some rock magnetic properties of mid cretaceous basalts from israel and india rajmahal traps and their bearing on palaeointensity experiments abstract a wide range of rock magnetic properties have been determined from two collections of mid cretaceous basalts one from israel the other from the rajmahal traps in northeast india deuteric oxidation is rare in both collections with titanium rich titanomagnetite being the principal remanence carrier in most cases there are a number of differences in rock magnetic properties between the two groups some of these seem to be primary whereas others appear to be caused by hydrothermal alteration and weathering which are more prevalent in the indian rocks these rocks are being used in palaeointensity experiments from which it is hoped to determine the strength of the earth s magnetic field during the long period of normal polarity in the mid cretaceous thellier palaeointensity experiments have been performed on two samples from each site the degree of agreement between the two results is highly variable the low blocking temperatures and the presence of secondary viscous components in many samples make thellier palaeointensity experiments very difficult a further problem is that of thermal alteration two main types of which are observed the first manifests itself as a large and sudden increase in partial thermoremanent magnetization ptrm capacity and the second as a steady decrease in the size of ptrm with increasing temperature

precipitation regime of dronning maud land antarctica derived from antarctic mesoscale prediction system amps archive data 1 the precipitation regime of dronning maud land dml antarctica was studied using antarctic mesoscale prediction system amps archive data precipitation is the most important component of the mass balance of the antarctic ice sheet precipitation studies of dml are particularly important because two deep ice core drilling sites kohnen station and dome fuji are located in this region for the correct interpretation of the ice core properties a thorough understanding of the precipitation regime is necessary we used the high resolution amps archive data for the years 2001 2006 to investigate the temporal and spatial distribution of precipitation the results were compared to a recently published mass balance map derived from glaciological data of western dml the mass balance map and the amps mean annual precipitation field show fairly similar patterns which are mostly related to topography and prevailing wind systems precipitation is found to generally decrease from the coast to the inland plateau along the escarpment between the low altitude coastal areas and the interior plateau local minima and maxima in precipitation correspond to the leeward and windward sides of topographical ridges interannual variability of monthly sums of precipitation is fairly high owing to the influence of cyclone activity on precipitation which affects not only the coastal regions but also the interior of the continent more than previously thought

a comparison of archaeointensity results from chinese ceramics using thellier s and shaw s palaeointensity methods summary a collection of chinese ceramics covering the time period 2700 7500 bp has been investigated using adaptations of both the thellier thellier 1959 and shaw 1974 palaoeintensity techniques several rock magnetic techniques were used to investigate the magnetic properties of the samples and on the basis of these measurements some samples were rejected because of their poor magnetic behaviour anisotropy of magnetic susceptibility ams thermo remanent magnetization trm and anhysteretic remanent magnetization arm were investigated based on the relationship between arm and trm anisotropy modified arms were used for anisotropy correction twenty samples were studied using the shaw method and 34 were studied using the thellier method an acceptable agreement between the results from the two methods was found general features of the secular variation of geomagnetic intensity determined from the present study are consistent with those of the global model of mcelhinny senanayake 1982

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

a palaeomagnetic study of jurassic intrusives from southern new south wales further evidence for a pre cenozoic dipole low the results of rock magnetic thermal demagnetization and thellier palaeointensity studies are presented for two high level intrusions from southern new south wales australia the gingenbullen dolerite gb 34 5 s 150 3 e and the gibraltar microsyenite gs 34 5 s 150 4 e were emplaced during the second of three major phases of igneous activity that affected the southern sydney basin and are k ar dated at 172 and 178 ma respectively the magnetic mineralogy of the two intrusions is different the gb is dominated by single domain sd pseudo single domain grains of magnetite whereas the gs has both sd magnetite and haematite components although the haematite component does not record a stable remanence the gb records two opposed components of magnetization above 100 c occupying distinct parts of the blocking temperature spectrum the lower blocking temperature lbt component resides between 150 and 400 c and is of normal polarity having a mean direction of d i 021 79 95 8 k 63 with a corresponding vgp at lat long 54 s 137 e dp 12 dm 13 this component is believed to be a tcrm or tvrm related to the initial opening of the tasman sea at 90 ma the higher blocking temperature hbt chrm component is recognized between 450 and 580 c and is of reverse polarity with a mean direction of d i 174 81 95 11 k 33 and a corresponding vgp at lat long 52 s 153 e dp 17 dm 18 the chrm for the gs resides in the 100 450 c region and although the scatter is high has a similar mean direction d i 167 79 95 24 k 26 to the hbt component of the gb with a pole position at lat long 54 s 158 e dp 30 dm 31 there is no evidence of the gb lbt component in samples from the gs suggesting that this intrusion was magnetically unaffected by the later event which is also seen for other intrusions in the sydney basin the vgps calculated from the chrm directions both plot on the jurassic segment of the australian apwp dunlop et al 1997 providing further palaeomagnetic confirmation for the k ar ages thellier palaeointensity results were of variable quality as expected for rocks of this age the mean vdm values calculated for the chrms of the gb and gs were 1 3 1022 and 4 1 1022 am2 respectively approximately 16 and 51 per cent of the present value on application of a cooling rate correction estimate the gb result falls to a minimum of 0 87 1022 am2 approximately 11 per cent of the present day value representing an overestimate of up to 56 per cent these values arising from a time window previously lacking in thellier estimates provide further confirmation of the existence of a pre cenozoic dipole low the vdm values derived from the overprint in the gb samples yield an average of 4 8 1022 am2 from a range between 44 and 81 per cent of the present day mean vdm and are tentatively attributed to the cretaceous normal superchron cns these results may document evidence for a previously unrecognized low dipole moment during the bulk of the cns a possibility that requires further investigation by performing palaeointensity work on igneous rocks with radiometric ages between 110 and 90 myr that carry unequivocal primary trms

genesis of the jurassic dongfengbeishan porphyry mo deposit in eastern yanbian ne china inferred from molybdenite re os and zircon u pb ages and whole rock elemental and zircon hf isotopic compositions abstract the dongfengbeishan porphyry mo deposit is located to the southeast of the lesser xing an range zhangguangcai range metallogenic belt in ne china la icp ms zircon u pb dating of the beishan monzogranite yields an age of 194 75 0 81 ma five molybdenite samples define a re os isochron age of 194 0 2 0 ma suggesting that mineralization was associated with emplacement of the beishan monzogranitic pluton monzogranite samples are classified as high k calc alkaline and are relatively enriched in light rare earth elements depleted in heavy rare earth elements nb ba p sr ti and zr and yield negative eu anomalies these characteristics are interpreted to record fractional crystallization of the parental magmas zircon ehf t values for beishan monzogranite samples range from 8 2 to 15 9 and two stage model ages tdm2 range from 217 to 711 ma indicating that the parental magma was produced during partial melting of juvenile lower crust combined with previous studies our data suggest that the dongfengbeishan porphyry mo deposit was associated with westward subduction of the paleo pacific plate in the early jurassic

palaeosecular variation in central mexico over the last 30 000 years the record from lavas summary 13 lava flows of known age ages from i4c dating which have been erupted in the last 30000 years have been studied to determine the palaeosecular variation of the geomagnetic field in central mexico samples were taken from two different monogenetic volcanic fields the michoacan guanajuato volcanic field six sites and the chichinautzin formation seven sites both part of the transmexican volcanic belt the lavas were studied in detail using rock magnetic methods magnetic susceptibility at room temperature low temperature susceptibility behaviour hysteresis loops curie temperatures combined with reflected light microscopy in order to deduce their magnetic mineralogy and the domain states of the magnetic minerals the magnetic carriers are titanomagnetites which show differing degrees of high temperature deuteric oxidation and seem to be predominantly pseudo single domain psd though in many cases are probably a mixture of domain states mean palaeomagnetic directions and palaeointensity values using shaw and thellier techniques were obtained using several specimens from each flow our data seem to indicate a sharp easterly swing in declination about 5000 years ago which is also observed in lake sediments from central mexico the calculated values of the virtual dipole moment vdm range from 3 1 to 14 9 x a m2 our data indicate that the virtual dipole moment seems to have increased gradually in magnitude over the last 30 kyr with a peak at about 9000 years bp these are features that have been observed in other parts of the globe and are probably caused by variations in the dipole part of the geomagnetic field

environmental signals in a highly resolved ice core from james ross island antarctica 1 the accumulation isotopic and chemical signals of an ice core from james ross island antarctica are investigated for the interval from 1967 to 2008 over this interval comparison with station satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice accumulation at james ross island is enhanced during years when the circumpolar westerlies are weak allowing more precipitation events to reach the northeastern antarctic peninsula the stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope temperature gradient across antarctica and preserves information about both summer and winter temperature variability in the region sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of james ross island and transported to the site by strengthened northerly and westerly winds in the winter a strong covariance with temperature means that the sea salt record may be able to be utilized in conjunction with the isotope signal as an indicator of winter temperature marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of james ross island this source region may have become significant only in recent decades when the collapse of nearby ice shelves established new sites of open water with high summer productivity these findings provide a foundation for interpreting the environmental signals in the james ross island ice core which extends though the whole holocene and represents the oldest ice core that has been recovered from the antarctic peninsula region

palaeointensity results for historic lavas from mt etna using microwave demagnetization remagnetization in a modified thellier type experiment summary the bane of conventional thellier type palaeointensity experiments is the thermal alteration of the samples during experimentation however high frequency microwaves can be used to stimulate the magnetic minerals directly thus eliminating the need for the bulk sample to be heated walton et al 1993 the microwave technique has been successfully applied to ceramics shaw et al 1996 1999 and here we present results for historic lavas from mt etna sicily 20 samples were randomly selected from 10 diverent historic flows dating from 1843 to 1983 hysteresis parameters were monitored as a check for alteration during experimentation and minimal alteration was found rock magnetic analysis and af plus microwave demagnetizations were carried out on all samples and microwave intensity analysis was carried out on those samples that were stable to microwave demagnetization 16 in total with one exception all samples gave high quality intensity results two or three subsamples from each sample were investigated and a weighted average calculated to give a single estimate of the field when the intensity values were compared with the sv model based on direct observatory measurements bloxham gubbins 1985 it was found that those samples that contained a high multidomain md component gave intensity values around 20 per cent lower than expected this can be explained by the cooling rate evect dodson mcclelland brown 1980 and or the presence of an md component mcclelland et al 1996 those samples with the lowest numbers of md grains gave field values which within error were the same as those for the model or slightly too high this is compatible with the cooling rate evect

the kamikatsura event and the matuyama brunhes reversal recorded in lavas from tjornes peninsula northern iceland abstract we report paleomagnetic results from four overlapping stratigraphic sections 55 flows through the lava pile in tjornes peninsula north iceland the initial aim of our study was to check the existence of intermediate directions previously interpreted as belonging to the matuyama brunhes geomagnetic reversal mbr and complete this record with thellier thellier paleointensity determinations and 40ar 39ar radioisotopic dating the directional results corroborate the findings by kristjansson et al 1988 a sequence of reversed transitional normal and transitional polarity r t n t is found in each section the polarity change is characterized by a jump from reversed virtual geomagnetic poles vgps to a quasi cluster of transitional vgps located over china followed by a second jump to a cluster of normal polarity before moving again towards intermediate polarities reversely magnetized flows exhibit a magnetic mineralogy well suited for paleointensity determination of these 25 flows 20 yielded paleointensity estimates of good quality unfortunately the systematic presence of coarse multidomain md titanomagnetite in the transitional and normal polarity flows hampered paleointensity estimates for these flows the virtual dipole moments vdm calculated for the reversed polarity flows vary from 4 9 to 7 0 1022 am2 with an arithmetic mean value of 5 5 0 8 1022 am2 this value is identical to the mean vdm obtained for the 0 3 5 ma time window and thus strengthens the conclusion that the recent geomagnetic field strength is anomalously high compared to that older than 0 3 ma 40ar 39ar isochron ages were obtained with the incremental heating technique on groundmass separates or phenocryst poor whole rock samples six of the transitionally magnetized lavas yielded isochron ages that are indistinguishable from one another at the 95 confidence level the weighted average age is 862 51 ka in the upper part of this volcanic sequence the normally magnetized flows yielded a weighted average age of 787 40 ka this finding supports the conclusion that a geomagnetic excursion within the matuyama chron is recorded in the lower part of the tjornes volcanic sequence whereas only the latest portion of the mbr is recorded by flows in the upper part of the lava pile this conclusion is supported via comparison of the vgps obtained from the lavas with those predicted by a geomagnetic field model

mid holocene palaeolimnological record of a southern hemisphere subtropical lake spanning the last 6000 years lake jennings fraser island australia the study of climate mechanisms in the southern hemisphere during the holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of northern hemisphere research the subtropical temperate climate transition zone of eastern australia provides a unique location to investigate long term environmental changes during the holocene lake jennings on fraser island was used to investigate climate change in this transition zone using palaeolimnological techniques the beginning of the lake jennings record 6000 to 3500 cal ybp is characterised by fluctuations in geochemical signals an abundance of sponge spicules and a lack of diatom species results suggest gradually increasing precipitation and water depth which affect nutrient cycling however the biological functioning of the lake is difficult to interpret due to the absence of diatoms possibly a result of turbidity dissolution and or predation by freshwater sponges during the late holocene 3500 cal

characteristic magnetic behavior of subaerial and submarine lava units from the hawaiian scientific drilling project hsdp 2 1 this study presents rock magnetic properties and the magnetic mineralogy of subaerial and submarine lava flows of mauna loa and mauna kea volcanoes collected from the 3109 m deep hsdp 2 drill hole in hawaii three different groups of magnetic behavior are recognized in the subaerial lava flows related to the degree of high temperature oxidation during extrusion group 1 shows homogenous titanomagnetite with low xmt low curie temperatures tc 100 200 c and weak median demagnetizing fields 20 mt further subdivision into 1a and 1b subgroups is based on the low temperature behavior of magnetic susceptibility ms and hysteresis loops which indicate a contribution from ferrimagnetic cr al spinel below ca 160 c in the 1b type samples group 2 samples with exsolution lamellae of ilmenite in the titanomagnetites have higher tc 480 580 c and higher coercive forces 20 40 mt group 3 the highest oxidation stage is characterized by titanohematite bearing assemblages with enhanced median demagnetizing fields 35 85 mt and a significantly different low temperature ms behavior ms core logging shows a systematic variation occurs in the subaerial lava flows directly related to the degree of high temperature oxidation and their flow morphology aa lava flows have higher mean ms than other lava flow types besides these factors ms appears to be also affected by the magma composition of the various shield building stages mauna loa subaerial lava flows generally show lower mean susceptibilities 4 6 3 10 3 si than subaerial mauna kea lava flows 9 8 5 10 3 si as submarine lava flows show no group 3 assemblages no high temperature oxidation influenced these rocks some hyaloclastites and pillow breccias show low ms 1 10 3 si small amounts of nearly pure magnetite tc 580 c and high coercive forces up to 110 mt suggesting single domain and or superparamagnetic behavior the controlling mechanism of the magnetic properties in the submarine lava units is the cooling and quenching rate of lava flows which creates large grain size variations in titanomagnetites of varying compositions hydrothermal alteration as described from ocean floor or icelandic basalts is not an important process that influences the magnetic properties in the ocean island basalts from the hsdp 2 drill hole

magnetic history of a dyke on mount etna sicily summary during the 1989 eruption of mount etna two fracture systems trending c n45 e and n150 e opened at the foot of its 3000 m high se crater and propagated quickly downslope to distances of 3 and 7 km respectively the northeastern fracture fed a flank eruption whereas the southeastern fracture remained dry and overed contrasting volcanological and geophysical evidence of the presence of magma at a shallow depth during the opening of this non eruptive fracture system a diverential magnetic network was set up on a short profile across its distant extremity initially the magnetic field did not display any change along the profile between frequent surveys however repeated measurements at intervals of about 3 months for two years revealed the slow build up of a 130 nt anomaly the anomaly vanishes laterally within 0 2 km of the surface expression of the fracture system this exceptional set of observations constrains the location and time of cooling of a shallow dyke the increase in magnetization of the dyke inferred by the rate of growth of the anomaly leads to the interpretation that the dyke was emplaced near the end of the eruption

a rock and paleomagnetic study of a holocene lava flow in central mexico abstract magnetic measurements of the tres cruces lava flow ca 8500 years bp central mexico show the presence of two remanence carriers a ti rich titanomagnetite with a curie temperature between 350 and 400 c and a ti poor magnetite with a curie temperature close to 580 c magnetic changes after heating indicate that the titanomagnetite exsolves into magnetite and ilmenite when the sample is heated to 580 c paleointensity estimates with the thellier and thellier method thellier e thellier o 1959 sur l intensite du champ magnetique terrestre dans le passe historique et geologique ann geophysique 15 285 376 were only successful up to temperatures of 350 to 400 c this temperature corresponds with the curie temperature of the titanomagnetite which is probably pseudo single or multi domain therefore the paleointensities should be interpreted with caution the magnetic composition changes after 580 c heating may explain the large variations in previous paleointensity determinations for the tres cruces rocks gonzalez s sherwood g bohnel h schnepp e 1997 palaeosecular variation in central mexico over the last 30 000 years the record from lavas geophys j int 130 201 219 using the shaw method shaw j 1974 a new method of determining the magnitude of the palaeomagnetic field application to five historic lavas and five archaeological samples geophys j r astr soc 39 133 141

permo carboniferous kiaman palaeointensity results from the western bohemian massif germany summary thellier palaeointensity analyses were carried out on samples from three quartz porphyry intrusions located within the western part of the bohemian massif close to the german czech republic border these intrusives have been dated at 28 275 ma which places them in the main part of the permo carboniferous kiaman reversed superchron p crs this age is consistent with the mean characteristic remanence direction calculated at d z 204 1 giving a vgp at 36 n 341 e palaeointensity values range from 6 6 pt to 22 1 pt with a mean value of 12 0 1 3 pt which has a corresponding vdm value of 3 0 i 1 2 x loz2 a m2 this suggests that the geomagnetic field strength recorded by the quartz porphyries is only 37 per cent of the current value supporting recent studies that report a field strength of between 25 and 40 per cent of the present day value during the p crs

a palaeomagnetic study of the basal gneiss region and jotun nappe complex central southern scandinavian caledonides summary in the southern sector of the scandinavian caledonides a metamorphic gneiss complex the basal gneiss region or bgr underthrusts a nappe complex of precambrian granulites the jotun nappe in an assemblage collectively recording orogenic events culminating in the scandian upper silurian and lower devonian episode palaeomagnetic study of a large regional sample spanning the combined outcrop identifies properties strongly controlled by metamorphic retrogression to amphibolite and greenschist facies low blocking temperature ibt components in the bgr have e directions with a mean of d 69 1 60 n 19 sites 95 7 0 sporadic higher blocking temperature components define a dual polarity northeast negative southwest positive ne sw axis with a mean of d 42 1 24 20 sites 95 8 1 granulite facies rocks in the jotun nappe yield a high quality palaeomagnetic record reflected in high lqn values and dominated by medium and high blocking temperature hbt components a dual polarity a axis defines a palaeofield migration from ne to e during uplift and cooling of this terrane with a predominance of normal polarities a smaller population of ibt b components show e directions distributed along the mesozoic palaeofield migration path for eurasia and probably acquired during brittle tectonic events of this age a magnetizations from 86 sites define mean south pole positions between 301 e 2 n and 325 e 10 s linked to uplift related cooling following the climactic scandian orogenic episode and dated at 420 400 ma from the collective geological and radiometric evidence both the outward and return segments of an apw loop may be represented the polar swathe correlates with i a higher blocking temperature component from the bgr ii the uplift magnetization record in the western orthotectonic caledonides of scotland and iii primary magnetizations from the siluro devonian molasse facies in britain this study shows that the westerly extension of the apw path identified by british siluro devonian data is not peculiar to that crustal segment but applies to continental europe and presumably to laurentia as well the pattern of remanence acquisition within the caledonides suggests contrasting zones of thermal and thermochemical remanence with the latter probably linked to fluid migration consequent upon orogenic loading

a doubling in snow accumulation in the western antarctic peninsula since 1850 1 we present results from a new medium depth 136 metres ice core drilled in a high accumulation site 73 59 s 70 36 w on the south western antarctic peninsula during 2007 the gomez record reveals a doubling of accumulation since the 1850s from a decadal average of 0 49 mweq y 1 in 1855 1864 to 1 10 mweq y 1 in 1997 2006 with acceleration in recent decades comparison with published accumulation records indicates that this rapid increase is the largest observed across the region evaluation of the relationships between gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong temporally stable and positive relationship with the southern annular mode sam furthermore the sam is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site r 0 66 the association between gomez accumulation and enso is complex while sometimes statistically significant the relationship is not temporally stable thus at decadal scales we can utilise the gomez accumulation as a suitable proxy for sam variability but not for enso

high field intensity results from recent and historic lavas a total of 45 recent and historic lava flows of mount etna sicily were sampled to investigate changes in the strength and orientation of the geomagnetic field in the region of the flows sampled 11 yielded one or more samples which provided anomalously high field intensity results a rock magnetic study has shown that a high resistance to alternating field demagnetization and group 2 low temperature susceptibility behaviour are the two factors common to these samples

a microcomputer controlled system for low temperature magnetic susceptibility measurements the change in magnetic susceptibility of basalts between liquid nitrogen and room temperatures can be used to distinguish three groups characterised by differences in iron oxide content senanayake and mcelhinny a microcomputer interface has been built that allows a bartington msi susceptibility meter to be operated remotely and measurements of temperature and susceptibility to be made automatically by an acorn atom bbc b or apple microcomputer when used in conjunction with a water jacket the system is able to make measurements of low temperature susceptibility under programme control

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

numerical simulation of stress induced piezomagnetic fields at etna volcano summary 3 d magneto elastic models based on finite element method fem have been developed to compute piezomagnetic fields caused by magmatic overpressure sources we solved separately i the elastostatic equation for the stress field and ii the coupled poisson s equation for magnetic potential field the numerical computations were focused on a more realistic modelling of etna volcano where remarkable magnetic changes have been observed during eruptive events we evaluated the effects of topography and medium heterogeneities considering different multilayered crustal structures constrained by seismic tomography and geological evidences when topography and magneto elastic heterogeneities are included in the numerical models the piezomagnetic field changes show significant deviations from the homogeneous half space solution generally it was found that the analytical model overestimates the expected magnetic changes the numerical models of the piezomagnetic field showed significant differences in presence of strong magnetization contrasts and in proximity of steep cliffs that is at the volcano summit the fem approach presented here allows considering a picture of a fully 3 d model of etna volcano which could advance the reliability of model based assessments of magnetic observations

a palaeointensity study of lower carboniferous transitional geomagnetic field directions the cockermouth lavas northern england palaeomagnetic and palaeointensity results are reported from a thin succession of lavas erupted in lower carboniferous times ca 355 ma in northern england characteristic magnetisations were apparently acquired at the time of eruption but the stable normal field direction is recovered from only two sites out of seven the remainder are not compatible with younger overprinting and are interpreted as thermo remanent magnetisations trms recording transitional fields palaeointensity studies employing the shaw method identify main field intensities averaging 20 8 t within the range of estimates of the lower carboniferous field intensity from studies elsewhere in contrast the lavas recording transitional field directions yield palaeointensity estimates which fall mostly between 10 and 20 of this value hence it is inferred that palaeozoic field inversions were like recent examples characterised by a general decline in the intensity of the field

alteration of magnetic minerals and its effect on the nrm of deccan trap flows of the narmada region india magnetic and geochemical investigations have been carried out on suites of deccan lava flows from both sides of the river narmada multidomain magnetite is more abundant in the flows on the southern side than among the northern ones flows from south of the river seem to have absorbed more water than those on the northern side possibly well after their emplacement multidomain magnetite bearing samples shattered often into pieces when standard cores of these were heated to a temperature beyond 570 k and several such samples lost their primary nrm direction

a palaeomagnetic study of a caledonian ophiolite summary a total of 89 sites have been sampled for palaeomagnetic studies from the caledonian ophiolite complex of northeast shetland 60 7dn 359 2de and a post ophiolite emplacement suite of lamprophyre dykes of these only 35 sites from the ultramafite facies of the complex yielded statistically significant results these sites define three distinct populations of magnetization directions which correspond to south palaeomagnetic poles at 47 2ds 244 2de a 18 0ds 323 4de b and 35 0ds 351 1de c of these only the c remanence can be assigned an unambiguous age of mid carboniferous the ages of the other two poles remain ambiguous due to the uncertainty in the apw path and the complexity of the ophiolite history nevertheless palaeomagnetism is shown to be successful in detecting low temperature low pressure alteration events that have affected the complex and which hitherto have gone undetected

molybdenite re os and u pb zircon dating and genesis of the dayana w mo deposit in eastern ujumchin inner mongolia abstract the dayana w mo deposit in eastern ujumchin of inner mongolia is a quartz vein type deposit in the mid western part of the central asian orogenic belt caob biotite monzogranite quartz porphyry and hornfels host w mo in quartz veins based on spatial relationships molybdenite was deposited first followed by wolframite this contribution presents precise laser ablation inductively coupled plasma mass spectroscopy la icp ms u pb zircon dating and geochemical analysis of the biotite monzogranite the u pb dating shows that the monzogranite is 134 1 ma major and trace element geochemistry shows that the monzogranite is characterized by high sio 2 and k 2 o contents a right inclined shape of the chondrite normalized ree patterns enrichment of large ion lithophile elements liles and depletion of high field strength elements hfses such as nb p ba the monzogranite is high k calc alkaline has a strong negative eu anomaly eu eu 0 04 0 45 low p 2 o 5 content high a cnk of 1 2 enriched in large ion lithophile elements liles such as rb th u nd and hf and notably depleted in ba sr p ti and nb these characteristics define the dayana monzogranite as a highly fractionated peraluminous granite re os isotopic analysis of seven molybdenite samples from the deposit yield an isochron age of 133 3 ma mswd 2 2 which indicates that the monzogranite and ore have the same age within error are probably genetically related and related to a major early cretaceous mineralizing event in china known as the yanshanian

indian ocean dipole influence on south american rainfall 1 the rainfall anomalies over south america are found to be influenced by the indian ocean dipole iod between subtropical la plata basin and central brazil the iod excites a dipolar pattern in rainfall anomalies rainfall is reduced enhanced over latter former during austral spring when iod reaches its peak phase a rossby wave train extends from the subtropical south indian ocean to the subtropical south atlantic the associated anomaly in surface circulation suggests an intensification of the south atlantic high the anomalous anticyclone in the lower troposphere causes anomalous divergence convergence of moisture over central brazil subtropical la plata basin these results based on the university of delaware precipitation analysis and the ncep ncar reanalysis data are corroborated by that of the scale interaction experiment frontier version 1 sintex f1 coupled general circulation model

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

magnetic properties of a columnar basalt from central mexico the variation of low field magnetic susceptibility with low temperature between 77 k and 300 k observed for a vertical columnar basalt from central mexico shows a rare pattern for continental basalt i e susceptibility decreases with temperature to about 40 70 of room temperature value and then increases up to about 60 100 at 77 k these results combined with other rock magnetic measurements including af and thermal demagnetization irm experiments lowrie fuller tests thermomagnetic analysis and optical and sem observations suggest the presence in the columnar basalt of predominantly single domain and pseudo single domain titanomagnetites with composition around tm60 and a small amount of very fine grained particles

mineralogy fluid inclusions and s pb h o isotopes of the erdaokan ag pb zn deposit duobaoshan metallogenic belt ne china implications for ore genesis abstract the recently discovered erdaokan ag pb zn deposit is located in the duobaoshan gold copper metallogenic belt in the eastern part of the central asian orogenic belt the ore bodies occur mainly as veins hosted in the breccia three stages of mineralization including early magnetite quartz pyrite middle silver sulfide bitumen quartz and late carbonate stages were recognized here we report results from electron microprobe analysis epma s pb h o isotopes and fluid inclusions studies to gain insights into the salient characteristics of the ore mineralization and mechanism of silver precipitation the silver occurs mainly as argentite pyrargyrite and invisible silver in the tetrahedrite grains in which ag fe and as isomorphically substituted cu zn and sb respectively the homogenization temperatures of fluid inclusions in the early middle and late stage mineralisation range from 96 to 179 c 78 to 178 c and 98 to 191 c respectively the fluid salinities vary from 0 35 to 5 54 wt nacl equiv the 34s values of the pyrite and galena show a range from 0 97 to 9 31 206pb 204pb vary from 18 0125 to 18 1864 207pb 204pb from 15 561 to 15 081 and 208pb 204pb from 38 0445 to 37 6979 with a mean of 18 0298 15 5125 and 37 7281 respectively the d and 18owater values of the quartz from the ore body range from 119 1 to 109 7 and 4 64 to 1 98 respectively based on these results we argue that the ore forming fluids were derived from a magmatic source with fluid mixing as the dominant mechanism for silver precipitation involving hydrocarbon fluid interaction as inferred from the presence of bitumen in the ore

hysteresis and susceptibility characteristics of magnetite and titanomagnetites interpretation of results from basaltic rocks abstract the hysteresis and susceptibility characteristics down to liquid nitrogen temperatures have been investigated in over one thousand basalt samples of tertiary age from the society islands norfolk island reunion mauritius france and australia the variation in these properties with temperature is similar to that observed by radhakrishnamurty synthetic samples covering grain sizes from single to multidomain grains of pure magnetite titanomagnetite and cation deficient titanomagnetites of varying composition have been investigated to determine their low temperature characteristics comparison of the results from these synthetic samples with those of natural basalts shows that the composition and domain state predominating in any given sample of basalt cannot be determined uniquely from low temperature characteristics alone however optical electron microprobe and af demagnetization characteristics can be combined with the low temperature properties to determine the predominant grain size and magnetite composition the results show that the simple classification scheme put forward by radhakrishnamurty is questionable samples showing increase in susceptibility and no change in coercivity down to liquid nitrogen temperature are not of the cation deficient type these properties appear to be those associated with titanomagnetites containing exsolved ilmenite lamellae formed during initial cooling this unique characteristic may be useful for the quick selection of samples most suitable for palaeointensity studies

40ar 39ar dating and preliminary paleointensity determination on a single lava flow from chifeng inner mongolia abstract a precise 40ar 39ar age and paleointensity data for the cretaceous lava flow from chifeng southern inner mongolia northeastern china are presented in this study detailed rock magnetic investigations including the variation of magnetization with temperature low temperature susceptibility and hysteresis loops show that pseudo single domain psd grain size high ti titanomagnetite is the main magnetic mineral in the studied lava flow both the microwave and double heating thellier techniques were used to determine the paleointensity yielding mean flow paleointensities of 15 6 3 2 t and 23 9 8 0 t respectively however the paleointensity results using the microwave technique are of higher quality mean q 12 for microwave compared to q 2 for thellier and yield higher internal consistency for the flow mean 21 standard deviation about the mean for microwave compared to 34 for thellier the microwave paleointensity result 15 6 3 2 t is therefore deemed the more reliable estimate for the paleointensity of the niutoushan lava flow 40ar 39ar age determination on the lava flow is 106 42 0 48 ma 2 relative to ga 1550 biotite 98 79 0 96 ma combining our 40ar 39ar dating and paleointensity results with other published paleointensity data suggests that the intensity of the earth s magnetic field during the middle cretaceous normal superchron cns was weak but variable throughout the whole cns

a paleomagnetic and rock magnetic study of tertiary volcanics from the vogelsberg germany abstract paleomagnetic results are presented for orientated cores from 37 sites in the vogelsberg germany tertiary volcanic province the available radiometric dates indicate that the main volcanic activity occurred between 18 and 15 5 ma early miocene with intermittent mainly intrusive activity continuing into the late miocene a stable natural remanent magnetization nrm direction was obtained from most sites by stepwise alternating field af demagnetization the mean direction excluding sites with intermediate nrm directions is d 358 6 i 64 0 95 5 2 n 31 this gives a virtual geomagnetic pole vgp of 85 1 n 200 9 e which agrees well with the late tertiary apparent polar wander path apwp for eurasia a reverse normal reverse magnetostratigraphy is observed which can be correlated with chrons 5cr 5c and 5br 17 6 15 2 ma results of rock magnetic and reflected light microscopy studies indicate that titanomagnetite and its oxidation products are the main magnetic phases present the grain size and degree of deuteric oxidation varies considerably between sites with the titanomagnetites of thin vesicular lava flows tending to be more oxidized than those in thick massive bodies low temperature susceptibility measurements show a range of behaviour with some samples possessing grains which unblock below room temperature

snowfall in coastal west antarctica much greater than previously assumed 1 a new antarctic accumulation distribution based on regional model output calibrated with 1900 in situ observations is used to re assess accumulation in 24 antarctic ice drainage basins when compared to the previous compilation good agreement is found for 19 of the 24 basins representing 93 of the ice sheet that is reasonably well covered with observations in contrast the amundsen sea sector of west antarctica and the western antarctic peninsula both data sparse regions are found to receive 80 96 more accumulation than previously assumed for the pine island and thwaites glaciers west antarctica which have recently undergone rapid acceleration and thinning this means a downward adjustment of their contribution to global sea level rise from 0 24 to 0 14 mm per year model time series do not show a significant change in antarctic accumulation over the period 1980 2004

palaeomagnetic correlation and dating of mineralization and intrusive events abstract in the mining district of santa eulalia chihuahua northern mexico the mineralization consisting of simple massive concentrations of lead zinc iron sulphides and oxides confined in largely unaltered cretaceous limestones has traditionally been related to several intrusive emplacement events that occurred during the tertiary however the relative age relationships of the intrusives volcanics and mineralization have proved difficult to establish in this work we report palaeomagnetic results which permit definition of the mean relative age relationships for the igneous units and their correlation with the mineralizing event the mean directions and pole positions for the intrusives mineralization and volcano sedimentary cover capping series indicate a tertiary age eocene miocene the intrusives show normal intermediate and reverse polarities suggesting several emplacement events or a long period of intrusion the direction and polarity of the remanent magnetization for the mineralization correlates with those for the felsites which occur as a complex set of sills and dykes and they are therefore penecontemporaneous with the mineralization

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

ground and marine magnetic surveys of the lower eastern flank of etna volcano italy abstract in 1996 and 1997 two high resolution magnetic surveys one on land and the other at sea were carried out on the lower eastern flank of mount etna the magnetic surveys covering an area of about 400 km2 aimed to elucidate the relationships between the main tectonic and morphologic features of this flank of mount etna major features include widespread nnw and nne trending active faults and the valle del bove a depression considered to be the source area of the chiancone deposit the largest etnean volcaniclastic sequence magnetic surveys show anomalies that roughly follow the trend of active main structures although few magnetization measurements are available for the most representative outcrops of the lower eastern side of mount etna interpretation of the anomalies defines the underground geometry of the chiancone deposit and its relationship with volcano stratigraphic units and the underlying sedimentary rocks in particular a volume of about 14 km3 was ascribed to the chiancone deposit such a large amount of material was likely produced by a catastrophic event and deposited at different periods at the exit of the valle del bove in an area produced by the interaction on a regional scale of the main tectonic structures affecting this flank of the volcano

geology and genesis of the early paleozoic zhengguang intermediate sulfidation epithermal au zn deposit northeast china abstract zhengguang is a partly eroded about 500 m being eroded structurally controlled intermediate sulfidation is epithermal gold zinc deposit characterized by wide distribution of base metal sulfides fe poor sphalerite and mn calcite hosted by the late cambrian early ordovician basaltic andesitic volcanic and volcano sedimentary rocks in northeast china the deposit is located 4 and 8 km from the early ordovician tongshan including several is veins about 500 m away in the east called east tongshan and duobaoshan porphyry copper deposits respectively a 484 8 8 7 ma mswd 198 of re os isochron age on pyrite indicates that it is the most ancient intermediate sulfidation deposit that has been dated four stages of veins have been discerned at zhengguang early magnetite chalcopyrite epidote chlorite and k feldspar pyrite chalcopyrite veins stage i were associated with restricted k feldspar epidote locally with chlorite alteration and propylitic epidote chlorite calcite assemblages two primary epithermal gold stages developed at zhengguang pyrite quartz fe poor sphalerite chalcopyrite galena electrum petzite hessite tetrahedrite tennantite adularia veins stage ii and mn calcite quartz pyrite fe poor sphalerite chalcopyrite galena hessite native gold stage iii plus a late barren stage characterized by little sulfides calcite chlorite hematite quartz stage iv gold occurs chiefly as micro inclusions of electrum and petzite in pyrite and sphalerite of stages ii and iii stable isotope analyses and fluid inclusion results indicate a magmatic hydrothermal component in the ore fluids fluid inclusion data from stage i yielded the highest salinity 6 9 wt nacl and homogenization temperature average 264 c calculated oxygen isotope composition of fluid 18owater up to 4 9 equilibrated with quartz indicates a magmatic hydrothermal source during stage i a progressive addition of meteoric water component is suggested from stage i to iv of zhengguang based on the average 18owater values equilibrated with quartz and homogenization temperatures stage i 18owater 3 3 th 264 c stage ii 18owater 1 4 th 182 c stage iii 18owater 3 4 th 154 c stage iv 18owater 6 3 th 121 c our new pyrite re os dating result shows that zhengguang formed at the same time with tongshan and duobaoshan within errors comparable sulfur isotopic compositions of pyrite from zhengguang and tongshan analogous low fe content in sphalerite and similar mineral assemblage and alteration pattern between zhengguang and east tongshan is veins collectively indicate a genetic connection between zhengguang and tongshan which may derive from fluids exsolved from the same magma chamber high temperature assemblages e g k feldspr pyrite chalcopyrite at zhengguang indicate that there is potential for the discovery of porphyry copper gold mineralization below the current level of diamond drilling the confirmation of the zhengguang as an early paleozoic epithermal deposit implies a good preservation and exploration potential of ancient epithermal deposits in eastern central asian orogenic belt

paleointensity of the earth s magnetic field recorded by two late quaternary volcanic sequences at the island of la reunion indian ocean a paleomagnetic study has been undertaken on two late quaternary volcanic sequences from the piton de la fournaise volcano island of la reunion in order to provide absolute paleointensities of the earth s magnetic field from a site in the southern hemisphere the pattern of secular variation recorded by both sequences clearly indicates that the extrusion rate of the lava flows was not constant with time a detailed investigation of the magnetic properties of the samples was carried out in parallel with paleointensity experiments which were performed with the thellier method samples with minimum overprint composed by single domain or pseudo single domain magnetite showing good thermal stability and a narrow blocking temperature spectrum were the most successful during thellier s experiments values of the paleofield strength from 19 to 55 mt have been obtained on 23 flows among the 30 which were sampled few variations 7 5 9 9 1022 a m2 are observed in the virtual dipole moments vdms determined on the youngest sequence 5 12 ka those values are within the range of fluctuations of the worldwide variations of vdms for this period on the other hand data from the oldest sequence 82 98 ka are the first paleointensity values obtained in that time period and the observed vdms extend from 4 1 to 8 8 1022 a m2 these results suggest that for this time interval the field did not depart from its average behavior

palaeomagnetic rock magnetic and microscopy studies of historic lava flows from the paricutin volcano mexico implications for the deflection of palaeomagnetic directions summary we report the results of a detailed rock magnetic study of basaltic andesites for one of the best documented cases of the first occurrence of a new volcano the 1943 1952 eruption of paricutin in central mexico 102 oriented standard palaeomagnetic cores corresponding to 12 sites were collected from seven different lava effusion episodes which cover the interval between 1943 september december and 1946 march august thermomagnetic investigations reveal that remanence is carried in most cases by ti poor titanomagnetite resulting from oxy exsolution that probably occurred during the initial flow cooling unblocking temperature and coercivity point to small pseudo single domain magnetic grains for these titano magnetites thermal and alternating field demagnetization indicates that the lavas are characterized by univectorial or two component magnetizations site mean declinations and inclinations range from 331 9 to 32 3 and from 17 6 to 51 3 respectively the overall mean direction for 12 sites is dec 1 8 inc 37 5 k 26 and 95 8 7 23 samples were pre selected for thellier palaeointensity experiments because of their stable remanent magnetization and relatively low within site dispersion thellier palaeointensity experiments have yielded widely dispersed palaeointensity values from the historically observed geomagnetic intensity although individual specimens yielded technically high quality palaeointensity results the values obtained are significantly different from the expected value of approximately 45 t the palaeomagnetic record is dominantly characterized by shallower than expected sitemean inclinations as compared with data from the teoloyucan geomagnetic observatory and estimates based on the international geomagnetic reference field 1945 and 1950 models several alternative interpretations are examined but no single factor resulting in abnormal shallow inclinations can be isolated direct field observations suggest that shallow inclinations and angular scatter can be associated with lava emplacement in terms of internal viscous deformation and or movement of parts of lava after cooling below the blocking temperatures during lava advance other factors analysed that could contribute to the shallow inclinations and angular scatter are high magnetic refraction effects and outcrop scale to regional magnetic field anomalies

an automated superconducting magnetometer and demagnetizing system summary a novel 3 axis superconducting magnetometer has been constructed using just one squid superconducting quantum interference device sensor the magnetometer has been placed in a large mu metal shield together with a non magnetic oven and 3 axis af demagnetizer once a sample is entered into the system a microprocessor controller executes a predetermined measuring and demagnetizing remagnetizing sequence the system was originally designed automatically to determine field magnitude values from ceramics and igneous rocks but has proved itself to be a useful general purpose palaeomagnetic instrument

genesis of the zhengguang gold deposit in the duobaoshan ore field heilongjiang province ne china constraints from geology geochronology and s pb isotopic compositions abstract the zhengguang gold deposit in the duobaoshan ore field hosted in volcanic rocks of the middle ordovician duobaoshan formation is one of the largest gold deposits in the northeastern great xing an range of the central asian orogenic belt caob the deposit comprises the no i ii and iii ore zones with a total resource exceeding 35 tonnes of au 100 000 tonnes of zn and 100 tonnes of ag a genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry type and epithermal mineralization zircon la icpms u pb dating reveals that the tonalite porphyry was emplaced at 462 1 1 8 ma middle ordovician the 34 s v cdt values of sulfide minerals range from 3 0 to 1 7 with an average of 2 33 indicating that sulfur was mainly derived from a magmatic source the pb isotopic compositions 206 pb 204 pb ranging from 17 572 to 17 629 207 pb 204 pb from 15 424 to 15 486 and 208 pb 204 pb from 37 206 to 37 418 suggest a major mantle component for pb and by inference for other ore metals therefore we suggest that the ore forming elements in the zhengguang gold deposit may be related to the mantle sourced tonalite porphyry on the basis of the geological characteristics and geochemical signatures documented in this study we conclude that the zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry as part of the duobaoshan porphyry epithermal ore system that is related to the subduction of the paleo asian ocean during the ordovician

an investigation of the magnetic variation within two recent lava flows summary samples collected in vertical sections from two recent 1169 ad and 1971 ad lava flows show significant variations in both the palaeomagnetic vector and the rock magnetic characteristics the age and the short cooling time of the flows both are less than 3 m thick are such that the observed range of palaeomagnetic variation is more than can reasonably be explained by secular variation the variations in palaeomagnetic and rock magnetic characteristics appear in part to be a response to the relative proportions of two coexisting ferrimagnetic phases one that displays a primary coarsegrained and ti rich composition and a second that has finer grained ti poor characteristics the use of af demagnetization in this study means that the latter phase will have a disproportionate influence on the palaeomagnetic results it has been suggested elsewhere that in such a magnetic system the ti poor phase may represent a crm formed at some temperature below its final curie temperature if so the results of this study imply that not only does it affect the palaeointensity estimate which requires a pure trm but it appears also to influence the palaeomagnetic direction to an extent that far exceeds the normal secular change that might be expected to occur during delayed acquisition such a result has important implications for palaeomagnetic studies that use lavas both in the selection of a suitable sampling strategy and in the geomagnetic interpretation of palaeomagnetic variation within single flow units

palaeomagnetic cleaning strategies abstract cleaning is a term used in palaeomagnetism to refer to laboratory methods designed to demagnetize preferentially the less stable components of magnetization although the diversity of methods suggests that there is a wide choice available this is illusory except in simple cases the wrong cleaning strategy may yield misleading results cleaning methods include thermal magnetic alternating field or a f low temperature chemical shock and microwave cleaning a cleaning strategy involves one or more cleaning methods applied in a specific sequence the design of a strategy is made easier with the a priori knowledge of magnetic mineralogy and granulometry or in other words rock magnetic properties although not a substitute for other rock magnetic experiments the variation of low field susceptibility with temperature k t not only provides information on magnetic mineralogy and granulometry but it also draws attention to chemical alteration that may occur during thermal cleaning apart from the rapid though reversible decrease of k associated with curie temperatures other diagnostic k t features include the low temperature about 140 c peak typical of multidomain md magnetite the high temperature hopkinson peak typical of fine grained magnetite and other magnetic minerals and the classic lepidocrocite maghemite haematite profile which is irreversible examples are given where the remanence caused by lightning can be effectively eliminated only by applying a f or low temperature lt pre treatment such remanence may be an isothermal remanent magnetization irm or a combination of irm and anhysteretic remanent magnetization arm as the unblocking temperature of relatively low coercivity md grains may extend to high temperature it is often desirable to suppress md remanence an example is given of palaeointensity determination with the without lt pre treatment the nature of the lt transition is briefly addressed in the light of a rare double low temperature peak which may reflect both the isotropic point and the verwey transition

magnetic and clast fabrics as measurements of grain scale processes within the death valley shallow crustal detachment faults 1 the rock product of shallow crustal faulting includes fine grained breccia and clay rich gouge many gouges and breccias have a fabric produced by distributed deformation the orientation of fabric elements provides constraints on the kinematics of fault slip and is the structural record of intrafault strain not accommodated by planar and penetrative surfaces however it can be difficult to quantify the deformational fabric of fault rocks especially the preferred orientations of fine grained minerals or to uniquely determine the relationship between fabric geometry and finite strain here we present the results of a fabric study of gouge and breccia sampled from low angle normal detachment faults in the black mountains death valley ca we measured a preferred orientation of the long axes of the clasts inherited from the crystalline footwall of the fault and compared the shape preferred orientation to the anisotropy of magnetic susceptibility of the fault rocks the two measurements of fabric exhibit systematic similarities and differences in orientation and anisotropy that are compatible with the large scale kinematics of fault slip the dominant carriers of the magnetic susceptibility are micron and sub micron scale iron oxides and clay minerals therefore even the finest grains in the fault rock were sensitive to the distributed deformation and the micro mechanics of particle interaction must have departed from those assumed by the passive marker kinematic model that best explains the fabric

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

permo triassic palaeomagnetism in the emei mountain region southwest china summary a palaeomagnetic study has been made of samples collected from permo triassic type sections in the emei mountain region of southwest china no results were obtained from the lower permian qixia formation limestones or the lower upper permian maokou formation limestones the upper permian longtanian emeishan basalt formation shows excellent stability to both alternating field and thermal demagnetization results from 24 flows 125 samples are all of normal polarity have a positive fold test cretaceous or tertiary folding and give a pole position at 54 5 n 254 3 e with dp 1 8 dm 3 5 the basalts were thus presumably extruded after the end of the kiaman reversed superchron the overlying upper permian xuanwei formation of red mudstones and sandstones changxingian in age also shows a positive fold test from n 12 samples after thermal treatment and has a positive reversals test at level c the pole position is close to that of the emeishan basalt and lies at 57 0 n 260 9 e with dp 4 3 dm 8 5 the lower triassic griesbachian to mid nammalian feixianguan formation is primarily a red sandstone sequence at this locality thermal treatment of the collection of 114 samples reveals two main components the a component is always observed below 600 c and probably represents a drm either from magnetite or specular haematite the 5 component resides in haematite and is often of the opposite polarity superimposed on the a component it is revealed only above 600 c and is a crm acquired during diagenesis although normal components dominate both the a and b components also have reverse polarities the normal a and normal b components are statistically indistinguishable and the normal b component shows a positive fold test the reverse b component is however not quite antiparallel to the normal b component and may therefore be a second crm acquired at a slightly different time to the normal b component all these components are thought to have arisen during deposition and diagenesis over a few million years as has been observed in other studies of redbeds the dominance of normal components is consistent with the observation that the earlier part of the griesbachian stage of the lower triassic is mainly a normal polarity chron the overall mean of the n 101 both normal and reverse a and 5 components is considered to be the best estimate of the palaeofield in the early triassic giving a pole position at 56 2 n 227 6 e with dp 1 t dm 3 4 this pole lies 15 2 away from the emeishan basalt pole suggesting a polar shift occurred near the permo triassic boundary a review of late permian and early triassic poles from the south china block shows a similar polar shift

snow precipitation at four ice core sites in east antarctica provenance seasonality and blocking factors snow precipitation is the primary mass input to the antarctic ice sheet and is one of the most direct climatic indicators with important implications for paleo climatic reconstruction from ice cores provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites dome c law dome talos dome and taylor dome in east ant arctica were analysed with air mass back trajectories cal culated using the lagrangian model and the mean composite data for precipitation geopotential height and wind speed field data from the european centre for med ium range weather forecast from 1980 to 2001 on an annual basis back trajectories showed that the atlantic indian and ross pacific oceans were the main provenances of precipitation in wilkes land 80 and victoria land 40 respectively whereas the greatest influence of the ice sheet was on the interior near the vostok site 80 and in the southwest ross sea 50 an effect that decreased towards the coast and along the antarctic slope victoria land received snowfall atypically with respect to other antarctica areas in terms of pathway eastern instead of western seasonality summer instead of winter and velocity old air age geopotential height patterns at 500 hpa at low 10 days and high 2 6 days frequen cies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the tasman sea eastern indian ocean at higher latitudes 60 70s than normal this could be considered part of an atmospheric blocking event with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low frequency positive anomalies

mineral magnetism and geomagnetic secular variation of marine and lacustrine sediments from central italy timing and nature of local and regional holocene environmental change abstract sediment core palaeomagnetic and mineral magnetic records from two crater lakes in central italy and from the western margin of the adriatic sea have been used to evaluate local and regional responses to holocene environmental change in all cores sediment magnetism reflects the interplay between catchment material and the in situ production of bacterial magnetite magnetotactic bacteria in the lakes the earliest holocene sediments record a waning catchment input that we attribute to rising lake levels and increased tree cover in the catchment from 9000 to 5000 yr bp both lakes become anoxic a consequence of water mass stratification driven by high lake levels bottom water anoxia also developed in the adriatic with sapropel s1 produced between 9000 and 7000 yr bp subsequently the lake and adriatic mineral magnetic records show evidence for increased catchment delivery consistent with pollen evidence for bronze age deforestation in the lakes this evidence is first recorded at 4300 yr bp and a number of distinct clearance events are recorded in comparison at adriatic site rf93 30 lithogenic input increases abruptly at 3500 yr bp and is followed by a slowly changing record of waxing and waning sediment delivery inter site comparisons of palaeomagnetic data point to a possible link between the magnitude of the bacterial magnetite component and the recorded magnetic inclination the sites are at near identical latitudes and have similar sediment accumulation rates but the adriatic sites have a core average magnetic inclination that is some 10 steeper than the lake average values we suggest that the large dipole moment of the magnetosome chains which in life produce the passive alignment of the bacterium along the local geomagnetic field line produce a more faithful albeit smoothed record of the geomagnetic field

absolute palaeointensity variation during a precursor to the matuyama brunhes transition recorded in chilean lavas abstract following a detailed radioisotropic dating and palaeomagnetic investigation of transitional polarity lava flows of the tatara san pedro volcanic complex 36 s 71 w in the quebrada turbia valley central chile brown et al 2004 palaeointensity analysis has been carried out to complete a characterisation of the full geomagnetic field vector during a period of transitional geomagnetic field behaviour at 791 7 3 0 ka 16 ky before the full matuyama brunhes transition mbt seventy one samples from 30 lava flows were analysed in total with 34 found suitable for palaeointensity experiments after conducting microwave palaeointensity experiments 16 lava flows from two sections 2 km apart yielded 31 successful individual palaeointensity determinations which record consistently weak field intensity values during the transitional directions mean value of 5 1 1 t from 11 flows excluding a flow immediately above a reversed polarity flow palaeointensity values are nearly an order of magnitude lower than the overlying normal polarity lavas ranging from 30 to 47 t and half the values recorded in the underlying reversed polarity lavas 7 and 13 t these post transitional field high palaeointensity values and comparisons with relative palaeointensity records from sedimentary rocks suggest that the quebrada turbia lavas may document a partial record of the mbt precursor and the latter stages of the mbt itself

the relationship between the magnitude and direction of the geomagnetic field during the late tertiary in eastern iceland summary during the late tertiary well over 1000 lavas were extruded in eastern iceland potentially they each record an instantaneous description of the palaeomagnetic field we have systematically attempted to determine the palaeofield magnitude from one specimen from each lava about one in every four studied has yielded a palaeomagnitude value to go with the palaeofield direction value previously obtained there is a slight preference for reversely magnetized specimens to yield results results from 106 lavas indicate an arithmetic mean value for the virtual dipole moment vdm of 8 2 0 5 1022 am2 the data suggest an asymmetry whereby the normal polarity field was maintained in magnitude over a wider range of directions than was the reversed polarity field possibly indicating its greater stability

the effects of heating on low temperature susceptibility and hysteresis properties of basalts abstract the variation of the low field susceptibility of basalts down to liquid nitrogen temperature always falls into one of three types that depend on the composition and grain size of the titanomagnetite grains present group 1 basalts contain predominantly unoxidised multidomain homogeneous titanomagnetites having x 0 3 group 2 basalts contain predominantly titanomagnetite grains with many exsolved ilmenite lamallae that subdivide the grains so that they act similarly to single domains group 3 basalts contain predominantly multidomain magnetite or magnetite rich titanomagnetite having x 0 15 after repeated heating to 615 c the group 1 basalts gradually oxidise above 300 c to produce the characteristics of group 2 basalts owing to the exsolution of ilmenite on the other hand both group 2 and 3 basalts are stable to oxidation until at least 500 c they are therefore the most useful material for palaeointensity studies

diagenetic and metallogenic ages of duobaoshan porphyry cu mo deposit in heilongjiang province the duobaoshan porphyry cu mo deposit is an important cu deposit in northeast china systematic isotope dating was conducted to determine the metallogenic age of the deposit la icp ms zircon u pb dating indicates that the parent granite porphyry rocks and the host rocks intruded at 474 8 4 7 ma and 478 1 4 1 ma respectively the biotite granodiorite outside the parent granite porphyry was formed at 483 9 4 5 ma meanwhile seven re os isotopic analyses of molybdenite yield a weighted average model age of 475 1 5 1 ma these data show that the ore forming process and the intrusion of the host rocks were completed in the early ordovician according to the ages of mineralization and intrusion of host rocks the sedimentary setting of the duobaoshan formation and the geochemical characteristics of rocks hosting the deposit the authors hold that the porphyry cu mo deposit was formed in an island arc regime related to plate subduction in the early ordovician and that the prospecting direction for such a type of porphyry copper deposits should be in the magma island arc belt distributed in duobaoshan yi ershi area

palaeomagnetism of a caledonian ophiolite complex karmoy southwest norway abstract the palaeomagnetism of the karmoy ophiolite suite emplaced at the southwest extremity of the scandinavian caledonides in middle upper ordovician times is described low intensities of magnetisation and low q n values in the bulk of the constituent facies are linked to the effects of low grade metamorphism but ultramafic pods that have experienced serpentinisation yield well defined single component magnetisations a predominant a component of magnetisation isolated in 35 samples yields a mean of d i 51 58 95 5 this population is discrete from a subsidiary b component recognised in 17 samples with a mean direction of 145 63 95 8 a minor c component d i 330 60 95 8 is also identified and small numbers of anti parallel components are identified in each case an upper ordovician ignimbrite from kattnakken northeast of karmoy yields an in situ component of d i 270 38 together with similar components recognised elsewhere this mean d direction is most closely compatible with directions recognised in upper silurian lower devonian rocks from the scottish sector of the caledonides it is interpreted as an overprint of this age but may include a component of local rotation two interpretations are considered for the remanence record in the karmoy complex the a component could record the influence of a thermal event linked to uplift of the continental margin and development of the adjoining north sea basin in mesozoic times if this margin has been tilted seawards by 20 since magnetisation no plausible tectonic model can bring the b component into conformity with the post 300 ma apparent polar wander apw path and it is alternatively proposed that both the a and b components record upper ordovician post emplacement remanences with this interpretation the data complement a range of palaeomagnetic results from middle upper ordovician igneous and metamorphic rocks from north atlantic bordering terranes yielding intermediate to high palaeolatitudes and contrasting with older and younger data collectively they imply that the iapetus ocean had effectively closed by these times and that large apw movements took place between mid ordovician and mid silurian times

palaeointensity studies of a late permian lava succession from guizhou province south china implications for post kiaman dipole field behaviour summary palaeomagnetic results are presented from a volcanic sequence in zhijin county guizhou province southern china the lavas and associated volcanic breccias comprising the sequence represent a southern extension of the emeishan volcanic province biostratigraphic dating of interbedded limestone units and stratigraphic constraints indicate that the section formed during the late permian 263 255 ma and is thus somewhat older than the emei stratotype section in sichuan province and close in age to reported estimates of the termination of the permo carboniferous kiaman reverse superchron rock magnetic analyses and reflected light microscopy indicate that the magnetic mineralogy of the lava units is dominated by fresh primary magnetites containing a significant fraction of single domain grains thermal demagnetization behaviour of the breccia units is poor but most lava samples have one or two components of remanence above 250 c the normal polarity characteristic remanence held by the lavas implies a post kiaman age for this succession and suggests that the termination of the kiaman occurred prior to 263 ma supporting recently published estimates according to standard criteria thellier palaeointensity results from the lavas are of good quality and reveal that the dipole field strength was comparatively low shortly after the termination of the superchron 80 per cent of samples record relative vdm values in the range 42 52 per cent of the present day value supporting recent studies of mid kiaman field intensity this suggests that a low energy dipole existed at least between 300 and 255 ma and does not appear to have been confined to the stable reverse polarity interval

microwave palaeointensity study of the jorullo volcano central mexico summary a single lava flow from the earliest eruption period ca ad 1759 1774 of the jorullo vol cano michoacan guanajuato volcanic field mgvf mexico has been sampled to determine the palaeointensity of the magnetic field at the time of extrusion both conventional thellier thellier experiments and two variants of the microwave palaeointensity technique coe variant of the thellier thellier method and the perpendicular applied field method have been con ducted high quality palaeointensity results mean of 46 6 6 3 t from 15 samples using all three methods have been obtained with both techniques in good agreement this study presents further evidence of the equivalence of both microwave and thermal methods and adds to the database of palaeomagnetic data from the monogenetic volcanoes of central america

indian ocean dipole and southern high latitude precipitation possible links southern high latitude precipitation during austral spring in relation to the indian ocean dipole iod and enso is investigated in the present study both the iod and enso generate rossby waves trains that create positive and negative pressure anomalies these anomalous pressure centres generate meridional moisture fluxes that impact the precipitation influence of the iod is detected mainly in the ross sea region where the southward moisture transport induced by the low pressure cell enhances precipitation during strong iod years east antarctica near 100 e is also characterised by enhanced precipitation induced by the southward moisture transport by a high pressure cell located south of australia in the dronning maud land precipitation is linked to the moisture advection through the atlantic during enso years and not during the iod years

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

the ordovician igneous rocks with high sr y at the tongshan porphyry copper deposit satellite of the duobaoshan deposit and their metallogenic role abstract a strong link between high sr y arc magmas and porphyry cu mo au deposits has been recognized in recent years the tongshan and duobaoshan deposits are representative large cu mo au deposits in ne china we report la icp ms zircon u pb crystallization age of 471 5 1 3 ma for tongshan ore related granitoid re os isotopic analyses of the two chalcopyrite samples from tongshan deposit show a model age range of 470 2 477 1 ma the duobaoshan and tongshan ore related granitoids show higher sr y and la yb ratios the 34 s values of sulphides from the duobaoshan and tongshan deposits vary from 2 3 to 0 0 belonging to a magmatic hydrothermal system the pb isotopic ratios of the sulphides from the duobaoshan and tongshan deposit range from 17 201 to 18 453 for 206 pb 204 pb 15 445 to 15 551 for 207 pb 204 pb and 36 974 to 37 999 for 208 pb 204 pb indicating the addition of lower crustal material the duobaoshan and tongshan granitoids were formed in a subduction related continental arc setting produced by partial melting of juvenile hydrous basalts underplating the deep continental crust during the ordovician

an integrated rock magnetic approach to the selection or rejection of ancient basalt samples for palaeointensity experiments abstract the rock magnetic properties of basalts are often useful indicators of suitability for use in palaeointensity experiments the normal approach to sample selection is based on the use of a limited amount of rock magnetic data possibly from only a single rock magnetic technique this approach may result in the exclusion of otherwise suitable samples or the inclusion of unsuitable samples this study stresses the importance of analysing results from a number of rock magnetic techniques before selecting or rejecting samples for use in palaeointensity experiments a new integrated rock magnetic method of sample selection or rejection is proposed which uses the combined results from thermal thermomagnetic and high temperature susceptibility and non thermal low temperature susceptibility hysteresis and alternating field demagnetisation rock magnetic techniques to define sets of rock magnetic behaviour for precambrian basalts with a mixed grain size of pure magnetite the behaviour of all samples in each set during both thellier and shaw palaeointensity experiments is categorised allowing a set of selection or rejection criteria to be defined this new approach to sample selection or rejection for palaeointensity experiments has value for basalts of all ages provided the sample collection is large enough and all available rock magnetic techniques are used

the triassic bilugangan deposit geological constrains on the genesis of one of the oldest mo deposits in inner mongolia china abstract the large bilugangan porphyry mo deposit is one of the oldest mo deposit in eastern part of the central asian orogen in inner mongolia the orogen is currently regarded as the most important phanerozoic region with widespread crustal growth between the siberian craton to the north and north china block to the south the bilugangan mo mineralisation is hosted by a porphyritic monzogranite and along the contact with the late permian linxi formation the mineralisation is disseminated in places and includes various types of hydrothermal veins the mineralising stages of the deposit includes the pre ore quartz k feldspar biotite pegmatite succeeded by quartz k feldspar molybdenite muscovite sericite pyrite veins quartz molybdenite chalcopyrite perthite muscovite sericite pyrite sphalerite and post ore quartz fluorite calcite sericite muscovite veins seven molybdenite samples from the mineralisation yield a re os mo weighted mean date of 238 1 ma which is the same within error as the re os isochron age of 238 2 ma and the ca 240 ma age of the porphyritic monzogranite this is the oldest porphyry mo type deposit in the eastern part of the orogen and the only large sized mo deposit in the region which shows that the east cao is prospective for triassic mineralisation thirty three samples of sulfide from the deposit have a narrow 34 s vcdt range of 1 5 to 4 3 indicating that the sulfur the sulfur has primarily a magmatic source the sulfides from the mo bearing veins have relatively concentrated pb isotopic compositions with 206 pb 204 pb ratios between 18 295 and 19 576 207 pb 204 pb ratios between 15 535 and 15 662 and 208 pb 204 pb ratios between 38 066 and 38 653 these values are consistent with those of the initial pb isotope ratios for whole rock samples from the porphyritic monzogranite and hornfels fifteen gangue quartz samples from various veins define a range of 18 o fluid values from 0 5 to 5 2 with d fluid values ranging from 115 to 60 indicating that the onset of the mineralising fluid was generated from in situ degassing of a magmatic source followed by an input of meteoric water during the late ore forming stage it is proposed that the deposit is a collision related dabie type deposit which is related to the closure of the paleo asian ocean between the north china block and siberian craton

evidence for magnetostrictive control of intrinsic susceptibility and coercive force of multidomain magnetite in rocks abstract it is shown that intrinsic susceptibility xi susceptibility in the absence of self demagnetizing fields as well as coercive force hc of multidomain magnetite in rocks are likely to be commonly magnetostrictively controlled presumably through internal stresses opposing domain wall motion we use observations of the thermal variation of observed susceptibility x per cm3 of magnetite in the sample and coercive force hc on cooling to 130 k for seven basaltic rocks and for 0 25 0 21 mm magnetite grains dispersed in cement as expected theoretically with magnetostrictively controlled xi a plot of 1 x versus j s 2 for each sample where is the polycrystalline magnetostriction coefficient and js is saturation magnetization gives a reasonably straight line whose 1 x intercept agrees with n average self demagnetizing factor of magnetite grains in the sample given by h c j r n h c j r h c j ri where jr is saturation remanence and ri is jr when n 0 as expected theoretically with magnetostrictively controlled hc a plot of hc versus j s for each sample reveals an approximate proportionality this also implies magnetostrictive control of xi because a plot of 1 x versus h c j s for each sample yields a straight line of 1 x intercept agreeing with n from h c j r n h c j r h c j ri as expected if hc and xi are both magnetorestrictively controlled

is the indian ocean sst variability a homogeneous diffusion process whereas the predominance of el nino southern oscillation enso mode in the tropical pacific sea surface temperature sst variability is well established no such consensus seems to have been reached by climate scientists regarding the indian ocean while a number of researchers think that the indian ocean sst variability is dominated by an active dipolar type mode of variability similar to enso others suggest that the variability is mostly passive and behaves like an autocorrelated noise for example it is suggested recently that the indian ocean sst variability is consistent with the null hypothesis of a homogeneous diffusion process however the existence of the basin wide warming trend represents a deviation from a homogeneous diffusion process which needs to be considered an efficient way of detrending based on differencing is introduced and applied to the hadley centre ice and sst the filtered sst anomalies over the basin 23 5n 29 5s 30 5e 119 5e are then analysed and found to be inconsistent with the null hypothesis on intraseasonal and interannual timescales the same differencing method is then applied to the smaller tropical indian ocean domain this smaller domain is also inconsistent with the null hypothesis on intraseasonal and interannual timescales in particular it is found that the leading mode of variability yields the indian ocean dipole and departs significantly from the null hypothesis only in the autumn season

palaeointensity results from the permo carboniferous kiaman reversed superchron the great whin and midland valley sills of the northern united kingdom summary fifty thellier palaeointensity determinations were made from the great whin sill gws of northern england and the midland valley sill mvs of central scotland which form the major part of a late carboniferous quartz dolerite complex palaeodirectional analysis confirms that the reversed polarity characteristic remanence carried by samples from both sills is consistent with the permo carboniferous reversed superchron palaeomagnetic results suggest that the two sills may not be exactly contemporaneous the mvs was intruded rapidly some time during the emplacement of the gws which was itself emplaced over a considerable time period the mvs may well represent the northernmost expression of the instrusive activity a mean palaeointensity of 22 9 2 6 t was calculated for the great whin sill with a corresponding vdm value of 5 9 1022 a m2 the palaeointensity value calculated from the midland valley sill was much lower 13 0 0 5 t with a corresponding vdm value of 3 3 1022 a m2 detailed rock magnetic analyses and stepwise thermal demagnetization studies reveal that the remanence carrier in both sills is magnetite of mixed domain state multidomain grains are less important in the midland valley sill and thus greater confidence is attached to palaeointensity results from this sill vdm values from this and other studies of the permo carboniferous reversed superchron p crs indicate that the dipole strength showed similar variations to that witnessed for the past 5 ma there is no conclusive support in favour of either the weak or strong field models that have been suggested for superchrons more palaeointensity results are needed from the termination of the p crs and the late permian early triassic in order to understand how the dipole field evolved during the p crs and its relationship to the so called mesozoic dipole low

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

evidence for the existence of a transitional geomagnetic field recorded in a proterozoic lava succession summary an anomalous palaeomagnetic field direction is recognized in a sequence of rapidly extruded subaerial basaltic lava flows within the mid proterozoic c 1300 ma gardar lava succession south greenland thermal demagnetization and component analysis link this direction to a thermoremanent magnetization trm acquired during primary cooling the direction which bears no resemblance to any other palaeomagnetic direction witnessed within the group is recorded by seven successive flows which appear to have been extruded and magnetized over a short period of time during a geomagnetic polarity transition palaeointensity experiments employing the modified thellier technique indicate that this transitional direction was acquired in a field with only 25 per cent of the magnitude of the stable polarity field the behaviour of the field direction during and after this transition reflects that witnessed in studies of much younger transitional sequences whereas that for the field intensity differs fundamentally from consistent observations from younger lava successions these results provide a significant contribution to our knowledge of the ancient geodynamo and may well document the oldest transitional field identified by a combined palaeomagnetic and palaeointensity study and the only one reported from the precambrian era

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

ages geochemistry and tectonic implications of the cambrian igneous rocks in the northern great xing an range ne china abstract the xinlin xiguitu suture zone located in the great xing an range ne china in the eastern segment of the central asian orogenic belt caob represents the boundary between the erguna and xing an micro continental blocks the exact location of the xinlin xiguitu suture zone has been debated especially the location of the northern extension of the suture zone in this study based on a detailed field geochemical geochronological and sr nd hf isotope study we focus our work on the cambrian igneous rocks in the erguna xing an block the xinglong granitoids mainly include 520 ma diorite 470 ma monzogranite and 480 ma pyroxene diorite the granitoids show medium to high k calc alkaline series characteristics with post collision granite affinity the circa 500 ma granitoids have low ehf t values 16 6 to 2 2 and ancient two stage model tdm2 ages between 1317 ma and 2528 ma these results indicate the primary magmas of the xinglong granitoids were probably derived from the partial melting of a dominantly paleo mesoproterozoic old crustal source with possible different degrees of addition of juvenile materials and formed in a post collision tectonic setting after the amalgamation of the erguna and xing an blocks compared with the xinglong granitoids the duobaoshan igneous rocks are consisted of the approximately coeval rhyolitic tuffs 491 5 ma and ultramafic intrusions 497 5 ma within the duobaoshan formation they are generally enriched in large ion lithophile elements liles and depleted in high field strength elements hfses e g nb ta and ti consistent with the geochemistry of igneous rocks from island arcs or active continental margins the ultramafic rocks have high positive ehf t values 1 3 to 15 and end t 1 86 to 2 28 and relatively young two stage model tdm2 ages and low initial 87sr 86sr ratios 0 70628 0 70853 indicating the partial melting of a depleted mantle source from a subducted slab in the ocean basin between the erguna xing an and songliao blocks the rhyolitic tuffs contain a group of phanerozoic zircons with ehf t values 4 6 to 15 0 suggesting that the rhyolitic tuffs were derived from juvenile lower crustal material with some ancient crustal material coupled with our previous geochemical and isotopic studies on early paleozoic igneous rocks we proposed that the collision of the erguna and xing an blocks at least took place ca 500 ma ago and that there exist in a westward subduction of an oceanic plate between the eruguna xing an and songliao blocks took place during the early ordovician up to now there are more evidences and constraints that the northern extension location of the xinlin xiguitu suture zone is located in the jifeng xinglong areas

palaeomagnetism rock magnetism and magnetic fabrics in precambrian metamorphic terranes of the huabei shield china abstract this study has investigated magnetic remanence rock magnetism and anisotropy of magnetic susceptibility ams in granulite and amphibolite grade metamorphic terranes of the huabei shield between inner mongolia in the west and the bohai sea in the east rock magnetic studies identify annealed metamorphic magnetite grains with multidomain properties as the remanence carriers a widely recorded stable remanence was probably fixed by grain shape effects granulite facies terranes are typically between one and two orders more strongly magnetised than amphibolite terranes and ams fabrics correlate mostly with metamorphic mineral fabrics observed in the country rocks progressive thermal demagnetisation identifies a range of two and three component structures resident in magnetite an important component recognised as a partial or complete remagnetisation by late mesozoic tertiary tectonic magmatic activity is present in basement at the southern margin of the outcrop miyun terrane and where extensive granite plutonism has occurred zhunhua terrane these components have directions corresponding to remanence in the yunmeng shan granite 119 114 ma d i 33 58 39 samples a 95 3 5 palaeopole at 201 e 64 n most remanence elsewhere was probably acquired during post tectonic uplift and cooling of the basement between 2200 and 1850 ma because palaeomagnetic directions are removed from the phanerozoic palaeofield path and they are distinct from the palaeomagnetic record in the overlying jixian supergroup deposited at 1840 900 ma these latter magnetisations are considered reliable indicators of the palaeofield during late palaeoproterozoic times because deformation of overlying supracrustal rocks is mostly slight and no prominent deflection of magnetic remanence by magnetic fabrics is observed palaeofield directions and poles attributed to the time of uplift related cooling are qian an terrane d i 215 71 a 95 9 17 samples pole at 99 e 10 n and north qianxi terrane d i 44 45 a 95 4 41 samples pole at 79 e 11 s in addition a more widely preserved shallow northerly component correlates with a nw e swathe of components recorded by uplift related cooling within the datong huan an granulite terrane in the west of the shield a preliminary palaeo mesoproterozoic apparent polar wander path for the huabei shield is defined from the palaeoproterozoic record in the metamorphic basement rocks and the meso neoproterozoic record in the overlying jixian supergroup it incorporates a loop between 2200 and 1850 ma and exhibits a general east to west trend in subsequent times