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

fabric analysis using the intercept method abstract the intercept method is a convenient yet powerful method for the numerical analysis of fabrics for geological applications it can be used when a set of objects e g pores grains or aggregates of a specific mineral lineaments etc with unique characteristics can be identified in an image the intercept method analyses boundaries of objects as a population of lines how intercepts are definined is therefore important in order to establish the significance of the intercept counts when the method is applied to digital images the subdivision of the information into square pixels must also be considered we apply a linear filter which minimizes the effects of grid anisotropy on the counting of intercepts analysis of the resulting rose of intercept counts by a fourier series considerably facilitates the interpretation of the data a rose of directions can readily be derived for the phase boundaries if a population of objects can be assumed to have started with an originally isotropic orientation and to have been deformed passively the fourier components of the rose of intercepts also give the sectional strain the fourier components also permit an objective test of the validity of describing a fabric as resulting from a homogeneous strain on an initially isotropic section two computer programs for the counting and analysis of intercepts on digital images are presented and applied in four examples which illustrate the usefulness of the intercept method for magmatic fabric measurement strain analysis and lineament analysis we also illustrate the importance of fourier series decomposition of rose of intercept counts for fabric interpretations intercept results are also shown to be compatible with those derived by other methods eigenvector surfor inertia tensor autocorrelation methods

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

determination of fabric and strain ellipsoids from measured sectional ellipses implementation and applications abstract geologists examine fabrics to constrain models of formation or of deformation of rocks and it is often convenient to summarise the results by a fabric ellipsoid as fabric data are commonly collected on planar sections through the rock estimating a fabric ellipsoid from sectional ellipses often with arbitrary orientations is an important task an algebraic method to calculate such an ellipsoid presented in an earlier paper has been implemented with the program ellipsoid it is used here on examples that illustrate questions and issues that arise when collecting selecting and processing sectional fabric data and when assessing the results the quality of fit of the ellipsoid to the data is assessed in all cases examples include a case in which the average sizes of markers on individual sections can be used in the determination of the ellipsoid and other cases in which such sizes are not useful a case in which sectional ellipses are not obtained from closed markers and a case in which data scatter and insufficient coverage of section orientations lead to a hyperboloid instead of an ellipsoid

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

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

the lebombo monocline and associated feeder dyke swarm diagnostic of a successful and highly volcanic rifted margin abstract as part of the karoo large igneous province lip the 700 km long and 182 ma old lebombo monocline outcrops inland of a younger mozambique lowland cover that separates it from the indian ocean detailed mapping of a particularly well exposed olifant river traverse across this monocline correlates basaltic and rhyodacitic lava units within the lebombo group to at least three hosted generations of intrusions within the monocline parallel northern lebombo dyke swarm implying that a much denser feeder dyke swarm is covered by younger flows measured attitudes and thicknesses of up to 197 lavas and 791 dykes statistically quantify a structural cross section from which a properly weighted lava log of nearly 5 km basalts inter bedded with an overlying 3 5 km of rhyodacites is constructed the geological section is compatible with a slightly deeper sub lava section through the innermost 30 km s of a relatively narrow east greenland margin to which the lebombo monocline can be rigorously compared in both cases field relationships are consistent with early tectonic extension being overwhelmed by dyke dilation within margin parallel swarm segments that may have been injected laterally from central magma chambers thus it is argued that the lebombo monocline is part of a successfully rifted margin that furthermore belongs to a distinct class of highly volcanic and relatively narrow margins which only form proximal to classical triple rift lip centers where an elevated magma flux sustains a magmatic mode of extension for the karoo lip this conforms with 1 a tight gondwana reconstruction of africa with antarctica 2 successful breakup during intense 182 ma emplacement of the lebombo group 3 triple rift formation together with a short lived 181 178 ma okavango dyke swarm and 4 anomalously thick igneous crust formation during continued 2 5 cm yr separation into a loose 155 ma plate configuration of africa and antarctica

magma flow directions of shallow dykes from the east greenland volcanic margin inferred from magnetic fabric studies abstract the role played by plume generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma flow directions in shallow intrusives from the east greenland volcanic margin we investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic affinity belonging to a dyke swarm associated with the tertiary opening of the north atlantic ocean the thickness of the sampled dykes ranges from 3 to 37 m the dykes are of doleritic texture and contain up to 12 of opaque minerals and 35 of plagioclase laths dykes showing a magnetic foliation plane within the dyke plane i e a magnetic fabric usually attributed to magmatic processes represent 40 of the samples from the studied swarm these dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate inverse magnetic fabrics where the maximum principal susceptibility axis lies near the pole to the dyke account for 60 of the data we interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy the flow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations the inferred flow directions are predominantly horizontal throwing a new light on volcanic margin development

magma flow in dikes from rift zones of the basaltic shield of tenerife canary islands implications for the emplacement of buoyant magma abstract dikes of rift zones in the miocene basaltic shield of tenerife have been studied along several profiles in order to record overall variations in lateral and vertical magma flow direction and sense dikes were sampled for anisotropy of magnetic susceptibility ams and other flow indicators and dike propagation indicators were also recorded at each sampling site bulk susceptibilities suggest a predominance of ferromagnetic minerals in the ams fabrics and most of the sampled dikes show normal fabrics magnetic fabrics have been classified according to clustering and imbrication shown by the maximum susceptibility axis on each dike margin a procedure that provides rapid information on the direction and sense of magma flow the flow of magma tends to be upward and steep beneath the volcanic centers of the basaltic shield massifs along the axes of rift zones and in those rift zones located across the flanks of the volcanic edifices roughly normal to the main rifts magma is mainly emplaced laterally and downward the flow of magma is mostly towards the external parts of the volcanic centers of the basaltic shield massifs and indicates that magma propagated toward regions of lower topography this interpretation agrees with magma being emplaced above the level of neutral buoyancy and with buoyancy as the driving pressure gradient the observed flow patterns can be explained in terms of density gradients within the volcanic edifices in which magma flow trajectories are toward less dense regions

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

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

magnetic versus crystallographic fabrics in a basaltic lava flow combined anisotropy of magnetic susceptibility ams and crystallographic studies were performed within a quaternary lava flow for which we have a thorough knowledge of the flow direction microscope examinations microprobe analyses and studies of rock magnetic properties show that ams is carried by homogeneous multidomain ti rich titanomagnetite xc0 6 this mineral forming either subhedral isolate individuals or grouped in various elongated aggregates represents a late crystallized interstitial phase ams determined from samples collected in the lower the middle and the upper part of the flow is characterized by a well defined magnetic foliation whereas magnetic lineation is generally poorly grouped and therefore meaningless the foliation plane of the lower and upper part of the flow show an obliquity which is interpreted as an opposite imbrication indicating a westward flow in agreements with the known flow direction in the lower part of the lava flow the tight correlation between ams and plagioclase lattice preferred orientation suggests that a silicate framework control the titanomagnetite crystallization and thus the orientation of the ams ellipsoid d 2005 elsevier b v all rights reserved

assessing spo techniques to constrain magma flow examples from sills of the karoo igneous province south africa abstract shape ellipsoids that define the petrofabrics of plagioclase in jurassic karoo dolerite sills in kwazulu natal south africa are rigorously constrained using the long axis lengths of plagioclase crystals and ellipse incompatibility this has been undertaken in order to determine the most effective technique to determine petrofabrics when using the spo 2003 programme launeau and robin 2005 the technique of segmenting an image for analysis is scrutinised and as a process is found redundant a grain size threshold is defined to assist with the varying grain sizes observed within and between sills where grains exceed the 0 2 mm size threshold images should be acquired at a high magnification i e 10 magnification petrofabrics are determined using the foliation and the lineation of the ellipsoid as defined by the maximum and minimum principal axes respectively of the resultant ellipsoid samples with strongly prolate fabrics are isolated allowing further constraint on the petrofabric to be made once the efficacy of the petrofabric determination process has been determined the resultant foliations and lineations then elucidate the most accurate petrofabric attainable the most accurate petrofabrics will be determined by using the correct magnification when the images are obtained and to run the analyses without segmenting the image the fabrics of the upper and lower contacts of the karoo dolerite sills are analysed in detail using these techniques and the fabrics are used as a proxy for magma flow

magma flow and thermal contraction fabric in tabular intrusions inferred from ams analysis a case study in a late variscan folded sill of the albarracin massif southeastern iberian chain spain abstract the effects of different petrological processes on the rock fabric of a folded sill from the albarracin massif southeastern iberian chain spain were studied by means of the anisotropy of magnetic susceptibility ams technique the most outstanding feature of the sill at outcrop scale is a network of joints linked to thermal contraction which define polygonal columns the analysis of the magnetic fabric taking the orientation of sill walls and column axes as a reference and using the restored directional data corresponding to the whole of k3 susceptibility axes has revealed magnetic fabrics related to two processes a magma flow with a sw trending flow vector characterized by a curved geometry of the magma foliations and b thermal contraction coeval to lava cooling early magnetite crystals grown in a relatively high viscosity calc alkaline magma are the main carriers involved in the ams fabric passive rotation of the early magnetic mineralogy within a medium viscosity magma explains the magnetic fabric linked to both magma flow and near solidus thermal contraction of the magma late variscan folding of the sill produced the rigid body reorientation of the magnetic fabric

patterns of magma flow in segmented silicic dikes at summer coon volcano colorado ams and thin section analysis abstract a complex pattern of magma flow is found in two silicic dikes of a radial swarm at summer coon an eroded stratovolcano in southern colorado the two intrusions are broken into multiple segments that suggest vertical dike propagation however anisotropy of magnetic susceptibility ams measurements and thin section observations suggest that magma flow was often subhorizontal and away from the center of the volcano segments that are proximal to the central intrusion are characterized by magma that flowed steeply upward at the proximal segment extremity then laterally along the segment and finally downward at the distal end of the segment magma flow in offset segment tips located far from the volcano center was subhorizontal towards the adjacent segment implying lateral propagation of segment tips towards one another this observation suggests relatively high driving pressure in distal dike segments as supported by dike thickening with radial distance from the center of the volcano the present study indicates that radial dike evolution at stratovolcanoes is dominated by lateral flow of magma and dike segmentation is a poor magma flow indicator a horizontally propagating radial dike has the potential to cause an eruption low on the flank of a composite cone which poses a significant yet largely unrecognized hazard to population centers and infrastructure that may surround the volcano

magnetic and plagioclase linear fabric discrepancy in dykes a new way to define the flow vector using magnetic foliation in basaltic dykes the magnetic lineation k1 maximum magnetic susceptibility axis is generally taken to indicate the flow direction during solidification of the magma this assumption was tested in tertiary basaltic dykes from greenland displaying independent evidence of subhorizontal flow the digital processing of microphotographs from thin sections cut in k1 k2 planes yields the preferred linear orientation of plagioclase which apparently marks the magma flow lineation in up to 60 of cases the angular separation between k1 and the assumed flow direction is greater than 45 this suggests that the uncorroborated use of magnetic lineations in dykes is risky a simple geometrical method is proposed to infer the flow vector from ams in dykes based solely on magnetic foliations

magnetic fabrics and rock magnetism of archaean and proterozoic dike swarms in the southern sao francisco craton brazil abstract magnetic fabric and rock magnetism studies were performed on three mafic dike swarms total of 38 dikes from the southernmost part of the sao francisco craton sfc minas gerais state se brazil they cut archaean granite gneiss migmatite and paleoprototerozoic terranes these swarms are classified as basic noritic sm nd age 2 65 ga basic rb sr age 1 87 ga and metamorphic rb sr age 1 87 ga suites in which the second is the most important magnetic fabrics were determined by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm in most sites magnetic susceptibility is dominantly carried by ferromagnetic minerals however in some sites the paramagnetic contribution exceeds 70 of bulk susceptibility mainly coarse to fine grained ti poor titanomagnetite up to pure magnetite carry the magnetic fabrics three primary ams fabrics are recognized which are all coaxial with the aarm fabric normal ams fabric is dominant in the basic suite 16 of 20 analyzed dikes and occurs in 4 and 3 dikes from the basic noritic and metamorphic suites respectively this fabric is interpreted as a result of magma flow in which the analysis of k max inclination permitted to infer that the majority of dikes were fed by inclined flows 30 k max k max intermediate ams fabric was found in 50 of dikes from the basic noritic and metamorphic suites but in only 2 dikes from the basic suite it is interpreted as due to vertical compaction of a static magma column with the minimum stress along the dike strike inverse ams fabric is a minority 2 dikes from each suite the parallelism between ams and aarm tensors for dikes with abnormal fabrics suggests a primary origin for them gyroremanent magnetization grm effect was negligible for the majority of dikes but it was found in two dikes from the basic suite with normal ams fabric magnetic fabrics recognized for the three studied swarms do not depend on magnetic mineralogy geochemical composition dike strikes nor the age of the swarms since the same magnetic minerals and magnetic fabric types are found in dikes from all suites inclined and horizontal flows allow us to infer the relative position of at least three magma sources or magma chambers from which the dikes were fed

the elusive feeders of the karoo large igneous province and their structural controls abstract dolerite sills in the central parts of the karoo large igneous province on the kalahari craton in south africa record the emplacement of magic magmas over 350 000 km2 but the feeders to the voluminous magmatism have yet to be identified extensive exploration and mining data across a 7400 km2 area and to a depth of 2 5 km in the northern karoo basin provide unprecedented access to the subsurface geometry of dolerite sills and their relationship to underlying basement strata the data show saucer shaped sills in the karoo supergroup with distinctly funnel shaped geometries along their base that are seated within basement rocks the funnel shaped dolerite structures are interpreted to represent the feeders to the overlying regional scale sill saucer complexes four distinct saucer geometries can be identified 1 cone shaped saucers that extend outwards from a single funnel shaped point type a 2 elongated saucers that dip towards multiple aligned funnel shaped points type b 3 the more commonly described elongated saucers with flat inner sills type c and 4 elongated saucers with a combination of type b and c geometries type d type a and c saucer geometries and point like contacts are consistent with analogue models of saucers for respective pipe like and linear feeders however the multiple pipe like feeders associated with type b and combination thereof with sheet like feeders type d represent saucer feeder relationships thus far not modelled notably the lower dolerite funnels are commonly rooted in older faults and or dykes within the basement rocks this spatial correlation emphasizes the significance of pre existing basement structures in the kalahari craton for the long range transfer of the magmas through the crust the distributed occurrence of numerous magma feeders across much of the craton is more consistent with thermal incubation of the sub lithospheric mantle beneath gondwana than the impact of a mantle plume

sampling strategies and the anisotropy of magnetic susceptibility of dykes abstract most studies of the anisotropy of magnetic susceptibility ams of dykes have assumed that susceptibility axes should define a unique orientation relative to the dyke walls and magma flow direction theoretical considerations however predict systematic variations of ams as a function of the amount of shear experienced by the flowing magma although this feature of ams might seem undesirable at first sight based in a theoretical model it has been suggested that actually we can take advantage of such variation in the orientation of the ams axes to infer magma flow directions more confidently than until now if proper attention is given to the scheme followed during sample collection in this work we report the results of a pilot study made to test those theoretical predictions we resampled two dykes from the ko olau dyke complex in o ahu and for which magma flow direction was previously inferred albeit with some uncertainty the resampling was made following the guidelines suggested by the theoretical work as closely as possible i e collecting more than one profile parallel to the dyke walls and across the dyke the results of our measurements provide the first empirical evidence supporting the occurrence of a cyclic fabric acquisition during the emplacement of at least some dykes the procedure described in this paper therefore constitutes a self contained approach that can be followed to test in a case by case basis the occurrence of such fabric behavior this in turn should provide enough elements to increase the reliability of the interpretation in the obtained results

spectral characteristics of the convective boundary layer over uneven terrain abstract the paper describes a convective boundary layer experiment conducted in april 1978 at the boulder atmospheric observatory and examines the spectral behavior of wind velocity and temperature from the observatory s 300 m tower from aircraft flights alongside the tower and from a surface network of anemometers for evidence of terrain influence on turbulence structure the gently rolling terrain at the site does not seem to affect the turbulence spectra from the tower in any perceptible manner except for minor shifts in the vertical velocity and temperature spectral peaks the aircraft vertical velocity spectra showed different shapes for alongwind and crosswind sampling directions as in earlier measurements over ocean surfaces and their peaks are displaced to higher wavenumbers compared with the tower spectra long term spectra of horizontal wind components from surface stations around the tower exhibit no particular sensitivity to site selection under near stationary conditions the peak of t

spectra of velocity components over complex terrain spectra have been measured over a variety of types of complex terrain on tops of hills and escarpments over land downstream of a water surface and over rolling terrain differences between spectra over many types of complex terrain and over uniform terrain can be explained by these hypotheses when air moves over terrain with changed characteristics then 1 for wavelengths very short relative to the fetch over the new terrain the spectral densities are in equilibrium with the new terrain 1 for wavelengths long compared to this fetch spectral densities remain unchanged if the ground is horizontal and decrease when the flow is uphill for the longitudinal velocity component only since vertical velocity spectra contain relatively less low wavenumber energy than horizontal velocity spectra energetic vertical velocity fluctuations tend to be in equilibrium with local terrain

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

when an inverse fabric is not inverse an integrated ams spo study in morb like dykes terra nova 23 49 55 2011 abstract magma flow direction is recorded in the macroscopic mineral petrofabric and magnetic fabric of the morb like rooi rand dyke swarm the bulk magnetic fabric is sub parallel to the dyke plane resulting from preferred orientation of grains during magma flow this is referred to as type a fabric a study of mineral shape preferred orientation reveals an additional fabric which is orthogonal to the average dyke orientation in 30 of the data this fabric is carried by both plagioclase and opaque grains and would typically be interpreted as inverse it is referred to here as type b fabric however because it is carried by the shape preferred orientation of macroscopic grains and is in most cases not coaxial to the anisotropy of magnetic susceptibility fabric it is interpreted as having been acquired during increased grain interaction during late stage magma flow associated with decreasing magma pressure

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

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

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

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

the magnetic zone axis a new element of magnetic fabric for the interpretation of the magnetic lineation abstract the magnetic zone axis is the common direction of the intersection of the magnetic foliations of different samples it is easily determined using tensors from the minimum susceptibility axes it provides useful information for the interpretation of the magnetic fabric particularly of the maximum axis a bootstrap method reveals small local disturbance of the magnetic foliation it yields also the confidence zone of the magnetic zone axis

magnetic fabric methods and applications fabric is a ubiquitous and significant feature of geological materials the processes involved in the formation and deformation of rocks and sediments leave their mark on the orientations of the constituent mineral grains petrofabrics thus provide essential keys to understanding the history of geological materials magnetic anisotropy is directly related to petrofabric and has become one of the most rapid sensitive and widely used tools for its characterization the relationship between magnetic fabric and petrofabric is complex and depends on various factors including the composition concentration and grain size of mineral grains ongoing research in geological applications is paralleled by studies of the fundamental mineral magnetic phenomena involved the papers in this book represent the current state of investigations in magnetic anisotropy studies as a discipline that integrates geological interpretations mineral fabric development technical advances and rock magnetic properties

two and three dimensional shape fabric analysis by the intercept method in grey levels the count intercept is a robust method for the numerical analysis of fabrics launeau and robin 1996 it counts the number of intersections between a set of parallel scan lines and a mineral phase which must be identified on a digital image however the method is only sensitive to boundaries and therefore supposes the user has some knowledge about their significance the aim of this paper is to show that a proper grey level detection of boundaries along scan lines is sufficient to calculate the two dimensional anisotropy of grain or crystal distributions without any particular image processing populations of grains and crystals usually display elliptical anisotropies in rocks when confirmed by the intercept analysis a combination of a minimum of 3 mean length intercept roses taken on 3 more or less perpendicular sections allows the calculation of 3 dimensional ellipsoids and the determination of their standard deviation with direction and intensity in 3 dimensions as well the feasibility of this quick method is attested by numerous examples on theoretical objects deformed by active and passive deformation on bse images of synthetic magma flow on drawing or direct analysis of thin section pictures of sandstones and on digital images of granites directly taken and measured in the field

magnetic and shape fabrics of magnetite in simple shear flows abstract the magnetite fabrics measured by anisotropy of magnetic susceptibility ams and by shape preferred orientation spo optical methods are classically used as flow kinematics indicators in lava flows the development of magnetite fabrics during simple shear strains 20 was performed using a suspension of 1 volume fraction of multidomain magnetite randomly contained in a mixture of silicone and wax we measured ams fabric and spo ellipsoids by calculating a quadratic shape tensor from oriented thin sections for jeffery 1922 fabrics are usable to determine the flow kinematics including the amount of applied finite strain for 8 fabric elements foliation and lineation are stabilised closely parallel to the flow plane and the shear direction respectively two and three dimensional numerical simulations using measured aspect ratios of magnetite point out that the large scattering of aspect ratios and the initial orientation distribution of particles are together responsible for a wide ranging loss of periodicity the stable ams and spo fabrics observed at large strains in experiments are the result of these primary fabric properties combined to collisions between particles and possibly their complex three dimensional shapes in addition the constant angular relationship observed at large strains between fabrics and flow components is related to the transient collisions consequently the determination of the lava flow kinematics by using fabric properties measured either by ams or by spo analyses should be indubitably associated to a detailed study of the three dimensional shape of the solid carriers regularly shaped populations of low elongated particles will be capable to produce cyclic to oscillating fabrics while the fabric of elongated particles will be more sensitive to the shape parameters and collisions ultimately favouring stable fabrics at large strains

first investigation of quartz and calcite shape fabrics in strained shales by means of x ray tomography abstract we document the evolution of the 3d fabric of shale along a km long strain gradient in the jaca basin southern pyrenees spain with respect to the distance from a thrust samples were collected in the cleavage free domain at the onset of the pencil cleavage domain within the pencil cleavage domain and within the slaty cleavage domain by combining high resolution x ray computed tomography xct and energy dispersive x ray spectroscopy eds the morphology and the shape preferred orientation spo of thousands of quartz grains calcite grains and pores was studied in the least deformed samples quartz and calcite display mean foliation parallel to bedding with comparable dispersion in the pencil cleavage domain quartz foliation still follows the bedding while calcite foliation is mostly governed by cleavage in the slaty cleavage domain calcite shows a much better organization with foliation parallel to cleavage mimicking closely the pore fabric by contrast the quartz shape fabric is much less defined scattered between bedding and cleavage planes this suggests that quartz grain act as rigid marker in the ductile matrix while calcite grain orientation is governed by dissolution precipitation processes

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

significance of magnetic and petrofabric in karoo feeder dykes northern lebombo abstract the orientation of magnetic and petrofabric in 14 mafic dykes of the northern lebombo dyke swarm nlds has been determined using the anisotropy of magnetic susceptibility ams and mineral shape preferred orientation spo in order to constrain the magma flow direction during dyke emplacement the n s striking nlds intruded the n s trending 700 km long lebombo faulted monocline between 182 and 178 ma the lebombo faulted monocline which forms the eastern most sub province of the karoo large igneous province lip is essentially a volcanic rifted margin with a protracted magmatic and tectonic history related to the break up of southern gondwana it also forms the southern limb of the karoo triple rift system which has been hypothesised to have formed by a mantle plume centred on the triple junction locus the other two arms of the rift which converge on the triple junction are the wnw trending okavango dyke swarm ods and ne trending save limpopo dyke swarm slds in the nlds it is found that the magnetic fabric which is of magmatic origin in 50 of the samples is carried predominantly by stoichiometric magnetite there is remarkable agreement between the orientations of the ams and spo fabrics and at least two dykes show coaxial ams and mineral spo fabric consistent with lateral magma flow from the north this direction is supported by the imbrication of the foliations of the well defined bulk ams and plagioclase spo fabric when viewed in a dyke co ordinate system although steeply plunging maximum axes occur in the spo fabric their possible use as magma flow vectors is questioned because they do not necessarily mimic the elongation of plagioclase grains visible in orientated thin sections the magnetic and petrofabric of the nlds is interpreted to have developed during lateral magma flow from the locus of the karoo triple junction

internal structure of basalt flows insights from magnetic and crystallographic fabrics of the la palisse volcanics french massif central we present a new interpretation of anisotropy of magnetic susceptibility ams fabrics in basaltic lava flows based on the detailed study of magnetic mineralogy and silicate crystallographic fabric of a quaternary lava flow from the french massif central la palisse we consider the model of ams fabric imbrication between magnetic foliation and flow surface as initially proposed for dykes at the two sampling sites the concordance between the flow direction deduced from the ams foliation and that deduced from field observations indicates that the imbrication model could apply to the lava flows however the flow senses inferred fromamsare systematically opposed between the two sampling sites suggesting permutations between k1 and k3 ams axes a configuration referred to as inverse fabric electron backscatter diffraction ebsd measurements show strong lattice preferred orientations lpo for plagioclase especially the 010 plagioclase plane which tends to be parallel to the flow clinopyroxene lpo remains less marked than plagioclase lpo whereas titanomagnetite does not display a significant lpo comparison between magnetic and crystallographic fabrics suggests that the ams fabric of the lava flow results from the distribution of titanomagnetite grains which is in turn controlled by the fabric of the silicate framework magnetic hysteresis parameters and anisotropy of remanent magnetization arm measurements exclude a significant contribution from single domain grains often called upon to explain inverse magnetic fabrics the origin of the observed inverse magnetic fabric may relate to the dip of the palaeosurface which is the only remarkable difference between the two sampling sites ams appears as a good tool to determine the direction of basaltic lava flows and coupling with local crystallographic fabric data provides a valuable control of relationships between magnetic fabrics and flow and thus contributes to better constrain the ams signature of lava flows

from the subtropics to the central equatorial pacific ocean neodymium isotopic composition and rare earth element concentration variations 1 neodymium isotopic compositions end and rare earth element ree concentrations were measured for filtered surface to deep waters 112 samples in the southern tropical pacific the relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic end variations occur end values increase for most of the water masses flowing from samoa to the solomon sea and in the papua new guinea png area as already observed furthermore water masses arriving from the eastern equatorial pacific 200 550 m depth also revealed radiogenic values possibly acquired in the vicinity of the south american coasts and galapagos islands these end variations affect the whole water column the most likely process causing such variations is boundary exchange between the numerous radiogenic slopes margins located in this area and seawater flowing past dissolution of atmospheric deposition and or diffuse streaming of volcanic ash are also suggested to explain the radiogenic end observed at the surface in the png area interestingly a positive europium eu anomaly characterizes the normalized ree patterns of most of the studied water masses this anomaly is consistent with the ree patterns of sediment and rock samples that are potential sources for the local waters such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic ree budget thanks to boundary exchange the data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing geotraces program www geotraces org

on the interpretation of normal and inverse magnetic fabric in dikes examples from the eger graben nw bohemian massif abstract recent studies of igneous rocks indicate that the predominant occurrence of normal inverse fabric in dikes may either reflect the presence of multi domain md single domain sd grains or it may result from different orientation mechanisms of magnetic minerals in magmas of different viscosities the ambiguity in physical vs geological cause of normal inverse magnetic fabric must be answered before any successful geological interpretation of magnetic fabric can be made in order to address this problem we studied magnetic fabric of selected dikes associated with the sw ne trending eger graben nw bohemian massif the studied area offered very extensive collection of rock types basanite bostonite camptonite tinguaite and trachybasalt magnetic susceptibility varies according to rock type and reflects the relative contents of magnetic minerals in most cases titanomagnetite with variable ti content was identified as main magnetic carrier the degree of anisotropy is relatively low in most cases less than 10 the shape of anisotropy ellipsoid ranges from slightly prolate to neutral and oblate several different types of magnetic fabric using anisotropy of low field magnetic susceptibility ams were observed in studied dikes so called normal and inverse magnetic fabrics and anomalous magnetic fabric comparing all studied sites it seems that the type of magnetic fabric is lithology dependent normal magnetic fabric with magnetic foliations and subhorizontal magnetic lineations both parallel to the dike margins was found in bostonite and trachybasalt dikes inverse magnetic fabric with magnetic lineations and magnetic foliations perpendicular to the dike margins was found in camptonite dikes anisotropy of anhysteretic remanent magnetization amr indicate that the observed inverse magnetic fabric may be caused by the presence of sd magnetic grains amr fabric being normal with respect to dike margins in contrast to that no single domain particles were revealed using frequency dependence and anhysteretic susceptibility measurements the ams measured in variable weak magnetic fields is field dependent for camptonite dike and field independent for other rock types i e bostonite basanite tinguaite and trachybasalt for further flow direction and tectonic interpretations of magnetic fabric in dikes it is suggested to use preferably the amr fabric at least for dikes which demonstrate significant field dependence of ams as it reflects the true rock fabric more accurately than ams fabric

interpreting anomalous magnetic fabrics in ophiolite dikes abstract anisotropy of magnetic susceptibility ams may reveal mineral orientation distributions defining magmatic flow axes in igneous dikes the mafic silicates are the best indication of magmatic flow but fe ti accessories may contribute more to the bulk susceptibility if the orientation distributions of the two subfabrics are incongruent anomalous fabrics will occur that do not reflect magma flow axes for ophiolite dikes ocean floor metamorphism changes the mineralogy producing new fe oxides by retrogression and exsolution from mafic silicates and by the oxidation of primary oxides incompatibly oriented ferro magnetic subfabrics may be isolated by anisotropy of anhysteretic remanence aarm anomalous ams fabrics in ophiolites elsewhere have been attributed to inverse fabric contributions from single domain magnetite in varying combinations however in ophiolite dikes from the troodos ophiolite of cyprus anomalous fabrics arise from ocean floor metamorphism extensively or completely replacing the original magnetite and titanomagnetite accessory phases with titanomagnetite fe 2 4 ti 0 6 o 4 tm60 and its oxidised versions titanomaghemite to varying degrees according to depth beneath the ocean floor distance from spreading axis and proximity to transform faults at best the oxide orientation distribution defined by aarm could only be indirectly related to magma flow if its nucleation orientation controlled by a host lattice however more commonly the topotactic lattice reorganization produces weaker arm fabric anisotropies although recrystallized oxidised tm60 dominates the bulk low field susceptibility its anisotropy is generally too feeble to compete with the flow fabric defined by the ams contribution from paramagnetic mafic silicates

magma flow revealed by magnetic fabric in the okavango giant dyke swarm karoo igneous province northern botswana to determine the magma flow direction of the giant 179 ma okavango dyke swarm of northern botswana we measured the anisotropy of magnetic susceptibility ams of 23 dykes dykes are located in two sections shashe and thune rivers which are about 300 km and 400 km from the presumed magma source respectively the nuanetsi triple point we collected samples from the margins of the dykes in order to use the imbrication of magnetic foliation to determine magma flow direction about half of the magnetic fabric in the dykes is inverse i e with the magnetic foliation perpendicular to the dyke plane lateral flow to the west and vertical flow is in evidence in the shashe section however the overall analysis of normal and inverse magnetic fabric data supports that lateral flow to the west was dominant in the shashe section across the thune section a poorly defined imbricated magnetic foliation also suggests lateral flow to the west

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

characterisation of grain size shape and orientation of plagioclase in the rooi rand dyke swarm south africa abstract magmatic type a fabric co exists with dyke orthogonal type b fabric in both the plagioclase and opaque grain fractions in dykes of the rooi rand dyke swarm rrds we present new data from the rrds pertaining to the size shape texture and orientation of plagioclase texturally the samples range from intersertal to sub ophitic and phenocrystic plagioclase phyric more than 90 of plagioclase grains are

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

emplacement of magma in eastern iceland dikes insights from magnetic fabric and rock magnetic analyses abstract the anisotropy of magnetic susceptibility ams coupled with mineral magnetic identification has been investigated in about 640 samples from 27 basaltic dikes of tertiary age in eastern iceland the dikes are a few meters thick and they have been sampled all across three types of magnetic fabrics with well defined mean principal axes of anisotropy are recognized in the first one the maximum axis is vertical and the minimum axis coincides with the pole of the dike plan geometrically normal fabric the second fabric shows opposite orientation geometrically inverse fabric the third type is when these two fabrics coexist with the normal one at the margins and the inverse one in the center of the dike mixed fabric no relationship is observed between the type of fabric and the width of the dikes each fabric is carried by clear magnetic assemblages made of low x 0 15 ti content fine grained magnetites for the normal one and high ti content around tm60 coarse magnetite grains for the inverse fabric upon heating the magnetic properties and the orientation of the anisotropy ellipsoid characterizing the inverse fabric in the mixed dikes change and evolve toward the normal type these two geometrically normal and inverse fabrics are interpreted as primary ones representing different physico chemical conditions during the emplacement of the magma the ams results indicate that during the volcanic events occurring about 10 myr ago the extrusion of the magma was vertical at the depth of the studied sites in eastern iceland

the crau field experiment turbulent exchange in the surface layer under conditions of strong local advection abstract turbulent fluctuations of atmospheric properties near the soil vegetation atmosphere interface have been investigated in a situation of strong local advection to this end an analysis has been made of data from the 1987 field experiment in la crau france where an extensive dry terrain with sparse vegetation was situated upwind from an irrigated field completely covered with grass the change in surface roughness was negligible the main effect being a change in surface heat flux in the experiment turbulence measurements were made of horizontal and vertical wind speed temperature and humidity at various locations over both terrains in this study 12 runs of 1 h are analysed roughly half of which were made when an advective inversion was present over the downstream terrain both vertical and horizontal velocity fluctuations are almost unaffected by the change in terrain temperature fluctuations are influenced by the fact that over the downstream terrain production of variance almost ceases and advection of variance becomes important this results in a deviation of the z l relation found for homogeneous situations also the temperature spectra of the unstable runs are affected showing a different inertial subrange roll off rate humidity fluctuations adjust rapidly to the new surface and for all but the lowest frequencies behave as if measured over homogeneous terrain

using magma flow indicators to infer flow dynamics in sills abstract fabrics from anisotropy of magnetic susceptibility ams analyses and shape preferred orientation spo of plagioclase are compared with field structures such as bridge structures intrusive steps and magma lobes formed during magma intrusion in jurassic sills this is to constrain magma flow directions in the sills of the karoo igneous province along the kwazulu natal north coast and to show how accurately certain structures predict a magma flow sense thus improving the understanding of the karoo sub volcanic dynamics the ams fabrics are derived from magnetite grains and are well constrained however the spo results are commonly steeply inclined poorly constrained and differ to the ams fabrics both techniques resulted in asymmetrical fabrics successful relationships were established between the ams fabric and the long axes of the magma flow indicators implying adequate magma flow prediction however where numerous sill segments merge either in the form of magma lobes or bridge structures the coalescence process creates a new fabric between the segments preserving late stage magma migration between the merged segments overprinting the initial magma flow direction

petrogenesis of jurassic a type granites associated with cu mo and w sn deposits in the central nanling region south china relation to mantle upwelling and intra continental extension abstract the central nanling region in south china was the site of uplift extensional deformation granite magmatism and hydrothermal activity from 180 to 150 ma information on the age petrological characteristics major and trace element contents whole rock sr and nd and zircon hf isotopic compositions of granitic plutons were synthesized to constrain the sources evolutionary processes and uplift cooling rates of intrusions that host cu mo and w sn deposits in this region the older 180 160 ma cu mo related granitoids are less differentiated a1 type alkaline rocks with faster cooling and uplift rates they have younger nd and hf two stage model ages and higher end t and ehf t values that indicate mantle derived magmas were moderately contaminated by upper crust the younger 160 150 ma w sn related granites are more differentiated a2 type aluminous rocks with slower cooling and uplift rates they have older nd and hf two stage model ages and lower end t and ehf t values that require more upper crustal contamination the time space distribution and characteristics of these granitoids and ore deposits are indicative of centralized mantle upwelling and gradational crustal extension the older rapidly uplifted less contaminated granitoids with cu mo mineralization occur near the center of an intra continental extension bulge produced by mantle upwelling whereas the younger slowly uplifted more contaminated granitoids with w sn mineralization occur on the periphery the results suggest that metals in the cu mo deposits may have come from the mantle whereas those in the world class nanling w sn polymetallic deposits were derived from early mesoproterozoic 1 4 1 6 ga crustal basement of the cathaysia block in south china

evidence of sheared sills related to flank destabilization in a basaltic volcano piton des neiges basaltic volcano la reunion has been deeply dissected by erosion exposing large volumes of debris avalanche deposits to shed light on the factors that led to volcano flank destabilizations we studied the structure the crystallographic and magnetic fabrics of the substratum of a debris avalanche unit this substratum is a complex of n50 seaward dipping sills that has been exposed by the avalanche structural observations show that the sill plane in contact with the avalanche is one of the latest intrusions in the sill complex in this uppermost sill the anisotropy of magnetic susceptibility ams is correlated to the crystallographic preferred orientation of magmatic silicate minerals allowing us to use ams as a proxy to infer the magmatic flow the ams fabric across the intrusion is strongly asymmetric which reveals that the contact sill was emplaced with a normal shear displacement of its hanging wall the shear displacement and the magma flow in the intrusion are both directed toward the nne i e toward the sea which is also the direction of the slope and of the debris avalanche runout because all the sills in the intrusion complex have a similar dip and dip direction it is likely that several of them also underwent a cointrusive slip toward the nne we conclude that this cointrusive normal slip repeated over many intrusions of the sill complex increased the flank instability of the volcano this incre mental instability may have ended up into the observed debris avalanche deposit at piton de la fournaise the active volcano of la reunion sill intrusion and cointrusive flank displacement have been inferred from geophys ical studies for the april 2007 eruption by providing direct evidence of sheared sills our study substantiates the idea that repeated sill intrusions may eventually trigger flank destabilizations in basaltic volcanoes