comment on magnetic studies of magma supply and sea floor metamorphism troodos ophiolite dikes by g j borradaile and d gauthier anisotropy of magnetic susceptibility is used as a proxy for the determination of magmatic flow direction in mafic dykes here we take advantage of the dataset from g j borradaile and d gauthier to comment three points 1 the sampling strategy 2 the geometric relationship between magnetic axis dyke and 3 an alternative interpretation to obtain a flow direction the magnetic lineations published by borradaile and gauthier correspond to the zone axis of the dyke and magnetic foliation poles questioning the reliability of the magnetic lineation as a flow estimate an alternative interpretation is based on the use of the tiling of the magnetic foliation plane against the dyke wall

flow directions in dikes from anisotropy of magnetic susceptibility data the bootstrap way one of the first applications of anisotropy of magnetic susceptibility ams was an attempt to determine flow directions from mafic dikes khan 1962 since the seminal work of knight and walker 1988 defining the expected behavior of ams in response to magma flow there has been increasing interest in using ams for this purpose here we present a quantitative method for interpretation of ams data from dikes using a parametric bootstrap first dikes must be sampled with at least five and preferrably more samples from within 10 cm of the dike margin the distributions of the eigenvalues and eigenvectors of the ams tensor are delineated by calculating eigenparameters of many bootstrapped paradata sets we generate paradata sets by first selecting a sample at random then calculating a replacement set of data by drawing tensor elements from normal distributions with the mean and standard deviation of the entire site the bounds containing 95 of the eigenparameters of the bootstrapped data serve as confidence limits for the parameter of interest classification of dikes proceeds as follows sites whose maximum and intermediate eigenvalues could not be distinguished are deemed uninterpretable in addition sites with principal eigenvectors with angles 45 away from the dike margin inverse or with markedly different directions on either side of the dike scissored are excluded the remaining dikes are classified as having unique flow direction information if the principal eigenvectors from at least one side are distinct from the dike plane based on the distribution of the bootstrapped principal eigenvectors if neither side has principal eigenvectors distinct from the dike plane the dikes are classified as having lineation information only a study comprising 251 dikes from the troodos ophiolite has 151 sites with directional data 38 sites with lineations only 7 inverse sites 5 scissored sites and 55 sites not fitting into any other category the flow directions interpreted from the data were generally southerly toward a fossil transform zone

the use of palaeomagnetism and rock magnetism to understand volcanic processes introduction this special publication provides a snapshot of our understanding of volcanic processes through the use of palaeomagnetic and rock magnetic techniques here we provide a context for the book placing individual chapters within the milieu of previous work including some magnetic techniques that were not used in the particular studies described herein thermoremanent magnetization is a powerful tool to understand processes related to heating and cooling of rocks including estimating the temperature of emplacement of pyroclastic deposits which may allow us to better understand the rates of cooling during eruption and transport anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics and allow the interpretation of flow dynamics in dykes lava flows and pyroclastic deposits as well as the location of the eruptive vents rock magnetic characteristics can help in the correlation of volcanic deposits but also provide means to date volcanic deposits and to better understand the processes of cooling of the deposits as the magnetic minerals can change with temperature in addition volcanic rocks may be key recorders of past magnetic fields allowing a better understanding of changes in field intensity and perhaps providing clues of how the magnetic field is formed over the past several decades palaeomagnetic and rock magnetic techniques have been applied to numerous problems in volcanology since aramaki akimoto s pioneering study in 1957 which used natural remanent magnetization nrm data to qualitatively estimate the temperature of emplacement of selected pyroclastic deposits in japan aramaki akimoto 1957 many studies have utilized and refined the approach of using progressive thermal demagnetization data to estimate emplacement temperatures of pyroclastic deposits and have demonstrated the utility of this approach in many settings another extensively utilized technique is that of anisotropy of magnetic susceptibility ams which was first applied to pyroclastic volcanic rocks by ellwood 1982 on ignimbrites in the san juan mountains sw colorado usa to estimate flow fabrics and in that study to infer source locations through triangulation it is staggering to think of the number and diversity of ams studies on volcanic rocks that have been undertaken since that time in a bit more than three decades remanent magnetization characteristics have long been used to correlate volcanic rocks and such data together with rock magnetic properties have been employed to study crystallization and cooling processes e g schlinger et al 1988 wells hillhouse 1989 as techniques have been refined and the sensitivity precision reliability and or speed of measurements for an array of modern instrumentation all have improved workers have been able to study volcanic problems in more detail pulling out details of the processes that have not previously been considered in addition the types of problems addressed have diversified considerably we intend this special publication to provide a representative suite of contributions that help to summarize the current array of studies that apply palaeomagnetism and rock magnetism to volcanic processes and to stimulate further research in this exciting science this book is a result of two sessions on volcanic processes and palaeomagnetism held at the international union of geodesy and geophysics congress in melbourne australia in july 2011 and at the american geophysical union annual meeting in san francisco usa in december 2011 from ort m h porreca m geissman j w eds 2015 the use of palaeomagnetism and rock magnetism to understand volcanic processes geological society london special publications 396 1 11 first published online january 20 2015 http dx doi org 10 1144 sp396 17 2015 the geological society of london for permissions http www geolsoc org uk permissions publishing disclaimer www geolsoc org uk pub ethics angharad hills at the geological society of london graciously and tactfully guided this book and the editors through the entire process from chapter solicitation to publication thermoremanent magnetization in volcanic rocks and emplacement temperature

flow patterns of magma in dikes makhtesh ramon israel directions of magma flow were measured in a system of radial dikes in makhtesh ramon israel the flow directions were determined from field observations of segments fingers grooves and groove molds of the dikes the study indicates that the mean axis of magma flow is subhorizontal toward the north in agreement with the direction of divergence of the radial dike system two modes of flow were observed 1 regular bedding parallel flow in the well stratified rock units and 2 irregular meandering flow in the massive rock units it is suggested that corrugated dike walls in well stratified host rocks cause magma channelization and random or self generated restrictions in massive host rocks cause the apparent meanders furthermore the major lithologic boundaries in the host units strongly affect segmentation of the dikes

magnetic fabrics of dike swarms from se bahia state brazil their significance and implications for mesoproterozoic basic magmatism in the sao francisco craton abstract magnetic fabrics were determined by applying two techniques anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence aar ams was performed in 81 dikes from ilheus olivenca and itaju do colonia swarms located in se bahia the dikes intrude high grade metamorphic terrains as old as 3 2 ga dikes are vertical or subvertical in dip and trend mainly e w they are tholeiitic in composition and are classified into two groups characterized by high tio 2 2 and incompatible elements contents and low tio 2 and incompatible elements contents respectively thicknesses vary from a few centimeters to ca 20 m average of 3 m 40 ar 39 ar data indicate ages of 1 012 ilheus dikes and 1 078 ga olivenca dikes rock magnetism shows that ti poor titanomagnetites up to pure magnetites pseudo single domain multidomain grain sizes carry the magnetic fabrics three types of ams fabric are recognized i normal fabric 64 dikes defined by the clustering of k 1 k 2 axes on the dike plane whereas k 3 axes are nearly perpendicular to it this fabric is interpreted as due to magma flow ii intermediate fabric seven dikes characterized by k 1 k 3 axes clustering close to dike plane and k 2 axes perpendicular to the dike wall it was interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike direction and iii inverse fabric nine dikes defined by k 2 k 3 plane parallel to the dike plane and k 1 perpendicular to dike wall aar measurements were performed in three dikes two of them with inverse and one with normal ams fabrics aar was coaxial for normal ams fabric and it resulted in intermediate and normal for inverse ams fabrics a combination of ams and aar fabrics suggests that the magmatic fabric for these dikes that should be flow was overprinted by some local event probably related to brasiliano orogeny processes after dike emplacement inverse ams fabric would record this event normal fabric is the most important one found for the studied swarms the analysis of k 1 inclination permitted one to infer that the dikes from ilheus were fed dominantly by horizontal fluxes k 1 k 1 60 dikes from itaju do colonia region have the steepest k 1 suggesting that this region could be closer to a magma source on the other hand a magma source near to olivenca area could be also inferred since the majority of the dikes were fed by inclined flow the existence of more than one source is supported by geochemical geochronological and paleomagnetic data which have shown that contemporaneous dikes were fed by compositionally distinct magmas the ams data also suggest that the majority of dikes were fed from upward flow coming from west to east and only a few of them were fed from upward flow from east to west

flow differentiation phenocryst alignment and compositional trends within a dolerite dike at rockport massachusetts systematic variations in the volume percent size and orientation of plagioclase phenocrysts up to 12 0 cm long occur across a 5 6 m thick porphyritic alkaline dolerite dike in rockport massachusetts field measurements indicate that phenocryst concentrations increase from nearly zero at the dike margin to 46 0 vol at its center average phenocryst size increases inward from 4 1 2 2 mm at the dike margin to 19 2 7 9 mm at the center the increase in size and abundance of phenocrysts toward the center of the dike is interpreted as resulting from flow differentiation the magma flow direction is assumed to have been upward and parallel to the dike margins n7 w stiike 88 e dip the strikes and dips of all elongate phenocrysts viewed in cross section within one traverse across the dike were measured and compared to the dike attitude to determine the degree of flow alignment across the dike average phenocryst strike deviations from dike strike increase inward 21 8 from the dike margin to its midpoint phenocryst dip angle deviations from dike dip increase inward by 18 8 this more pronounced clow alignment of phenocrysts nearer the dike margins is interpreted as being a function of the more extreme velocity gradients and resulting shear due to flow within the marginal zones of the magma than within its interior at least the outer few centimetres of phenocryst free chilled dike margins may form primarily by rapid quenching of phenocryst free magma rather than by flow differentiation whole rock major and minor element trends across this dike may be produced in part by flow differentiation a1 2 o 3 cao p 2 o 5 and na 2 o increase inward with plagioclase phenocryst concentrations whereas sio 2 k 2 o feo tio 2 mgo and mno decrease this inward decrease in certain oxides together with an inward within dike decrease in the anorthite content of the cores of plagioclase phenocrysts cannot be attributed to flow differentiation the inward decreasing chemical trends are believed to have resulted from one or a combination of several of the following processes the concentration of silica and incompatible elements in glass now devitrified within chilled dike margins compared to interiors plagioclase fractionation continuous tapping of partial melts increasingly depleted of silica and incompatible elements tapping of a zoned magma chamber and greater crustal contamination of marginal liquids superposed on the chemical trends the inward decrease in plagioclase anorthite content resulted from fractional crystallization

mafic intrusions east of svalbard imaged by active source seismic tomography a seismic refraction and reflection tomography experiment was performed across the igneous province east of svalbard which is a part of the cretaceous high arctic large igneous province seismic travel times from 12 ocean bottom seismometers hydrophones deployed along a 170 km line are inverted to produce smooth 2d images of the crustal p wave velocity and geometry of the acoustic basement and moho the inversion of travel times was complemented by forward elastic wave propagation modeling integration with onshore geology as well as multichannel seismic magnetic and gravity data have provide additional constraints used in the geological interpretation the seismic p wave velocity increases rapidly with depth starting with 3 km s at the sea floor and reaching 5 5 km s at the bottom of the upper sedimentary layer the thickness of this layer increases eastward from 2 km to 3 5 km on average the p wave velocity in the crystalline crust increases with depth from 5 5 km s to 6 8 km s the crustal thickness is typical for continental shelf regions 30 34 km finger shaped high velocity anomalies one reaching 12 and two of 4 6 velocity perturbation are obtained these velocity anomalies are concomitant with lower cretaceous basaltic lava flows and sills in the shallow sediments and elongated gravity and magnetic highs traced towards the northern barents sea passive continental margin we interpret the obtained velocity anomalies as signatures of dikes emplaced in the basement during breakup and subsequent spreading in the arctic amerasia basin

magnetic fabrics and rock magnetism of proterozoic dike swarm from the southern sao francisco craton minas gerais state brazil magnetic fabric and rock magnetism studies were performed on 32 mafic dikes of a proterozoic dike swarm from the southern sao francisco craton sfc minas gerais state se brazil magnetic anisotropies were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of remanent magnetization arm the latter was performed imposing both anhysteretic total aar and partial paar and isothermal remanence magnetizations airm partial anhysteretic remanence anisotropy was performed based on remanent coercivity spectra from a pilot specimen of each site in most sites ams is dominantly carried by ferromagnetic minerals however in some sites the paramagnetic contribution exceeds 70 of bulk susceptibility rock magnetism and thin section analysis allow classifying the dikes as non hydrothermalized and hydrothermalized magnetic measurement shows that the mean magnetic susceptibility is usually lower than 5 10 3 si ti poor titanomagnetites up to pure magnetite pseudo single domain psd grain sizes carry the majority of magnetic fabrics for non hydrothermalized dikes whereas coarse to fine grained ti poor titanomagnetites carry the majority of magnetic fabrics for hydrothermalized dikes three primary ams fabrics are recognized which are coaxial with arm fabric except for two dikes from both non hydrothermalized and hydrothermalized dikes normal ams fabric surprisingly is not dominant 31 the parallelism between ams paar0 30 paar30 60 and paar60 90 fabrics in the hydrothermalized dikes indicates that magnetic grains formed due to late stage crystallization or to remobilization of iron oxides due to hydrothermal alteration after dike emplacement have acquired a mimetic fabric coaxial with the primary fabric given by coarse grained early crystallized ti poor titanomagnetites this fabric is interpreted as magma flow in which the analysis of kmax inclination permitted the inference that the dikes were fed by horizontal or subhorizontal fluxes kmax 30 intermediate ams fabric is the most important 41 in the investigated swarm it is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike arm determinations for these sites also remained intermediate except for two dikes in one of them airm fabric resulted in normal ams fabric while for the other aar fabric resulted in inverse ams fabric a combination of ams and arm fabrics suggest that magmatic fabric for both dikes were overprinted by some late local event probably related to brasiliano orogenic processes after dike emplacement inverseinverse ams fabric is a minority four dikes arm determinations also remained inverse suggesting a primary origin for inverse ams fabric

effect of post magmatic processes on magnetic fabric of teschenite association rocks of the outer western carpathians abstract volcanic and subvolcanic alkaline rocks of the teschenite association of the outer western carpathians are characterized by intensive late magmatic post magmatic and also hydrothermal changes that modified their composition not only in rock forming minerals but also in accessory magnetic minerals magnetite titanomagnetite maghemite as indicated by magnetic susceptibility ranging from 10 5 to 10 1 si units the magnetic fabric of the most sills and dykes investigated is very roughly conformable to the shapes of the bodies corresponding to the most common type of magnetic fabric in dykes and sills which no doubt originates through magma flow however the fabric shows large variation much larger than expected for volcanic magnetic fabric which can be ascribed to late magmatic or post magmatic alterations of magnetic minerals diminishing the magnetic fabric homogeneity even though the teschenite association rocks occur in the sole part of the silesian thrust sheet their magnetic fabric and that of host sedimentary rocks show only very weak indications of ductile deformation consequently the silesian thrust sheet responded to the tectonic movements creating thrust sheet structure by faulting and thrusting of the deformed zones and not by ductile deformation of the bulk of the thrust sheet

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

magma flow exsolution processes and rock metasomatism in the great messejana plasencia dyke iberian peninsula magma flow in dykes is still not well understood some reported magnetic fabrics are contradictory and the potential effects of exsolution and metasomatism processes on the magnetic properties are issues open to debate therefore a long dyke made of segments with different thickness which record distinct degrees of metasomatism the messejana plasencia dyke mpd was studied oriented dolerite samples were collected along several cross sections and characterized by means of microscopy and magnetic analyses the results obtained show that the effects of metasomatism on rock mineralogy are important and that the metasomatic processes can greatly influence anisotropy degree and mean susceptibility only when rocks are strongly affected by metasomatism petrography scanning electron microscopy sem and bulk magnetic analyses show a high temperature oxidation exsolution event experienced by the very early ti spinels during the early stages of magma cooling which was mostly observed in central domains of the thick dyke segments exsolution reduced the grain size of the magnetic carrier multidomain to single domain transformation thus producing composite fabrics involving inverse fabrics these are likely responsible for a significant number of the abnormal fabrics which make the interpretation of magma flow much more complex by choosing to use only the normal fabric for magma flow determination we have reduced by 50 per cent the number of relevant sites in these sites the imbrication angle of the magnetic foliation relative to dyke wall strongly suggests flow with end members indicating vertical dominated flow seven sites and horizontal dominated flow three sites

the mechanism of flow and fabric development in mechanically anisotropic trachyte lava anisotropy of magnetic susceptibility ams and electron back scattered diffraction ebsd of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in tertiary volcanic province of the nw czech republic revealed two fabric types the high degree of ams fabric is associated with sanidine textural domains similar to normal kink bands type i fabric and occupies the whole body except the sw margin folded fabric and low anisotropy of ams also in the sw margin reveals sanidine alignment domains resembling reverse kink bands type ii fabric the flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their 010 planes and also by readjustment of the textural domain boundaries according to the fibre slip theory this microfabric study suggests that the type ii fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit type i fabric is interpreted to originate from type ii fabrics by further stretching of highly attenuated fold limbs asymmetric type i fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow the trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics

reply to comment by dario bilardello on new late pennsylvanian paleomagnetic results from parana basin southern brazil is the recent giant gaussian process model valid for the kiaman superchron

magma flow within dykes in submarine hyaloclastite environments an ams study of the miocene cabo de gata volcanic units this research has been funded by projects cgl2005 03511 bte hi2006 0073 prin2009 prin 2009h37m59 and prin 2010 11 2010tt22sc and 2010tt22sc 003

magma flow inferred from preferred orientations of plagioclase of the rio ceara mirim dyke swarm ne brazil and its ams significance

field impressed anisotropies of magnetic susceptibility and remanence in minerals the application of alternating af or direct df magnetic fields to samples containing dispersed particles of magnetite titanomagnetite or maghemite has been found to alter significantly the measured low field susceptibility anisotropy even though the particle orientation is unchanged the acquisition of isothermal remanent magnetization irm is also strongly dependent on the previous af treatment given to the samples a method of quantifying the changes brought about by application of the fields is described the samples studied were intrinsically isotropic or only weakly anisotropic and the computed impressed susceptibility or irm ellipsoids produced by the applied fields were ellipsoids of revolution with the unique axis aligned with the applied field axis the size and shape of the field impressed ellipsoids were strongly dependent upon particle size these effects might thus form the basis of a rapid nondestructive means of estimating particle size in rocks the results also have important implications for magnetic fabric analysis and the static af demagnetization of rocks in particular to ensure that the intrinsic magnetic fabric is measured without any field impressed component of anisotropy samples should not be subjected to static af demagnetization prior to the determination of either low field susceptibility anisotropy or irm anisotropy samples should also not carry a significant remanence such as an irm acquired in a field greater than about 5 mt prior to low field susceptibility anisotropy analysis

preliminary anisotropy of magnetic susceptibility studies on 2367 ma bangalore karimnagar giant dyke swarm southern india implications for magma flow abstract anisotropy of magnetic susceptibility ams fabrics have been studied for the first time on a well constrained paleoproterozoic bangalore karimnagar giant mafic dyke swarm at ca 2367 ma in the dharwar craton south india a total number of 43 samples from nine sites representing five n e trending dykes have been subjected to ams and conventional rock magnetic studies the magnetic fabric is principally ferromagnetic in origin as the magnetic susceptibility values are 10 3 si which is further supported by isothermal remanent magnetization irm studies hysteresis loops isothermal remanent magnetisation irm thermomagnetic properties and optical observations indicate that pseudo single domain psd low titanium magnetite particles dominate the low field susceptibility of samples the magnetic fabrics results correspond well with the comprehensive field studies however the degree of anisotropy results ranges from 0 4 to 12 8 with a mean total anisotropy of 4 7 the principal ams axes for samples from all the sites are tightly clustered on equal area plots and two main fabrics were revealed in the bangalore karimnagar giant dyke swarm in the first the maximum susceptibility axes is sub horizontal and parallel to the dyke walls minimum susceptibility axes plot near the pole of the dyke it is interpreted as the primary magma flow direction a second fabric with maximum susceptibility axis is sub horizontal and perpendicular to the dyke walls and is interpreted as a result of vertical compaction at a late stage of crystallization preliminary results suggest that dyke propagation in the bangalore karimnagar giant dyke swarm preserve a flow induced fabric slightly upwards to the ne and magma flow is sub horizontal

lower cretaceous tholeiitic dyke swarms from the ponta grossa arch southeast brazil petrology sr nd isotopes and genetic relationships with the parana flood volcanics the lower cretaceous dykes of the ponta grossa arch the most important dyke swarms in brazil are associated with the flood basalts and rare acid flows of the northern parana basin the ponta grossa pg dykes are formed by two pyroxene tholeiites and rare acid rocks the basaltic dykes may be distinguished into two main groups a dominant high tio2 2 wt hti group and a subordinate low tio2 2 wt lti group characterized for similar mgo content by high and low incompatible element contents respectively most pg dykes do not show chemical and isotope evidence supporting important crustal contamination pg dykes with 87sr86sr 0 0 7060 plot in the mantle array sr 17 and nd 3 and can be considered virtually uncontaminated intra dyke chemical variations suggest that the normal or reverse differentiation trends may be related to pre emplacement low pressure differentiation processes the important chemical differences between incompatible element poor and incompatible element rich basaltic dykes cannot be accounted for in terms of fractional crystallization but are compatible with different melting degrees of a garnet peridotite mantle source e g 9 and 20 melting for the hti and lti tholeiites respectively field distribution of the magmatism chemistry and sr nd isotope compositions support that the pg dykes may be related to the flood volcanics of northern parana and not to those of the central and southern parana paleomagnetic data indicate that pg dykes are younger than the parana volcanics all the results suggest that pg dykes were probably feeders of the stratoid volcanics erupted in northern parana towards the continental margin and later eroded chemistry and isotopic data reveal that asthenospheric mantle components were not significant factors in the genesis of pg dykes dyke emplacement occurred during early phases of rifting and or flexuring cutting flood volcanic suites

magnetic fabric and its significance in the 1400 ma mealy diabase dykes of labrador canada an anistropy of magnetic susceptibility ams study of the relatively fresh mealy diabase dyke swarm indicates a correlation between the ams and the deformational effects in the rocks several ams components were revealed during experimental work on 211 samples that had been heated to 640 c during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields seventeen sites with slight or no deformation have a magnetic fabric composed of two major components the stable component attributed to a primary shape anisotropy has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike n 60 e respectively this configuration is consistent with an origin due to a post emplacement stress field whereby horizontal extension acted on a vertical sheet of partially crystallized magma the orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement the unstable component removed by fields up to 250 mt is attributed to induced domain anisotropy produced by mild tectonic stress during the grenville orogeny the approximate orientation of its principal components as found by the method of substitutional ellipsoids suggests an east west directed maximum stress four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed but which may be largely composed of domain and stress induced anisotropies developed during the grenville orogeny

shallow intrusive directions of sheeted dikes in the troodos ophiolite anisotropy of magnetic susceptibility and structural data sheeted dikes play a central role in the formation of oceanic crust it is commonly assumed that sheeted dikes intrude vertically upward from elongated mid ocean ridge mor magma chambers but there are no direct observational data bearing on this hypothesis this assumption contrasts with the intrusive behavior of subaerial volcanoes where magmas rise into shallow central magma chambers that laterally feed vertically oriented dikes the authors have studied intrusive directions of sheeted dikes in a structural analogue to oceanic crust the troodos ophiolite structural and magnetic fabric data of 65 dikes provide consistent results and suggest a broad distribution of shallow 20 degree to nearly vertical upward magma transport directions these data suggest that horizontal emplacement has to be considered for sheeted dikes at mors implying more centralized mor plumbing systems than previously thought such plumbing systems provide ample opportunity for complex mixing fractionation and contamination of mor lavas in magma chambers and tabular magma storage volumes whether the mor magma supply is linear or centralized also has a fundamental effect on crustal accretion processes and the geometry of hydrothermal convection systems

magnetic fabric and its significance in the florianopolis dyke swarm southern brazil summary magnetic fabric was determined by applying the anisotropy from the low field magnetic susceptibility ams technique in 62 mafic dykes from the mesozoic florianopolis santa catarina island dyke swarm southern brazil these dykes cut the crystalline basement rocks which are mainly proterozoic they are vertical or subvertical in dip and trend mainly ne although nw trending dykes are also found dykes are tholeiitic in composition and are geochemically similar to those from the ponta grossa swarm thicknesses vary from 0 3 to 60 m polished sections show that titanomagnetites carry the ams in these dykes hysteresis parameters show that the magnetic minerals fall in the psd range two types of magnetic fabric are recognized type i is characterized by k1 k2 parallel to the dyke wall representing magma flow within the dykes type ii with k1 k3 parallel to the dyke wall was found in four dykes type i is found in 94 per cent of the dykes and approximately 20 per cent of these have k1 inclinations of less than 30 suggesting horizontal or subhorizontal flow about 80 per cent have k1 inclinations of greater than 30 due to inclined to vertical flow the comparison of ams studies from both the florianopolis and the ponta grossa dykes suggests a source position closer to santa catarina island than the ponta grossa arch

variations in magnetic anisotropy and opaque mineralogy along a kilometer deep profile within a vertical dyke of the syenogranite porphyry at cinovec czech republic abstract vertical variations in magnetic fabric and paragenesis of the ferrimagnetic minerals for a virtually upright dyke of the altenberg syenogranite porphyry were investigated using profile data of borehole e 16 to a depth of 922 7 m eastern krusne hory mts nw bohemia it was revealed that this dyke likely consists of two magma pulses indicated both by magnetic fabric and by opaque mineralogy in most of the profile the magnetite grains are oriented parallel to the sub vertical dyke only at the base of the upper magma pulse in a depth interval of 200 400 m are these grains oriented sub horizontally being thus perpendicular to the dyke walls this pattern can be interpreted as a consequence of a static vertical compaction of the magma of the basal portions of the upper pulse due to the pressure of the ascending lower pulse the large planes of the ferrimagnetic minerals are oriented perpendicular to the shortening direction

non scaled analogue modelling of ams development during viscous flow a simulation on diapir like structures development of magnetic fabric within a diapirically ascending columnar body was investigated using non scaled analogue model made of plaster of paris containing small amount of fine grained homogeneously mixed magnetite the apparatus for the modelling consists of a manual squeezer with calibrated spring and a perspex container set of weak coloured layers at the bottom of the container was forced to intrude overlying fine grained sand through a hole in a board attached to the squeezer the development of ams fabric is correlated with complex flow pattern indicated by coloured and originally horizontal plaster layers strongly constrictional and vertical fabric in the base and in the lower domain of the diapir resulting from convergent and upwards flows is overprinted by subhorizontal oblate fabrics due to vertical flattening and initial divergent flow in the apical parts the measured ams fabrics are compared with natural examples of magmatic stocks and dykes

magnetic fabric studies of the nipissing sill province and senneterre dykes canadian shield and implications for emplacement the 2 21 ga nipissing diabase sills intrude the huronian supergroup of the southern province coeval senneterre dykes in the adjacent portion of the superior province are potential feeders for the sills anisotropy of magnetic susceptibility ams data were obtained from both of these units to study flow patterns and test emplacement models the sills exhibit three distinct paleomagnetic directions that are likely primary and represent a time correlation tool within the magmatic event two of the three directions are also found in senneterre dykes sites in the northern cobalt embayment carry an n1 reverse paleomagnetic signature they possess maximum ams axes that trend north northwest south southeast interpreted as the direction of magma emplacement in one area the data rule out a cone sheet emplacement mechanism the n3 paleomagnetic signature is restricted to a sill and or dyke like bodies near lake timiskaming where the ams axes are dominantly north northwest south southeast similar to that of the nearby n1 reverse sites sites in a geographically restricted area farther south carry an n1 normal paleomagnetic direction the ams patterns in these sites exhibit very poor within and between site consistency compatible with the magma having crystallized statically in this volumetrically minor magmatic pulse in the sudbury elliot lake area the nipissing diabase is deformed and outcrops exhibit east west elongation parallel to the fold axes of the enclosing huronian sedimentary rocks ams fabrics are interpreted as reflecting this deformation rather than primary magmatic flow three of eight senneterre dyke sites show horizontal flow patterns whereas the remainder have more complicated ams patterns

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

a new plumbing system framework for mantle plume related continental large igneous provinces and their mafic ultramafic intrusions abstract the magmatic components of continental large igneous provinces lips include flood basalts and their plumbing system of giant mafic dyke swarms radiating linear and the recently discovered circumferential type mafic sill provinces a lower crustal magmatic underplate mafic ultramafic m um intrusions associated silicic magmatism and associated carbonatites and kimberlites this paper proposes a new plumbing system framework for mantle plume related continental lips that incorporates all of these components and provides a context for addressing key thematic aspects such as tracking magma batches upstream and downstream and their geochemical evolution assessing the setting of m um intrusions and their economic potential interpreting deep magmatic component identified by geophysical signatures and estimating magnitudes of extrusive and intrusive components with climate change implications this plumbing system model and its associated implications needs to be tested against the rapidly improving lip record

magma flow and feeder chamber location inferred from magnetic fabrics in jotunitic dykes rogaland anorthosite province sw norway abstract the ca 930 920 ma rogaland anorthosite province of southwest norway is cross cutted by up to several km long dykes of the jotunite kindred the fabric of three major jotunitic dykes from this igneous complex the vetteland varberg and lomland dykes is investigated here using measurements of the anisotropy of magnetic susceptibility ams made along transversal sampling sections the petrofabric in the three studied dykes has an overall magmatic character and it is shown through image analysis that the ams which is controlled by the shape preferred orientation of low ti titanomagnetite grains can be used as a proxy for its orientation the average magnetic fabrics taken as flow markers give valuable information on the geometry of the dykes and enable to locate the feeder magma chambers it appears that each dyke is connected to its own chamber in agreement with the conclusions of published geochemical studies a model of emplacement along a set probably two conjugate sets of active shear zones is proposed this model takes into account in particular the local occurrence of asymmetrical distributions of magnetic fabrics

runoff to boreal lakes linked to land cover watershed morphology and permafrost thaw a 9 year isotope mass balance assessment stable isotopes of oxygen and hydrogen were measured in water samples collected annually from a representative suite of 50 lakes in northeastern alberta over a 9 year period and are interpreted using a steady state isotope mass balance model to determine water yield and runoff ratios for the lake watersheds and residence time of the lakes this isotopic perspective on hydrology of the region provides new insight into the role of land cover watershed morphometry climatic drivers and permafrost thaw on lakes bog cover permafrost and presence of thaw features in bogs are found to be the dominant hydrologic drivers although morphometric properties such as elevation lake area and drainage basin area are also influential in addition to quantifying the hydrologic fluxes the analysis establishes contrasting conditions in more southerly lakes located in the stony mountains and west of fort mcmurray as compared with more northerly sites in the birch mountains caribou mountains and northeast of fort mcmurray mainly because of contributions from thawing permafrost at the northerly sites distinct hydrologic conditions are also noted for shield systems north of lake athabasca where bogs and permafrost are absent while permafrost thaw is not directly labelled by oxygen and hydrogen isotope composition isotope mass balance calculations suggest that contributions of up to several hundred millimetres per year are occurring in 14 of the 50 lake watersheds under study several of these lakes have water yields in excess of precipitation in some years and regional groups of lakes display significant correlations between water yield and percentage of bogs that have collapsed copyright 2015 john wiley sons ltd

tectonic implications of the 1419 ma nova guarita mafic intrusives paleomagnetic pole amazonian craton on the longevity of nuna abstract the nuna supercontinent was probably assembled in the paleoproterozoic but its paleogeography and the timing for its demise are still a matter of debate a paleomagnetic and geochronological study carried out on the mesoproterozoic nova guarita dyke swarm northern mato grosso state sw amazonian craton provides additional constraints on the duration of this supercontinent paleomagnetic af and thermal treatment revealed south southwest northeast magnetic directions with downward upward inclinations for 19 analyzed sites these directions are carried by psd magnetite with high unblocking temperatures as indicated by additional magnetic tests including thermomagnetic curves hysteresis loops and the progressive acquisition of isothermal remanence in selected samples a positive contact test with the host granite in one of the studied dykes further attests to the primary origin of the characteristic magnetic component a mean site direction was calculated at d m 220 5 i m 45 9 95 6 5 k 27 7 which yielded a paleomagnetic pole located at 245 9 e 47 9 s a 95 7 0 40 ar 39 ar dating carried out on biotites from four analyzed dykes yielded well defined plateau ages with a mean of 1418 5 3 5 ma the nova guarita pole precludes a long lived nuna configuration in which laurentia baltica north china and amazonia formed a long and continuous block as previously proposed for the paleoproterozoic it is nevertheless fully compatible with a samba amazonia baltica link at mesoproterozoic times

fabric of the rio ceara mirim mafic dike swarm northeastern brazil determined by anisotropy of magnetic susceptibility and image analysis 1 anisotropy of magnetic susceptibility ams and petrofabric studies of the early cretaceous rio ceara mirim dike swarm reveal that shape preferred orientation of opaque grains controls the magnetic fabric the 350 km long swarm is characterized by relatively thick dikes of the order of 20 m up to 150 m in width the strong magnetic susceptibility of these rocks around 5 10 2 si is attributed to magnetite with low ti content the magnetite usually forms euhedral to subhedral equant to skeletal grains the resulting ams has a large proportion of abnormal fabric types as observed in 58 of the 50 dikes studied the remaining 42 of the dikes show a normal fabric regionally characterized by steep magnetic foliations and subhorizontal lineations in the central eastern part of the swarm however the lineation plunges downdip suggesting a magmatic feeder zone the shape alignment of the plagioclase supports the inferred regional flow pattern indicating a primary origin for the normal ams inverse to highly imbricate magnetic fabrics have lineations perpendicular to or at a high angle to the dike wall a shape lineation of opaque grains lies generally close to the magnetic lineation while the foliation is provided by the oblate shaped plagioclase fabric petrofabric studies indicate that the abnormal magnetic fabric is unrelated to flow competition of interstitial magnetite grains crystallizing either along as well as perpendicular to the magma stretching direction seems to account for the weak magnetic anisotropy and the irregular distribution of the ams types on the swarm

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

applicability of ams technique as a flow fabric indicator in dykes insight from nandurbar dhule deccan dyke swarm determination of the nature of magma flow vertical or lateral from rock fabrics in a dyke swarm holds significant importance in deciphering its emplacement mechanism depth of magma chamber and its association with mantle plumes nandurbar dhule dyke swarm from western india consists of 210 mappable tholeiitic large linear dykes intruding the country rocks of deccan basalt we discuss here the development of flow controlled rock fabrics in these dykes as a function of their thicknesses magnetic fabric obtained from anisotropy of magnetic susceptibility ams analysis of the samples collected from these dykes was used as a proxy for rock flow fabric samples from the central parts of the thicker dykes strike perpendicular thickness 10 m show random and inconsistent development of magnetic fabrics than their marginal counterparts petrography suggests the development of relatively clear shape preferred orientations of the elongated mineral grains only at the margin of a thick dyke thinner dykes strike perpendicular thickness 10 m show both consistent magnetic fabrics and clear shape preferred orientations we propose that the center of a thick dyke fails to provide due to high flow velocity slower cooling rate lack of friction induced shearing and draining back of magma a favorable condition where a flow fabric can efficiently develop and b magnetic fabric can effectively mimic the flow fabric thinner dykes and the margins of the thicker dykes are hence better candidates for observing flow fabrics represented by magnetic fabrics this work is also motivated by the reservations expressed by earlier researchers in using the ams technique for magma flow characterization especially for giant dyke swarms we have critically evaluated their reservations in light of our results and commented on the applicability of the ams technique on such studies

evidence for recent temperature induced water migration into permafrost from the tritium content of ground ice near mayo yukon territory canada determinations of the tritium 3h content of ground ice collected near mayo yukon territory indicate that since the mid 1950s atmospheric water has infiltrated permafrost to depths of up to 50 cm the rate of tritium infiltration into permafrost at two plots irrigated with tritiated water in 1983 suggests that tritium movement is principally due to temperature induced mass transport rather than molecular diffusion

the parana etendeka continental flood basalt province a historical perspective of current knowledge and future research trends abstract the development of ideas concerning continental flood basalt provinces is not new and many studies were completed on specific provinces before the advent of plate tectonics the parana etendeka province is not an exception and actually is an example of a province that has been thoroughly studied for 100 years in this work i present a brief summary of various aspects of this province from a rather general point of view including many references of difficult access to a reader not versed on the portuguese language key features include the presence of alkaline volcanism along the edges of the main basin before and after a markedly tholeiitic event the uneven spatial distribution of eruptive products relative to the location of continental rupture the apparent lack of a pattern of temporal activity across the whole province and the close relationship between the structure of the underlying sedimentary basin and the distribution of volcanic rocks by bringing together information relevant to all of those key features an evolutionary model emphasizing the role played by the changing local structure is outlined this model is an example of how key observations many of which were overlooked for 50 years provide the required impetus for the completion of future research that has the potential to substantially change the form in which this province has been visualized for at least the past 30 years

rock texture and magnetic lineation in dykes a simple analytical model abstract we develop two simple models for simulating the combination of magnetic sub fabrics related to magma flow in dykes the basic assumptions are i the petrofabric is representative of the flow fabric and ii the petrofabric is composed of s c type structures related to flow the first model consists of summing the magnetic tensors of two identical sub fabrics differing solely by their relative rotation this model accounts for the possible change of the macroscopic magnetic lineation from a flow related fabric to a lineation situated at the geometric intersection between the two sub fabrics such a result is obtained in the case of oblate to highly oblate sub fabric ellipsoids the second model integrates the effect of very oblate grains of variable orientations into calculating the shape controlled magnetic tensor of each sub fabric and emphasizes the possible under estimation of fabric superposition due to microscopic disordering the magma fluxes along the east greenland volcanic margin are illustrated by the flow pattern within the major dyke swarm the magmatic flow vectors inferred from the imbrication of magnetic foliation at the dyke margins are primarily horizontal the classic use of magnetic lineation can lead to contradictory results giving flow vectors perpendicular to the flow directions the magnetic lineation is situated close to the zone axis of magnetic foliation planes over a wide range of scales throughout the dyke swarm suggesting that the contradiction may arise from the association of several textural domains at the sample scale forward modelling of macroscopic magnetic fabrics using the first model yields good agreement with the measured magnetic fabric of the east greenland dykes our results which are applicable to strained sedimentary rocks highlight the possible misuse of the magnetic lineation due to combination of magnetic textures the exchange between a microscopic lineation i e mineralogical lineation and a macroscopic lineation i e intersection lineation is particularly expected for dykes that generally bear oblate magnetic textures

contemporaneous alkaline and tholeiitic magmatism in the ponta grossa arch parana etendeka magmatic province constraints from u pb zircon baddeleyite and 40ar 39ar phlogopite dating of the jose fernandes gabbro and mafic dykes abstract we report the first high precision id tims u pb baddeleyite zircon and 40ar 39ar step heating phlogopite age data for diabase and lamprophyre dykes and a mafic intrusion jose fernandes gabbro located within the ponta grossa arch brazil in order to constrain the temporal evolution between early cretaceous tholeiitic and alkaline magmatism of the parana etendeka magmatic province u pb dates from chemically abraded zircon data yielded the best estimate for the emplacement ages of a high ti p sr basaltic dyke 133 9 0 2 ma a dyke with basaltic andesite composition 133 4 0 2 ma and the jose fernandes gabbro 134 5 0 1 ma a 40ar 39ar phlogopite step heating age of 133 7 0 1 ma from a lamprophyre dyke is identical within error to the u pb age of the diabase dykes indicating that tholeiitic and alkaline magmatism were coeval in the ponta grossa arch although nearly all analysed fractions are concordant and show low analytical uncertainties 0 3 0 9 ma for baddeleyite 0 1 0 4 ma for zircon 2 pb loss is observed in all baddeleyite fractions and in some initial zircon fractions not submitted to the most extreme chemical abrasion treatment the resulting age spread may reflect intense and continued magmatic activity in the ponta grossa arch

anisotropy of out of phase magnetic susceptibility as a potential tool for distinguishing geologically and physically controlled inverse magnetic fabrics in volcanic dykes abstract among the mechanisms of the mass transport within the earth s crust and the upper mantle the magma movement within the dykes is very important in some dykes the magma movement is represented by almost free flow infilling more or less open fractures in the host rocks while it has character of forceful injection of the host rocks in the other dykes the magnetic fabric originated by the free flow is characterized by the magnetic foliation and magnetic lineation approximately parallel to the dyke plane normal fabric whereas the forceful injection gives rise to the magnetic foliation perpendicular to the dyke plane defining the intermediate or inverse magnetic fabric it is known however that the inverse magnetic fabric can also originate through the free flow of magma in the case when the minerals carrying the ams are represented by single domain sd grains in order to distinguish between the two mechanisms controlling the intermediate inverse fabric the anisotropy of magnetic remanence amr is often used because it indicates the shape preferred orientation of ferromagnetic minerals regardless of their domain state we show that not only amr but also the anisotropy of out of phase magnetic susceptibility opams is conformable with particle shape regardless of the magnetic state of the particle consequently the opams which is measured automatically with the standard ams using the kly 5 kappabridge may substitute the amr at least in some cases of volcanic dykes

magnetic anisotropy produced by magma flow theoretical model and experimental data from ferrar dolerite sills antarctica summary volcanic rocks forming sills dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement we model a sill as a steadystate flow of a bingham fluid driven by a pressure gradient in a horizontal conduit the magma velocity as a function of depth is calculated from the motion and constitutive equations vorticity and strain rate are determined for a reference system moving with the fluid the angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations it is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction and that the magnetic foliation plane changes periodically from horizontal to vertical the results are compared with the magnetic fabric of ferrar dolerite sills victoria land east antarctica derived from low field susceptibility measurements

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

diverse magma flow directions during construction of sheeted dike complexes at fast to superfast spreading centers abstract dike intrusion is a fundamental process during upper oceanic crustal accretion at fast to superfast spreading ridges based on the distribution of magma along fast spreading centers inferred from marine geophysical data models predict systematic steep flow at magmatically robust segment centers and shallow magma flow toward distal segment ends anisotropy of magnetic susceptibility ams fabrics from 48 fully oriented block samples of dikes from upper oceanic crust exposed at hess deep rift and pito deep rift reveal a wide range of magma flow directions that are not consistent with such simple magma supply models the ams is interpreted to arise from distribution anisotropy of titanomagnetite crystals based on weak shape preferred orientation of opaque oxide and plagioclase crystals generally parallel to ams maximum eigenvectors most dike samples show normal ams fabrics with maximum eigenvector directions ranging from subvertical to subhorizontal the distributions of inferred magma flow lineations from maximum eigenvectors show no preferred flow pattern even after structural correction we use a kolmogorov smirnov test ks test to show that the distribution of bootstrapped flow lineation rakes from pito deep are not statistically distinct from hess deep and neither are distinguishable from oman and troodos ophiolite ams data magma flow directions in sheeted dikes from these two seafloor escarpments also do not correlate with available geochemistry in any systematic way as previously predicted these results indicate distinct compositional sources feed melt that is injected into dikes at fast to superfast spreading ridges with no preference for subhorizontal or subvertical magma flow collectively results imply ephemeral melt lenses at different along axis locations within the continuous axial magma chamber and either direct injection or intermingling of melt from other deeper ridge centered or off axis sources

magma flow pattern of the 1 78 ga dyke swarm of the north china craton during the initial assembly of the supercontinent nuna columbia constraints from rock magnetic and anisotropy of magnetic susceptibility studies abstract the geodynamic origin of the 1 78 ga dyke swarm in the north china craton ncc is long debated it is considered either a post collision process or paleoplume related constraining its origin is essential for the reconstruction of the ncc position within the supercontinent nuna also referred to as columbia here we report on the rock magnetism and anisotropy of magnetic susceptibility ams of thirty three 1 78 ga dykes to constrain the magma center of the igneous event the samples were collected from the entire swarm across the ncc magnetite appears to be the dominant magnetic mineral in all the dykes occasionally with minor maghemite while the magnetite grain size within the dykes is generally increasing from south to north ams results of the dykes portray a magma flow related fabric over half of the studied dykes show a predominance of horizontal to subhorizontal magmatic flow while a few have been formed by vertical intrusion these observations imply that the 1 78 ga dyke swarm may have been generated by sustained magma flow from a magmatic source centered at the south margin of the ncc during dyke propagation some localized magma subchambers may have been formed they could be responsible for the less common vertically intruded dykes and the ew trending dykes therefore a plume related tectonic setting for the 1 78 ga dyke swarm is more compelling with the eruption center along the margin of the ncc it may serve as an essential criterion to search for possible counterparts in other tectonic units within nuna columbia to evaluate the proximity of the ncc with them

an ams study of magma transport and emplacement mechanisms in mafic dykes from the etendeka province namibia abstract the henties bay outjo dyke swarm hod in nw namibia is part of the early cretaceous parana etendeka large igneous province the dykes are dominantly doleritic compositionally equivalent to the erupted lava series and thus the hod provides a look at the feeder systems of a flood basalt province the subvertical dykes mostly strike ne sw and minor nw se parallel or perpendicular to the damara belt in which they intruded we present a magnetic fabric study using the anisotropies of low field magnetic susceptibility ams and of anhysteretic remanent magnetization aarm with the aim to derive magma flow directions and better constrain emplacement mechanisms within the dyke swarm magnetic susceptibility and its anisotropy in the dykes is mainly controlled by distribution anisotropy of titanomagnetite that mimics the flow oriented silicate fabric the anisotropy is low in most samples supporting a magmatic origin in 66 of 110 investigated samples the ams fabric is normal with the max axis inferred flow orientation within the dyke plane most samples yielded vertical to subvertical flow orientations regardless of location near or distant from the former rifted margin the anomalous magnetic fabrics where max is inclined to the dyke plane are attributed to two mechanisms one is the single domain effect of titanomagnetite which was found by unequal orientations of ams and aarm fabrics the other case anomalous fabric is rotation of the ams axes by shear within the magma producing symmetric imbrication of ams fabric on opposite dyke walls or more commonly asymmetric magnetic fabrics which we relate to tectonic shear at the dyke walls during emplacement field support for syn emplacement shear is given by dyke segmentation geometries including locally curved segment tips en echelon arrangements and left right stepping displacements regionally syn emplacement shear is consistent with the observed reactivation during gondwana breakup of transcrustal shear zones in the damara mobile belt

higher tritium concentrations measured in permafrost thaw lakes in northern alberta tritium concentrations were measured in a survey of 24 lakes 15 wetlands and 133 groundwaters in the oil sands region of northeastern alberta and compared with both recent precipitation and precipitation sampled during the 1960s tritium peak caused by atmospheric thermonuclear weapons testing water samples from lakes included a group of 14 thaw lakes that had higher runoff attributed to melting of permafrost in peat plateaus within their watersheds while tritium in all lakes was found to be intermediate between recent and 1960s concentrations the thaw lakes were found to be significantly enriched in tritium compared with other lakes as were unfrozen wetlands characterized by a thick sequence of low hydraulic conductivity peat the results provide further evidence of different water sources to the thaw lakes and may indicate that melting of modern permafrost in part formed since the 1950s is occurring in these systems copyright 2015 john wiley sons ltd

paleomagnetism and magnetic fabric of middle jurassic dykes from western patagonia argentina abstract jurassic volcanism in patagonia is widespread although associated dyke swarms are conspicuous they have been almost neglected in previous geologic studies of this region radiometric paleomagnetic and magnetic anisotropy studies are reported from a middle jurassic basic to intermediate dyke swarm exposed in the sierra de mamil choique western patagonia in an area of over 350 km2 two whole rock k ar determinations indicate that these dykes were intruded at around 170 ma an anisotropy of magnetic susceptibility ams study on 15 dykes 74 block samples shows that they carry different kinds of magnetic fabric both normal and inverse apparently governed by compositional differences a paleomagnetic study of these samples suggests that ti poor titanomagnetite is the probable carrier of the characteristic remanence mean site characteristic directions pass a reversal test grade c a paleomagnetic pole computed by averaging vgps from each individual dyke is situated at 70 2 s 190 4 e n 13 95 9 7 not substantially apart from other middle jurassic poles from south america further refinement of the jurassic south american apparent polar wander path is needed to establish whether or not the mamil choique dykes were affected by a small tectonic rotation

an ams study of different silicic units from the southern parana etendeka magmatic province in brazil implications for the identification of flow directions and local sources abstract in the southern portion of the parana etendeka magmatic province in brazil extensive silicic dacite rhyolite deposits occur at the top of a sequence of low ti pahoehoe to rubbly basalts the internal architecture of the silicic deposits and their eruptive style as well as the location of their sources are still unsatisfactorily known in an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive and test the hypothesis of local sources we carried out anisotropy of magnetic susceptibility ams studies on the two main silicic units caxias do sul dacites and santa maria rhyolites with the best exposures in an area previously mapped in detail magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites rock magnetism properties indicate that pseudo single domain magnetite carries the fabrics and the remanence magnetic fabrics were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm both ams and aarm tensors are coaxial indicating that the ams fabric is not affected by the effect of magnetite single domain grains magnetic data from several dacitic coulees caxias do sul unit indicate flows from se to nw the location and spatial distribution of these lavas support the hypothesis of local sources aligned along a ne sw trend these data are in agreement with the alignments of structures dome shaped hills observed in field work and dem images on the other hand magnetic data obtained in santa maria rhyolites indicate that flow directions in two different areas are distinct towards nw ne and w suggesting that they derived from different emission centers so regarding the silicic volcanism in the studied region our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit in contrast we propose the occurrence of local volcanic events implying in the existence of different sources possibly characterized by local emission centers

origin and hydrogeological setting of saline groundwater discharges to the athabasca river geochemical and isotopic characterization of the hyporheic zone abstract identifying impacts of oil sands development on aquatic ecosystems requires understanding of the natural background water quality in the athabasca oil sands region of alberta this is challenging because the athabasca river is incised directly into bitumen saturated sands of the mcmurray formation and other saline cretaceous and devonian formations this study compares the geochemical and isotopic composition of porewater sampled from the alluvial sediment beneath the athabasca river with regional groundwater data to identify the geological origin of these saline groundwaters and improve characterization of natural background sources of solutes entering the athabasca river terrain conductivity surveys conducted along the athabasca river were used to identify areas with evidence of saline groundwater discharge porewater samples were obtained from the alluvial sediment using drive point piezometers installed between 1 and 3 m below the water sediment interface and were analyzed for 18o 2h 34s so4 18o so4 87sr 86sr 13c dic 13c doc 3h and 14c the porewater in the alluvial sediment showed variable degrees of mixing with the overlying athabasca river water but the geochemical and isotopic composition in zones 1 3 and 5 are consistent with discharge of saline groundwater from cretaceous or devonian units the low percentages of modern carbon and 18o 2h 34s so4 18o so4 and 87sr 86sr signatures in the deepest porewater samples from zones 1 3 and 5 indicate glaciogenic water with high total dissolved solids originating from devonian sourced solutes theses saline groundwater discharge zones occur where higher horizontal hydraulic gradients coincide with areas of higher salinity in the adjacent cretaceous and devonian aquifers and areas with vertical connectivity with underlying devonian aquifers the results of this study demonstrate the influence of groundwater surface water interactions and saline bedrock formation water discharge to water quality along some reaches of the athabasca river which need to be considered in monitoring and water management strategies

isotope geochemistry of frost blister ice north fork pass yukon canada oxygen 18 and deuterium abundances vary with depth in ice from a frost blister at a spring site near north fork pass yukon they indicate that the ice was formed by continuous downward freezing under nearly ideal closed system conditions in a water filled cavity weighted mean values of 18o and 2h for the ice samples indicate that the frost blister ice was formed from groundwater similar to that of nearby springs the slope of the regression line 5 1 for the 18o and 2h data of the frost blister ice suggests that nonequilibrium fractionation conditions existed during freezing tritium concentrations in the ice show irregular variations with depth the weighted mean 3h concentration for the ice is however similar to that of the spring water

magma injection directions inferred from a fabric study of the popes harbour dike eastern shore nova scotia canada a 15 m wide dike at popes harbour on the eastern shore of nova scotia shows an increase in both the size up to 1 m and density up to 50 of predominantly pelitic xenoliths toward the dike center these features reflect flowage differentiation processes during dike emplacement flow direction is indicated by sillimanite xenocrysts that represent the unassimilated products of xenolith disaggregation the xenocrysts are highly aligned parallel to the dike margins northwest southeast with a mean plunge of 20 se suggesting that the magma last moved and may have been injected in a subhorizontal northwestward direction the available information indicates that lateral injection of magma in mafic dikes is more common than predominantly vertical movement this study shows that an analysis of fabrics in mafic dikes should be useful in further evaluating the role of lateral magma injection in dike formation

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

magnetic fabric and inferred flow direction of dikes conesheets and sill swarms isle of skye scotland abstract we have measured the ams of 16 dikes 35 conesheets and three sills associated with the cuillin hills magmatic center of the isle of skye in the inner hebrides of scotland and of nine dikes located in the regional dike swarm of skye sixty three intrusives totalling 734 samples were studied to determine the plumbing of the skye volcanic system low field susceptibility versus temperature k t identified three different mineral phases in the area namely ti rich magnetite pyrrhotite and titanomaghemite the petrofabrics of the 63 intrusives yielded coherent flow azimuths regardless of their time of emplacement three main types of magnetic fabric a c were found fabric type a plane kmax kint parallel to the dike plane represents the magma flow direction within the intrusives and is the dominant fabric 55 of all the intrusives within the cuillin hills magmatic center and its regional dike swarm the kmax inclinations show that 55 of the intrusives were fed by horizontal to sub horizontal ams inclination of the kmax axis is equal or less than 30 magma fluxes and the rest of them were fed by inclined to vertical fluxes horizontal magma flow means lateral magma injection inside fractures and becomes more probable as the source is located further away

magnetic fabric and petrology of miocene sub volcanic sills and dykes emplaced into the sw flysch belt of the west carpathians s moravia czech republic and their volcanological and tectonic implications abstract magnetic fabrics were investigated in the sub volcanic bodies occurring within the sw flysch belt of the western carpathians magnetite or low ti titanomagnetite is the principal carrier of the anisotropy of magnetic susceptibility ams in these rocks though various fe ti oxides were also identified in minor amounts the magnetic fabric in almost all sills and dykes is conformable to the shapes of the bodies and no doubt originated through more or less free magma flow that requires relatively open voids to be injected that likely originated in an extensive tectonic regime in an ankaramite sill where the rock creates typical hexagonal columns the magnetic fabric is related rather to the column axes than to the overall shape of the sill the magnetic fabric formation in this sill is controlled by the post emplacement process of the creation of the columns at some studied localities signs of post magmatic middle miocene tectonic deformation are observed in the field the youngest known in the flysch belt as the magnetic fabric is unrelated to those signs we conclude that these young tectonic movements did not penetrate ductilely in the volume of the volcanic body it seems that the strain was focused to thin zones along the faults since it did not change the preferred orientation of magnetic minerals in the rock volume substantially

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

ams measurements on obsidian from the inyo domes ca a comparison of magnetic and mineral preferred orientation fabrics abstract measurements of the anisotropy of magnetic susceptibility ams on lavas can yield information concerning flow directions deformation regimes and relative shear rates here we report results of measurements made on samples of rhyolitic obsidian collected from obsidian dome ca comparisons of ams measurements with previously determined 3d microlite orientation distributions in these samples serve as a calibration of the ams technique despite the low values of bulk susceptibility 1 06 7 04 10 3 si found in the dome relative to typical values in basalts 10 2 si the degree of anisotropy is extremely high in all specimens 3 4 10 7 furthermore susceptibility tensors exhibit a wide range of shapes varying from prolate to triaxial and flattened ellipsoids b parameter from 8 6 to 6 4 corresponding to various degrees of microlite dispersion our results also indicate that despite the tight clustering of principal susceptibility axes obtained on each site bulk flow directions inferred from the orientations of k max axes may be misleading because the orientation of the local extension changes from place to place within the dome however it is shown that the ams of each specimen provides a good measure of the direction of local extension consequently it is possible to interpret spatial variations in flow regime from systematic changes in the orientation of principal susceptibility axes as the proposed association between the local deformation regime and ams is strongly dependent on the aspect ratio of the crystals embedded in the flowing lava some caution must be exerted when interpreting ams results from other flows and a direct comparison between different flows may not be granted in many occasions

composite magmatic magnetic fabrics evidences late ams in syn tectonic dikes in the monteiro sume plutonic volcanic complex ne brazil abstract interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility ams are based on the orientation of the magnetic fabric recorded next to the dike walls however uncertainties remain when ams is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma we study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks the dikes have magnetic susceptibilities mostly between 10 3 and 10 2 si carried by fe ti oxides ams shows fabrics that would be consistent with a lateral movement of the magma however the anisotropy of anhysteretic remanence aar and silicate shape preferred orientation spo indicate that the melt moved upward based on the steeply plunging lineations detected by aar and spo furthermore the obliquity of the aar foliations in the dike margins indicates a component of transtension resolved in the dike walls as there is no evidence for internal deformation of titanomagnetite ams would record its late growth in the tectonic extension direction the magnetic subfabric concealed by late ams therefore documents an earlier tectonic episode and evidence the limits of using just ams directions to constrain the emplacement of syntectonic magmas

emplacement process of ferrar dolerite sheets at allan hills south victoria land antarctica inferred from magnetic fabric summary we analyse 10 representative intrusions from two sets of inclined diabase ferrar dolerite sheets exposed at allan hills south victoria land antarctica using petrographic and rock magnetic methods to determine microfabrics and infer magma flow directions at least one diabase sample was collected at the margins of each intrusion magnetite and pyrrhotite contribute to magnetic fabrics of the samples thirty six magnetic fabric directions inferred from the mutual arrangement of either the magnetic lineation or the magnetic foliation plane and local macroscopic flow indicators e g horn shaped apophyses and kinks at the tips and margins of each intrusion reveal composite i e both lateral and vertical flow paths recorded along each intrusive segment petrographic textures and multiple flow directions inferred at sheet segment tips reveal that passive injection of magma via hydrofracturing produced the local shallow large igneous province plumbing as a sill dominated intrusive complex very close to or intersecting the palaeosurface this contrasts with classic arrays of either vertically or laterally injected blade like dykes

thick dyke emplacement and internal flow a structural and magnetic fabric study of the deep seated dolerite dyke of foum zguid southern morocco 1 knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the earth s surface because many questions still persist we used the long thick and deep seated foum zguid dyke morocco to investigate dyke emplacement and internal flow by means of magnetic methods structural analysis petrography and scanning electron microscopy we also investigated how the host rocks accommodated the intrusion regarding internal flow 1 important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall 2 anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility ams results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the ams maximum principal axis and 3 a dominant upward flow near the margins can be inferred the magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling whereas in the core the magnetic properties have been affected by high temperature exsolution and metasomatic effects due to slow cooling regarding dyke emplacement this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and or folding of the host sedimentary strata dewatering related to heat as recorded by thick quartz veins bordering the dyke in some localities may have also helped accommodating dyke intrusion the spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip

anisotropy of magnetic susceptibility sedimentological igneous and structural tectonic applications as was noted by graham 1954 anisotropy of magnetic susceptibility ams data has many applications to the study of geological processes this type of anisotropy expresses directional variation in the magnetization induced in a rock most notably in its iron oxides and especially in its magnetite and hematite the ams is commonly expressed by an ellipsoid of which the principal axes are k1 k2 and k3 from greatest to least this ellipsoid is generally interpreted in terms of the distribution and shape of grains of magnetic minerals in a rock although the ellipsoid determined depends also on magnetocrystalline anisotropy and on factors of instrumental technique ellwood et al in press 1987 the challenge for the geoscientist in analyzing ams data is first to identify the origin of the ams geometry then second to relate that geometry to the natural processes which produced the inferred or measured distribution of magnetic materials

internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties

field impressed magnetic anisotropy in rocks the application of alternating af or direct df magnetic fields to two weakly anisotropic rock specimens which remain static significantly alters their measured low field anisotropy of magnetic susceptibility ams by superimposing an anisotropy which has the form of an ellipsoid of revolution with its unique axis aligned along the field axis previous af history is also shown to influence the acquisition of isothermal remanent magnetization irm these effects can be quite substantial and thus it is essential that rocks should not be used for low field ams analysis or for irm anisotropy studies if they have previously been subjected to static af demagnetization ams studies should also not be carried out on rocks which carry a significant remanence e g an irm acquired in 5 mt the field impressed effects were also strongly dependent upon whether the ferrimagnetic particles in the rocks were predominantly multidomain md or uniaxial single domain sd the results were consistent with our recent work on synthetic specimens containing magnetite titanomagnetite or magnemite and add support to our suggestion that these effects could provide a rapid nondestructive means of determining the predominant domain state md or uniaxial sd of ferrimagnetic particles in rocks

determining paleo flow directions from groundmass fabrics in the lyttelton radial dykes new zealand abstract the poles to 010 of groundmass feldspar in radial dykes cutting the dissected miocene volcano lyttelton banks peninsula form generally oblique girdles about the paleo flow direction the obliquity is a response to velocity gradients of magma within the dykes and the sense of obliquity relative to each dyke wall provides a unique determination of the sense of flow the fabrics give support to the model of blanchard et al 1979 for the movement of rigid particles in flowing magmas this method of flow determination overcomes the problem inherent in most others which provide a flow line but no sense of movement along that line methods of sampling and examples of the feldspar fabrics are described together with the relationship of these fabrics to other dyke features such as secondary shears and stretched vesicles

an early cretaceous paleomagnetic pole from ponta grossa dikes brazil implications for the south american mesozoic apparent polar wander path paleomagnetic results from the early cretaceous ponta grossa dike swarm are reported these dikes crosscut sediments and basement rocks associated with the ponta grossa arch a tectonic feature in the eastern border of the paleozoic mesozoic parana basin these dikes are vertical or subvertical and trend mainly nw and ne samples from 127 dikes were submitted to both alternating field and thermal demagnetizations 121 of them yielded characteristic directions interpreted as original thermal remanent magnetizations both normal and reversed polarities as well as intermediate directions 6 dikes are recorded the paleomagnetic pole is located at 30 3 e 82 4 s n 115 95 2 0 k 43 8 this pole along with the available paleomagnetic poles for the parana basin volcanics serra geral formation recalculated in this paper in the light of reported 40 ar 39 ar ages describe an apparent polar wander path segment corresponding to a clockwise rotation 6 9 of the south american plate this movement is compatible with the initial phase of the south atlantic opening with rifting progressing from south to north however the calculated plate velocity is higher than the predicted velocities reported so far based on oceanic floor magnetic anomalies the new data reported in this paper allowed the calculation of a mean early cretaceous pole 60 3 e 83 8 s n 7 95 2 9 which can be discriminated from the middle late jurassic 191 3 e 86 2 s n 3 95 7 8 and late cretaceous 346 5 e 84 1 s n 5 95 4 9 mean poles for south america indicating a more complex movement of the continent than the simple east west drift generally proposed

single domain particles in rocks and magnetic fabric analysis magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes we have recently demonstrated however in laboratory produced samples that as theoretically expected susceptibility anisotropy is dependent on particle size multidomain particles of magnetite or similar strongly magnetic particles with shape anisotropy exhibit a maximum susceptibility parallel to their easy remanent magnetization axes whereas uniaxial single domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state by demonstrating uniaxial single domain anisotropy characteristics for the first time in a rock specimen we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro or ferrimagnetic particles in rocks in particular apparently foliated rocks can actually be lineated and vice versa moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment

magnetic fabrics and rock magnetism of the xiong er volcanic rocks and their implications for tectonic correlation of the north china craton with other crustal blocks in the nuna columbia supercontinent abstract the tectonic background of the paleoproterozoic xiong er volcanic rocks xvr is important for understanding the tectonic evolution of the north china craton ncc as well as its paleogeographic position during the assembly of the nuna columbia supercontinent here we report the results of the first anisotropy of magnetic susceptibility ams study of the xvr and use the interpreted flow directions to constrain the emplacement mechanism and to assess its geological significance for the reconstruction of the nuna columbia supercontinent thirty lavas were sampled from three sections in western henan province detailed rock magnetic analyses including measurements of hysteresis loops magnetization versus temperature curves and first order reverse curves were performed to identify the main magnetic phases and grain sizes the inferred directions from the ams results reveal a radial flow pattern with an eruption center probably located near xiong er mountain our data suggest that the xvr may have been emplaced in a triple conjugated continental rift on the south margin of the ncc probably initiated from a paleoplume based on this interpretation a comparison of geological and paleomagnetic results among the proposed crustal blocks in the nuna columbia supercontinent suggests a close linkage of the ncc with sao francisco congo rio de la plate and siberia

magnetic fabrics study and inferred flow directions of lavas of the old pali road o ahu hawaii abstract a section 600 700 m deep in the koolau tholeiitic lava shield volcano consists of mostly thin pahoehoe and aa flows cut by occasional dikes and outward dipping gravity driven intrusive sheets a magnetic fabric study of 250 specimens from 18 sites shows a tight clustering of k1 axes for some of the lava flows and is thought to fairly reliably define the lava flow direction a systematic plunge of the k1 axes appears to define an imbrication and yields a flow azimuth the azimuth differs by 60 from that anticipated but is readily explained by a change in shape of the koolau volcano during growth the tightest clustering is in massive aa lava flows 5 m thick samples collected from near the flow base give the most consistent orientations compound pahoehoe lavas with many small flow units give the least tightly clustered anisotropy of magnetic susceptibility ams axes and in some flows the orientation is random the gravity driven sheet has an ams fabric indicating a down dip magma flow direction after the koolau volcano was deeply eroded a cinder cone and lava flows of nephelinite were formed in the rejuvenation stage of volcanism the nephelinite is normally magnetized and the ams fabric indicates a generally downslope flow

geochemistry of wistarburgh glass ca 1739 1777 implications for batch recipes and distinction from other south jersey wares the wistarburgh factory was america s first successful glassworks since it operated largely prior to the american revolution little is known about its products and confusion surrounds the authenticity of some of the objects attributed to this factory however analysis of alkali lime glass sherds from the glassworks site shows that green wistarburgh bottle glass is much more calcic and is enriched in various trace elements notably the rare earth elements compared with later south jersey glass for which analytical data are available the compositional data indicate that wistarburgh s proprietors made use of a batch recipe containing approximately 68 wt local sand 24 dolomitic limestone and 3 each of soda ash and potash in addition to green bottle glass blue aquamarine and colourless potash lead glass and colourless potash glass were also recovered from the wistarburgh factory site suggesting that a range of specialized glasswares was produced by this factory resume l usine de wistarburgh a ete la premiere productrice de verre en amerique du nord les produits de cette usine qui fut surtout en production avant la revolution americaine ne sont cependant pas tres bien connus et des doutes persistent concernant la vraie provenance de plusieurs objets attribues au site de wistarburgh l analyses d eclats de verre de couleur verte trouves au site demontre cependant que ce verre est plus riche en calcium et en divers elements traces en terres rares particulierement que les autres types de verres de cette region les donnees de composition indiquent que le verre de wistarburgh a ete cree a partir d un melange de 68 de sable local 24 de calcaire dolomitique 3 d ecarbonate de sodium anhydre e t3 d e potasse en plus des eclats verts des morceaux de verre bleu et sans couleur riches en potasse et en plomb et de verre sans couleur riche en potasse ont ete retrouves au site de l usine de wistarburgh et suggerent que plusieurs types de verres specialises ont etes manufactures a cet endroit owen 697

landscape gradient assessment of thermokarst lake hydrology using water isotope tracers thermokarst lakes are widespread in arctic and subarctic regions in subarctic quebec nunavik they have grown in number and size since the mid 20th century recent studies have identified that these lakes are important sources of greenhouse gases this is mainly due to the supply of catchment derived dissolved organic carbon that generates anoxic conditions leading to methane production to assess the potential role of climate driven changes in hydrological processes to influence greenhouse gas emissions we utilized water isotope tracers to characterize the water balance of thermokarst lakes in nunavik during three consecutive mid to late summer seasons 2012 2014 lake distribution stretches from shrub tundra overlying discontinuous permafrost in the north to spruce lichen woodland with sporadic permafrost in the south calculation of lake specific input water isotope compositions i and lake specific evaporation to inflow e i ratios based on an isotope mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics nearly all lakes sampled were predominantly fed by rainfall and or permafrost meltwater which suppressed the effects of evaporative loss only a few lakes in one of the southern sampling locations which overly highly degraded sporadic permafrost terrain appear to be susceptible to evaporative lake level drawdown we attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of nunavik predicted climate driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region if coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff conditions favorable for mineralization and emission of methane these water bodies may become even more important sources of greenhouse gases

magnetic susceptibility and partial anhysteretic remanence anisotropies in the magnetite bearing granite pluton of tourao ne brazil abstract rock magnetism and magnetic fabric studies were performed in the tourao granite western part of serido belt ne brazil this pluton 350 km2 is composed of k rich calc alkalic monzogranites and was emplaced between a set of ne and e trending dextral strike slip shear zones electronic and optical microscopy thermomagnetic curves hysteresis data and coercivity spectra revealed that magnetite fine and coarse grained is the unique ferromagnetic mineral in these rocks anisotropy of low field magnetic susceptibility ams was measured in 83 sites and for many sites from central and southern parts of the intrusive body a large scatter was noticed anisotropy of partial anhysteretic remanence paar was determined for 29 sites in the 0 50 mt paar0 50 and 19 sites in the 50 90 mt paar50 90 windows to isolate the fabric contribution of the remanence bearing grains magnetite in most sites ams is dominantly carried by magnetite whereas in some sites the paramagnetic contribution exceeds 60 of the bulk susceptibility the paar0 50 is assumed to be related to coarse grained early crystallized magnetites while the paar50 90 is interpreted as due to fine needle shaped magnetites hosted in biotites the combined analysis of these magnetic techniques permits interpretation in terms of fabric formation in the tourao granite and the inference that at least two successive kinematic events were recorded in this intrusive body devoid of any solid state deformation overprint the ams and paar0 50 fabrics for most of the sites correlate with the early nne trending magmatic fabric whereas paar50 90 reveals a different fabric probably related to late partitioning of magmatic straining along the e trending shear zones in the southern part of the body a completely different paar0 50 fabric is correlated with the late intrusion of charnockite stocks