar in magmas at the time of the eruption biasing the results to slightly older ages or from non synchronous excursional field behaviour at near antipodal locations or possibly a precursory phase prior to the main excursion

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

the different climatic response of pedogenic hematite and ferrimagnetic minerals evidence from particle sized modern soils over the chinese loess plateau abstract in recent years increasing interest in loess studies has focused on qualitative and quantitative paleoclimatic reconstruction using the imperfect antiferromagnetic mineral hematite however the linkage between the hematite formation and climatic variables remains controversial here we present the results of a comprehensive investigation of the magnetic properties and statistical analysis of a suite of clay and silt fractions of modern soil samples from 179 sites across the chinese loess plateau clp and adjacent regions our objective was to clarify the relationships between modern climatic variables and pedogenic hematite as well as pedogenic ferrimagnetic minerals first order reversal curve measurements were also conducted on representative particle sized subsamples from a n s transect to understand the differences in magnetic mineralogy between the two fractions our results show that pipette extraction separates the fine grained superparamagnetic sp and most of the single domain sd magnetic grains into the clay fraction and that the remaining silt fraction displays the magnetic properties of coarse pseudo single domain psd or a mixture of multidomain md psd and a few sd particles only the pedogenic clay fraction shows a strong correlation with climatic variables the application of redundancy analysis helps to distinguish the climate variables controlling the formation of ferrimagnetic minerals and hematite during pedogenesis on the clp pedogenic ferrimagnetic minerals are sensitive to mean annual precipitation while pedogenic hematite formation is preferentially dependent on mean annual temperature the confirmation of the temperature dependent nature of hematite on the clp provides a new possibility for quantitatively reconstructing the paleotemperature history of chinese loess paleosol sequences

magnetic hysteresis properties of interacting and noninteracting micron sized magnetite produced by electron beam lithography the magnetic hysteresis properties for well defined micron sized magnetite samples produced by electron beam lithography ebl are presented in addition to measuring standard hysteresis parameters first order reversal curve forc diagrams are also reported ebl produces samples that consist of particles with very tightly constrained size distributions and spatial distributions that govern the degree of intergrain magnetostatic interactions are accurately controlled and known thus ebl samples are significantly better characterized compared to powdered samples which are conventionally used to characterize the size dependency of magnetic hysteresis properties of naturally occurring magnetic minerals compared with the hysteresis properties of powdered samples of the same nominal sizes ebl samples display more multidomain like md behavior the influence of magnetostatic interactions fields on hysteresis properties is analyzed when magnetostatic interactions are effectively in only one direction the hysteresis properties become more single domain like and if the interactions are in more than one direction hysteresis becomes more md like in agreement with numerical models

the origin of the calcites from pb zn veins in the harz mountains federal republic of germany abstract studies of the ree distribution in calcites from hydrothermal banded pb zn mineralizations as well as in calcites from pelitic and psammitic unmetamorphosed rocks and magmatites of the harz mountains revealed that the calcite of the banded ores crystallized from hybrid magmatic metamorphic solutions these were rather rich in ree3 fe3 and probably zn2 and pb2 ion concentrations the absence of any negative eu anomalies points to oxidizing conditions the sulphides have crystallized from a different solution it is suggested that the necessary hs rich solutions stem from near surface hydrothermal convection cells set up by nearby granitic intrusions the alternating deposition of calcite and sulphide banded ores may be explained by assuming that farther away from the intrusions the hs rich solutions were intermittedly admixed with the hybrid fluids this caused a decrease in temperature an interruption of calcite deposition and sulphide mineralization near the intrusion continuous mixing of these two fluids became more common and consequently banded ores are rather rare

remanence stability and magnetic fabric development in synthetic shear zones deformed at 500 c shear experiments were performed on magnetite bearing calcite aggregates to examine magnetic fabric development and remanence stability in a deforming system using elevated temperature and pressure to encourage deformation by crystal plastic processes samples composed of 1 wt pseudo single domain magnetite 1 2 m in a calcite matrix were created with either strong or weak initial fabrics and deformed in coaxial simple shear to strains up to 1 5 at constant strain rates between 6 10 5 and 1 10 4 s 1 at 500 c and confining pressure of 300 mpa samples were given weak field thermal remanent magnetizations prior to deformation demagnetization of postdeformation remanence reveals that a primary remanent magnetization can withstand deformation at pressures and temperatures approximately equivalent to greenschist facies metamorphic conditions on laboratory time scales but this stability is found to depend on the character of the predeformation fabric the origin of secondary remanence components acquired during deformation is uncertain but is likely to partially result from thermal viscous remagnetization complete postdeformation remagnetization in initially anisotropic samples appears to involve a stress softening or piezoremanent magnetization mechanism postdeformation anisotropy measurements show progressive changes in magnetic fabric strength with strain in the absence of a strong initial magnetic anisotropy magnetic fabric intensity increases linearly as a function of strain however deformation that overprinted an existing fabric results in an apparent decrease of the initial anisotropy at low strains followed by rapid increases in magnetic fabric strength with increasing strain our results underscore the important role that initial fabric can play in determining the character of deformation fabrics

low temperature first order reversal curve forc diagrams for synthetic and natural samples first order reversal curve forc diagrams were measured on a variety of synthetic and natural submarine basalts and potsherds samples as well as for a mixture between room temperature and 10 k measuring forc diagrams allowed us to examine the behavior of the coercivity field and interaction field distributions with decreasing temperature generally as the temperature is decreased forc contours were observed to expand in all directions e g the maximum coercivity peak migrates toward a higher coercivity for synthetic magnetite samples there were abrupt changes in the forc distribution at the verwey transition 120 k while in the more complex natural magnetite samples the forc distribution gradually progressed with temperature as the temperature decreased forc diagrams were found to display different domain state characteristics for example samples with dominant superparamagnetic signals became single domain sd like a sd like sample stayed sd like and a psd like sample became more sd like in addition to these general features we also observed some more specialized features first in both synthetic and natural magnetite samples a secondary higher coercivity peak is occasionally present below the verwey transition which we suggest is a twinning contribution second the coercivity increases by a factor 15 between 300 k and 20 k in some of the seamount samples third the effect of field cooling zero field cooling on forc diagrams is negligible with the hysteresis parameters hc and hcr displaying a greater dependency finally it is shown that in mixtures of magnetite and hematite the hematite contribution disappears on cooling below the morin transition leaving a strong well defined magnetite signal

biochemical vs detrital mechanism of remanence acquisition in marine carbonates a lesson from the k t boundary interval abstract an apparently complete carbonate rich cretaceous tertiary boundary interval in odp section 119 738c 20r 5 from the southern kerguelen plateau provides a unique insight into processes of magnetization acquisition in marine carbonates the boundary interval is characterized by a 1 m thick clay rich zone distinct depositional lamina are preserved within the basal 15 cm of this zone the upper part is bioturbated previous studies have demonstrated that the bulk of the detrital fraction in the laminated and bioturbated carbonates has the same local source and hence the two intervals likely had similar initial detrital assemblages magnetic properties of these rocks however differ significantly the laminated sediments have a higher content of non silicate bound iron yet approximately an order of magnitude lower intensity of the natural remanent magnetization compared to the bioturbated rocks our detailed rock magnetic study indicates that in the bioturbated interval the dominant iron bearing phase is single domain magnetite likely of biogenic origin in the laminated interval apart from a small ferromagnetic fraction with multi domain like behavior non silicate bound iron is mainly sequestered in paramagnetic phases likely poorly crystalline oxyhydroxides it appears that a shut down of biological productivity after the k t event allowed preservation of the initial detrital early authigenic iron phases that are dominated by reactive iron oxyhydroxides with recovery of the normal biological activity as evidenced by resumption of bioturbation the oxyhydroxides had been replaced with biogenic magnetite thus produced biochemical magnetization led to a several fold increase in the remanence our results suggest that in areas where bioavailable iron constitutes a significant part of the detrital input such as in pelagic marine environments distant from clastic sources the biochemical remanent magnetization may be the dominant process of magnetization acquisition

crevice type caves as initial forms of rock landslide development in the flysch carpathians crevice type caves formed along joints are very common in the polish flysch carpathians more than 600 have been recorded the caves represent accessible parts of the widened cracks which are basic initial forms of development of deep seated rock landslides structural features of four selected caves situated in different parts of the carpathians were studied in order to determine relations between joint systems and landslide formation the studies prove that the main rock scarps often represent effects of earlier propagation of the cracks cutting surfaces due to loading and unloading shearing stress the cracks are structural forms developed along joints or faults the cutting surfaces represented by cracks caves develop a long time before the main gravitational mass movements whereas the sliding surfaces shearing zones are formed or significantly modified ad hoc during the gravitational transport of rock masses occurrence of the deep initial cracks causes modification of shape of the sliding surfaces which are noncircular the mountain slopes cut by many cracks are permanently developed thus the periodic increase of activity of external factors floods downpours earthquakes etc leads to common formation of the landslides earlier prepared by crack development this model of slope evolution enables us to interpret the occurrence of the landslide phases in the holocene during which increasing of frequency of the landslides is observed

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

assessment of the usefulness of lithic clasts from pyroclastic deposits for paleointensity determination 1 paleomagnetic and rock magnetic measurements were carried out on lithic clasts found within pyroclastic deposits to assess their potential for paleointensity determinations the use of multiple lithologies in a single paleointensity determination would provide confidence that the result is not biased by alteration within one lithology lithic clasts were sampled from three historically active volcanoes lascar in the chilean andes mt st helens united states and vesuvius italy at lascar triple heating paleointensity experiments allow development of new selection criteria for lithic clasts found within pyroclastic deposits using these criteria the lascar data yield a mean paleointensity of 24 3 1 3 t 1 n 26 which agrees well with the expected value of 24 0 t this indicates that pyroclastic rocks have promise for paleointensity determinations pyroclastics however still suffer from the range of problems associated with conventional paleointensity experiments on lava flows samples from mt st helens are strongly affected by multidomain md behavior which results in all samples failing to pass the paleointensity selection criteria at vesuvius md grains magnetic interactions and chemical remanent magnetizations contributed to failure of all paleointensity experiments rock magnetic analyses allow identification of the causes of failure of the paleointensity experiments however in this study they have not provided adequate preselection criteria for identifying pyroclastics that are suitable for paleointensity determination

thermochemical remanent magnetization in precambrian rocks are we sure the geomagnetic field was weak 1 thellier paleointensity determinations from two dikes of the early proterozoic 2 46 ga matachewan dike swarm canada yield field values of 2 14 0 18 and 9 81 1 65 t corresponding values of virtual axial dipole moment are very low 0 54 0 05 1022 and 2 49 0 42 1022 am2 respectively when compared with the modern field the characteristic remanent magnetization chrm was isolated over a narrow range of high unblocking temperatures 520 580 c detailed rock magnetic analyses indicate that the chrm is carried by nearly stoichiometric pseudo single domain magnetite scanning electron microscopy sem reveals that the magnetite is in the form of fine intergrowths with ilmenite formed by oxyexsolution during cooling the high temperature oxidation defined in the sem images could have continued at temperatures below the curie point of magnetite in this case the chrm would be a thermochemical remanent magnetization tcrm rather than a thermal remanent magnetization trm estimates of the tcrm trm ratio show that the thellier data could underestimate the true field value by a factor of 4 without violating experimental selection criteria this uncertainty in trm fidelity translates into a potential range of field values that spans that defined by the modern field 8 1022 am2 and proposed low precambrian levels 2 1022 am2 therefore understanding further how tcrm is acquired and records the field represents a major challenge if these and many other similar rocks are to be used in thellier studies aimed at defining the strength of the precambrian field

effect of maghemization on the magnetic properties of nonstoichiometric pseudo single domain magnetite particles the effect of maghemization on the magnetic properties of magnetite fe3o4 grains in the pseudo single domain psd size range is investigated as a function of annealing temperature x ray diffraction and transmission electron microscopy confirm the precursor grains as fe3o4 ranging from 150 to 250 nm in diameter whilst mossbauer spectrometry suggests the grains are initially near stoichiometric the fe3o4 grains are heated to increasing reaction temperatures of 120 220 c to investigate their oxidation to maghemite fe2o3 high angle annular dark field imaging and localized electron energy loss spectroscopy reveal slightly oxidized fe3o4 grains heated to 140 c exhibit higher oxygen content at the surface off axis electron holography allows for construction of magnetic induction maps of individual fe3o4 and fe2o3 grains revealing their psd vortex nature which is supported by magnetic hysteresis measurements including first order reversal curve analysis the coercivity of the grains is shown to increase with reaction temperature up to 180 c but subsequently decreases after heating above 200 c this magnetic behavior is attributed to the growth of a fe2o3 shell with magnetic properties distinct from the fe3o4 core it is suggested there is exchange coupling between these separate components that results in a vortex state with reduced vorticity once fully oxidized to fe2o3 the domain states revert back to vortices with slightly reduced coercivity it is argued that due to a core shell coupling mechanism during maghemization the directional magnetic information will still be correct however the intensity information will not be retained

magnetic characteristics of cv chondrules with paleointensity implications 1 we have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the cv type 1 mokoia and 2 allende allende has been previously extensively studied and is thought to have a high potential of retaining an extra terrestrial paleofield few paleomagnetic studies of mokoia have previously been undertaken we report a range of magnetic measurements including hysteresis first order reversal curve analysis forcs demagnetization characteristics and isothermal remanent irm acquisition behavior on both mokoia and allende chondrules the mokoia chondrules displayed more single domain like behavior than the allende chondrules suggesting smaller grain sizes and higher magnetic stability the mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the allende chondrules irm acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral likely to be a feni phase taenite kamacite and or awaruite contributing to 48 of the mokoia chondrules and 42 of the allende chondrule characteristics forc analysis revealed that generally the allende chondrules displayed low field coercivity distributions with little interactions and the mokoia chondrules show clear single domain like distributions paleointensity estimates for the two meteorites using the remc and preisach methods yielded estimates between 13 and 60 t and 3 56 t respectively for allende and 3 140 t and 1 110 t respectively for mokoia from the data we suggest that mokoia chondrules carry a non primary remagnetization and while allende is more likely than mokoia to retain its primary magnetization it also displays signs of post accretionary magnetization

tectonic climatic and diagenetic control of magnetic properties of sediments from kumano basin nankai margin southwestern japan abstract integrated ocean drilling program iodp site c0002 was cored in the kumano basin which is a forearc basin in the nankai margin of southwest japan the uppermost 1052 5 m of sediment in the accretionary prism slope and overlying forearc basin was recovered discontinuously during expedition 315 magnetic minerals from site c0002 were studied to understand sedimentary tectonic and diagenetic processes in this forearc environment four rock magnetic units a b c and d are identified in the forearc basin sediments of unit a high concentrations of detrital magnetic iron oxides in surface sediments give way to progressive diagenetic dissolution with depth nevertheless large titanomagnetite particles survived diagenetic dissolution along with magnetic nanoinclusions within host silicates that preserve a relict magnetic signal that records climatic modulation of sediment delivery to the kumano basin the authigenic iron sulphides ferrimagnetic greigite and paramagnetic pyrite formed in association with gas hydrates and anaerobic oxidation of methane in the forearc basin sediments of unit b methane venting from deeper within the slope sediments of unit c and accretionary prism sediments of unit d has given rise to formation of pyrite aggregates along sediment fractures and has contributed to further diagenetic depletion of magnetic signals in these units structural evolution of the kumano basin has caused migration of the gas hydrate stability zone ghsz through time so that the site c0002 sediments record both the present and fossil ghsz positions magnetic properties of kumano basin sediments provide insights into the interplay between diagenetic climatic and tectonic processes that controlled the sedimentary evolution of this forearc basin

the effects of annealing and concentration on the hysteresis properties of magnetite around the psd md transition abstract hysteresis parameters h cr h c j rs j s and their ratios h cr h c j rs j s have been measured for a large number of accurately prepared grain size fractions of magnetite in the range between 5 and 150 m for several grain size fractions three different concentrations of magnetite are used 100 0 1 and 0 002 vol most of the measurements were repeated after annealing the specimens to 600 c for some specimens in the pseudo single psd and multidomain md range h c and h cr have been measured as functions of temperature plots of the results from h c h cr h c and j rs j s versus the grain size reveal curves with a convex and a concave part concentration and annealing affects the values of the hysteresis parameters especially for grains coarser than 25 m but the shape of the curves remains the same the inflection point from convex to concave for all curves occurs at 25 m and it appears to be independent of concentration and annealing it is therefore proposed to define the transition from psd to md as the inflection point of these curves

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

greigite formed in early pleistocene lacustrine sediments from the heqing basin southwest china and its paleoenvironmental implications abstract the ferrimagnetic iron sulfide greigite fe 3 s 4 occurs widely in sulfidic lacustrine and marine sedimentary environments knowledge of its formation and persistence is important for both magnetostratigraphic and paleoenvironmental studies although the formation mechanism of greigite has been widely demonstrated the sedimentary environments associated with greigite formation in lakes especially on relatively long timescales are poorly understood a long and continuous sequence of pleistocene lacustrine sediments was recovered in the heqing drill core from southwestern china which provides an outstanding record of continental climate and environment integrated magnetic geochemical and paleoclimatic analysis of the lacustrine sequence provides an opportunity to improve our understanding of the environmental controls on greigite formation rock magnetic and scanning electron microscope analyses of selected samples from the core reveal that greigite is present in the lower part of the core part 1 665 8 372 5 m greigite occurs throughout this interval and is the dominant magnetic mineral irrespective of the climatic state the magnetic susceptibility record which is mainly controlled by the concentration of greigite matches well with variations in the indian summer monsoon ism index and total organic carbon toc content with no significant time lag this indicates that the greigite formed during early diagenesis in greigite bearing intervals with the increase b c value increase and tends to be stable at about 50 mt therefore we suggest that values could estimate the variation of greigite concentration approximately in the heqing core greigite favored more abundant in terrigenous rich and organic poor layers associated with weak summer monsoon which are characterized by high values high fe content high rb sr ratio and low toc content greigite enhancement can be explained by variations in terrigenous inputs our studies demonstrate that not only the greigite formation but also its concentration changes could be useful for studying climatic and environmental variability in sulfidic environments

strain partitioning across a subduction thrust fault near the deformation front of the hikurangi subduction margin new zealand a magnetic fabric study on iodp expedition 375 site u1518 abstract understanding the distribution of strain along thrust and splay faults in active accretionary systems is crucial to understand the mechanical properties of the sediments and the strength of the fault zone and its slip behavior this paper investigates the distribution of strain through sediment compaction and texture development across the p paku fault a major splay fault near the deformation front of the hikurangi subduction margin new zealand using the anisotropy of magnetic susceptibility technique ams international ocean discovery program site u1518 penetrated hanging wall fault zone and footwall sequences to a maximum depth of 484 9 meters below seafloor a total of 330 discrete samples was subjected to ams measurements and magnetic remanence data used to reconstruct the axial orientation of each sample in a geographic reference frame the ams display distinct fabric differences between hanging wall through the fault zone and footwall domains demonstrating that strain is partitioned across the fault zone hanging wall sequences show a strike parallel northeasterly lineation of kmax and weakly prolate shapes typical for a component of northeast southwest lateral shortening in contrast footwall sequences are more oblate and show a clustering of kmax in northerly direction this demonstrates that strain in the footwall is dominated by gravitational loading however a component of sub horizontal east westerly strain parallel to the convergence direction of the pacific plate exists strain decoupling between hanging and footwall sequences occurs near the top of the p paku fault zone differences in the degree of magnetic susceptibility between footwall sediments incorporated into the fault zone and the underlying undeformed footwall sequences are indicative for the progressive dewatering of the underconsolidated footwall sequences

magnetic detection and characterization of biogenic magnetic minerals a comparison of ferromagnetic resonance and first order reversal curve diagrams australian research council grant number dp120103952 australia new zealand iodp consortium anzic grant number le0882854

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

isothermal magnetization of samples with stable preisach function a survey of hysteresis remanence and rock magnetic parameters isothermal magnetization curves like hysteresis loops initial curves back field curves acquisition curves and demagnetizing curves of isothermal remanent magnetization are commonly used for rock magnetic purposes in this study we investigate the relations among these curves and other useful magnetization curves saturation initial curve and induced and remanent hysteretic magnetization curves in order to compare coercivity and domain state parameters which can be derived from them most natural samples especially sediments are weakly magnetic and possess relatively stable preisach functions their magnetization states can therefore be described by classical preisach theory this approach verifies well known rules and establishes some formerly unreported relations between isothermal magnetization curves and parameters it is possible to point out sets of mathematically independent isothermal magnetization curves and to state theoretical interrelations between dependent curves by simply inspecting preisach diagrams furthermore we define six elemental isothermal magnetization curves from a general partition scheme of the preisach diagram they can be easily obtained from common measurements and generate all above mentioned curves the experimental applicability of our results is demonstrated for three single domain pseudo single domain multidomain marine sediment samples a physical rationale of the elemental curves reveals favorable properties for the investigation of interaction and domain state as a spin off from the general results a new hysteresis based procedure for the measurement of hcr is presented we also propose an apparently more robust hysteresis derived domain state parameter and a generalized version of the well known r parameter all presented methods can be applied without actually measuring preisach functions

late miocene pliocene asian monsoon intensification linked to antarctic ice sheet growth environmental conditions in one of earth s most densely populated regions east asia are dominated by the monsoon while quaternary monsoon variability is reasonably well understood pre quaternary monsoon variability and dynamics remain enigmatic in particular little is known about potential relationships between northern hemispheric monsoon response and major cenozoic changes in antarctic ice cover here we document long term east asian summer monsoon easm intensification through the late miocene pliocene 8 2 to 2 6 ma and attribute this to progressive antarctic glaciation our new high resolution magnetic records of long term easm intensification come from the late miocene pliocene red clay sequence on the chinese loess plateau we identify underlying mechanisms using a numerical climate model simulation of easm response to an idealized stepwise increase in antarctic ice volume we infer that progressive antarctic glaciation caused intensification of the cross equatorial pressure gradient between an atmospheric high pressure cell over australia and a low pressure cell over mid latitude east asia as well as intensification of the cross equatorial sea surface temperature sst gradient these combined atmospheric and oceanic adjustments led to easm intensification our findings offer a new and more global perspective on the controls behind long term asian monsoon evolution

inconsistent magnetic polarities in magnetite and greigite bearing sediments understanding complex magnetizations in the late messinian in the adana basin southern turkey 1 we present paleomagnetic rock magnetic and scanning electron microscope data from three upper messinian stratigraphic sections from the adana basin southern turkey the collected samples are from fine grained units which were deposited during the messinian salinity crisis within subchron c3r paleomagnetic results reveal an inconsistent polarity record related to a mixture of magnetite and greigite that hinders determination of a reliable magnetostratigraphy three classes of samples are recognized on the basis of paleomagnetic results the first is characterized by a single magnetization component with normal polarity that is stable up to 530 580 c and is carried by magnetite the second is characterized by a single magnetization component with reversed polarity that is stable up to 330 420 c this magnetization is due to greigite which developed after formation of slumps and before tectonic tilting of the studied successions the third is characterized by reversed polarity which is stable up to 530 580 c we interpret this component as a primary magnetization carried by fine grained and magnetically stable detrital magnetite results indicate that in the adana basin the assumption that a primary magnetization is carried by magnetite and a magnetic overprint carried by greigite does not hold because a late magnetic overprint has also been found for magnetite bearing samples our data illustrate the complexity of magnetostratigraphic reconstructions in successions characterized by variable mixtures of magnetic minerals with different magnetic stability that formed at different stages we demonstrate the need to perform detailed magnetic mineralogy analyses when conducting magnetostratigraphic studies of clay rich sediments from marine or lacustrine environments

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

high resolution magnetic and palynological records of the last deglaciation and holocene from lake xiarinur in the hunshandake sandy land inner mongolia high resolution mineral magnetic and pollen records from overlapping piston cores from lake xiarinur 42 37 n 115 28 e document detailed changes in environment and vegetation since the last deglaciation in the hunshandake sandy land inner mongolia the formation of lake xiarinur commenced during the bolling allerod warming as reflected by an abrupt shift in sedimentary facies from eolian sands to lacustrine sediments at a core depth of 3 5 m 14 1 cal kyr bp the pollen records demonstrate that desert vegetation with sparse herbs occurred before 14 1 cal kyr bp which was succeeded by meadow grassland vegetation from 14 1 13 3 cal kyr bp the bolling allerod a dramatic decrease in pollen concentration occurred between 13 3 and 11 7 cal kyr bp corresponding to the younger dryas the remarkable increases in pollen and pediastrum concentrations at 11 7 cal kyr bp suggest that the environment began to ameliorate and the most humid conditions prevailed until 8 5 cal kyr bp the maxima of m

origin of two verwey transitions in different generations of magnetite from the chesapeake bay impact structure usa 1 we observed two different verwey transition temperatures in fragments of crystalline basement rocks and impact sediments from the chesapeake bay impact structure usa our study aims to the question if this feature can be used as shock indicator in impact craters we distinguished three generations of magnetite 1 primary magnetite in crystalline basement rocks has average grain sizes up to several hundreds of micrometers and shows a regular tv at 121 k 2 shocked magnetite occurs in fragments of crystalline basement rocks and also in the suevite and impact breccia these magnetites show two verwey transitions a regular one and a low temperature transition ltv at around 89 k ltv is related to a small grain size fraction whereas a larger grain size fraction some hundreds of micrometers causes the regular tv the small grain size fraction contains a distinctly higher amount of superficially oxidized material due to the high surface volume ratio which causes a decrease of the verwey transition temperature ltv 3 a secondary magnetite generation shows also two verwey transition temperatures one at 121 k and a ltv range between 91 and 105 k the ltv in this generation is also linked to thin oxidized surface layers this study shows that especially the verwey transition temperature of small magnetite grains reacts very sensitively to surface oxidation and can therefore not be used as a reliable pressure indicator for impact structures on earth

low temperature magnetic properties of magnetite using first order reversal curve analysis implications for the pseudo single domain state 1 low temperature magnetic hysteresis properties of nearly stoichiometric magnetite were studied using the first order reversal curve forc technique forc distributions were measured at 20 k after cooling in zero magnetic field or cooling in the presence of a strong 1 5 t magnetic field five polycrystalline samples ranged in mean grain size and shape representing mostly single domain sd pseudo single domain psd and multidomain md magnetic hysteresis behavior the forc distributions measured from psd magnetite after zero field cooling zfc manifest an unusual behavior characterized by two distinct maxima located almost symmetrically with respect to the zero interaction field hu 0 axis on a forc diagram in contrast the low temperature forc distributions for sd and md samples have a single maximum located at the hu 0 axis the appearance of two maxima on low temperature forc distributions is interpreted as a manifestation of a perminvar like behavior due to stabilization of the magnetic domain structure by irregularities of crystalline lattice induced by twinning in monoclinic magnetite the experimental data suggest that the effect of monoclinic twinning on remagnetization is only pronounced within a certain grain size range the double maxima zfc forc distribution appears to be a distinctive property of psd hysteresis behavior which cannot be reproduced by mixing sd and md magnetites

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

east asian monsoon evolution since the late miocene from the south china sea abstract the south china sea scs has become a global focus for paleoclimatic and paleoceanographic studies due to its location which makes it highly sensitive to the east asian monsoon and to pacific ocean changes we present here a refined magnetostratigraphy for the last 6 5 ma for hole u1431d which was recovered during iodp expedition 349 in the central scs magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite bearing layer at 130 5 132 0 meters below sea floor the greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event environmental magnetic results indicate that the east asian summer and winter monsoon were stable from 6 5 to 5 ma the summer monsoon intensified at 5 ma and then weakened gradually since 3 8 ma in contrast the winter monsoon weakened at 5 ma and has then been enhanced since 3 8 ma and more stable from 0 6 ma spectral analysis indicates that the east asian summer monsoon was driven directly by low latitude insolation changes before 3 2 ma and that it has been affected by both low latitude insolation and high latitude ice volume changes since 3 2 ma

variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites implications for relative paleointensity signal recording widespread geological preservation of biogenic magnetite makes it important to assess how such particles contribute to sedimentary paleomagnetic signals we studied a sediment core from the south china sea that passes the strict empirical criteria for magnetic uniformity used in relative paleointensity studies such assessments are based routinely on bulk magnetic parameters that often fail to enable identification of mixed magnetic mineral assemblages using techniques that enable component specific magnetic mineral identification we find that biogenic and detrital magnetites occur in approximately equal concentrations within the studied sediments we analyzed normalized remanence signals associated with the two magnetite components to assess whether co occurring biogenic and detrital magnetites record geomagnetic information in the same way and with the same efficiency paleomagnetic directions for the two components have no phase lag which suggests that the biogenic and detrital magnetites acquired their magnetizations at equivalent times however we find that the biogenic magnetite is generally 2 4 times more efficient as the detrital magnetite in contributing to the natural remanent magnetization nrm despite their approximately equal magnetic contributions variations in the concentration and efficiency of remanence acquisition of the two components suggest that a significant part of the nrm is controlled by nongeomagnetic factors that will affect relative paleointensity recording we recommend that methods suited to the detection of variable recording efficiency associated with biogenic and detrital magnetites should be used on a routine basis in relative paleointensity studies

remanence acquisition efficiency in biogenic and detrital magnetite and recording of geomagnetic paleointensity relative paleointensity rpi variations of earth s magnetic field are widely used to understand geomagnetic field behavior and to develop age models for sedimentary sequences rpi estimation is based on a series of assumptions one key assumption that is rarely considered is that all magnetic particles in the sediment acquired a magnetization in an identical manner in this paper we test this assumption for sediments from the eastern equatorial pacific ocean that record well documented global rpi variations over the last 780 kyr the magnetization is carried by two stable single domain magnetic components which we identify as magnetite magnetofossils and titanomagnetite nanoparticle inclusions within larger silicate particles by analyzing signals carried by the two components separately we determine for the first time that magnetic nanoparticle inclusions can cause their host particles to record reliable but inefficient sedimentary paleomagnetic signals the magnetization carried by biogenic magnetite is acquired more efficiently than that carried by the nanoparticle inclusions variations in the concentration of both components are modulated climatically so that they record nearly identical rpi signals in many sediment types there is no correlation between the concentrations of different magnetic components so that variable remanence acquisition efficiency will complicate rpi recording our work demonstrates that detailed assessment of paleomagnetic recording by each constituent magnetic component needs to become a routine part of sedimentary rpi analysis

magnetic properties and paleointensities as function of depth in a hawaiian lava flow the outcome of paleointensity experiments largely depends on the rock magnetic properties of the samples to assess the relation between volcanic emplacement processes and rock magnetic properties we sampled a vertical transect in a 6 m thick inflated lava flow at hawaii emplaced in 588 ad its rock magnetic properties vary as function of distance from the flow top the observations can be correlated to the typical cooling rate profile for such a flow the top and to a lesser extent the bottom parts of the flow cooled faster and reveal a composition of tm60 in which the magnetic remanence is carried by fine grained titanomagnetites relatively rich in titanium with associated low curie and unblocking temperatures the titanomagnetite in the slower cooled central part of the flow is unmixed into the magnetite and ulvospinel end members as evidenced by scanning electron microscope observation the remanence is carried by coarse grained magnetite lamella tm0 with high curie and unblocking temperatures the calibrated pseudo thellier results that can be accepted yield an average paleointensity of 44 1 2 4 t this is in good agreement with the paleointensity results obtained using the thermal izzi thellier technique 41 6 7 4 t and a recently proposed record for hawaii we therefore suggest that the chance of obtaining a reliable paleointensity from a particular cooling unit can be increased by sampling lavas at multiple levels at different distances from the top of the flow combined with careful preliminary testing of the rock magnetic properties

rock magnetism of hematitic bombs from the araguainha impact structure brazil 1 hematite impact bombs are one of the most striking and enigmatic features of the large araguainha impact structure in central brazil they have both porous or massive textures elongated shapes from 5 to 50 cm in diameter and botryoidal textures that suggest hydrothermal origin some authors have considered these objects as a possible analog of hematite nodules found in mars and consequently related to a hydrothermal system here we report rock magnetic measurements x ray diffraction and mossbauer spectra for both massive and porous samples for a detailed description of the hematite room temperature magnetic measurements including hysteresis loops back field and saturation magnetization acquisition forc as well as x ray diffraction and mossbauer experiments are compatible with both massive and porous types being almost pure hematite room temperature forcs after heating in a he atmosphere show two peaks the original high coercivity peak of hematite and a low coercivity one probably maghemite at the bc and bb origin thus indicating significant modification of the magnetic mineralogy of the material during thermal treatment in reducing conditions however conditioning in an oxidizing environment heating in air seemed to block generation of this low coercivity material in subsequent heating in a reducing ar atmosphere therefore we conclude that this material was not heated greatly in its generation this would not be likely for impact ejected bombs so origin from post impact hydrothermal activity seems likely

low temperature cycling of isothermal and anhysteretic remanence microcoercivity and magnetic memory abstract this paper reports low temperature cycling ltc through the verwey transition of anhysteretic remanence arm partial arms and partially demagnetised saturation isothermal remanence sirm induced at room temperature in pseudo single domain and multidomain md magnetite the remanences were cooled in zero field to 50 k and then heated back to room temperature by inducing partial arms over different field ranges and by partially alternating field demagnetising sirms it was possible to isolate both low coercive force and high coercive force fractions of remanence on cooling through the verwey transition a sharp increase in the remanence was observed the relative size of the jump increased as the high coercive force fraction was increasingly isolated this behaviour is interpreted as being due to both an increase in the single domain multidomain threshold size on cooling through the verwey transition and to the reduction or elimination of closure domains in the low temperature phase in addition the memory ratio i e the fraction of remanence remaining after ltc divided by the initial remanence was found to be higher for the high coercive force fraction than the low coercive force fraction in our interpretation the high coercivity fraction behaviour is associated with reversible domain re organisation effects whilst the low coercive force fraction s behaviour is associated with irreversible domain re organisation and de nucleation processes due to the decrease in magnetocrystalline anisotropy on cooling to the verwey transition the high coercive force fraction is likely to be magnetoelastically controlled thus a rock displaying high coercive force behaviour is likely to carry a palaeomagnetically meaningful remanence with high unblocking temperatures in addition ltc analysis can be used to identify the domain state dominating the natural remanence in magnetite bearing rocks

revisiting a domain state independent method of palaeointensity determination abstract the use of a domain state independent method the wilson method of acquiring absolute palaeointensities is tested using three sets of historical lavas from mexico italy and iceland the wilson method works by plotting continuous thermal demagnetisation curve data for the original natural remanent magnetisation against those for a laboratory induced thermoremanence by comparing the predicted intensities with the known fields a new empirically derived rejection criterion is proposed that accounts for chemical alteration and improves the accuracy of the palaeointensity estimates the wilson palaeointensity estimates are compared with palaeointensity determinations made on sister samples using standard thellier type heating generally the wilson palaeointensity estimates compare favourably for samples that yielded technically correct thellier type determinations however at one locality the wilson method did not yield any estimates due to severe chemical alteration in contrast it was still possible to determine palaeointensity estimates from the lower temperature thellier data to assess the wilson palaeointensity protocol s ability to return a correct estimate for a true multidomain system a synthetic multidomain magnetite sample was imparted with a thermoremanent magnetisation the wilson protocol returned the correct palaeointensity within error in contrast the thellier type protocol failed as the wilson method is significantly faster than thellier type methods it is suggested that the wilson method should be tried as a first approach in palaeointensity studies or for samples dominated by multidomain material

magnetic mineral dissolution recorded in a lacustrine sequence from the heqing basin sw china and its relationship with changes in the indian monsoon abstract the dissolution of magnetic oxides is an important process in many lake environments understanding this phenomenon is crucial for the paleoenvironmental interpretation of the magnetic properties of lake sediments in order to reveal its effects on sedimentary magnetic properties and to assess the possible associated paleoenvironmental implications we carried out detailed rock magnetic analyses of the selected samples from a 920 kyr lacustrine sequence from the heqing basin sw china the results indicate that the sedimentary magnetic properties are controlled by the concentration and grain size of magnetite and maghemite high magnetic susceptibility intervals contain more fine grained magnetite and maghemite while low intervals contain only minor amounts of residual magnetite the decreased content of fine grained maghemite from high to low intervals reflects the dissolution of magnetic oxides during deposition intervals affected by strong magnetic dissolution have a high toc content and correspond to times of high antarctic temperatures suggesting that magnetic mineral dissolution intensity was associated with variations in the strength of the indian summer monsoon ism notably the ism is sensitive to southern hemisphere warming weak magnetic dissolution indicates a dry climate occurred since 320 kyr in the heqing basin this dry cool event was widespread across the eastern bay of bengal equatorial indian ocean and northern australia and was linked to a strengthened indian ocean dipole iod since the moisture source of the heqing basin was mainly from the above regions we infer that the influence of the iod extended northwards to sw china

impact of climate change on the magnetic mineral assemblage in marine sediments from izu rear arc nw pacific ocean over the last 1 myr abstract a rock magnetic study was conducted on upper pleistocene marine sediments from international ocean discovery program expedition 350 site u1437 in order to highlight the paleoenvironmental changes in the nw pacific ocean influenced by the east asian monsoon regime remanent magnetization analyses hysteresis properties first order reversal curves and low temperature magnetic measurements were carried out along with electron microscope observations the results indicate that coarse grained titano magnetite is the dominant magnetic phase in the magnetic mineral assemblage time series analysis supports that this assemblage is modulated by global climate changes over the last 1 myr during the interglacial stages magnetic minerals are more abundant and are dominated by coarse grained titano magnetite of both terrigenous likely from mainland china and volcanic izu arc front japan origin during the glacial stages the magnetic mineral content is lower probably reflecting partial dissolution of ti magnetite and the magnetic assemblage is composed of terrigenous coarse grained titano magnetite and of higher coercivity presumably finer eolian particles likely hematite as a result of the enhancement of the winter monsoon in continental asia the magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals bulk organic geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods additional x ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources

micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system 1 chondrules in chondritic meteorites record the earliest stages of formation of the solar system potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions using first order reversal curves forcs we map the coercivity distributions and interactions of 32 chondrules from the allende karoonda and bjurbole meteorites distinctly different distributions and interactions exist for the three meteorites the coercivity distributions are lognormal shaped with bjurbole distributions being bimodal or trimodal the highest coercivity mode in the bjurbole chondrules is derived from tetrataenite which interacts strongly with the lower coercivity grains in a manner unlike that seen in terrestrial rocks such strong interactions have the potential to bias paleointensity estimates moreover because a significant portion of the coercivity distributions for most of the chondrules is 10 mt low coercivity magnetic overprints are common therefore paleointensities based on the rem method which rely on ratios of the natural remanent magnetization nrm to the saturation isothermal remanent magnetization irm without magnetic cleaning will probably be biased the paleointensity bias is found to be about an order of magnitude for most chondrules with low coercivity overprints paleointensity estimates based on a method we call remc which uses nrm irm ratios after magnetic cleaning avoid this overprinting bias allende chondrules which are the most pristine and possibly record the paleofield of the early solar system have a mean remc paleointensity of 10 4 mt karoonda and bjurbole chondrules which have experienced some thermal alteration have remc paleointensities of 4 6 and 3 2 mt respectively

magnetic mineral dissolution in pleistocene fluvio lacustrine sediments nihewan basin north china abstract the nihewan fluvio lacustrine sequence north china has recorded late pliocene pleistocene climatic and environmental changes and contains valuable information on early human evolution in high latitude east asia we carried out a combined mineral magnetic and geochemical investigation on a sequence from the xiantai section eastern nihewan basin results suggest that large amplitude magnetic property variations between so called high magnetic and low magnetic units mainly result from preservation dissolution cycles of detrital magnetic minerals in alternating oxic and anoxic depositional environments in our preservation dissolution model the high and low magnetic units represent glacial and interglacial deposits respectively this contributes to a better understanding of the link between magnetic properties and climate in the xiantai fluvio lacustrine sequence based upon this relationship early humans may have occupied the xiantai and xiaochangliang sites during an interglacial period during both interglacial and glacial periods at the donggutuo site and during a glacial period at the maliang site our work provides a paleoenvironmental context for early human adaptation and occupation in mainland east asia during the early pleistocene

a geomagnetic paleointensity record of 0 6 to 3 2 ma from sediments in the western equatorial pacific and remanent magnetization lock in depth

magnetic characteristics of synthetic pseudo single domain and multi domain greigite fe3s4 1 we report the magnetic properties of pure synthetic pseudo single domain psd and multi domain md greigite and the grain size dependence of the magnetic properties of greigite for the first time the dominantly psd like and md like behavior are demonstrated by hysteresis first order reversal curve diagrams low temperature cycling ltc of room temperature saturation isothermal remanent magnetization sirm and low temperature sirm warming curves variations in a range of magnetic properties clearly correlate with grain size characteristic psd md behavior is preserved at low temperatures which coupled with the small decrease in remanence during warming rule out the presence of substantial superparamagnetic behavior in the studied samples ltc sirm measurements indicate a continuous demagnetization of remanence during cooling knowledge of this expanded range of magnetic properties of greigite should be widely useful in environmental magnetic and paleomagnetic studies